If It Ain't Broke, Why Fix It?

Something old and a few things new in the choices of insulation material and installation.

May 06, 2009
May/June 2009
A version of this article appears in the May/June 2009 issue of Home Energy Magazine.
Click here to read more articles about Building Envelope
In the last two decades there has been tremendous growth in the variety of insulation products, and in our understanding of those products. This has accompanied a boost in fraudulent and near-fraudulent claims (for example, that reflective foils are a good alternative to wall or subslab insulation). There are also new types of insulation that are better suited for some installations than for others. Most importantly, the development of building science and sophisticated measurement tools has allowed the shortcomings of standard insulation methods to be better understood.

It is important to understand that the published R-value of an insulating material is based on laboratory testing. This testing does not take into account the degrading effects of air infiltrating through the building envelope, which can increase heating-and-cooling costs by up to 40%. Most insulation works by trapping pockets of air (or other gases) to retard the conduction of heat. For this reason, any batt insulation can be a reasonable insulator if it is properly applied with no voids, and if the cavity is airtight. But the real world of construction is rarely airtight, and fiberglass batting with air passing through it loses R-value. With this in mind, it is easy to see why insulation that both has a high R-value and is airtight has a decided advantage. Often, airtightness is not a factor of the material itself but of the application technique. Fiberglass and cellulose can be applied on-site under pressure using special equipment to create a dense-pack that results in much greater airtightness than loosely packed or batt insulation.


Fiberglass insulation is the workhorse of the industry and the product most associated with the word “insulation.” (The various types of insulation are summarized in Table 1.) The R-value of fiberglass insulation ranges from R-2.6 to R-4.4 per inch for batts and most loose-fill installations. Properly installed in airtight walls, it works well. However, if it is installed with any voids at all, performance can degrade markedly. In walls, this appears to be due primarily to air convection around, and possibly through, the batts. The Residential Energy Services Network (RESNET), in order to include insulation effectiveness in its rating standards, assumes that R-38 batts with 2% voids and/or minor compression will provide only an R-22 insulating value. Conservation Service Group’s Bruce Harley, at an Affordable Comfort conference, commented on the subject that “Like a boat with a hole in it, I don’t care about how thick the wall is, I care about the size of the hole.”

Poor installation is so common that the California Energy Commission expects that virtually all builders will initially fail to meet suggested quality guidelines. Adding a layer of rigid insulation or building double walls so that there are always at least two layers of insulation will ameliorate the effect of imperfections, and also reduce thermal bridging through the wood studs. (For an example of effective double wall construction, see “Wisdom Way Solar Village,” HE March/April ’09, p. 24.) The Maine State Housing Authority’s Green Building standards do not consider the use of fiberglass batts that nominally meet code for walls to qualify unless the wall includes a layer of rigid insulation.

Insulating attics with one or more layers of fiberglass batts alone is another recipe for not getting what you pay for. Fiberglass manufacturer Owens Corning did a study in their own lab that found R-19 batts laid in a standard-truss attic measured only R-13.6, and double R-19 batts (R-38) measured a meager R-25.6. Blowing a layer of cellulose over an attic already insulated with batts or blown fiberglass is usually a good investment, because the blown-in cellulose has better gap-filling and air-sealing properties than fiberglass batts. (Hint: Be sure to test for and seal any air leaks below the fiberglass before you add anything on top!)

That said, there are advantages to fiberglass, primarily price. Installed perfectly, or in a redundantly insulated wall, it can work well. Large insulation contractors, often famous for sloppy work, can sometimes install fiberglass for less than a small builder would pay to buy it. If you are in a position where fiberglass must be used, shop around, and police the installation quality.

Fiberglass batts are now available in different densities. For instance, 3 ½ -inch batts come in R-11, R-13, and R-15. Prices vary. Compressing a 6-inch R-19 batt into a 3 ½ -inch space will provide approximately R-15 and could be cheaper than installing an R-15 batt. One note: Many R-19 batts are 6 inches or more, and when installed in a 5 ½ -inch cavity, they provide approximately R-17.5. Measured whole-wall performance, due primarily to conduction through the wood framing and somewhat affected by compression of the batts, was only R-13.5 in a test of an R-19 wall by Oak Ridge National Laboratory. Attention should be paid to framing techniques to reduce thermal bridging that will degrade the performance of all cavity insulations.

Cellulose insulation is often dense-packed, but dense-packing also works well with fiberglass in both retrofitting and new construction, because it provides better air sealing than loosely packed insulation of both kinds. Fiberglass can also be sprayed damp with a binder or dry behind plastic sheeting or net mesh. The catch is expense, but installed performance is superior to that of standard batts. Sprayed fiberglass also attenuates sound much better than standard batts.

Fiberglass (like cellulose and rock wool) can also be incorporated into an encapsulated product that can be sprayed onto smooth or rough surfaces, such as metal roofs, concrete basement walls, ducts, pipes, or rim joists. It has the consistency of shaving cream and can be troweled smooth or textured, as desired. A great advantage is that it need not be covered with Sheetrock, since it has a class A rating (zero flame spread).


Once considered inferior, cellulose has grown into an excellent insulation product. The R-value per inch ranges from 3.2 to 3.6. It is composed of recycled newspaper and a fire retardant. Stabilized cellulose also contains an adhesive, usually starch. Years ago, insufficient density was a problem and led to significant settling over time. Today, cellulose is often installed dense-pack to densities of 3.5–4.5 lb/ft3 to ensure that voids are filled and gaps do not form over time due to settling. The only drawback to dense-pack is greater cost and a reduction in R-value from 3.5 to 3.2 per inch. New fiberization technology now commonly used produces more-resilient cellulose, and nonsettling densities as low as 2 lb/ft3 are plausible. (Oddly, there is still no ASTM standardized test to measure settling in walls.) Significant voids can still be left when cellulose and other insulations are blown into old walls that have undetected blocking. Using an infrared camera during installation can solve this problem, but this adds to the labor and the cost. Dense-pack installation uses a long tube that detects most obstructions. We always recommend using a contractor familiar with this method, because, as with any trade, there are many tricks to ensuring good performance. If installed properly, dense-packed cellulose will perform well and will also substantially decrease air leakage in an old house.

Blown into an attic, cellulose normally settles a good deal. Installers can specify a written guarantee of settled depth, with markers installed to facilitate checking by the homeowner. New cellulose products are available that provide a higher R-value-weight ratio. These products allow ceiling installations in excess of R-50 without cosmetic problems caused by nails popping in the Sheetrock.

Cellulose can also be installed in open wall cavities. For dry installations, a tough, cross-linked polyethylene material through which the cellulose is blown is placed on the framing after wiring and plumbing is completed. This method provides a good vapor barrier as well as the possibility of visually confirming the absence of voids. A less expensive alternative uses a fabric net rather than polyethylene. (This fabric net is not a vapor barrier.)

Spraying cellulose into open cavities with an adhesive binder is an excellent option that is growing in popularity. Cost and availability will depend on the proximity of an installation contractor. This method can be messy, and problems can arise if the installer does not follow the guidelines for proper moisture content before the drywall is installed. Drying time can delay the application of Sheetrock.

One new cellulose technology on the horizon that has been the subject of recent research at Oak Ridge National Laboratory has a phase change material (PCM) mixed in. The PCM causes 12 inches of cellulose to act like 4 inches of concrete in terms of its ability to store and release heat, but R-value is unaffected. Pilot installations in houses are planned for 2009.


Cotton insulation, using recycled factory castoffs (a.k.a. preconsumer materials) and other cotton fiber textiles, has become popular in recent years. It is available only in batt form, making it suitable primarily for open cavities in walls. Unlike fiberglass batts, cotton batts should be used only for the cavity depth specified (such as 5 ½ -inch batts for 2 x 6 walls). Cotton insulation is available in R-13 for 3 ½ -inch batts and R-19 for 5 ½ -inch batts. Many builders find the batts difficult to cut, and it should be noted that cotton dust could cause respiratory problems; installers who work with cotton should always wear masks.

Cementitious Foam

Cementitious foam is a lightweight material with the decidedly unconcretelike R-value of 3.9 per inch. Composed only of magnesium oxide (derived from seawater), calcium, and silicate, it is essentially just a mineral and contains no petrochemicals. Once cured, the foam can be cut with a saw, but it is not an adhesive, like urethane foams; it can crack; and the seal to the studs can come loose over time. Cementitious foam is not a vapor barrier; however it is virtually fireproof, and it is often specified for this reason.

Are You Confused Yet?

Confused about sprayed foam? Is it safe? Is it green? You are in good company, including many producers, installers, builders, and homeowners. Claims that a product is “environmentally safe” abound, but there are many complex variables that cloud the issues around what is safe and what is good for the environment.

Suffice it to say that any product that prevents heat loss or gain from a building can claim to be green, because most people now accept the simple reality that a Btu saved is a Btu earned for the environment. But there’s more to it than that. Embodied energy creates excess CO2 during production and transportation; substances that contribute to global warming off-gas during production and application; and off-gassing of some substances may have long-term harmful effects on occupants’ health. Urea-formaldehyde foams, first used in the early 1980s and now banned by most states, may pollute indoor air long after they are installed. Modern sprayed polyurethane foams (SPFs) stabilize quickly after installation, and most, but not all authorities consider them safe for humans. How much they contribute to global warming is still under debate.

All SPFs consist of two parts, mixed 50/50. Part A is polymeric isocyanate, a petroleum derivative. Part B is a mixture of catalyst, surfactants (determine whether cells are closed or open), fire retardants, blowing agent (creates the bubbles), and polyols (which can be petroleum or soy based). So when you read claims about a “green” soy-based foam made from recycled plastic, 85%–95% of that foam still comes from fresh petroleum, and only 5%–15% comes from soy and/or recycled plastic.

The formulas are proprietary trade secrets, the chemicals and reactions are very complex, the promotional claims are frequently outlandish, and the long-term safety and stability of the end product may be unknown. Sorry to say there is currently no final word on what is “green” for the planet and safe for humans. Any builder, designer, or homeowner who is considering installing sprayed-foam insulation (or for that matter, any insulation) should learn as much as possible about the product first.
Caveat emptor!
Sprayed Polyurethane Foam

There are a variety of sprayed polyurethane foams (SPFs), with different densities, installation methods, and chemical formulas (see “Are You Confused Yet?”). SPFs are either open cell or closed cell. Open-cell SPFs are also referred to as ½ lb—meaning weight per cubic foot—or low-density foams. These foams expand to over 100 times their liquid size and require trimming and disposal of the waste. They cure soft, and the bubbles that form during the expansion reaction are open. These pockets fill with ambient air; therefore the R-value of open-cell SPFs is close to that of still air, about 3.6 per inch. This is similar to the R-value of both fiberglass and cellulose, because all three are based on the principle of trapping dormant air. Open-cell SPFs form a more effective air barrier than conventional blown fiberglass or cellulose, because they are spray applied and conform to seal the wall cavity. Open-cell SPFs do not form a vapor barrier.

Closed-cell SPFs are referred to as 2-lb, or medium-density foams. These foams expand to 20 to 30 times their liquid size and seldom require trimming. Closed-cell SPFs cure rigid, and the microscopic bubbles that form during the expansion reaction remain closed. This traps the reaction gases, or blowing agent, and the R-value of a closed-cell SPF is specific to that gas—between R-5.5 and R-7 per inch. Blowing agents are often trade secrets. Closed-cell foam structure is very strong and can increase shear and racking strength by 300%.  Closed-cell SPFs form a very good vapor barrier, with a permeability rating of less than 45 ng.

Both forms of urethane spray foams, opened-cell and closed-cell, are expensive, but they can provide excellent air sealing and R-value. One option is to specify a thin layer of polyurethane sprayed on the framing and exterior siding, and to fill the remainder of the cavity with fiberglass or cellulose. Beware of very-high-performance claims (such as R-20 for a 2 x 4 wall). These claims tend to ignore the deleterious effect of the solid-wood farming that makes up 20%–30% of the wall.

Nonurethane Foams

At least two nonurethane foams on the market are suitable for retrofitting in sealed wall cavities. One is a powdered product that is mixed with water on-site and injected into cavities. This is a reformulation of the old urea-formaldehyde product; it is specifically designed to eliminate the possibility of high formaldehyde levels caused by installer error. The liquid is mixed at the factory and then baked into a dry powder, which contains no free formaldehyde (it says “No Formaldehyde” on the material safety data sheet (MSDS)). (Although some formaldehyde is re-formed when water is added to the powder for installation, the manufacturer states that the residential product is specifically formulated to promptly and completely rebind, leaving no potential for free formaldehyde.) According to the manufacturer, this provides all the insulating benefits of urea-formaldehyde without any of the risks. The fact that this product does contain formaldehyde may give some installers pause, but the manufacturer claims that off-gassing levels are comparable to those of fiberglass batts—at less than 0.1 ppm, nearly unmeasurable. In all products containing urea-formaldehyde, formaldehyde levels could rise if the product comes in contact with water or persistent very high humidity.

Another product that can be used to retrofit sealed wall cavities is tripolymer foam. As the name suggests, it is a combination of several chemicals, though it contains no formaldehyde. The manufacturer claims that it is nontoxic and has a shrinkage rate of about 1%. (This could cause gaps to occur, depending on the depth and width of the cavity.) This is also a cold-setting foam, which does not expand after leaving the tube. R-value is also impressive at 5.1 per inch.

Rigid Insulation

This review does not cover rigid insulation boards in depth. Briefly, you will get the best R-value bang for the buck with white expanded polystyrene (EPS or Styrofoam). EPS is best used where space allows it to be installed at a greater than normal depth; R-value can be as low as R-3 per inch, depending on manufactured density. Extruded polystyrene (XPS) is R-5 per inch. It comes in pink or blue boards, typically with tongue-and-groove joints. Polyisocyanurate (such as Thermax) is usually foil faced; it starts out at greater than R-7 per inch but declines over about 15 years to stabilize at R-5.5 per inch. Foil taping the joints should extend the duration of the higher insulating value.

Other Types of Insulation

FOIL AND REFLECTIVE BUBBLE PACK. Reflective foil and reflective bubble pack insulations are frequently sold as comparable to fiberglass in performance, but any such claim is generally a fraud. Despite vigorous marketing and wishful thinking, foil alone is a good radiant-heat reflector, but it has near-zero R-value. If foil is installed next to a sealed ¼-inch to ¾-inch vertical air space, this air space can be up to R-3, as opposed to R-1, without foil insulation. Installing radiant foil alone under concrete is another thermal disaster—no air space, minuscule R-value. Reflective surfaces where heat flow is downward and there is an air space (such as floors, and the underside of roof sheathing in summer) can perform well with appropriate detailing. Attic reflective foils work well at keeping out summertime heat but are generally not cost-effective in northern climates. Reflective bubble pack should not be used as a sole insulation under a slab floor; despite claims to the contrary, the R-value tests out at around 2.4 (see “Foil Bubble Pack: Subslab Insulation?” HE Nov/Dec ’04, p. 6).

A variety of wool insulation products are in use worldwide. These are typically minimally processed, washed, and sold either in batts or loose. Avoid unwashed wool, unless you are willing to tolerate a house that smells strongly like a sweater! An Internet search is the best way to find up-to-date info on suppliers of wool insulation.

EMBODIED ENERGY that is, the amount of energy used to manufacture and transport a given material—is an important consideration for many in choosing building products. Estimates of the embodied energy (EE) in various types of insulation can vary widely, depending on the source, but the numbers we came up with will give you an idea (see Table A).

Note that despite the wide range of figures, any one of these insulations will probably save enough energy over the first heating/cooling season to fully make up for the embodied energy.
Green Is In

Whether or not a material is green or not depends on the way the word green is defined. Some insulation can be hazardous if it is not treated properly. And making some insulation products uses more energy than making other insulation products (see “Embodied Energy”). But if energy efficiency is green, then insulating a house is a primary green activity, since, if done correctly, it makes a home more energy efficient and comfortable.
Insulation may at last come into it’s own. There is more recognition of insulation installation as a skilled profession; there is greater sex appeal due to the popularity of green building; and there has recently been a dramatic spike in government support for energy efficiency. The variety of products and proven technology bode well for the interesting times ahead.   

David Kaufman is an energy consultant with Energy Solutions in Maine. E-mail him at dk@energyforbuildings.com.

Al Heath is a builder and energy consultant with Energy Solutions in the Portland, Maine area and the Mid-Coast area of Maine.  E-mail Al at alzane2000@yahoo.com.

>> For more information:

For information about research at Oak Ridge National Laboratory into whole-wall R values of various insulation materials, phase change materials, and other building technologies, go to: www.ornl.gov/sci/roofs+walls/articles/index.html.

For more on some of the insulation products mentioned in this article, see:

Guardian UltraFit. Tel: (800)245-5784; Web: www.guardianbp.com.
Blown-in-Blanket. Tel: (800)525-8992; Web: www.bibs.com.     

Par-Pac. Tel: (877)937-3257; Web: www.parpac.com.    
Regal Wall. Tel: (800)848-9687; Web: www.regalind.com.
Nu-Wool. Tel: (800)968-9866; Web: www.nuwool.com.   

Bonded Logic. Tel: (480)812-9114; Web: www.bondedlogic.com.
Cementitious Foam Airkrete. Tel: (315)834-6609; Web: www.airkrete.com.    
Encapsulated Spray Fiberiffic. Tel: (800)525-8992; Web: www.fiberiffic.com.

Icynene. Tel: (800)758-7325; Web: www.icynene.com.       
Demilec. Tel: (877)362-6496; Web: www.demilecusa.com.
Biobased. Tel: (800)803-5189; Web: www.biobased.net.    

Other Foams
Retrofoam. Tel: (800)580-3626; Web: www.retrofoam.com.
Tripolymer. Tel: (914)428-2517; Web: www.tripolymer.com.

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