Sunday, July 4, 2010
Insulating our way to Net-Zero: Wet Spray Cellulose
Our builder put a lot of thought into deciding what insulation to put where, balancing effectiveness against cost. One of his favorite products is wet-spray cellulose insulation, in this case from Applegate Insulation, a product that requires one fifth of the energy needed to produce an equivalent amount of fiberglass. Made from 85% recycled paper content, largely newspaper, and treated for fire and mold resistance with borate and with a dry adhesive, it is sprayed under pressure into the cavity with a small amount of water, completely filling all the nooks and crannies, reducing the flow of heat and virtually eliminating air infiltration. After completely filling the cavity, a rotating stud scrubber brush is run over the area, leveling it even with the tops of the studs. The cellulose will dry over the next 24 hours, becoming firmer to the touch. No dangerous outgassing is involved, as it does not contain any formaldehyde or respirable microscopic fibers.
The finished surface is quite smooth and spongy to the touch, and the 3.5" of cellulose provides an R-value of 13.3, which when added to the R-3 of the SIS (Dow Structural Insulated Sheathing) on the outside, results in an overall stable R-value of 16.3 for the walls. Our builder believes that the superior air sealing power and the added thermal mass provided by the wet spray cellulose make that R-value a conservative estimate. It is notable that contrary to initial impressions, wet spray cellulose is quite fire retardant, a result of both the fire retardants applied to the paper and its heavy oxygen-limiting density, providing up to a 50% increase in fire resistance. It is also a very good product with respect to air quality, as indicated by the American Lung Association of Virginia choosing to use it in it's Breathe Easy headquarters.