/h2/Apples and Oranges: Why Expanding Foam Insulation is Different
What you really need is thermal insulation plus an air sealing barrier. Expanding foam insulation gives you both.
Compared to batt products, blown-in insulation offers a much improved ability to fill spaces behind wires, pipes, in difficult-to-reach spots and non-uniform cavities. Researchers at the U.S. Department of Energy’s Oak Ridge National Laboratory found that the actual R-value of insulation batts as typically installed was about 15% less than the published R-value. Another advantage of dense pack and wet spray insulation is the air sealing benefits they offer. While neither dense pack fiberglass nor cellulose insulation qualify as air barriers, both can help reduce the air infiltration through leaky walls that is commonly found in older homes.
One drawback to wet spray insulation is the added time required for the insulation to dry before wall cavities can be enclosed. Drying times depend on ambient temperature and humidity conditions, but can be 36 hours or more. Wet spray fiberglass typically dries out more quickly. If wall cavities are enclosed before the insulation is allowed to reach a balanced moisture content, excess moisture trapped in the cavity can encourage the growth of mold, creating indoor air quality and durability issues.
Expanding foam insulation performs much better than its R-value.
Improved Air Quality
Better Humidity Control
Lower Energy Costs
THE IMPACT OF WEIGHT
When installing insulation above ceilings, homeowners should take into consideration the impact that the insulation weight can have on the ceiling structure of the home. The impact of weight is primarily an issue in northern climates where R-values of 30 and higher are commonplace.
Fiber Glass Insulation
Fiber glass insulation is extremely thermally efficient, yet light in weight. Homeowners can install fiber glass insulation up to R-70 over 1/2 inch ceiling drywall with framing spaced 24 inches on centers without causing drywall sag.
Based on U.S. Gypsum weight limit
recommendations for backloaded standard
drywall1 and the installed density of shredded newspaper insulations, there is potential for ceiling drywall to sag at R-values above R-30 for regular cellulose insulation when installed over 1/2 inch ceiling drywall with framing spaced 24 inches on centers.