How to Apply Drywall Over a Rigid Foam Board on an Interior Ceiling

Measure the length of the ceiling across the joists at a perpendicular angle. You will be cutting 1-by-3 inch boards to this length. Then measure the ceiling in the other direction and divide by 2. This will tell you how many boards you need to cut.

Cut the boards to the length determined in Step 1. If needed, cut more than one board to fit the length of the ceiling. Measure and mark the 1-by-3 boards and cut along the mark with a circular saw.

Use a chalk line to snap lines every 2 feet across the joists. Start with the first line 3 inches from the edge of the ceiling. Use a stud finder, if necessary, to locate and mark where the joists are for future reference.

Attach the first board to the edge of the ceiling about 3 inches in from the wall at the first chalk line. Drill the board in place with drywall screws. Repeat with boards at each additional chalk line.

Hang drywall to the 1-by-3 boards. Drill them in place with their length following the length of the boards. Use drywall screws every foot to anchor them along the sides and screw several in the middle as well. Continue until the ceiling is covered. You can cut the drywall, if necessary, by scoring it with a utility knife and snapping off the unwanted portion. The drywall is heavy so you will need to have someone help you raise it to the ceiling and hold it while you attach it.

Measure and mark where openings need to be in the drywall, such as for an electrical light housing. Use a utility knife to cut through the board so that the housing can be accessed.

Finish the ceiling once the drywall is hung. Apply a thin layer of drywall compound over the screw heads and along the seams with a flat-edge trowel. Tear strips of drywall tape and place them over the mudded seams. Then cover the tape with another thin layer of compound. Let this dry for a day.

Sand the compound smooth and apply a third layer the next day. Feather this layer out further onto the drywall and let it dry for another day. Sand the final coat then finish the ceiling as desired.