How to Install an Egress Window on a Cinder Block

Chisel away any rough areas around the rough opening, using a hammer and chisel.

Measure the rough opening's length along the bottom edge and transfer this measurement to a treated 2-by-10 board. Cut the board to the appropriate length using a miter saw. Lay the board on the rough opening's bottom edge.

Measure the rough opening's length along the top edge and transfer this measurement to four treated 2-by-6 boards. Lay the boards on top of each other, with their ends lined up, and secure them together with deck screws. This forms the rough opening's header.

Ask a friend to lift the header into position against the rough opening's top edge. Position the header so the boards' skinny edges touch the rough opening. Measure the distance between the header and the 2-by-10 on the rough opening's bottom edge and transfer this measurement to four 2-by-10 boards. Cut the boards with a miter saw.

Set the two side boards against the rough opening's left and right sides, between the bottom edge's 2-by-10 board and the header. Hammer the boards' bottom edges to push them tight against the cement block. Drill 1/8-inch pilot holes through the bottom 2-by-10 board, with a hammer drill. Drill six to eight equally spaced holes through the board, one row following the cement blocks' front edges and one row following the cement blocks' back edges. Drive 2 1/2-inch masonry screws through each pilot hole.

Center the egress window in the rough opening. Place a level along the window's bottom edge. Insert wooden shims, equally spaced, along the bottom edge to level the window. Place a level against the egress window's left side and insert shims to level the window. Secure the wood shims in place with nails and remove the egress window.

Place a tube of silicone sealant into a caulk gun. Apply a bead of sealant around the egress window's nailing fin, which is the flange running around the egress window's perimeter. Position the window in the opening again. Check the window with the level once more and secure it in place by driving a nail through each hole in the nailing fin and into the wood frame around the rough opening.