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Q.When 1/2-inch drywall is installed on ceiling joists spaced 24 inches on-center, will the drywall sag? If the ceiling has blown-in cellulose insulation, will the drywall be more likely to sag than it would under fiberglass batt insulation?

A.Corresponding Editor Paul Fisette responds: According to drywall manufacturers, 1/2-inch drywall can be installed on ceiling framing spaced at 24 inches on-center. However, I have known 1/2-inch drywall to sag when installed on 2-foot centers. For a better installation, either use 5/8-inch drywall, or first strap the ceiling with 1x3s installed at 16 inches on-center.

I don’t think that the difference in density between cellulose and fiberglass is enough to make any difference in the drywall sagging.