Tag Archives: Insulation Saves Money

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.

Hint: Use Fire Rated: 5/8″Fire Rated Drywall or Sheetrock with Fire Proof Caulking to Create the Air Tight Seal

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

Tips for Sealing Air Leaks

re-posted from:http://www.energysavers.gov/tips/insulation_sealing.cfm

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 to Contact Scotty, Scotts Contracting to schedule a FREE Energy Analysis for your Property.


How Insulation Works-Typical-St Louis Brick Home used in Examples

CAD Drawing-Insulation-St Louis Brick Home-Examples

How Insulation Works
Top View: Brick Home with Zero Insulation
Brick Home Wall Detail with Zero Insulation
Brick Home with Insulation in Wall Cavity

Why Insulate Your House?

Heating and cooling account for 50 to 70% of the energy used in the average American home. Inadequate insulation and air leakage are leading causes of energy waste in most homes. Insulation:

  • saves money and our nation’s limited energy resources
  • makes your house more comfortable by helping to maintain a uniform temperature throughout the house, and
  • makes walls, ceilings, and floors warmer in the winter and cooler in the summer.

The amount of energy you conserve will depend on several factors: your local climate; the size, shape, and construction of your house; the living habits of your family; the type and efficiency of the heating and cooling systems; and the fuel you use.

Once the energy savings have paid for the installation cost, energy conserved is money saved -saving energy will be even more important as utility rates go up.

This fact sheet will help you to understand how insulation works, what different types of insulation are available, and how much insulation makes sense for your climate. There are many other things you can do to conserve energy in your home as well. The Department of Energy offers many web sites(http://ornl.gov/sci/roofs+walls/insulation/ins_07.html) to help you save energy by sealing air leaks, selecting more energy-efficient appliances, etc.

How Insulation Works

How Insulation Works
  • Heat flows naturally from a warmer to a cooler space. In winter, the heat moves directly from all heated living spaces to the outdoors and to adjacent unheated attics, garages, and basements – wherever there is a difference in temperature.
  • During the summer, heat moves from outdoors to the house interior.
  • To maintain comfort, the heat lost in winter must be replaced by your heating system and the heat gained in summer must be removed by your air conditioner. Insulating ceilings, walls, and floors decreases the heating or cooling needed by providing an effective resistance to the flow of heat.
  • Reflective insulation or Radiant Barriers works by reducing the amount of energy that travels in the form of radiation. Some forms of reflective insulation also divide a space up into small regions to reduce air movement, or convection, but not to the same extent as batts, blankets, loose-fill, and foam.

Reference> http://ornl.gov/sci/roofs+walls/insulation/ins_01.html

Weatherization for the Attic

Attic Insulation-Energy Solutions

  • Part 1 on Home Weatherization Series

Attic Insulation-I’ve put a little information to explain Attic Insulation for a Home. It takes a whole house approach to Reduce a Home’s Energy Needs.

  • The Attic Area and Attic insulation being just one area.  When Combined with a Green Roofing System- The pair combined are your First Defense Against Rising Energy Costs.

Air Infiltration areas be resolved before adding insulation- Stop the Air (Hot or Cold) From Entering or Leaving a Home.

  • This includes: proper attic ventilation, ceiling protrusions(Light Boxes / Ceiling Fan), access points, mechanical and electric points, Attic Knee Walls, Obtrusion’s-
  • Anything that will allow the unconditioned air from the Exterior of the Home

Adding Radiant Barriers for Existing Buildings-in a nutshell this bounces the Exterior Temperature back outside. Radiant Barriers are being used in more Construction Projects in today’s construction techniques to assist homeowners with additional savings on utility bills.

  • Attached to the Underneath Side of Existing Rafters- Best Option for Retrofits
  • Reflective Radiant Barriers have R-Values that range from R-3.7 to R-17

Prior Experience: R30 2×4 Vaulted Roof System Example #105:

  • Light Color Shingles on Exterior
  • 1 in roof decking
  • 2×4 Rafters 16″ Space
  • R13 Batt Insulation
  • Double Sided Radiant Barier
    • Also Acts as Vapor Barrier
  • Adequate Ventilation Provided by
    • Automatic Power Attic Fan Peak of Roof
    • Proper Vents in Soffits and Gable Ends

Energy Savings:

  • Reduced the Need for 1 window AC unit in Typical Two Story Stick Built Home-
  • This translates to a Savings of $30 / Month during Cooling Months or $120-$160 / Year.
    • This Application Payed for itself in the 1st Summer 06. At the time of writing this article the estimated savings for 5 yrs is $600.  This Pays for 100% of the Materials used in the Green Roof System for the Upstairs Bedroom Remodel.
  • The Only drawback reported by owner (which wasn’t really a drawback since it was his teen-age sons room) was the decrease in cell phone reception,
    • This is caused by the Reflective Nature of the Reflective Foil Radiant Barrier.

Attic Add Insulation to meet Suggested Guidelines for the St Louis Area

Energy Star, Department of Energy, US Government Suggestions for Optimum Home Energy Savings (Reference Links Below)

  • w/ no insulation Add Insulation to achieve=R38 to R60
  • If existing 3-4 inches Add Insulation to achieve=R38
  • Suggested needed R value of Insulation on Attic Floor=R25 to R30

Insulation when used in conjunction with a Radiant Barrier can lower the Cost of Insulation by reducing the Amount of Insulation Needed

Scotts Contracting is Available to assist you in improving your “Homes Energy Efficiency”

When Scotty comes over to perform an estimate.

  1. He will inspect for the above mentioned problem areas.
  2. Discuss the various solutions.
  3. Next-Determine the Materials and Labor Needed to Complete and Fix the Areas Quoted in the Project.
  4. I’ll then submit a Project Proposal that will discuss project in detail.
  5. Answer any Questions, Explain Procedures, and determine the least obtrusive time to Weatherize your Home.
  6. Computerized Energy Audits for your Home for Estimated Energy Savings are also available- [Equest, Sam, HEED are just a few of the programs I am currently using. The Latest Simulated Advisory Model Beta is in the testing stages and being offered by the US Department of Energy].

Looking forward to meeting you and discussing the ways I can help with Lowering your Energy Bills for your Home or Business.Green Me UP-Scotty

Feel free to utilize the above information to Weatherize Your Home or Schedule a Free Green site evaluation-

Scotts Contracting will Weatherize Your Building Against the High Energy Costs of the Summer Time Cooling Costs

I will Save You $Money$!!!!

Scott’s Contracting

Green Me UP-Scotty


Referrence Materials:


Frost on Roof or Lack of Frost is a sure sign…

On the Frosty Mornings when you are outside your house scraping your cars windshield to prepare for your drive to work. Take a look at the Roof of your Home. -Lack of Frost or Snow on your Roof is a sure indication that it was melted by the Heat as it rises from the Interior of your House into the Attic Area-

Frost on Roof or Lack of Frost is a sure sign…

  • Does the Frost or Snow cover the whole roof?
  • Are there places where the snow and frost melt first? (not caused by the Suns Rays)
  • Is there Frost and Snow on the Garage Roof but not on the House Roof?
  • Does your Neighbors House have Frost and Snow on their Roof- but-Your Roof Doesn’t?

Any or All the above may mean that:

  1. Lack of Insulation In the Attic
  2. Air Infiltration from the Interior of the House into the Attic Area
  3. Uninsulated Heating Ducts inside the Attic

Scotts Contracting can Inspect your Attic for Proper:

  1. Insulation Levels
  2. Adequate Ventilation
  3. Uninsulated Heating Ducts
  4. Air Infiltration

Email scottscontracting and Scotty will provide a Free Estimate to Fix any of the Above Issues on your Home. I will also provide a Cost Saving Analysis that will provide a ROI on your Investment.

Weatherization doesn’t cost it Saves! Rule of Thumb: For Every $1 Spent on Weatherization- You will Save $2 on your Home’s Energy Bills

  • Example: By adding ___ Inches of Insulation you will save $__ amount on the Energy needed to heat your Home= Lower Heating Bills and Greater Comfort Levels

Additional Green Blog Posts:Energy Star Home Improvement Tips ,Insulation and Thermal Performance ,Which Kind Of Insulation Is Best? ,Radiant Barriers for your Attic,Insulating Roofs, Walls, and Floors, Roof and Attic Ventilation ,

Email scottscontracting and Scotty will provide a Free Estimate to Fix any of the Above Issues on your Home.

Radiation, Convection, Conduction-Warm to Cold

Convection is the movement of air in response to heat Convection happens inside walls too

Warm air rises, cool air sinks. Because walls and windows are usually cooler than the middle of a room, they spur convective loops that can feel like a draft. A similar thing can happen inside a wall cavity.

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

thermal bridge - wood Wood is a better insulator than nothing at all. Snow melts off the uninsulated rafter bays more quickly than directly above the wooden trusses, which have an R-valuearound 1.1 per inch, or R-4 for a 2×4 top chord.

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

Solar radiation Solar radiation. Solar heat radiates through the vacuum of space and warms the earth.

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.

Insulation and Thermal Performance

On Mon, Oct 25, 2010 at 9:50 AM, Scott’s Contracting <scottscontracting> wrote:

Thermal Performance is Just the Beginning

attic_blow.jpg InsulSafe ® 4, made by CertainTeed Corporation, is a formaldehyde-free, loose-fill, fiberglass insulation suitable for open-blow attic applications. The product contains recycled glass cullet and carries Greenguard™ certification for low emissions.


We last took a broad look at insulation materials exactly ten years ago: in the January/February 1995 issue. A lot has happened since then—manufacturers have introduced new insulation materials, new product formulations have eliminated problem materials such as HCFCs, and improved understanding of performance and health risks has informed our building practices.

But the fundamental issues have not changed over ten years. Insulation remains a critically important component of any green building—whether residential or commercial. No matter the type of insulation used, if it is used appropriately, its environmental benefits over a building’s life will almost certainly far outweigh any negatives—and dwarf any environmental differences among the alternative materials.

This article provides a survey of insulation materials, beginning with an examination of what insulation is and how it works. Much of the article focuses on life-cycle considerations for different insulation materials: environmental and health issues associated with resource extraction, manufacture, use, and disposal.

Understanding Insulation

To really understand insulation materials, you have to understand the basics of heat flow. There are three primary mechanisms of heat flow:

  1. conduction,
  2. convection, and
  3. radiation.

Thermal conduction is the movement of heat from direct contact: one molecule is activated (excited) by heat and transfers that kinetic energy to an adjacent molecule. We generally think of conduction occurring between solid materials—the handle of a hot skillet conducting its heat to your hand, for example—but thermal conduction also occurs with liquids and gases.

Convection is the transfer of heat in liquids and gases by the movement of those molecules from one place to another. As air is warmed, it expands, becomes more buoyant, and rises—a process called natural convection. Forced convection is the distribution of warm air by use of a fan or air handler.

 Finally, radiation is the transfer of heat from one body to another via the propagation of electromagnetic waves. A warmer body will radiate heat to a cooler body. When you sit in front of a fireplace and look into the fire, your face is warmed by the radiant transfer of energy from that heat source to your face. That radiant energy is not affected by air currents and occurs even across a vacuum—as we know from lying in the sun!

 Most insulation materials function by slowing the conductive flow of heat. Materials with low thermal conductivity more effectively block heat flow than materials with high thermal conductivity.

The R-value of an insulation material measures its resistance to heat flow. R-value is the inverse of U-factor, which is a measure of heat transfer, usually measured in Btu/hr·ft 2·°F or W/m 2·°C. Most insulation materials work by trapping tiny pockets of air (or some other gas).

The performance of that insulation material is determined primarily by the conductivity of the air, or other gas, in those spaces. If convection is prevented, a 1” (25 mm) air space has a conductivity of about 0.18 Btu/hr·ft 2·°F (1.02 W/m 2·°C). Its resistance to conductive heat loss, the inverse of that value, is R-5.5 per inch (RSI-38/m).

With fiber insulation materials, such as fiberglass, cellulose, and cotton, pockets of air are trapped between the fibers.

With cellular insulation materials, such as polystyrene, polyisocyanurate (polyiso), and polyurethane, the air—or other gas—is trapped within the plastic cells comprising the foam.

While resistance to conductive heat flow is the primary operative property of insulation materials, convection and radiation can come into play as well. With polyiso insulation, for example, according to Richard Roe of the Atlas Roofing Corporation in an August 2002 article in Interface magazine, 60–65% of the heat transfer is attributed to the conductivity of the blowing agent gases trapped in the cells, while 20–25% is attributed to the thermal conductivity of the solid polymer matrix, and 10–15% is attributed to radiation.

One key design features of an insulation material is keeping the air pockets small enough to limit convection within those spaces and radiation across those spaces.

With fiber insulation materials, the fibers have to be packed densely enough to effectively stop airflow through the material. (Air blowing through the insulation would carry heat by convection.)

With insulation materials that incorporate radiant barriers (foil-faced batt insulation, radiant-barrier bubble-pack insulation, and reflective barriers on rigid foam sheathing), the reflective surface functions by reducing radiant heat transfer. To function in this capacity, the reflective surface has to be next to an air space. The surface may function by reflecting heat radiation or (more commonly) by emitting less radiant energy from it. This is why a radiant barrier can reduce heat loss even when the reflective (low-emissivity) surface is facing the cold side.

Note that air leakage is a type of convection. Air leakage allows conditioned air to leak out of a building and unconditioned air to leak in—bypassing the insulated portions of the envelope. In older homes air leakage around windows, through poorly fitting doors, and across poorly detailed walls can sometimes account for over half of the total wintertime heat loss! Air leakage can also occur through an insulation material, which can reduce that material’s effective R-value. Loose-fill fiberglass, for example, usually allows more airflow than does cellulose insulation.

Life-Cycle Considerations with Insulation Materials

In this portion of the article, we examine the four primary life-cycle stages of any building material: raw material acquisition; manufacturing; the use phase, including indoor air quality concerns; and end-of-life disposal and recyclability.

 In each of these life-cycle stages we highlight key differences among insulation materials and discuss recent developments. Summaries of the key life-cycle considerations are presented by insulation material in the accompanying table.

Raw material acquisition

JM_install.jpg All Johns Manville fiberglass insulation is now produced with formaldehyde-free binders.


Fiberglass. The most prevalent type of insulation in North America, fiberglass is produced from silica sand with various additives, including boron. Most fiberglass also contains a fairly high percentage of recycled glass.

The recycled content can be pre-consumer (post-industrial) glass cullet from float-glass manufacture or post-consumer glass collected through bottle recycling programs.

In 2003 the fiberglass insulation industry used 1.1 billion pounds (500 million kg) of recycled glass, according to the North American Insulation Manufacturers Association (NAIMA), though the industry-wide split between pre-consumer and post-consumer recycled glass is not available.

 According to Robin Bectel of NAIMA, fiberglass insulation represents the second-largest market for recycled bottle glass (after the packaging industry).

Most U.S. fiberglass insulation has a minimum 20–30% recycled content. Owens Corning, for example, has been third-party certified by Scientific Certification Systems (SCS) to contain at least 30% recycled content—4% post-consumer and 26% pre-consumer, according to Jim Worden of the company. Johns Manville has an SCS-certified minimum recycled content of 25%; CertainTeed claims a minimum recycled content of 20–25% to meet U.S.

Environmental Protection Agency (EPA) requirements under the Comprehensive Procurement Guidelines (CPG); and Knauf Fiberglass claims a minimum 20% recycled content, all of it post-consumer. Recycled-content information for Guardian Fiberglass was not available.

Mineral wool. Mineral wool is made from both iron ore blast-furnace slag (an industrial waste product from steel production) and rock such as basalt. In 2003 the mineral-slag wool industry used 514 million pounds (233 million kg) of slag. This is down 45% from the slag use in 1992. Mineral-slag wool production is down in part because building codes are shifting away from the passive fire resistance that mineral wool provides toward active sprinklering of buildings.

Cellulose. Cellulose insulation is made primarily from post-consumer recycled newspaper, with up to 20% ammonium sulfate and/or borate flame retardants. While cellulose insulation used to be one of the highest-value uses of old newspaper, today dozens of de-inking plants in North America turn old newspaper into new newsprint. Producing cellulose insulation from old newspaper can be referred to as downcycling; from an environmental standpoint, turning a waste product back into a new form of the same material is preferable to turning it into a lower-grade material. (Note that producing fiberglass insulation from beverage bottles or glass cullet is also downcycling.)

Plastic foam insulation. Plastic foam insulation materials, including extruded polystyrene (XPS), expanded polystyrene (EPS), polyisocyanurate, and the various types of spray polyurethane insulation, are all produced primarily from petrochemicals. Both natural gas and petroleum are common feedstocks, and both have significant environmental impacts associated with their extraction, refining, and transport. At least two open-cell, spray polyurethane insulation products are manufactured in part from soybeans. Two-component BioBase 501 (see EBN Vol. 12, No. 9) and HealthySeal 500 are produced with soy oil comprising approximately 40% of the polyol component. (Polyurethanes are produced by reacting an isocyanate with a polyol, which is a type of alcohol.) The resultant polyurethane foam ends up being about 25% soy-derived and 75% petrochemical-derived.

Polystyrene. Recycled polystyrene can be incorporated into polystyrene foam insulation fairly easily, since polystyrene is a thermoplastic. At least one EPS insulation product contains recycled polystyrene: Polar 10 from Polar Industries is made with up to 40–60% post-industrial recycled content (see EBN Vol. 10, No. 2). The only XPS product that includes recycled content today is Owens Corning Foamular®, which is SCS-certified to contain a minimum of 15% pre-consumer recycled polystyrene.

Polyisocyanurate. Polyiso insulation incorporates a relatively small amount (9–10%) of recycled content to comply with CPG minimums. A portion of the polyol used in polyiso is produced from recycled PET bottles. The polyiso industry is one of the largest users of recycled, mixed-color PET bottles, according to the Polyisocyanurate Insulation Manufacturers Association (PIMA). The foil facings on many polyiso boardstock products may also contain some recycled content. header_left.gifheader_right.gif
Bonded_Logic.jpg Bonded Logic’s cotton insulation is manufactured from pre-consumer recycled denim waste.


Cotton insulation. Cotton insulation is made today by two manufacturers. Bonded Logic, Inc. and Inno-Therm, Inc. make batt insulation products from pre-consumer recycled denim scrap. The cotton or cotton-polyester fibers are treated with a nonhalogenated flame retardant. UltraTouch, produced by Bonded Logic, contains approximately 85% pre-consumer recycled fiber saturated with borate flame retardants to provide fire resistance. Inno-Therm is believed to be using a mix of borate and ammonium sulfate flame retardants. In addition to its use in batt insulation products, cotton insulation is used by Payless Insulation, Inc. in insulated flexible duct products; Bonded Logic supplies the cotton insulation for these products.

Cementitious foam insulation. The totally inorganic, cementitious Air Krete ® is produced from magnesium oxide, derived from seawater, and from a ceramic talc mined in Governor, New York. While essentially the same material as it was when last covered in EBN ( Vol. 6, No. 7), Air Krete has undergone some modest refinements, according to vice-president Bruce Christopher. “We have continued to improve both the product and the equipment for installation,” he told EBN. But he noted that friability—the fragility of the cured foam—remains their biggest challenge. “If there is a downside to Air Krete, it’s its friability.” Despite its resistance to the idea, the company may decide to add a little plastic to make it less friable, said Christopher. The challenge in adding plastic would be maintaining the superb fire resistance of the insulation material. While cost is highly variable, depending on location, size of the job, and other factors, it averages 30–50¢ per board foot, according to Christopher. Air Krete remains a very good alternative to another foamed-in-place insulation material used primarily for insulating masonry block, Tripolymer ® foam, produced by the C. P. Chemical Company. Tripolymer foam is a foamed phenol-formaldehyde insulation—a material that some manufacturers of urea-formaldehyde foam insulation (UFFI) switched to after formaldehyde emissions from UFFI led to its discontinuance in the 1970s.

Radiant barriers. Radiant barriers could be produced with recycled aluminum, but this is rarely if ever done, because very pure aluminum is needed to achieve the thin foils. Recycled polyethylene, however, can be used for the foam that is sometimes used with radiant barriers. Low-E ® Insulation, produced by Environmentally Safe Products, Inc., uses polyethylene foam with 40% post-consumer recycled content. In its TempShield™ radiant insulation product, Sealed Air Corporation uses 20% recycled-content cellular polyethylene for the insulation laminated between layers of reflective foil. A number of manufactured panel products have reflective facings glued to one side.

Manufacturing and transport

Fiberglass. Fiberglass insulation is manufactured with binders (typically phenol-formaldehyde) that hold the glass fibers together. The only fiberglass insulation material that did not contain a binder, Owens Corning’s Miraflex™ (see EBN Vol. 4, No. 1) was pulled off the market late in 2004. Manufacture of Miraflex was actually discontinued at the beginning of 2003, according to Gale Tedhams, Owens Corning’s product manager for residential insulation, but enough material had been stockpiled to sell it through 2004—mostly through Lowe’s stores. “It just had a very limited market,” Tedhams told EBN. Owens Corning did not promote the health benefits of not having a binder but focused on the packaging benefits—rolls of the insulation take up half the space of standard fiberglass. While the product carried a “slight price premium,” according to Tedhams, it was “very expensive to manufacture.” See additional discussion of binders used in fiberglass insulation under “Use phase and IAQ concerns.”

Cellulose. Because cellulose is inherently combustible, flame retardants are required to make it an acceptable material for building insulation. As has been the case for the past ten years, the primary flame retardants used in cellulose insulation are ammonium sulfate, borax, and boric acid. According to Daniel Lea, executive director of the Cellulose Insulation Manufacturers Association (CIMA), these additives are typically used in combination, though a few manufacturers offer products that use all-borate retardants.

Polyisocyanurate. The biggest environmental news in foam boardstock insulation has been the elimination of HCFC-141b in polyiso. The industry completed the transition from that ozone-depleting compound to the blowing agent pentane at the end of 2002. (Some manufacturers continued using stockpiled HCFC-141b in early 2003 while plant modifications were completed.) The transition to an ozone-safe formulation was a big step for polyiso, and it renders the product significantly better environmentally than extruded polystyrene (XPS), which in North America is still made with an HCFC blowing agent. In an industry that is generally slow to change, these changes in polyiso have been dramatic. In 1992 polyiso was all produced with CFC-11. By mid-1993 the polyiso industry had shifted completely to HCFC-141b, which has only about 10% the ozone depletion potential of CFC-11. Atlas Industries then led the transition away from HCFCs, introducing its ozone-friendly AC-Ultra™ in February 1998 (see EBN Vol. 7, No. 5). By May 2001 the company had fully converted three of its plants to pentane (see EBN Vol. 10, No. 5), with others converted early in 2002.

Polystyrene. Polystyrene has some fairly troubling chemical precursors in its production. The polystyrene used in both XPS and EPS is made by reacting ethylene (from natural gas or crude oil) with benzene (from crude oil, via naphtha catalytic reforming) to produce ethyl-benzene. The ethyl-benzene is converted into vinyl-benzene or styrene monomer, which is then polymerized into polystyrene. Benzene is listed in the 10th Report on Carcinogens, put out by the National Toxicology Program of the U.S. Department of Health and Human Services, as a “known carcinogen.” The International Agency for Research on Cancer (IARC) of the World Health Organization lists benzene as a “confirmed human carcinogen” and styrene monomer as a “possible human carcinogen.” Some material safety data sheets (MSDS) for polystyrene list residual styrene monomer as a constituent of the foam at levels up to 0.2%. While benzene is also used in polyiso and polyurethane production, these insulation materials are less likely than polystyrene to contain residual toxic chemicals.

Extruded polystyrene. XPS and EPS differ in how the foam is expanded—and they use quite different blowing agents. EPS has long been made with non-ozone-depleting pentane, but XPS still relies on HCFCs. Though the XPS industry led the charge in replacing CFCs with far-less-damaging HCFCs, it is today the only type of boardstock insulation that remains harmful to stratospheric ozone. Amofoam (now Pactiv) was the first company to switch from CFC-12 to HCFC-142b, in 1990, and the entire XPS industry completed that transition in 1992. The transition away from HCFC-142b is not likely in the U.S. until close to the 2010 EPA deadline for doing so (see EBN Vol. 11, No. 7), according to Worden at Owens Corning. While European manufacturers of XPS shifted to either HFC-134A or carbon dioxide in 2002, more stringent energy standards and different construction systems in North America make the same sort of conversion more difficult here, says Worden. European XPS is a higher-density product with a lower R-value.

Expanded polystyrene. Expanded polystyrene (EPS) continues to be made with non-ozone-depleting pentane as the expanding agent. Some manufacturers are using a low-pentane formulation that results in lower pentane emissions. (While not an ozone-depleting compound, pentane can generate ground-level smog.) The more distributed production of EPS, compared with XPS, may reduce shipping energy consumption to some extent.

Flame retardants and polystyrene. All foam plastic insulation materials rely on flame retardants to meet fire-resistance standards. EPS and XPS are produced using the brominated flame retardant HBCD (hexabromocyclododecane) at concentrations of 0.5–2.0% by weight. HBCD is not the focus of as much attention as another class of brominated flame retardants (PBDEs), but some evidence indicates that it is more bioaccumulative than PBDEs and just as likely to be toxic to humans (see EBN Vol. 13, No. 6).

Flame retardants and polyisocyanurate. Ironically, until recently flame retardants were not used in most polyiso insulation. With HCFC blowing agents, this thermoset plastic foam was able to achieve the required Class I fire ratings without any added flame retardant. But with the substitution of pentane blowing agents for HCFC-141b, manufacturers now must add flame retardants. Although manufacturers rarely divulge their formulations (and can apparently get around the requirement to list the flame retardant in the MSDS because it is part of one component or the other (the polyol or isocyanate), the most common flame retardant used in polyiso today is believed to be TCPP (tris(chloropropyl) phosphate), a compound that relies on both phosphorous and chlorine as the fire-retarding components. The typical concentration in the foam insulation is 5–14% by weight. While a halogenated compound, TCPP is much less likely to be a persistent bioaccumulative toxin than HBCD, according to the PBT Profiler software from EPA.

Spray polyurethane. While polyiso manufacturers had to eliminate their use of HCFC-141b by January 1, 2003, manufacturers of closed-cell (high-density) spray polyurethane were given an extension for the transition to non-ozone-depleting blowing agents. HCFC-141b for spray polyurethane cannot be sold after December 31, 2004, though polyurethane installers can use inventoried HCFC-based chemicals until July 1, 2005, according to Ken Gayer, the global business manager for foam blowing agents at Honeywell Specialty Materials, which produces the non-ozone-depleting blowing agent HFC-245fa under the tradename Enovate 3000. Most spray polyurethane companies are converting to Honeywell’s HFC-245fa. While significantly more expensive than HCFC-141b, the resultant foam achieves similar energy performance. The ozone depletion potential of HFC-245fa is zero, but the global warming potential is similar to that of HCFC-141b. Hydrocarbon blowing agents are avoided with spray polyurethane because of flammability concerns and difficulties with the vapor pressure, according to Gayer. header_left.gifheader_right.gif
Icynene.jpg Low-density, open-cell polyurethane produced by Icynene is material-
efficient and uses water as the blowing agent.


Open-cell polyurethane, including the products made by Icynene, Inc. and Demilec, Inc. as well as the newer soy-based foams, are produced with water as the blowing agent. They do not achieve R-values as high as those of closed-cell polyurethane, but they are more resource-efficient, using just one-fourth to one-third the material used for a comparable volume of closed-cell polyurethane.

Flame retardants and spray polyurethane. Both closed-cell (high-density) and open-cell (low-density) polyurethane insulation contain flame retardants, but these are non-brominated flame retardants. While manufacturers are reluctant to share this information, the best available information indicates that the two flame retardants most commonly used in spray polyurethane are TCPP, which contains chlorine but not bromine, and RDP (resorcinol-bis-diphenylphosphate), which is totally halogen-free.

Use phase and IAQ concerns

Fiberglass and mineral wool. Concerns about mineral and glass fibers possibly being carcinogenic have been widely publicized over the past ten years—especially by competing industries. These concerns resulted in cancer warning labels being required for most products, but more recently these concerns are waning. In October 2001, IARC changed its classification for fiberglass and mineral wool from “possible human carcinogen” to “not a known human carcinogen.” This change has allowed mineral wool (slag wool and rock wool) manufacturers to drop the warning labels. Fiberglass insulation continues to carry the cancer warnings because, in addition to the IARC listing, the National Toxicology Program added glass fibers to its Report on Carcinogens in 1990. According to Angus Crane, the vice president and general council for NAIMA, glass fibers were added to the NTP possible-carcinogen list because of the IARC-reported studies. Now that IARC has dropped the possible-carcinogen listing for glass fibers, the material is likely to be dropped from the NTP list. NAIMA has petitioned NTP to delist glass fibers, but that process typically takes several years. Crane hopes to see the listing removed in late 2005 or early 2006. If and when that happens, the industry will petition the State of California to remove the requirement under Proposition 65 that fiberglass insulation products include a warning about cancer. Meanwhile, the carcinogenicity of formaldehyde, which could be released in very small quantities from the phenol-formaldehyde binder used in most fiberglass insulation, has recently been upgraded. In June 2004, IARC changed its classification of formaldehyde from a “probable human carcinogen” to a “confirmed human carcinogen.” Most of this binder is volatized and dissipated during a baking stage of the manufacturing process, but residual formaldehyde may remain in the product. Johns Manville, one of the five major producers of fiberglass insulation in North America, switched to 100% acrylic binder for its fiberglass insulation product line in 2002 (see EBN Vol. 11, No. 3). The other major fiberglass insulation manufacturers have all had their products certified as low-emitting by Greenguard™.

 Mineral wool. For cavity-fill and attic applications, rock wool and slag wool are similar to fiberglass in look and feel, though the density is greater and the sound control better. The fire resistance of mineral wool is also significantly better than that of fiberglass, because of both the higher density and the significantly higher temperatures required for melting. While these fire-resistance properties used to be a major selling point, greater reliance on sprinklers in buildings, rather than passive fire resistance, is resulting in decreased use of mineral wool, according to Crane of NAIMA. For below-grade applications, one rigid mineral-wool product, Roxul drainboard, offers superb performance, owing to its hydrophobic properties and its excellent drainage characteristics (see EBN Vol. 4, No. 6). This material has never been actively marketed in the U.S., but Roxul products in general are becoming more widely available here.

Cellulose. Cellulose insulation has never been required to carry indoor air quality warnings, and the fiberglass and mineral wool industries remain upset that their products have come under greater scrutiny than cellulose. “Our competitors have not gone through the testing,” said Angus Crane of NAIMA. “It is dangerous to assume that an untested material is safe,” he told EBN. The editors at EBN continue to take the position that all fiber insulation products (fiberglass, mineral wool, and cellulose) are safe if properly installed, and we would much prefer to see insulation manufacturers focus on the positive benefits of all insulation, rather than potential risks of their competitors’ products. The health concerns with cellulose range from inhalation of dust during installation to VOC emissions from printing inks (which are now almost entirely vegetable-based) and limited evidence of toxicity of boric acid flame retardants. For more on health issues with cellulose insulation see EBN Vol. 2, No. 5. As for installation and performance, cellulose insulation has evolved considerably over the past 20 years. According to Daniel Lea of CIMA, the average installed density of cellulose insulation has dropped from 2.6 pounds per cubic foot (42 kg/m 3) in 1984 to 1.6 pcf (26 kg/m 3) today. “R for R, today’s cellulose insulation products are almost 40% lighter than those of 1984,” said Lea. Most cellulose insulation today is being installed as “cellulose wall-cavity spray,” a process that has sometimes been referred to as “wet-spray” cellulose. CIMA is trying to discourage the use of the term wet-spray because it implies a process that is far wetter than is the case. “I think there is a perception that the material is applied almost as a fibrous papier-mâché,” said Lea. “That is far from the case; if you were to touch wall spray seconds after it’s applied, you probably couldn’t tell that water was added during the installation process,” he said. The typical installed moisture content today is 30–35%, according to Lea, while a moisture content as high as 60% was not uncommon 15 years ago.

 Fiber insulation installation. Quality dust masks or respirators should be used while installing fiberglass, mineral wool, and cellulose. (Cotton insulation is the only fiber insulation material that can be installed safely without protective measures.) Building design and detailing should ensure that fibers cannot enter forced-air distribution or ventilation systems. Airtight construction practices should be used to ensure that fiber insulation stays where it was installed.

Polystyrene. Indoor air quality concerns with XPS and EPS are similar to concerns addressed previously relating to manufacturing: the potential release of residual styrene monomer and flame retardants. The brominated flame retardants used in polystyrene present a greater health concern than the nonbrominated flame retardants used in polyisocyanurate, spray polyurethane, and cellulose insulation.

Polyisocyanurate. Now that polyiso is no longer produced with HCFCs, it is the environmentally preferred rigid boardstock insulation for above-grade applications. (Polyiso is not recommended for below-grade applications because it can absorb moisture.) Polyiso manufacturers disagree as to whether rigid foam produced today with hydrocarbon blowing agents achieves an R-value comparable to that of the older material made with HCFC-141b. The conductivity of the hydrocarbon blowing agent is higher than that of HCFC-141b, and this has led Dow Chemical to downgrade the rated R-values for all of its polyiso insulation, including Thermax ®. However, Richard Roe of Atlas Roofing argues that the smaller cell size of foam produced with hydrocarbon blowing agents, the slower diffusion rate of the hydrocarbon out of the polymer cells, and the lower absorption of the hydrocarbon blowing agent by the polymer collectively result in better long-term R-value stability. Most polyiso manufacturers are now using new long-term thermal resistance (LTTR) values for reporting aged R-values. This method was adopted in Canada in mid-2002 and in the U.S. in January 2003. This method produces 5-year aged R-values that are lower than the 6-month aged R-values that had previously been reported. The bottom line is that the rated long-term stabilized R-value of polyiso is now between R-6 and 6.5 per inch (RSI-42 to 45 per meter), depending on thickness and facings.

Closed-cell polyurethane. Closed-cell, high-density polyurethane is a very good performer owing to the low-conductivity gas in the cellular structure. It is used both for cavity installation and as an insulating roofing material, which is typically referred to as spray polyurethane foam or SPF. The closed-cell structure gives SPF structural properties. There should be no significant impact on R-value with the shift to non-ozone-depleting HFC-245fa blowing agent, which is becoming the industry standard. Polyurethane also exhibits superb adhesive properties and good compressive strength.

Open-cell polyurethane. Open-cell polyurethane is most commonly installed into open cavities, though formulations are available for filling closed cavities from holes at the top. This is a nonstructural foam, though these materials seal very well, and their flexibility allows for some movement of the framing materials as shrinkage and expansion occur. These properties make them very effective insulation materials for older buildings. Both closed-cell and open-cell polyurethane must be installed by trained professionals. Special care is required to ensure the safety of insulation installers working with these materials; other people should not be in the space while polyurethane insulation is being installed. Once cured, polyurethane insulation is considered by most IAQ experts to be quite inert.

End-of-life reuse and recyclability

Loose-fill and batt insulation. It is difficult to salvage loose-fill or batt insulation and reuse it, though this can be done. Virtually no fiber insulation is recycled after use in buildings—due to contamination with dust and other materials. Scrap insulation generated during installation can be collected and reused quite easily. header_left.gifheader_right.gif

Insulation Materials – Summary of Environmental and Health Considerations

Insul_table.gif[enlarge image]

Rigid boardstock insulation. Rigid insulation can be salvaged and reused if it is protected during removal. For roof insulation applications, reuse is most feasible when protected-membrane or inverted roof configurations are used (see EBN Vol. 7, No. 10). In this system, a non-water-absorbing rigid insulation, such as XPS, is laid on top of the roof membrane, and ballast is installed on top of the insulation. When re-roofing is required, the insulation can be removed and stored for safekeeping, then reinstalled after the new roof membrane is laid down. Of the rigid insulation materials, only polystyrene can be recycled. This thermoplastic can be melted and re-expanded into either polystyrene insulation or packaging. Unfortunately, very little polystyrene is being recycled currently. Polyiso and polyurethane cannot be recycled because these foams are thermoset plastics.

Final Thoughts and Recommendations

Insulation is a key component of any green building. More important than the decision of what type of insulation to install is the decision of how much insulation should be installed. From an environmental standpoint, a thicker layer of a relatively nongreen insulation material is almost always better than an inadequate thickness of the greenest insulation material available. This point cannot be over-emphasized. However, assuming that adequate R-values can be achieved, choosing a green insulation material over a nongreen one can be a very good decision. The accompanying table should help to identify materials that meet your needs and satisfy the environmental priorities of your project.

Summary recommendations:

• Provide the highest feasible insulation levels.

• With lower R-value materials, increase insulation thickness.

• Avoid extruded polystyrene due to the ozone-depletion potential of blowing agent.

• Except where moisture may be an issue, use polyiso instead of either XPS or EPS.

• Rigid mineral wool, such as that made by Roxul, is a very good foundation insulation material due to its superb drainage properties.

• With highly conductive framing systems, especially steel, minimize thermal bridging by wrapping the frame with a layer of rigid board insulation.

• Choose high-recycled-content insulation materials when doing so will not result in significant loss of R-value compared with other materials.

• With roof insulation, consider a protected-membrane roof so that insulation can be reused.

 • Address air leakage and moisture resistance in insulation detailing.

A good source of information on building science issues is www.BuildingScience.com.

• For chemically sensitive individuals, test potential insulation materials for reaction before installation.

• Choose an insulation contractor who recycles scrap insulation. – Alex Wilson

Contact Scotts Contracting for a Free Green Estimate on your Green Building Initiatives

Insulating Roofs, Walls, and Floors


It’s 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.
Click the photo examples of the three grades.

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 EPS, XPS, 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 (click photo to enlarge) 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 (CMU) 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 (click drawing to enlarge).

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.

EPS, XPS, 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.

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. More on Enclosure Design.

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 BuildingScience.com.


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 BuildingScience.com.


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.

OTHER THERMAL BRIDGES Uninsulated slab edges
Window frames
Wall and roof penetrations