Spray foam attic insulation provides all the benefits of any insulating material in terms of energy savings in heating and cooling costs, but it has some distinct advantages and disadvantages when compared to other forms of insulation. Its benefits include its high R-value, its ability to expand and completely fill gaps in small and awkward spaces, and the fact that it can be sprayed on the underside of the attic roof to prevent heat transfer through the roof. Some types of foam can be used to not only insulate, but also to create an effective vapor and sound barrier. One disadvantage of this insulation is the expense, as professional installation is required. Moreover, the chemical nature of the material makes it flammable, dangerously toxic when burned and a skin and eye irritant; concerns also exist about possible emissions from the foam as it ages.
Increasing the impermeability of the building envelope to air leaks is one of the main benefits of spray foam attic insulation. As it expands, it completely fills gaps between joists and rafters. Along with sealing the home from air leaks, its superior insulating action provides for increased energy savings.
Compared to other forms of insulation, foam does not compact nor deteriorate quickly. This means that it retains its effectiveness longer than other types of insulation, including batts and blown-in cellulose. Also, there is less of a problem with dust and insulation materials getting into living spaces.
Closed-cell foam insulation creates an effective vapor barrier, preventing problems with condensation when cold air meets warm, moist air. This reduces moisture buildup and the problems associated with it, including the growth of molds and mildew. The vapor barrier is superior to that created by other materials that can be compromised by piercing with screws or nails. Foam insulation also acts as a sound barrier. This makes it a good choice for those who want to finish an attic.
One of the disadvantages of foam attic insulation is the expense when compared to other types of insulation. Large insulating projects are best done by professionals. Installing foam attic insulation is a major job, requiring expensive equipment and exacting knowledge of the material. It also requires personal protective covering during installation due to the insulation being an eye and skin irritant.
Another disadvantage is that some forms of spray foam use hydrochlorofluorocarbons (HCFCs) as the blowing agent. This gas contributes to damaging the earth’s ozone layer. The chemical nature of foam attic insulation can also be a problem. The foam material itself is flammable and if burned, releases toxic fumes. There is some concern about offgassing of hazardous vapors, including volatile organic compounds (VOCs), as the foam insulation ages.
Unlike closed-cell foams, open-cell light density foam requires an additional vapor barrier to prevent condensation and moisture problems. This presents an additional expense. Some controversy exists in the industry about the use of foam attic insulation on the underside of the roof. Its use might cause excessive heat buildup in the roofing material that could decrease its lifespan.