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