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Insulation ABCs

By HHI Staff

Insulations are made from different materials, and there may be negative health effects associated with some of them. In most cases insulation stays inside walls or ceilings where it was placed. However, there have been instances in which insulation has migrated into the living space during installation or remodeling, and cases where insulation moves through the gaps and cracks in the walls or into ductwork, causing health problems for occupants. On the whole however, insulation installers are at greater risk than occupants of insulated houses.


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(From Healthy House Building for the New Millennium: A Design & Construction Guide, by John Bower, published by The Healthy House Institute.)(This article is from the archives of the original Healthy House Institute, and the information was believed accurate at the time of writing.) 


Insulating materials


Even though insulation is not usually a problem, many people are concerned about the negative health effects which can potentially be very serious. Therefore, I will cover the most common residential insulations on the market today (foam products, cellulose, and fiberglass) as well as alternative products.


Foam Insulation


Expanded polystyrene (beadboard), extruded polystyrene, and polyisocyanurate are the usual rigid foam insulating boards that are available today. I discussed some of these materials in Chapter 6 in conjunction with the foundation and in Chapter 9 as sheathing. They all outgas small amounts of chemicals that, in theory, can cause reactions in sensitive individuals. Surprisingly, I have found that when sensitive people are exposed to these products, they are often not affected. Apparently, the rate of outgassing is so slow that the concentration of airborne chemicals is too low to be a problem.


Polyisocyanurate foam is currently manufactured with a CFC chemical that damages the ozone layer. Until recently, all manufacturers of extruded polystyrene used similar chemicals, but they have begun switching to HCFC chemicals that have 94% less potential for ozone depletion. They still aren’t perfect, but there has been considerable improvement. Expanded polystyrene uses pentane, a hydrocarbon gas, instead of CFCs or HCFCs. The pentane can contribute to localized smog but has almost no effect on the ozone layer because of its short lifetime in the atmosphere.


Foam insulation is also available in a form that can be injected into walls, ceilings, or floors by trained installers. It typically has the consistency of shaving cream when installed, then hardens to a rigid or semi-rigid product. The most notorious of these foam insulations was urea-formaldehyde foam insulation (UFFI). This material was popular during the energy crisis of the 1970s. Unfortunately, when improperly installed, it released large amounts of formaldehyde into the indoor air. I once spoke with a very conscientious installer of this material who felt that, in his opinion, it was impossible to install it correctly. He said it was so tricky to work with that you either got a great deal of shrinkage, which meant that it didn’t insulate very well, or it gave off formaldehyde gas. Because of these drawbacks, UFFI has virtually disappeared from use.


Air-Krete is a relatively new foam insulation available in some parts of the country. Like UFFI, it is injected into wall cavities where it hardens. Unlike UFFI, it is quite benign. Air-Krete releases no formaldehyde and is well tolerated by most sensitive people. Air-Krete is a very lightweight cement-like product, so it outgasses very little, but it is quite expensive, costing up to six times more than fiberglass insulation.


Cellulose Insulation


Cellulose insulation is made from recycled newspapers that often contain toxic inks. It is chemically treated (usually with boron compounds) to make it fire-resistant and to discourage insects from nesting in it. There are actually very few regulations dealing with cellulose insulation, so it could become contaminated with virtually anything.

Cellulose insulation can be installed in two different ways—wet or dry. The dry method, used most often in existing houses, involves “blowing” the insulation through hoses into small holes drilled in the side of a house. The holes are then plugged. Since dry cellulose is a very finely ground material, during installation it can filter its way through gaps in the structure into the living space where it will be breathed by the occupants. This can be minimized by requiring the installer to have an assistant indoors at all times to watch for any insulation that is getting into the house. If any material enters the occupied space, work should stop immediately until any leakage points are sealed. Special care should be taken when insulating walls to which cabinets or indoor soffits are attached, near false ceilings, and around ducts.


Wet cellulose is more suited to new construction. The insulation, moistened with water and/or a small amount of glue, is sprayed into wall cavities before they are enclosed. It must be allowed to dry thoroughly before being covered up or the excess moisture will encourage mold growth.


There are a number of cases of people becoming ill after their house was insulated with cellulose insulation. In the cases I am aware of, dry cellulose was the culprit. It became a problem because it did not remain within the wall or roof cavity. During installation it filtered into the living space where it was breathed by the occupants. In one case, the furnace ductwork was accidentally filled. When the furnace was turned on, the fan blew cellulose throughout the house.


Fiberglass Insulation


One of the most publicized concerns about the health effects of insulation has to do with fiberglass. There is scientific evidence that suggests that fiberglass can cause lung cancer in much the same way as asbestos. This is based on the proposition that asbestos causes cancer not because of what it is, but because of its small fiber size (Very small fibers can be inhaled deeply into the lungs, where they become lodged and damage tissue). Some people now believe fiberglass can also cause lung cancer when the glass fibers are small enough.


Two types of fiberglass insulation are commonly used in houses: fiberglass batts and a chopped fiberglass product. The batts are usually placed between the framing members of a house before the walls are enclosed. Chopped fiberglass can be poured out in an attic or blown into the wall cavities of existing houses through small holes drilled in the walls, in the same way dry cellulose insulation is installed. Most of the health concerns are linked to chopped fiberglass insulation because of its small fiber size. Because of the way it can be blown into the walls of existing houses, it is more likely to enter the living space. For chopped fiberglass, I suggest the same precautions as those used with dry cellulose.


Fiberglass batt insulation is held together with a formaldehyde-based resin that can release small amounts of formaldehyde gas. This has been a concern to many sensitive individuals. I have heard it said that yellow fiberglass is less noxious than pink insulation, but after researching the various products, I found no significant difference.


Alternative Insulations


There are many kinds of materials that can be used to insulate houses, such as feathers, sawdust, or straw. Most turn out not to be very suitable because they are prone to insect attack. Natural cork is insect-resistant, but it is relatively scarce and fairly expensive. Air-Krete is considered an alternative product.


One of the newest alternative insulations on the market is made from cotton. Cotton batt insulation is actually made of a cotton/polyester blend. It usually has a bluish color from recycled jeans. Since cotton is flammable, it must be chemically treated to render it flame-resistant. The chemicals are similar to those used on cellulose insulation.


Although they don’t seem to outgas in the conventional sense, if cotton insulation is sniffed, the flame-retardant chemicals will leave a biting sensation in your nose. Cotton batt insulation is equivalent in price to fiberglass, but it is not widely available, so additional shipping costs are involved.


Working with Insulation


Even if fiberglass doesn’t cause lung cancer, it is definitely an irritant and certain precautions are necessary when working with it. The following are recommended by fiberglass manufacturers. You should use a tightly fitting respirator because the fibers can irritate the respiratory tract (Small fibers can easily get around a loose fitting respirator). You should wear eye protection because fiberglass can irritate the eyes. Wear long-sleeved, loose-fitting clothing and gloves because fiberglass can irritate the skin. Wash with soap and warm water after handling to remove particles from the skin. Launder work clothes separately and wipe out the washer to avoid contaminating other clothes. Very few workers follow these simple safety precautions.


Figure 12-1 shows how I protect myself when dealing with fiberglass insulation. I would recommend these same precautions when working with any kind of insulation capable of being dusty—fiberglass, cotton, or cellulose.


Most packages of batt insulation (cotton or fiberglass) are compressed for shipping. When the package is opened, the batts must be fluffed up to their full thickness by slapping the sides of the batts or shaking them. For example, twelve-inch thick batts are slightly over 6" thick directly out of the package, but they easily fluff up to 12". Unless at the proper thickness, they will not have full insulating value.


Insulating the Model Healthy House


After analyzing all of the options, I decided to use fiberglass batt insulation in the Model Healthy House. The decision was not based solely on the healthfulness of the material, because there are healthier alternatives. Air-Krete is less noxious but its high cost and limited availability discouraged me from using it. Cotton insulation is another option, but it too is not widely available.


With an airtight house having a good diffusion retarder (see Chapter 13), I have found that it really doesn’t matter what kind of insulation you use inside the walls because it simply cannot migrate into the living space. If it can’t reach the interior of the house, it can’t affect the occupants. Of course, I wouldn’t recommend an extremely hazardous product like UFFI.


From building other healthy houses for sensitive individuals, I have found that if you use airtight construction techniques, it is possible to use a less-than-healthy insulation and not worry about it contaminating the living space. Therefore, I based my selection of fiberglass on its insulating ability, cost, ease of installation, availability, and my personal past experience—always keeping in mind its potential health effects.




An airtight house is more energy-efficient than a loosely built house because it can be designed to have the proper amount of ventilation—neither too much, nor too little. For the Model Healthy House, I decided to go the extra mile and use enough added insulation—enough to be called superinsulation—so that the future homeowners would have a very low heating bill. Superinsulation is healthy for the homeowner’s pocketbook and it places less demand on the supply of electricity. And if all houses were superinsulated, electric utilities would have less need to build new, polluting generating plants or to increase the capacity of existing plants.


Considering the way I constructed the 101⁄2” thick superinsulated double exterior wall system (Chapter 6), I was able to use approximately three times as much insulation as is typically found in a 2x4 wall. The roof is also insulated considerably better than average.


Ordering the Correct Size


Most builders use fiberglass batts that are 141⁄2" or 221⁄2" wide. This is to allow for the thickness of a 2x4 (11⁄2") in wood framing that is spaced 16" or 24" on center. I used steel wall studs placed 24" on center. Steel studs are quite thin, so I ordered batts that were a full 24" wide by 31⁄2" thick. They are rated at R-11, and because the walls contain three layers of these batts, the total R-value is 33. By using the recently developed, and more expensive, R-15 batts (also 31⁄2" thick), the same wall thickness could have had an R-45 insulating value. I considered the new batts, but decided that R-33 was sufficient for the Indiana climate.


Since my 2x12 rafters were spaced 48" on center, I used 24" wide batts there also and compressed the edges slightly to make them fit. The batts used in the roof structure were 12" thick and rated at R-38.


Many fiberglass batts are sold with a kraft paper or aluminum foil facing. Because I used drywall with a foil diffusion retarder laminated to the back side of it (more on that in the next chapter), there was no need for a second diffusion retarder inside the wall. Therefore, I ordered all the fiberglass batt insulation unfaced.


Cutting Fiberglass


When cutting the fiberglass insulation to size, I found that a utility knife worked well cutting directly on the concrete slab (Figure 12-2). The concrete wore down the point somewhat, but it still cut easily. Wherever there were electrical outlets, I was careful to fit the insulation closely in order to eliminate any gaps. Air spaces do not insulate nearly as well as fiberglass.


Ceiling Batts


I installed the 12" fiberglass batts in the ceiling prior to insulating the walls. The batts were simply laid in place on top of the hat channel. I found that when working overhead, it was especially important to wear eye protection. My goggles quickly became coated with fine glass fibers. I normally wear glasses, but they weren’t sufficient to keep the fibers out of my eyes. Goggles are a must.


Wall Batts


For the walls, I first placed batts vertically in the outer wall of load-bearing studs. Then I added a second layer horizontally between the two exterior walls. The third layer was placed vertically between the studs of the inner wall (Figure 12-3). This method seemed to work easily and resulted in a full 101⁄2" of insulation in the walls.


Where two steel studs were located next to each other, I stuffed scraps of fiberglass inside them with a metal yardstick (Figure 12-4).


The Smell of Formaldehyde


Once the entire house was insulated (Figure 12-5), a noticeable odor of formaldehyde pervaded the indoors. Workers are advised to have plenty of ventilation when working with fiberglass batts, and a cartridge-style face mask is an excellent precaution. I have seen no research on how long it takes for the formaldehyde odor of insulation to dissipate, but once the drywall was hung and sealed, the insulation was isolated from the living space and the smell of formaldehyde disappeared.




Insulation continues to be a topic of interest among many people concerned about their health. While it isn’t often a health problem in houses, I attribute the interest to the massive negative publicity in the 1970s that was heaped on one particular type of insulation—urea-formaldehyde foam insulation (UFFI). Although UFFI has long been off the market, a fear of insulation seems to lives on. One of the results has been the introduction of various less-toxic products. Unfortunately, one of these newer insulations—cotton—is no longer available. Apparently there wasn’t enough demand to justify producing it. However, the fiberglass insulation industry has responded to the negative publicity surrounding their product, and begun offering a less hazardous fiberglass batt insulation. While it isn’t yet produced in a wide variety of sizes, it can be used in many situations. To minimize contact with the fiberglass itself, it is packaged in a finely perforated plastic sleeve. (The perforations minimize moisture problems.) It is also made by a different process, so it doesn’t require any type of formaldehyde-based resin binder. Instead it is made from longer, springier strands of fiberglass that are less likely to become airborne and enter deeply into an exposed person’s lungs.


Even with the healthier products currently on the market, it is still important to build a house in an airtight manner. This is for several reasons, but primarily to minimize moisture problems hidden inside wall cavities. And put quite simply, airtight houses (with mechanical ventilation systems) give you the most control of the air indoors, so they are the healthiest houses that can be built.


As I mentioned in the “Update” at the end of Chapter 6, the most recent research into steel framing shows that the heat loss through each stud is somewhat greater than it is with wood framing. So, in order to minimize heat losses, if I were building this same house today, I believe I would consider using fiberglass batts with a higher R-value. (I used three layers of R-11 batts in the walls, and today I would consider switching to R-15 batts.) However, I believe that more benefit would be obtained by using an insulating sheathing. As I mentioned in the “Update” at the end of Chapter 8, I can’t really justify the extra labor involved with installing a foil air barrier on the outside of a house, so I believe—if I were doing it today—I’d use a foam board sheathing instead of the foil wind barrier, and seal the seams with caulking.


(From Healthy House Building for the New Millennium: A Design & Construction Guide, by John Bower, published by The Healthy House Institute.)
(This article is from the archives of the original Healthy House Institute, and the information was believed accurate at the time of writing.)
(Note: The views expressed in this article are those of the author, and do not necessarily represent those of The Healthy House Institute, LLC.)


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Insulation ABCs:  Created on January 25th, 2012.  Last Modified on January 9th, 2013


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