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Q.What is the typical drying time for wet-spray cellulose insulation? What happens if the insulation freezes before it dries? Will it dry after it warms up in the spring?

A.Extensive research has been done on the drying of wet-spray cellulose by the Canada Mortgage and Housing Corporation (CMHC). The CMHC found that if the insulation was applied with the proper amount of water, the moisture content of the wood studs, plate, and sheathing rose considerably during the first 30 days after installation. However, the sheathing and framing dried to near normal levels in two to five months. The presence of a vapor retarder and/or wall ventilation did not seem to affect the drying time or the final moisture levels. A slight amount of fastener corrosion and mold growth did occur, but not enough to be of concern.

In another test, "worst case" conditions were simulated by using wet lumber and very wet cellulose, in a very humid climate (Newfoundland). In that case, the insulation and wood had not dried after two years. There have been other cases reported of walls not drying out and water dripping out from the baseboards. But in these cases the insulation was too wet when installed, and was trapped between a polyethylene vapor retarder on the inside and foil-faced insulation board on the outside.

Freezing of the wet insulation before it dries will delay the drying process, but does not seem to cause any problems. There will be no mold growth or significant corrosion at temperatures below freezing.