How to Insulate Existing Cinder Block Walls

Lay a 2-inch-by-4-inch board at the base of one cinder block wall and apply construction adhesive on a zigzag pattern over one entire side. Press the board up to the base of the wall and insert concrete nails through board at 6-inch intervals. Lay additional boards end to end around the perimeter of the room to create a baseboard.

Apply an identical board along the entire top perimeter of the cinder block wall to form the top plate.

Measure the height of one cinder block wall with a tape measure and cut 2-inch-by-4-inch boards to the same length using a power saw.

Apply more construction adhesive to the back of one of the boards and position it vertically at the far left of the wall. Press it against the wall and insert concrete nails through it at 6-inch intervals. Install additional boards at 16-inch intervals around the perimeter of the wall.

Place one panel of rigid foam board in between two of the wooden wall boards and insert 1-inch nails along both sides of the panel every 6 inches. Position the nails over the underlying wooden boards to provide traction for the nails.

Install additional panels in between each vertical board in the same manner until insulating the entire room.

Place the end of a polyethylene vapor barrier at the top left of one wall and staple it in place along the sides where they meet the underlying wood strips. Continue stapling it to the wall all the way to the floor and cut the excess off using a utility knife. Apply the vapor barrier over all of the surfaces overlapping each row by 1 inch to prevent gaps.

Apply strips of fiberglass tape to all seams where the rows of plastic overlap to prevent air leaks.