Category Archives: Air Infiltration

1st Floor Weatherization-Benton Project

3 Main Energy Efficiency Measures Taken on the Benton Project

  1. R22 Insulation installed in 2×6 Wall Framing Members
  1. Vapor and Air Filtration Barrier
  1. Additional HVAC Cold Air Return Duct
Scotts Contracting Installs R22 Insulation

R22 Batt Type Insulation-Friction Fit-
Johns Mansfield No Itch Insulation

Photo is the Water and Vapor Barrier used to seal the wall frame-Scotts Contracting,St Louis Renewable Energy
Water and Air Barrier

The Above Photo is the Water and Vapor Barrier used to seal the wall frame.  This material is recycled Billboard Sign Material.  The true R-Value of the Material is not known.  We do know that the material is Ten Times stronger and thicker than normal vapor barriers on the Market today.

I added an additional HVAC ‘Return’ Air Duct to help
the Efficiency of the Electric Furnace

Scotts Contracting-St Louis Renewable Energy
before Modern Day Insulation they used Hair, Newspaper,
and other Miscellaneous Materials

Thank you for stopping by St Louis Renewable Energy. Feel free to comment in the section below or contact Scotty for any Home Improvement Projects or Energy Reducing Needs and Scotty, Scotts Contracting will respond ASAP. Company Web Address:


Fire Proof-Air Tight-Electrical Junction Box Cover

Air Sealing a Ceiling Electrical Junction Box

CAD Design-Weatherize-Insulate-Fire Block-Electrical Junction Box
Air Sealing Ceiling Electrical Junction Box

CAD Diagram explains how to Build and Air Tight Electrical Junction Box located in most Attics

Sealing Air Leaks

Warm air leaking into your home during the summer and out of your home during the winter and can waste a lot of your energy dollars. One of the quickest dollar-saving tasks you can do is caulk, seal, and weatherstrip all seams, cracks, and openings to the outside.

You can save on your heating and cooling bill by reducing the air leaks in your home.

Fire Proof /Air Tight Electrical Junction Box Cover used in Attics

Hint: Use Fire Rated: 5/8″Fire Rated Drywall or Sheetrock with Fire Proof Caulking to 

Create the Air Tight Seal

Tips for Sealing Air Leaks

Pie chart shows how air escapes from a typical home: 31% floors, ceiling, walls; 15% ducts; 14% fireplace; 13% plumbing penetrations, 11% doors; 10% windows; 4% fans and vents; 2% electric outlets.How Does the Air Escape?
Air infiltrates into and out of your home through every hole and crack. About one-third of this air infiltrates through openings in your ceilings, walls, and floors.
  • First, test your home for air tightness. On a windy day, carefully hold a lit incense stick or a smoke pen next to your windows, doors, electrical boxes, plumbing fixtures, electrical outlets, ceiling fixtures, attic hatches, and other locations where there is a possible air path to the outside. If the smoke stream travels horizontally, you have located an air leak that may need caulking, sealing, or weatherstripping.
  • Caulk and weatherstrip doors and windows that leak air.
  • Caulk and seal air leaks where plumbing, ducting, or electrical wiring penetrates through walls, floors, ceilings, and soffits over cabinets.
  • Install foam gaskets behind outlet and switch plates on walls.
  • Look for dirty spots in your insulation, which often indicate holes where air leaks into and out of your house. You can seal the holes with low-expansion spray foam made for this purpose.
  • Look for dirty spots on your ceiling paint and carpet, which may indicate air leaks at interior wall/ceiling joints and wall/floor joists. These joints can be caulked.
  • Install storm windows over single-pane windows or replace them with more efficient windows, such as double-pane. See Windows on page 18 for more information.
  • When the fireplace is not in use, keep the flue damper tightly closed. A chimney is designed specifically for smoke to escape, so until you close it, warm air escapes—24 hours a day!
  • For new construction, reduce exterior wall leaks by installing house wrap, taping the joints of exterior sheathing, and comprehensively caulking and sealing the exterior walls.
  • Use foam sealant around larger gaps around windows, baseboards, and other places where warm air may be leaking out.
  • Kitchen exhaust fan covers can keep air from leaking in when the exhaust fan is not in use. The covers typically attach via magnets for ease of replacement.
  • Replacing existing door bottoms and thresholds with ones that have pliable sealing gaskets is a great way to eliminate conditioned air leaking out from underneath the doors.
  • Fireplace flues are made from metal, and over time repeated heating and cooling can cause the metal to warp or break, creating a channel for hot or cold air loss. Inflatable chimney balloons are designed to fit beneath your fireplace flue during periods of non-use. They are made from several layers of durable plastic and can be removed easily and reused hundreds of times. Should you forget to remove the balloon before making a fire, the balloon will automatically deflate within seconds of coming into contact with heat.
Cutaway house illustration showing areas of home where air leaks. Refer to caption for list.Sources of Air Leaks in Your Home
Areas that leak air into and out of your home cost you lots of money. Check the areas listed below.

  1. Dropped ceiling
  2. Recessed light
  3. Attic entrance
  4. Sill plates
  1. Water and furnace flues
  2. All ducts
  3. Door frames
  4. Chimney flashing
  1. Window frames
  2. Electrical outlets and switches
  3. Plumbing and utility access
Scotts Contracting is available to assist you in improving your Home or Business Energy Demands.  Please use this form below to Contact Scotty, Scotts Contracting to schedule a FREE Energy Analysis for your Property.

Roof Venting and Its Importance for your Home

A Crash Course in Roof Venting

Understand when to vent your roof, when not to, and how to execute each approach successfully

Article Re-Posted from:

Click to enlarge image

So much information has been devoted to the subject of roof venting that it’s easy to become confused and to lose focus. So I’ll start by saying something that might sound controversial, but really isn’t: A vented attic, where insulation is placed on an air-sealed attic floor, is one of the most underappreciated building assemblies that we have in the history of building science. It’s hard to screw up this approach. A vented attic works in hot climates, mixed climates, and cold climates. It works in the Arctic and in the Amazon. It works absolutely everywhere—when executed properly.

Unfortunately, we manage to screw it up again and again, and a poorly constructed attic or roof assembly can lead to excessive energy losses, ice dams, mold, rot, and lots of unnecessary homeowner angst.

Here, I’ll explain how to construct a vented attic properly. I’ll also explain when it makes sense to move the thermal, moisture, and air-control layers to the roof plane, and how to detail vented and unvented roofs correctly.

Theory behind venting
The intent of roof venting varies depending on climate, but it is the same if you’re venting the entire attic or if you’re venting only the roof deck.

In a cold climate, the primary purpose of ventilation is to maintain a cold roof temperature to avoid ice dams created by melting snow and to vent any moisture that moves from the conditioned living space to the attic. (See “Energy Smart Details” inFHB #218 for more on ice dams.)

In a hot climate, the primary purpose of ventilation is to expel solar-heated hot air from the attic or roof to reduce the building’s cooling load and to relieve the strain on air-conditioning systems. In mixed climates, ventilation serves either role, depending on the season.

Vent the attic

A key benefit of venting the attic is that the approach is the same regardless of how creative your architect got with the roof. Because the roof isn’t in play here, it doesn’t matter how  many hips, valleys, dormers, or gables there are. It’s also easier and often less expensive to pile on fiberglass or cellulose insulation at the attic floor to hit target R-values than it is  to achieve a comparable R-value in the roof plane.

The success of this approach hinges on the ceiling of the top level of the house being absolutely airtight before any insulation is installed. (See “Attic-Insulation Upgrade” in FHB #200.) It’s also important to ensure that there isn’t anything in the attic except lots of  insulation and air—not the Christmas decorations, not the tuxedo you wore on your wedding day, nothing. Attic space can be used for storage, but only if you build an elevated platform above  the insulation. Otherwise, the insulation gets compressed or kicked around, which diminishes its Rvalue. Also, attic-access hatches are notoriously leaky. You can build an airtight entry  attic, but you should know that the more it is used, the leakier it gets.

How do people get this simple approach wrong? They don’t follow the rules. They punch a bunch of holes in the ceiling, they fill the holes with recessed lights that leak air, and they stuff mechanical systems with air handlers and a serpentine array of ductwork in the attic. The air leakage from these holes and systems is a major cause of ice dams in cold climates and a major cause of humidity problems in hot climates. It’s also an unbelievable energy waste no matter where you live.

Don’t think you can get away with putting ductwork in an unconditioned attic just because you sealed and insulated it. Ductsealing is faith-based work. You can only hope you’re doing a good-enough job. Even when you’re really diligent about airsealing, you can take a system with 20% leakage and bring it down to maybe 5% leakage, and that’s still not good enough. With regard to recessed lights and other ceiling penetrations, it would be great if we could  rely on the builder to air-seal all these areas. Unfortunately, we can’t be sure the builder  will air-seal well or even air-seal at all. So we have to take some of the responsibility out of the builder’s hands and think of other options.

In a situation where mechanical systems or ductwork has to be in the attic space or when there are lots of penetrations in the ceiling below the attic, it’s best to bring the entire attic area inside the thermal envelope. This way, it’s not as big a deal if the ceiling leaks air or if the ducts are leaky and uninsulated.

Vent the roof deck

If the attic space is going to be conditioned, either for living or mechanical purposes, or if a home design calls for a vaulted ceiling, provision R806.3 in the International Residential Code calls for the roof deck above the space to be vented continuously from the eave to the ridge. This is easy to accomplish in simply constructed roofs and difficult, if not impossible, to accomplish in roofs that have hips, valleys, dormers, or  skylights that interrupt the rafter bays.

If you choose to vent the roof deck, then be serious about it and really vent it. The code calls for a minimum of 1 in. of airspace between the top of the insulation and the back of the roof sheathing. That’s not enough. For best performance, the airspace in the vent chute should be a minimum of 2 in. deep. Unless you’re bulk-filling rafter bays between 2×10 or 2×8 rafters with closed-cell spray foam, this approach will likely require you to fur out the rafters to accommodate additional insulation to achieve desired R-values. That can be a pain, but you won’t run into the problems associated with having too little air circulating under the roof. To be sure your roof is getting enough ventilation, there are simple calculations that you can follow.

Beyond the decreased capacity for insulation when venting the roof deck, venting the roof deck or the attic has some other drawbacks worth considering. In cold climates, snow can enter the soffit and ridge vents, melt, and potentially cause rot. Similarly, in coastal environments or in regions with lots of rain and wind, moisture can be forced into the vents and into the roof assembly. In hurricane-prone zones with frequent high-wind events, vented-soffit collapse can pressurize a building, which can cause windows to blow out and the roof to be blown off. Finally, in wildfire zones, floating embers can enter the vents and cause roof fires. If any of these issues are of concern, there is another option.

Click to enlarge image

Create an unvented roof

Through provision R806.4, the IRC also allows you to build an unvented roof assembly. Unvented assemblies work particularly well on complex roofs that would be difficult or impossible to vent properly or on roofs where it would be difficult to insulate properly if the roof were vented.

It should be noted, however, that in high-snow-load areas, you still need a vented over-roof to deal with ice damming. In essence, you’re creating a hybrid vented/unvented roof system.The goal in an unvented roof is to keep the roof deck—the principal condensing surface in roof assemblies—sufficiently warm through the year to prevent condensation from occurring. In most climates, builders have to insulate the roof sheathing to prevent condensation from occurring within the assembly. The exception is hot-dry climates such as in Phoenix, where condensation isn’t as big an issue.

Condensation control is most often accomplished by installing rigid foam above the roof deck or by installing air-impermeable spray-foam insulation directly against the underside of the roof deck. The code also allows for air-permeable insulation, such as fiberglass or cellulose, to be used under the roof deck as long as rigid foam is used above the roof sheathing. Flash-andbatt (or flash-fill) assemblies are also allowed. Any of these approaches can adequately prevent condensation from occurring within the roof when the rigid foam or spray foam is installed at the appropriate thickness.

If you’re spraying foam on the underside of the roof deck, be sure you’re using the right product. Closed-cell spray foam works in all climates, but especially well in climate zones 5 through 8, where high R-values are desired and where airimpermeable insulation also must be a vapor retarder. Lowdensity, open-cell foam is permissible, but in climate zones 5 and above, it has to be covered with a vapor-retarder coating, like rigid foam or painted drywall.

Also pay attention to roofing materials. Asphalt shingles require special attention when installed on unvented roof assemblies in hot-humid, mixedhumid, and marine climates due to inward vapor drive. To keep moisture out of the roof assembly, a roofing underlayment with 1 perm or less (class-II vapor retarder) must be installed under the shingles. Also, check to be sure that you are in compliance with the manufacturer warranties when installing shingles over an unvented roof in all climates. Some manufacturers don’t warranty or offer only a limited warranty when their products are used over an unvented roof assembly.

Shingles that are installed on unvented roof assemblies operate at slightly higher temperatures, roughly 2°F to 3°F warmer than shingles on vented assemblies. This can reduce  their service life by roughly 10%. You can vent the roof cladding, which will increase its  longevity, but the expense of fastening battens over the roof sheathing, then adding another layer of plywood over the battens as a nail base for the shingles, may not be worth the expense. After all, the shingle color and the roof orientation are much more significant concerns when it comes to shingle life.

Unvented roofs

Unvented roofs aren’t nearly as common as vented assemblies, and builders may not be familiar with detailing them correctly. While there are certainly a variety of ways to build an unvented roof assembly that performs well, here are three examples worth considering

Option 1: Insulate below the roof The most conventional approach to insulating a roof is to put all the insulation below the roof deck. This approach is especially prevalent in retrofits when the existing roof is in good  shape but the attic is being conditioned

Prevent condensation with the right amount of insulation

Click to enlarge image
An unvented roof assembly is possible only if you keep the roof sheathing warm enough to prevent conditioned air from condensing against it. The map at right, which is based on table R806.4 of the IRC, lists the minimum R-values required to prevent condensation in unvented assemblies in various climate zones. The thickness of the insulation will vary depending on the type. These R-value requirements are intended only to prevent condensation and don’t supersede the code-required R-values for energy efficiency, which are also listed.
The success of a vented attic or roof deck relies on its airtightness. The space above the top plate of exterior walls—at the bottom of each rafter bay—is especially important. Baffles placed in this area channel intake air into either the attic space or vent chutes, and also prevent insulation from falling into the soffit and blocking airflow.
Click to enlarge image
Site-built: 2-in. chutes and baffles Cut 1-in.-thick rigid polyiso insulation into 2-in.- wide spacer strips, and glue them to the inside face of each rafter with a spray-foam adhesive like Pur Stick ( Cut the polyiso insulation to fit snugly in each rafter bay, and foam it in place against the spacer to create a 2-in. chute or baffle.

Size: Custom-cut polyiso foam
Cost: $23 per sheet
Source: Dow

Click to enlarge image
Prefab: fast and functional The AccuVent soffit insulation baffle is made of rigid recycled plastic. It’s more durable than other foam-based products and installs quickly with staples. These baffles should still be air-sealed with spray foam, but they’re a good option if you’re looking for a stock product.

Size: 41 in. by 22 in.
Cost: $1.68 each
Source: Berger Building Products

Drawings: John Hartman
From Fine Homebuilding212, pp. 68-72
July 14, 2011

Air Sealing Your Home- Weatherization, Tips, Photos, Suggested Sealing Techniques

WHAT  A R E  T H E  B E N E F I T S  O F  A I R
S E A L I N G ?
Air infiltration can account for 30 percent or
more of a home’s heating and cooling costs
and contribute to problems with moisture.

In the previous post: Suggested Reading- How to Design and Build an Energy Efficient Home
I covered many aspects of Designing and Building an Energy Efficient Home. 

This blog posting will cover Air Infiltration

Seal plumbing behind tub
electrical penetrations
Attic living space
Knee wall
Attic space
Unwanted air leakage
Attic Ventilation
Seal tub penetration
Seal kneewall to create a continuous air barrier.
Seal and insulate exterior wall before installing bath tubs.
Attic ventilation
Rafter Sheet
dropped soffit
Seal chases
 top and bottom plates
Soffit vent
Caulk bottom plate
to subfloor
electrical fixtures to drywall
Caulk band joist to subfloor and plates
Seal electrical penetrations
Seal bottom
Tape or caulk exterior
Seal plumbing penetrations
sill plate-Caulk bottom plate to subfloor
sheathing seams
Seal dropped soffit ceilings, plumbing and electrical penetrations, etc
Seal exterior sheathing joints, and top and bottom plates. chases.

and More.

Download the Free Technology Fact Sheet on Air Sealing / Air Filtration.  Sealing Air Leaks will SAVE YOU MONEY.

Air infiltration control in housing: A guide to international practice (Bulletin no. 139 from Division of Building Technology, Royal Institute of Technology, Stockholm, Sweden)

Wind and trees; air infiltration effects on energy in housing (Report – Center for Environmental Studies, Princeton University)

Applicable Models for Air Infiltration and Ventilation Calculations

Minimising Air Infiltration in Office Buildings: (BR 265) (Building Research Establishment Report)

Infiltration and Air Leakage

Air tightness and air leakages of new lightweight single-family detached houses in Estonia [An article from: Building and Environment]

Which Kind Of Insulation Is Best?

Email: Scotts Contracting to Schedule a Green Proposal

for Your Next Project 

Scotts Contracting Offers Green Insulation Installs for the St Louis Area



  • Why Insulate Your House?
  • How Insulation Works

Which Kind of Insulation is Best?

  • What Is an R-Value?
  • Reading the Label
  • Insulation Product Types

Insulating a New House

  • Where and How Much
  • Air Sealing
  • Moisture Control and Ventilation
  • Installation Issues
    • Precautions
    • Attics
    • Walls
  • Design Options
    • Crawlspaces and Slabs
    • Advanced Wall Framing
    • Metal Framing
    • Insulating Concrete Forms
    • Massive Walls
    • Structural Insulated Panels
    • External Insulation Finish System
    • Attic Ventilation or a Cathedralized Attic

Adding Insulation to an Existing House

  • Where and How Much
  • How Much Insulation Do I Already Have?
  • Air Sealing
  • Moisture Control and Ventilation
  • Insulation Installation, the Retrofit Challenge
    • Precautions
    • Attics
    • Walls
    • Basement Walls
    • Floors and Crawlspaces

Resources and Links
About This Fact Sheet

Which Kind Of Insulation Is Best?

Based on our email, this is one of the most popular questions homeowners ask before buying insulation. The answer is that the ‘best’ type of insulation depends on:

  • how much insulation is needed,
  • the accessibility of the insulation location,
  • the space available for the insulation,
  • local availability and price of insulation, and
  • other considerations unique to each purchaser.

Whenever you compare insulation products, it is critical that you base your comparison on equal R-values.

What Is an R-Value?
Insulation is rated in terms of thermal resistance, called R-value, which indicates the resistance to heat flow. The higher the R-value, the greater the insulating effectiveness. The R-value of thermal insulation depends on the type of material, its thickness, and its density. In calculating the R-value of a multi-layered installation, the R-values of the individual layers are added.

The effectiveness of an insulated ceiling, wall or floor depends on how and where the insulation is installed.

  • Insulation which is compressed will not give you its full rated R-value. This can happen if you add denser insulation on top of lighter insulation in an attic. It also happens if you place batts rated for one thickness into a thinner cavity, such as placing R-19 insulation rated for 6 1/4 inches into a 5 1/2 inch wall cavity.
  • Insulation placed between joists, rafters, and studs does not retard heat flow through those joists or studs. This heat flow is called thermal bridging. So, the overall R-value of a wall or ceiling will be somewhat different from the R-value of the insulation itself. That is why it is important that attic insulation cover the tops of the joists and that is also why we often recommend the use of insulative sheathing on walls. The short-circuiting through metal framing is much greater than that through wood-framed walls; sometimes the insulated metal wall’s overall R-value can be as low as half the insulation’s R-value.

Reading the Label
No matter what kind of insulation you buy, check the information on the product label to make sure that the product is suitable for the intended application. To protect consumers, the Federal Trade Commission has very clear rules about the R-value label that must be placed on all residential insulation products, whether they are installed by professionals, or whether they are purchased at a local supply store. These labels include a clearly stated R-value and information about health, safety, and fire-hazard issues. Take time to read the label BEFORE installing the insulation. Insist that any contractor installing insulation provide the product labels from EACH package (which will also tell you how many packages were used). Many special products have been developed to give higher R-values with less thickness. On the other hand, some materials require a greater initial thickness to offset eventual settling or to ensure that you get the rated R-value under a range of temperature conditions.

Insulation Product Types
Some types of insulation require professional installation, and others you can install yourself. You should consider the several forms of insulation available, their R-values, and the thickness needed. The type of insulation you use will be determined by the nature of the spaces in the house that you plan to insulate. For example, since you cannot conveniently “pour” insulation into an overhead space, blankets, spray-foam, board products, or reflective systems are used between the joists of an unfinished basement ceiling. The most economical way to fill closed cavities in finished walls is with blown-in insulation applied with pneumatic equipment or with sprayed-in-place foam insulation.
The different forms of insulation can be used together. For example, you can add batt or roll insulation over loose-fill insulation, or vice-versa. Usually, material of higher density (weight per unit volume) should not be placed on top of lower density insulation that is easily compressed. Doing so will reduce the thickness of the material underneath and thereby lower its R-value. There is one exception to this general rule: When attic temperatures drop below 0°F, some low-density, fiberglass, loose-fill insulation installations may allow air to circulate between the top of your ceiling and the attic, decreasing the effectiveness of the insulation. You can eliminate this air circulation by covering the low-density, loose-fill insulation with a blanket insulation product or with a higher density loose-fill insulation.

Blankets, in the form of batts or rolls, are flexible products made from mineral fibers, including fiberglass or rock wool. They are available in widths suited to standard spacings of wall studs and attic or floor joists. They must be hand-cut and trimmed to fit wherever the joist spacing is non-standard (such as near windows, doors, or corners), or where there are obstructions in the walls (such as wires, electrical outlet boxes, or pipes). Batts can be installed by homeowners or professionals. They are available with or without vapor-retarder facings. Batts with a special flame-resistant facing are available in various widths for basement walls where the insulation will be left exposed.
Blown-in loose-fill insulation includes cellulose, fiberglass, or rock wool in the form of loose fibers or fiber pellets that are blown using pneumatic equipment, usually by professional installers. This form of insulation can be used in wall cavities. It is also appropriate for unfinished attic floors, for irregularly shaped areas, and for filling in around obstructions.
In the open wall cavities of a new house, cellulose and fiberglass fibers can also be sprayed after mixing the fibers with an adhesive or foam to make them resistant to settling.
Foam insulation can be applied by a professional using special equipment to meter, mix, and spray the foam into place. Polyisocyanurate and polyurethane foam insulation can be produced in two forms: open-cell and closed-cell. In general, open-celled foam allows water vapor to move through the material more easily than closed-cell foam. However, open-celled foams usually have a lower R-value for a given thickness compared to closed-cell foams. So, some of the closed-cell foams are able to provide a greater R-value where space is limited.
Rigid insulation is made from fibrous materials or plastic foams and is produced in board-like forms and molded pipe coverings. These provide full coverage with few heat loss paths and are often able to provide a greater R-value where space is limited. Such boards may be faced with a reflective foil that reduces heat flow when next to an air space. Rigid insulation is often used for foundations and as an insulative wall sheathing.
Reflective insulation systems are fabricated from aluminum foils with a variety of backings such as kraft paper, plastic film, polyethylene bubbles, or cardboard. The resistance to heat flow depends on the heat flow direction, and this type of insulation is most effective in reducing downward heat flow. Reflective systems are typically located between roof rafters, floor joists, or wall studs. If a single reflective surface is used alone and faces an open space, such as an attic, it is called a radiant barrier.
Radiant barriers are installed in buildings to reduce summer heat gain and winter heat loss. In new buildings, you can select foil-faced wood products for your roof sheathing (installed with the foil facing down into the attic) or other locations to provide the radiant barrier as an integral part of the structure. For existing buildings, the radiant barrier is typically fastened across the bottom of joists, as shown in this drawing. All radiant barriers must have a low emittance (0.1 or less) and high reflectance (0.9 or more).

Adding Insulation to an Existing House (Smart Approaches)

[Where and How Much] [How Much Insulation Do I Already Have?] [Air Sealing] [Moisture Control and Ventilation] [Insulation Installation, the Retrofit Challenge]
Does your home need more insulation? Unless your home was constructed with special attention to energy efficiency, adding insulation will probably reduce your utility bills. Much of the existing housing stock in the United States was not insulated to the levels used today. Older homes are likely to use more energy than newer homes, leading to higher heating and air-conditioning bills.

Where and How Much
Adding more insulation where you already have some, such as in an attic, will save energy. You can save even greater amounts of energy if you install insulation into places in your home that have never been insulated. Figure 1 shows which building spaces should be insulated. These might include an uninsulated floor over a garage or crawlspace, or a wall that separates a room from the attic. Figure 3 can give you general guidance regarding the appropriate amount of insulation you should add to your home, and the rest of this page will provide more specific information.

A qualified home energy auditor will include an insulation check as a routine part of an energy audit. For information about home energy audits, call your local utility company. State energy offices are another valuable resource for information. An energy audit of your house will identify the amount of insulation you have and need, and will likely recommend other improvements as well. If you don’t have someone inspect your home, you’ll need to find out how much insulation you already have.

After you find out how much you have, you can use the ZipCode tool to find out how much you should add. This recommendation balances future utility bill savings against the current cost of installing insulation. So the amount of insulation you need depends on your climate and heating fuel(gas, oil, electricity), and whether or not you have an air conditioner. The program is called the ZipCode because it includes weather and cost information for local regions defined by the first three digits of each postal service zip code. The program also allows you to define your own local costs and to input certain facts about your house to improve the accuracy of the recommendations. However, some personal computer security systems won’t allow Java programs to run properly. The recommended R-values table can be helpful in those cases, because it will provide recommendations based on insulation and energy costs for your local area.

Look into your attic. We start with the attic because it is usually easy to add insulation to an attic. This table will help you figure out what kind of insulation you have and what its R-value is.

Look into your walls. It is difficult to add insulation to existing walls unless:

  • You are planning to add new siding to your house, or
  • You plan to finish unfinished space (like a basement or bonus room).

If so, you need to know whether the exterior walls are already insulated or not. One method is to use an electrical outlet on the wall, but first be sure to turn off the power to the outlet. Then remove the cover plate and shine a flashlight into the crack around the outlet box. You should be able to see whether or not insulation is in the wall. Also, you should check separate outlets on the first and second floor, and in old and new parts of the house, because wall insulation in one wall doesn’t necessarily mean that it’s everywhere in the house. An alternative to checking through electrical outlets is to remove and then replace a small section of the exterior siding.

Look under your floors. Look at the underside of any floor over an unheated space like a garage, basement, or crawlspace. Inspect and measure the thickness of any insulation you find there. It will most likely be a fiberglass batt, so multiply the thickness in inches by 3.2 to find out the R-value (or the R-value might be visible on a product label). If the insulation is a foam board or sprayed-on foam, use any visible label information or multiply the thickness in inches by 5 to estimate the R-value.

Look at your ductwork. Don’t overlook another area in your home where energy can be saved – the ductwork of the heating and air- conditioning system. If the ducts of your heating or air-conditioning system run through unheated or uncooled spaces in your home, such as attic or crawlspaces, then the ducts should be insulated. First check the ductwork for air leaks. Repair leaking joints first with mechanical fasteners, then seal any remaining leaks with water-soluble mastic and embedded fiber glass mesh. Never use gray cloth duct tape because it degrades, cracks, and loses its bond with age. If a joint has to be accessible for future maintenance, use pressure- or heat-sensitive aluminum foil tape. Then wrap the ducts with duct wrap insulation of R-6 with a vapor retarder facing on the outer side. All joints where sections of insulation meet should have overlapped facings and be tightly sealed with fiber glass tape; but avoid compressing the insulation, thus reducing its thickness and R-value.

Return air ducts are often located inside the heated portion of the house where they don’t need to be insulated, but they should still be sealed off from air passageways that connect to unheated areas. Drywall- to-ductwork connections should be inspected because they are often poor (or nonexistent) and lead to unwanted air flows through wall cavities. If the return air ducts are located in an unconditioned part of the building, they should be insulated.

Look at your pipes. If water pipes run through unheated or uncooled spaces in your home, such as attic or crawlspaces, then the pipes should be insulated.

Air sealing is important, not only because drafts are uncomfortable, but also because air leaks carry both moisture and energy, usually in the direction you don’t want. For example, air leaks can carry hot humid outdoor air into your house in the summer, or can carry warm moist air from a bathroom into the attic in the winter.

Most homeowners are aware that air leaks into and out of their houses through small openings around doors and window frames and through fireplaces and chimneys. Air also enters the living space from other unheated parts of the house, such as attics, basements, or crawlspaces. The air travels through:

  • any openings or cracks where two walls meet, where the wall meets the ceiling, or near interior door frames;
  • gaps around electrical outlets, switch boxes, and recessed fixtures;
  • gaps behind recessed cabinets, and furred or false ceilings such as kitchen or bathroom soffits;
  • gaps around attic access hatches and pull-down stairs;
  • behind bath tubs and shower stall units;
  • through floor cavities of finished attics adjacent to unconditioned attic spaces;
  • utiltity chaseways for ducts, etc., and
  • plumbing and electrical wiring penetrations.

These leaks between the living space and other parts of the house are often much greater than the obvious leaks around windows and doors. Since many of these leakage paths are driven by the tendency for warm air to rise and cool air to fall, the attic is often the best place to stop them. It’s important to stop these leaks before adding attic insulation because the insulation may hide them and make them less accessible. Usually, the attic insulation itself will not stop these leaks and you won’t save as much as you expect because of the air flowing through or around the insulation. There are many fact sheets that will help you stop these air leaks:

Moisture Control and Ventilation
We talk about moisture control in an insulation fact sheet because wet insulation doesn’t work well. Also, insulation is an important part of your building envelope system, and all parts of that system must work together to keep moisture from causing damage to the structure or being health hazards to the occupants. For example, mold and mildew grow in moist areas, causing allergic reactions and damaging buildings.
When Is Moisture a Problem?

When moist air touches a cold surface, some of the moisture may leave the air and condense, or become liquid. If moisture condenses inside a wall, or in your attic, you will not be able to see the water, but it can cause a number of problems. Adding insulation can either cause or cure a moisture problem. When you insulate a wall, you change the temperature inside the wall. That can mean that a surface inside the wall, such as the sheathing behind your siding, will be much colder in the winter than it was before you insulated. This cold surface could become a place where water vapor traveling through the wall condenses and leads to trouble. The same thing can happen within your attic or under your house. On the other hand, the new temperature profile could prevent condensation and help keep your walls or attic drier than they would have been.

Four Things You Can Do to Avoid Moisture Problems:

1. Control liquid water. Rain coming through a wall, especially a basement or crawlspace wall, may be less apparent than a roof leak, especially if it is a relatively small leak and the water remains inside the wall cavity. Stop all rain-water paths into your home by:

  • making sure your roof is in good condition,
  • caulking around all your windows and doors, and
  • keeping your gutters clean – and be sure the gutter drainage flows away from your house.
  • If you replace your gutters, choose larger gutters and gutter guards to help keep rain from dripping onto the ground near the house.

Be sure that the condensate from your air conditioner is properly drained away from your house. You should also be careful that watering systems for your lawn or flower beds do not spray water on the side of your house or saturate the ground near the house. It is also a good idea to check the caulking around your tub or shower to make sure that water is not leaking into your walls or floors. You can place thick plastic sheets on the floor of your crawlspace to keep any moisture in the ground from getting into the crawlspace air, and then into your house.

2. Ventilate. You need to ventilate your home because you and your family generate moisture when you cook, shower, do laundry, and even when you breathe. More than 99% of the water used to water plants eventually enters the air. If you use an unvented natural gas, propane, or kerosene space heater, all the products of combustion, including water vapor, are exhausted directly into your living space. This water vapor can add 5 to 15 gallons of water per day to the air inside your home. If your clothes dryer is not vented to the outside, or if the outdoor vent is closed off or clogged, all that moisture will enter your living space. Just by breathing and perspiring, a typical family adds about 3 gallons of water per day to their indoor air. You especially need to vent your kitchen and bathrooms. Be sure that these vents go directly outside, and not to your attic, where the moisture can cause problems. Remember that a vent does not work unless you turn it on; so if you have a vent you are not using because it is too noisy, replace it with a quieter model. If your attic is ventilated, it is important that you never cover or block attic vents with insulation. Take care to prevent loose-fill insulation from clogging attic vents by using baffles or rafter vents. When you think about venting to remove moisture, you should also think about where the replacement air will come from, and how it will get into your house. When natural ventilation has been sharply reduced with extra air-sealing efforts, it may be necessary to provide fresh air ventilation to avoid build-up of stale air and indoor air pollutants. Special air-to-air heat exchangers, or heat- recovery ventilators, are available for this purpose. For more information about controlled ventilation, see the Whole-House Ventilation Systems Technology Fact Sheet.

3. Stop Air Leaks. It is very important to seal up all air-leakage paths between your living spaces and other parts of your building structure. Measurements have shown that air leaking into walls and attics carries significant amounts of moisture. Remember that if any air is leaking through electrical outlets or around plumbing connections into your wall cavities, moisture is carried along the same path. The same holds true for air moving through any leaks between your home and the attic, crawlspace, or garage. Even very small leaks in duct work can carry large amounts of moisture, because the airflow in your ducts is much greater than other airflows in your home. This is especially a problem if your ducts travel through a crawlspace or attic, so be sure to seal these ducts properly (and keep them sealed!). Return ducts are even more likely to be leaky, because they often involve joints between drywall and ductwork that may be poorly sealed, or even not sealed at all.

4. Plan a moisture escape path. Typical attic ventilation arrangements are one example of a planned escape path for moisture that has traveled from your home’s interior into the attic space. Cold air almost always contains less water than hot air, so diffusion usually carries moisture from a warm place to a cold place. You can let moisture escape from a wall cavity to the dry outdoors during the winter, or to the dry indoors during the summer, by avoiding the use of vinyl wall coverings or low-perm paint. You can also use a dehumidifier to reduce moisture levels in your home, but it will increase your energy use and you must be sure to keep it clean to avoid mold growth. If you use a humidifier for comfort during the winter months, be sure that there are no closed-off rooms where the humidity level is too high.
Insulation Installation, the Retrofit Challenges

Whether you install the insulation yourself or have it done by a contractor, it is a good idea to educate yourself about proper installation methods because an improper installation can reduce your energy savings.
Also, if your house is very old, you may want to have an electrician check to see if:

  • the electrical insulation on your wiring is degraded,
  • the wires are overloaded, or
  • knob and tube wiring was used (often found in homes built before 1940).

If any of these wiring situations exists in your house, it may be hazardous to add thermal insulation within a closed cavity around the wires because that could cause the wires to overheat. THIS IS FOR FIRE SAFETY. The National Electric Code forbids the installation of loose, rolled, or foam-in-place insulation around knob and tube wiring. Adding thermal insulation to the ceiling or walls of a mobile home is complex and usually requires installation by specialists.

If adding insulation over existing insulation, do NOT use a vapor barrier between the two layers!

On unfinished attic floors, work from the perimeter toward the attic door. Be careful about where you step in the attic. Walk only on the joists so that you won’t fall through the drywall ceiling. You may need to place walking boards across the tops of the joists to make the job easier. Remember that it is important to seal up air leaks between your living space and the attic before adding insulation in your attic.
Installing batts and rolls in attics is fairly easy, but doing it right is very important. Use unfaced batts, especially if reinsulating over existing insulation. If there is not any insulation in your attic, fit the insulation between the joists. If the existing insulation is near or above the top of the joists, it is a good idea to place the new batts perpendicular to the old ones because that will help to cover the tops of the joists themselves and reduce thermal bridging through the frame. Also, be sure to insulate the trap or access door. Although the area of the door is small, an uninsulated attic door will reduce energy savings substantially.

In some houses, it is easier to get complete coverage of the attic floor with blown-in loose-fill insulation. It is best to hire an insulation contractor for this job. Loose-fill insulation must be prevented from shifting into vents or from contacting heat-producing equipment (such as recessed lighting fixtures). Block off those areas with baffles or retainers to hold the loose-fill insulation in place.
When you stack new insulation on top of existing attic insulation, the existing insulation is compressed a small amount. This will slightly decrease the R-value of the existing insulation. This effect is most important if the new insulation is more dense than the old insulation. You can compensate for this stacking effect and achieve the desired total R-value by adding about one extra inch of insulation if the old insulation is fiber glass, or about 1/2 inch if the old insulation is rock wool or cellulose.

Reflective Systems are installed in a manner similar to placing batts and blankets. Proper installation is very important if the insulation is to be effective. Study and follow the manufacturer’s instructions. Often, reflective insulation materials have flanges that are to be stapled to joists. Since reflective foil will conduct electricity, avoid making contact with any bare electrical wiring.

Radiant barriers may be installed in attics in several configurations. The radiant barrier is most often attached near the roof, to the bottom surface of the attic truss chords or to the rafter framing. Do not lay a radiant barrier on top of your insulation or on the attic floor because it will soon be covered with dust and will not work. A separate DOE fact sheet is available for radiant barriers to show which parts of the country are most likely to benefit from this type of system.

If your attic has NO insulation, you may decide to insulate the underside of the roof instead of the attic floor. (This option is more often used in new houses and is described in Design Option: ATTIC VENTILATION OR A CATHEDRALIZED ATTIC). If you choose the cathedralized attic approach, all attic vents must be sealed. Spray-foam is then often used to insulate the underside of the roof sheathing. If batts are used for this purpose, they must be secured in a manner similar to that described below for insulating under floors. It is best to hire an insulation contractor with experience in this type of installation for this job.


Installing insulation in the cavity of exterior walls is difficult. However, when new siding is to be installed, it is a good idea to consider adding thermal insulation under the new siding. The Retrofit Best Practices Guide provides useful information about adding insulation when you remodel the outside of your house. It usually requires the services of a contractor who has special equipment for blowing loose-fill insulation into the cavity through small holes cut through the sidewall, which later are closed. It is sometimes feasible to install rigid insulation on the outdoor side of masonry sidewalls such as concrete block or poured concrete. However, if that is not an option, you can use rigid insulation boards or batts to insulate the interior of masonry walls. To install boards, wood furring strips should be fastened to the wall first. These strips provide a nailing base for attaching interior finishes over the insulation. Fire safety codes require that a gypsum board finish, at least 1/2 inch thick, be placed over plastic foam insulation. The gypsum board must be attached to the wood furring strips or underlying masonry using nails or screws.
The first-floor band joist may be accessible from the basement or crawlspace. Make sure it is properly insulated as shown in Figure 1. More detailed drawings and insulation techniques for the band joist are shown in the Wall Insulation Technology Fact Sheet.

Basement Walls
When using batt or rigid insulation to insulate the inside of concrete basement walls, it is necessary to attach wood furring strips to the walls by nailing or bonding, or to build an interior stud-wall assembly on which the interior finish can be attached after the insulation is installed. The cavity created by the added framing should be thick enough for the desired insulation R-value.

The kraft paper or standard foil vapor retarder facings on many blanket insulation products must be covered with gypsum or interior paneling because of fire considerations. Some blanket products are available without these facings or with a special flame resistant facing (labeled FS25 – or flame spread index 25) for places where the facing would not be covered. Sometimes the flame-resistant cover can be purchased separately from the insulation. Also, there are special fiber glass blanket products available for basement walls that require less framing and can be left exposed. These blankets have a flame-resistant facing and are labeled to show that they comply with ASTM C 665, Type II, Class A.

Floors and Crawlspaces
If you have a floor over a crawlspace, you can EITHER:

  • Insulate the underside of the floor and ventilate the crawlspace, OR
  • Leave the floor uninsulated and insulate the walls of an unventilated crawlspace.

When batts or rolls are used on the underside of a floor above an unheated crawlspace or basement, fit the insulation between the beams or joists and push it up against the floor overhead as securely as possible without excessive compaction of the insulation. The insulation can be held in place, either by tacking chicken wire (poultry netting) to the edges of the joist, or with snap-in wire holders. Batts and rolls must be cut and fit around cross-bracing between floor joists or any other obstructions. Strips of insulation may be cut off and stuffed into tight spaces by hand. Don’t forget to place insulation against the perimeter that rests on the sill plate. If you insulate above an unheated crawlspace or basement, you will also need to insulate any ducts or pipes running through this space. Otherwise, pipes could freeze and burst during cold weather.

Reflective Systems are installed in a manner similar to placing batts. Proper installation is very important if the insulation is to be effective. Study and follow the manufacturer’s instructions. Often, reflective insulation materials have flanges that are to be stapled to floor joists. Since reflective foil will conduct electricity, one must avoid making contact with any bare electrical wiring.

Spray-foam can be used to insulate the underside of a floor. The spray foam can do a good job of filling in the space around wires and other obstructions and in filling any oddly-shaped areas. It is best to hire an insulation contractor with experience in this type of installation.

When a fiberglass blanket is used to insulate the walls of an unventilated crawlspace, it is sometimes necessary to attach wood furring strips to the walls by nailing or bonding. The insulation can then be stapled or tacked into place. Alternatively, the insulation can be fastened to the sill plate and draped down the wall. You should continue the insulation over the floor of the crawl space for about two feet on top of the required ground vapor retarder. Because the insulation will be exposed, be sure to use either an unfaced product or one with the appropriate flame spread rating. When rigid foam insulation boards are used to insulate the walls of an unventilated crawlspace, they can be bonded to the wall using recommended adhesives. Because the insulation will be exposed, be sure to check the local fire codes and the flame-spread rating of the insulation product. If you live in an area prone to termite damage, check with a pest control professional to see if you need to provide for termite inspections.

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Scott’s Contracting

Radiation, Convection, Conduction-Warm to Cold

Convection is the movement of air in response to heat

When air is heated, it expands, and therefore becomes less dense, so it rises. The rising warm air displaces cooler air, which sinks. When the motion is constant, it’s called a convective loop.

Woodstoves and windows cause convective loops by heating or cooling (respectively) the air closest to them.

Even in homes with airtight walls and ceilings, convective loops can feel like a cool draft and be uncomfortable to the people in the room.

Convective loops can occur inside poorly insulated wall cavities, too, degrading the performance of the insulation.

Heat flows through materials by conduction

Conduction is the flow of heat energy by direct contact, through a single material or through materials that are touching.

Substances that conduct heat readily are called conductors, while substances that don’t conduct heat readily are called insulators. Metal is a good conductor; foam is a good insulator. Wood falls somewhere in between.

Radiation heats objects, not air

Radiation is the transfer of heat by electromagnetic waves that travel through a vacuum (like space) or air.

Radiation cannot pass through a solid object like plywood roof sheathing. When the sun shines on asphalt shingles, heat is transferred to the plywood sheathing by conduction. After the plywood has been warmed by conduction, it can radiate heat into the attic.

Radiant barriers are materials (for example, aluminum foil) with a low-emissivity (low-e) surface. Although radiant barriers have a few applications in residential construction—they are sometimes integrated with roof sheathing—they are rarely cost-effective when compared to conventional insulation options.

Scott’s Contracting

Insulating Roofs, Walls, and Floors


Its not unusual for a house to have three or four types of insulation: spray foam, loose fill, rigid foam, and/or batts. Each type has multiple uses, but most also have limitations on where they can be used.

The best insulation for each location depends on a number of factors, including cost, ease of installation, available space, and the material’s resistance to moisture.
All insulation types perform best when they’re installed well. Some (like batts and blankets) can lose significant R-valuewith even a slightly sloppy installation.

Grading installation quality

The Residential Energy Services Network (RESNET), a national association of home-energy raters, long struggled with the question of how to estimate the R-value of walls that vary widely in performance depending on the skill of the insulation installer. Eventually, RESNET developed a useful rating system for insulation installation quality. The system is described in an article published in the January/February 2005 issue of Home Energy magazine, “Insulation Inspections for Home Energy Ratings,” by Bruce Harley. The RESNET rating system recognizes three levels of insulation installation quality: Grade I, Grade II, and Grade III.

Grade I is the best installation

“In order to qualify for a Grade I rating, insulation must … fill each cavity side to side and top to bottom, with no substantial gaps or voids around obstructions (that is, blocking or bridging—as seen in the grade II photo below), and it must be split, or fitted tightly, around wiring and other services in the cavity. In general, no exterior sheathing should be visible through gaps in the material,” Harley wrote. “Compression or incomplete fill amounting to 2% or less of the surface area of insulation is acceptable for Grade 1, if the compression or missing fill spaces are less than 30% of the intended fill thickness (that is, 70% or more of the intended insulation thickness is present).”

The standard for a Grade II installation is somewhat lower

“A Grade II rating represents moderate to frequent defects: gaps around wiring, electrical outlets, plumbing, other intrusions; rounded edges or ‘shoulders,’ larger gaps, or more significant compression. No more than 2% of the surface area of insulation missing is acceptable for Grade II.”

Grade III installations are the worst
“A Grade III rating applies to any installation that is worse than Grade II.” For further information on the RESNET grading system—including illustrations of good jobs and sloppy jobs—see “Assessing the Quality of Insulation Installed in New York Energy Star Labeled Homes.”



Because foundations aren’t really exposed to vast temperature swings, less insulation is needed there. Insulation in a basement should be chosen to do more than slow the flow of heat through these relatively stable environments; the best choices of basement insulation stop air and water, too. Basement walls and floors can be insulated on the inside or the outside, inside being the easier method for retrofits and outside being easier (in general) for new construction.

Exterior insulation choices should be moisture tolerant

Below-grade walls and floors should be insulated on the outside with, spray foam, or rigid mineral wool. Because polyisocyanurate can absorb water, it should not be used under a slab or on the outside of a foundation. Polyisocyanurate performs well, however, when used on the inside wall of a basement or crawlspace.

The most common insulation under slabs is XPS, although EPS also works if its density is adequate and if it is rated for ground contact. If the insulated slab must bear heavy loads, XPS is usually a better choice than EPS.

Closed-cell spray polyurethane foam can also be used under a slab.
Basement walls can be insulated on the exterior or interior with EPS, XPS, spray polyurethane foam, or rigid mineral wool (for example, Roxul drainboard).

To insulate a basement wall from the inside, the foam should be applied directly to the concrete, in order to keep moist interior air away from the cool, damp surface and lower the risk of condensation. To allow any accumulated moisture to dry to the inside, a semipermeable foam (EPS or XPS) is the best choice. To meet code requirements for a thermal barrier, the foam will probably need to be protected with a layer of gypsum drywall; fiberglass-faced drywall is more moisture resistant than paper-faced drywall.

Under no circumstances should fiberglass batts be used to insulate basement walls. Because fiberglass batts are air-permeable, they are unable to prevent moist interior air from contacting colder basement walls. That’s why fiberglass-insulated basement walls can easily become damp and moldy.


Although some builders insulate the floor above a crawlspace (the crawlspace ceiling), most building scientists recommend building a sealed, insulated crawlspace that includes wall insulation. It usually requires less insulation (and involves fewer tricky details) to cover a short wall around the perimeter than the whole floor.

Sealed crawlspaces should be built and insulated exactly like basements.

Of course, a well-detailed insulated crawlspace needs more than just insulation. Among the other critical details are careful air-sealing of the rim-joist area and (if the crawlspace has a dirt floor) installation of a ground cover.

Slabs on grade

Some builders insulate slab perimeters without insulating under the slab. In all but the warmest climates, however, it’s better to install a continuous layer of EPS, XPS, or spray polyuyrethane foam under the entire slab. Some builders modify an ICF  for use as a form for the slab that includes insulation.

If the home has in-floor radiant heat, it’s especially important to include a thick layer of foam directly under the entire slab. Experts disagree on exactly how much foam to add, but they all agree that at least some is a good idea. Engineer John Straube of Building Science Corp. says that after about 4 in.—perhaps 6 in. if the slab includes radiant heat—the money is better spent elsewhere. However, Passivhaus builders sometimes install up to 14 in. of sub-slab insulation.

Soil has a measurable R-value, so it can insulate the bottom of the slab from the exterior air to some extent. But soil is also a nearly infinite heat sink. The average soil temperature varies depending on the climate and the soil depth; however, if the soil has an average temperature of 55°F and the interior of a house has an average temperature of 72°F, heat will always want to flow from the warm side of the slab toward the soil. That’s why it’s important to insulate under a slab.


The strategy adopted for insulating a home’s above-grade walls depends on the wall construction used.

  • Walls built from SIPs or ICFs already include insulation.
  • Concrete-block  walls are best insulated from the exterior with rigid foam or spray polyurethane foam.
  • Wood-framed walls can be insulated with cavity insulation (fiberglass batts, sprayed-in-place fiberglass, cellulose, or spray polyurethane foam), on the interior (with rigid foam board), on the exterior (with rigid foam board or spray polyurethane foam), or with a combination of approaches (for example, some cavity insulation and exterior foam sheathing).

Thermal bridging
The effective R-value of a framed wall assembly with cavity insulation is always less than the R-value of the insulation alone, as thermal bridging through the studs degrades the performance of the wall. Thermal bridging can be reduced, and the thickness of the wall increased, by:

  • adding foam sheathing to the exterior of the wall;
  • adding a layer of rigid foam under the interior drywall; or
  • building a double-stud wall with staggered studs.

Foam sheathing

The performance of any wood-framed wall will be improved by installing exterior rigid foam sheathing; the usual choices are XPS or polyisocyanurate. Although EPS can be used, it is more fragile than the other two options.
Adding foam insulation to the outside of a wall affects the wall’s ability to dry out when it gets wet. Different types of foam insulation have different permeance ratings, but after a few inches they’re all pretty impermeable to moisture. Most foam-sheathed walls are designed to dry to the inside. This means that interior plastic vapor barriers should never be used on foam-sheathed walls.

According to Joseph Lstiburek and Peter Baker of Building Science Corp. (see link below), adding 1 in. of R-5 insulation to a 2×6 wall insulated with fiberglass batts increases the effective R-value of the wall from 14.4 to 19.4, a 35% gain with only a 15% increase in wall thickness.

Adding 2 in. of foam raises the R-value from 14.4 to 23.8, an improvement of 65%. A layer of insulating foam on the outside of walls also reduces the risk of condensation by raising the dew point of the surface where water vapor is likely to collect.

Thick foam sheathing is safer than thin foam sheathing. To learn more about determining a safe thickness for exterior foam, see “Calculating the Minimum Thickness of Rigid Foam Sheathing.”


Flat ceilings under unconditioned attics can be insulated with fiberglass batts, blown fiberglass, or blown cellulose, but cellulose works best—especially in very cold temperatures when convective loops can degrade the performance of fiberglass. Regardless of the type of insulation used, more is always better, and it’s usually an inexpensive upgrade as space is less of a limiting factor than it would be for walls.

Spray polyurethane foam can also be used to insulate a flat ceiling, although at a much higher cost than cellulose. An advantage of spray foam is that it air-seals as it insulates. With all types of attic insulation, air-sealing before insulating is almost more important than type and depth of insulation.

Attic-floor insulation should extend over the top plates of perimeter walls. To provide enough room for the necessary depth of attic insulation, be sure to specify raised-heel roof trusses.

Locating insulation at the attic floor has several advantages over locating insulation along the slope of the roof:

  • It’s cheaper, easier, and faster to install thick insulation at the attic floor.
  • Unconditioned attics are easier to vent than insulated rafter bays.
  • It’s easier to detect and pinpoint roof leaks when the attic is unconditioned.


Sloped ceilings and roofs can be insulated from above (by installing rigid foam on top of the roof sheathing), by installing insulation between the rafters, from below (by installing rigid foam under the rafters), or by a combination of some or all three of these insulation methods. Any of these methods will work. Although installing insulation on top of the roof sheathing is more foolproof, it’s also less common.
,or polyisocyanurate foam can be installed above roof sheathing. Two or more layers of rigid foam with staggered seams can be topped with eave-to-ridge 2x4s to create vent channels, followed by a second layer of roof sheathing. Exterior insulation like this with staggered seams disrupts conductive heat flow through the framing assembly.

Installing insulation in rafter bays is risky, as interior moisture can migrate through the insulation (either by diffusion or by piggybacking with exfiltrating air) and contact the cold roof sheathing, leading to condensation. This problem can be prevented by using closed-cell spray polyurethane foam, with or without a ventilation channel under the roof sheathing.


Although adding insulation to an existing home is always more challenging than insulating a new home, weatherization contractors have developed many cost-effective methods of improving existing insulation levels.

It’s important to manage any moisture problems in a home before engaging in air-tightening measures or insulation improvements. Inspect the home to identify any leaks or high-moisture areas, and be sure that the home is equipped with adequate mechanical ventilation.

Among the tried-and-true methods used by experienced weatherization workers:

  • To insulate a basement floor, install a continuous layer of XPS foam on top of the concrete. Top the foam with 2×4 sleepers and a plywood subfloor. If a low ceiling makes every inch critical, the sleepers can be omitted; in that case the plywood subfloor should be mechanically fastened through the foam to the concrete.
  • Basement or crawlspace walls can be insulated with interior XPS, EPS, or closed-cell spray polyurethane foam. The foam should be protected with a thermal barrier (for example, 1/2-in. drywall).
  • Above-grade frame walls can be insulated by blowing dense-packed cellulose into stud cavities through holes drilled through the siding. When insulation is complete, the holes are plugged.
  • If siding is being replaced, rigid foam or spray polyurethane foam can be installed on top of the exterior sheathing. Exterior foam retrofit jobs require considerable trim work around windows and doors, however.
  • Flat ceilings under unconditioned attics are usually easy to insulate with blown-in cellulose.
  • Improving the insulation over a sloped ceiling is often easier from the exterior than the interior. Rigid foam insulation can be added above the roof sheathing in conjunction with new roofing.

After air-sealing and insulation work is complete, the renovated home should be tested for radon. Radon levels often increase after a home has been weatherized.
If a house is undergoing extensive remodeling, it’s worth considering a deep energy retrofit.

Scott’s Contracting

Insulation: Guidelines, Facts, Applications,


Thicker is better
In cold weather, a puffy parka holds in your body heat. Insulation does the same thing for a house. The thicker the insulation, the better it works to reduce heat flow from the inside of a home to the outside during winter, and from outside to inside during summer.
The thermal barrier of a home should consist of a continuous layer of insulation on all sides—including the lowest floor, the exterior walls, and the ceiling or roof.

Doubling the thickness of insulation will double the insulation’s R-value, cutting heat loss in half. Each time the insulation layer is doubled in thickness, this rule applies. The energy saved per year by doubling insulation from R-10 to R-20, however, will be considerably more than the energy saved by doubling insulation from R-20 to R-40, because of the law of diminishing returns. In some cases, like an attic, it’s worth piling on more insulation because there is plenty of room. It’s much more expensive to add that much insulation to exterior walls.

It takes more than just insulation to slow heat
Stopping air leaks is just as important—maybe more important—than adding insulation. Unless builders prevent air from leaking through walls and ceilings, insulation alone won’t do much good. Not only are drafts uncomfortable, but air moving through insulated cavities can cut the efficiency of the insulation by as much as 50%.
Some insulation types make good air barriers, and some don’t. In all cases, it’s best to keep the insulation tight to the air barrier.


When there is no insulation in a roof or wall, the framing is the most insulated part of the assembly. It has the highest R-value. Softwood lumber has an R-value of 1.25 per inch, so a 2×6 stud has an R-value of almost 7. As soon as you put insulation between the studs or rafters above R-7, however, the framing becomes the weak thermal link. If the framing cavities are filled with closed-cell spray foam insulation, the insulation has an R-value of about 36. At that point, the studs or rafters become a glaring weakness in the design.

Building scientists call this phenomenon “thermal bridging” because the studs or rafters bridge the space between inside and outside the thermal envelope.

If you look for it, thermal bridging can sometimes be seen from either inside or outside. Inside, it can cause a problem called ghosting, or cold stripes behind the drywall during winter. These cold stripes can encourage condensation that leads to the accumulation of dust particles on the drywall; eventually, visible vertical stripes may form. Outside, you can see the effect of thermal bridging in snow-melt patterns on roofs and drying patterns on walls.

A continuous layer of rigid foam installed on the inside or outside of a wall or roof drastically reduces thermal bridging through the framing.


Heat flows from hot to cold; it can’t be stopped, but it can be slowed
If we measure the rate at which heat flows through a building material or building assembly—for example, a wall or a roof—we can calculate a number (the R-value) to indicate its insulating ability. The higher a material’s R-value, the better the material is at resisting heat flow through conduction, convection, and radiation (outlined above). Insulation manufacturers report R-values determined by tests following ASTMstandards (for example, ASTM C518).

Common insulation types and their R-values
Residential insulation materials have R-values that range from about 3 to 7 per inch. The amount of insulation installed in any given building assembly depends on the climate, the part of the house being insulated, the project budget, and local code requirements.

  • Batts and blankets: R-3.1 to R-4.1 per in.
  • Blown-in and loose-fill insulation: R-2.6 to R-4.2 per in.
  • Rigid foam: R-3.6 to R-6.8 per in.
  • Closed-cell spray foam: R-6 to R-6.8 per in.
  • Open-cell spray foam: R-3.5 to R-3.6 per in.

Green homes go beyond code minimum

The U.S. Department of Energy has developed a list of recommended insulation levels for different climate zones. The climate zones are represented on the map (click to enlarge). Houses heated by natural gas, fuel oil, or an electric heat pump should use the R-values set out by the DOE and listed below as a base. Because electric heat is relatively expensive, houses with electric resistance heat need more insulation than shown in the table below.

In some parts of the country, minimum code requirements for insulation already (or may soon) exceed these DOE recommendations. For example, the 2009 International Residential Code requires cold-climate builders to include a minimum of R-20 wall insulation and R-15 basement wall insulation.

DOE-Department of Energy-recommended R-values for various parts of a house

Zone Attic Wall Floor Slab edge Basement wall (framing cavity insulation) Basement wall (continuous rigid insulation)
1 R-30 to R-49 R-13 to R-15 R-13 R-4 R-11 R-10
2-3 R-30 to R-60 R-13 to R-15 R-13 to R-25 R-8 R-11 R-10
4 R-38 to R-60 R-16 to R-21 R-25 to R-30 R-8 R-11 R-4
5 R-38 to R-60 R-16 to R-27 R-25 to R-30 R-8 R-11 to R-19 R-10 to R-15
6-8 R-49 to R-60 R-18 to R-27 R-25 to R-30 R-8 R-11 to R-19 R-10 to R-15

In any case, green builders almost always exceed minimum code requirements for insulation thickness. Many energy consultants, including Betsy Pettit and Joseph Lstiburek, now recommend that cold-climate homes include R-60 ceilings, R-40 above-grade walls, R-20 basement walls, and R-10 basement slabs.

Some builders go further; for example, an Illinois home designed to meet the rigorous German Passivhaus standard is insulated to nearly R-60 on every side—even under the slab.


Insulation can’t work in a wind tunnel
No matter what type of insulation you choose, it will perform poorly if installed in a house that is riddled with air leaks. Because many types of insulation (like loose fill and batts) work by trapping air, leaky walls, roofs, and floors mean poor thermal performance. For this reason, building scientists are fanatical about air-sealing. To get the most out of batts and blown insulation, every house needs an air barrier adjacent to or contiguous with the insulation layer.
Some types of insulation are fairly effective at stopping air infiltration. For example, when rigid foam is used as wall sheathing, it can be an effective barrier, as long as the seams are taped. Spray polyurethane foam creates a very effective air barrier.

But neither rigid foam nor spray foam addresses air leaks at the seams where different components meet, such as under the bottom plates of walls. An air barrier is only effective if all of these seams and intersections are addressed with gaskets, glues, or sealants.

Of all available insulation materials, fiberglass batts are the most permeable to air leakage—so permeable that fiberglass is used to make furnace air filters. Because it doesn’t restrict air flow, fiberglass is often singled out and derided for its poor performance.

In fact, much of the criticism of fiberglass insulation is unwarranted. As long as fiberglass is installed in a house with an adequate air barrier, it will perform well. Fiberglass performs best when installed in a framing cavity (for example, a stud bay or joist bay) with an air barrier on all six sides.
Installation details for high-quality fiberglass batts have been incorporated into the insulation installation guidelines established by the home raters from the Residential Energy Services Network (RESNET).

For every location in a house, there are always several ways to create an effective air barrier. However, not all methods are equally easy to achieve. In many locations, including rim-joist areas, spray polyurethane foam is so much faster than alternative methods that its use has become almost universal among builders of high-performance homes.

Moisture can piggyback on air
There’s another benefit to stopping air: less moisture in roofs and walls. That’s because most moisture problems in walls and roofs are caused by moisture transported by air. Vapor diffusionis a much smaller problem.

Moisture can accumulate in a wall or ceiling when warm, humid interior air leaks through cracks in the shell. When this exfiltrating air encounters a cold surface—for example, OSB wall sheathing—the moisture in the air can condense into liquid and puddle in the wall cavity. The same thing can happen in summer, when warm, humid outdoor air leaks through cracks in the wall. If the home is air-conditioned, the moisture in this infiltrating air can condense when it reaches any cool surface—drywall, ductwork, etc. The best way to limit this type of moisture migration is to install an effective air barrier. If air isn’t leaking through cracks in a home’s walls and ceilings, the problem is nipped in the bud.

Insulation can stop air
Some insulation types act as air barriers, while others act like air filters. If you choose an insulation that doesn’t stop air flow, it’s important to install an adjacent air barrier material.

Best to worst at stopping airflow:
Spray foam
Rigid foam
Blown-in fiberglass
Fiberglass batts


Vapor permeability can be a good thing or a bad thing — vapor retarders slow wetting, but they also slow drying, which may be more important. As long as you design a roof, wall, or floor assembly with these concepts in mind, then almost any type of insulation can work.

Least to most vapor permeable:
Foil-faced polyisocyanurate
Closed-cell spray foam
Open-cell spray foam
Blown-in fiberglass
Fiberglass batts

More on the vapor permance of insulation materials at


Although residential wall insulation is traditionally installed in stud cavities, the best place to locate wall insulation is outside the frame. This exterior insulation reduces the thermal-bridging effect that studs have in a wall, because each piece of framing can act as a thermal bridge through the cavity insulation. These thermal bridges seriously degrade the performance of the wall.

The thermal-bridging effect can be partially addressed by using rigid foam sheathing—usually 1 in. or 2 in. of XPS or polyisocyanurate. Even better are wall designs that place all the insulation—6 in. to 10 in. of rigid foam—outside the framing.

When insulation is outside the frame, framing materials stay warm and dry. When stud bays are not filled with insulation, the work of electricians and plumbers is greatly simplified.
Houses with foam sheathing should not include an interior polyethylene vapor retarder.


Insulation can stop air
Some insulation types act as air barriers, while others act like air filters. If you choose an insulation that doesn’t stop air flow, it’s important to install an adjacent air barrier material.

Best to worst at stopping airflow:
Spray foam
Rigid foam
Blown-in fiberglass
Fiberglass batts


Vapor permeability can be a good thing or a bad thing — vapor retarders slow wetting, but they also slow drying, which may be more important. As long as you design a roof, wall, or floor assembly with these concepts in mind, then almost any type of insulation can work.

Least to most vapor permeable:
Foil-faced polyisocyanurate
Closed-cell spray foam
Open-cell spray foam
Blown-in fiberglass
Fiberglass batts

More on the vapor permance of insulation materials at


Although residential wall insulation is traditionally installed in stud cavities, the best place to locate wall insulation is outside the frame. This exterior insulation reduces the thermal-bridging effect that studs have in a wall, because each piece of framing can act as a thermal bridge through the cavity insulation. These thermal bridges seriously degrade the performance of the wall.

The thermal-bridging effect can be partially addressed by using rigid foam sheathing—usually 1 in. or 2 in. of XPS or polyisocyanurate. Even better are wall designs that place all the insulation—6 in. to 10 in. of rigid foam—outside the framing.

When insulation is outside the frame, framing materials stay warm and dry. When stud bays are not filled with insulation, the work of electricians and plumbers is greatly simplified.
Houses with foam sheathing should not include an interior polyethylene vapor retarder.


Uninsulated slab edges
Window frames
Wall and roof penetrations

–contact for additional details Scott’s Contracting

Re: Guest Post: Touch n Seal, Insulation- Local Manufacturer

Weatherize Your Home with Touch ‘n Seal Insulating Foam Sealants

Air Sealing Your Home with Insulating Foam Saves Money and Energy

Hi Scotty – I just discovered your website and blog – love it!!  I work in public relations for Fenton-based Touch ‘n Seal and wanted to submit this press release to you for publication consideration.

Carolyn Schinsky
Ryan Public Relations
(314) 822-9784 Office
(314) 308-1682 Cell
Media Contacts:
Carolyn Schinsky / Ryan PR / 314-822-9784/
  Weatherize Your Home with Touch ‘n Seal Insulating Foam Sealants
Air Sealing Your Home with Insulating Foam Saves Money and Energy
ST. LOUIS—Sept. 13, 2010—It’s common knowledge that air leaks from drafty windows and gaps and cracks around the house can cause even a well-insulated home’s energy bills to soar.  All year long, a leaky house wastes energy and creates an often uncomfortable living environment.  However, weatherizing a home by sealing air leaks, gaps and cracks with Touch ‘n Seal insulating foam sealants and products can reduce energy loss by up to 38 percent.
“The first step in weatherizing a home is to determine where air leakage is occurring,” says Michael Sites, Product Specialist at Touch ‘n Seal.   “Some leaks around windows and doors may be obvious, but be sure to also inspect for cracks and gaps around places like electrical outlets, plumbing pipes, dryer vents and phone jacks.” 
Touch 'n Seal No-Warp FoamNo Warp Window & Door Foam Stops Drafts to Minimize Energy Loss
One of the most common sources of air leaks are drafty windows and doors.  However, Touch ‘n Seal’s gun-applied No-Warp Window & Door Insulating Sealant provides a quick and easy solution to this age-old problem.   No-Warp is a bright white expanding one-component polyurethane foam that is specially formulated for use around window and door frames – providing airtight insulation that blocks drafts, moisture and insects without bowing the frame.
“NoWarp is a great fenestration foam sealant because it expands fully to seal gaps and cracks, but won’t put undue pressure on window and door frames,” says Sites. “Most foams are inappropriate for use in these areas, because the excessive pressure can warp frames and jambs, rendering the window or door inoperable.”
 Constant Pressure Dispensing System Delivers More Spray Foam, Twice as Fast 

Air sealing with spray foam insulation creates a barrier that holds in heat in the winter months and keeps home cooler in the summer. Commonly used for weatherproofing attics, walls, ceilings and crawl spaces, spray foam provides CPDS 1000superior efficiency because it expands to fit the applied area, completely preventing drafts and air infiltration that can let dust, pollen and allergens into the structure.

Contractors can cut costs when applying spray foam insulation and enhance service offerings with Touch ‘n Seal’s new CPDS 1000 Constant Pressure Dispensing System.  The CPDS 1000 is a self-contained, portable, constant pressure spray foam system that dispenses Class I fire retardant, thermal insulating and sound dampening 2-component polyurethane spray foam – twice as fast as foam kits. As contractors around the country are discovering, the CPDS 1000 is an affordable alternative to buying or hiring a foam dispensing truck, saving both time and money.

With an internal air compressor, the CPDS 1000 operates on a standard 120V power supply.  “Efficiency, energy savings and environmental awareness are key factors when weatherizing a home or building,” states Sites. “The CPDS 1000 is the culmination of all these things – it provides reduced chemical waste, reduced fossil fuel consumption, reduced overall energy consumption and no ozone depleting chemicals.” 

Air-Seal & Resist Flames with Gun Foam II Sealant
Most homes have a multitude of unnoticed sources of energy loss.  Some leaks that often get overlooked are cracks and gaps in basement and foundation walls, Gun Foam II Polyurethane foam sealantdropped ceilings over cabinets and attic chases – small enclosures around ducts and plumbing – all which lead to skyrocketing energy bills.   “Air-sealing floor penetrations and air leaks in walls with Touch ‘n Seal’s Gun Foam II Insulating Sealant is a quick and easy way to prevent energy loss,” says Sites. “It provides weatherization in a variety of areas common in most residential construction.”
Gun Foam II is ideal for use at the juncture of the sill and the slab or foundation, and any penetration through floors or ceilings such as electrical lines, HVAC ducting or pipes. It fills cracks and holes in the exterior sheeting (due to poor application or penetrations made for utility services), at the corner and tee joints in framing, and any other place where air might penetrate the exterior envelope.
Touch ‘n Seal Gun Foam II Insulating Sealant is a gun-applied, bright orange one-component polyurethane foam that is more cost effective and easier to install than traditional fire blocking methods such a s gypsum, cement or fiberglass.  Though not a firestop, Gun Foam II withstands flaming over twice as long as the leading competitor, lending crucial seconds to dangerous situations.
“Weatherizing a home not only makes it more comfortable, the long term financial rewards are significant. In addition to saving money on energy bills, when Congress passed the stimulus bill earlier this year, it tripled the tax credit for weatherization home improvements through 2010,” concludes Site. 
# # #
About Touch ‘n Seal:
Convenience Products, the manufacturer of Touch ‘n Seal products, is headquartered in St. Louis, Missouri.   Touch ‘n Seal insulating foams and sealants are the benchmark for performance in commercial and industrial building and maintenance, OEM manufacturing and specialty applications. A full line of one and two-component spray foams, caulks and adhesives are available, including fire blocking foam  (ICC-ES: ESR-1926), Low Pressure Window & Door Foam, Drywall Panel Adhesives, Two-Component, Disposable Units, Mining Specialty Units, One-Component Disposable Cylinders and Fire Break Caulks.  The company also manufactures Touch ‘n Foam one-component foams for the do-it-yourself market.  For more information, visit

Carolyn Schinsky
Ryan Public Relations
(314) 822-9784 Office
(314) 308-1682 Cell

Scott’s Contracting

Stopping Energy Loss by Bad Air Filtration

Stopping Air Filtration

by Scotty Scotts Contracting St Louis Renewable Energy

This Green Build Blog Post- 2 additional areas Bad Air can enter your home and how to stop the air.

In all the research I do on Energy Efficiency for Homes. There is one theme that presents itself in all the areas of Improving a Buildings Efficiency. Stopping Air Filtration. To make this simple and easy to understand I’m going to use Good Air and Bad Air.

Good Air: is the Air inside the house from whatever heating or cooling source you utilize.

Bad Air is: Un-Wanted Air that enters your Home from Exterior Sources

This Green Build Blog Post will center around exterior walls of your Existing Home and the various spots that air Enters your Home. In the Aticle:$1 Dollar Spent Earns $2 Dollars I mentioned sealing around the “obtrusions”.
I‘m now going to point out 2 additional areas Bad Air can enter your home and how to stop the air.
      • Inside the Basement or Crawl Space is the Box Sill of your Home. Seal theAreas against Bad air by caulking the Cracks and Joints where all the boards join together and the point where the Wall attaches to the Foundation-(Sill Plate, Box Sill, Floor Joists)

          • Electrical Outlets- Easy fix install: Outlet Plate Receptacle Insulating Sealer

          My goal as a Green Builder is to lower the energy needed in the Homes and Business’s I service. I do this by taking a whole house approach to a Home’s Energy Needs by retrofitting homes and business for future Energy Efficiency. Whether you choose to DIY or Hire outside Assistance-Build Green-Scotty

          Scotts Contracting offers Free Green Site Inspections

          Scott’s Contracting