Adding an Egress Window to a Block Basement

Mark the rough opening on the cement block wall with painter's tape. Adjust the tape until you have it placed exactly where the egress window's rough opening will be in the wall. Use the sill plate as the opening's top edge.

Divide the rough opening's width in half and place a mark on the wall along the bottom edge with a piece of chalk. Drill through the mark with a 16-inch-long 1/2-inch masonry bit in a hammer drill.

Go outside and use the hole you just drilled as a reference for marking the egress window's rough opening on the wall's exterior side. Drill two more holes, one through each of the rough opening's bottom corners, using the same drill bit.

Return to the wall's interior side. Remove the painter's tape and snap a chalk line from pilot hole to pilot hole to mark the rough opening on the wall and up to the sill plate from each corner pilot hole. Cut a 1/2-inch-deep line along the chalk lines with a 12-inch diamond blade in a concrete saw.

Make a second cut over the first cut, this time making the cut about 4 inches deep. Go to the wall's exterior side. Snap a chalk line from pilot hole to pilot hole to mark the rough opening's dimensions. Cut along the chalk line with the 12-inch diamond blade and concrete saw.

Return inside. Hit the cement blocks out of the opening with a 4-lb. sledgehammer. Clean up the edges to make them as smooth as possible using a 1/2-inch chisel and hammer.

Mix cement in a wheelbarrow according to the manufacturer's directions. Crinkle up newspaper and stuff it into the cement blocks' holes in the rough opening's bottom edge. Scoop some of the cement mixture up with a trowel and smooth it over the newspaper and cement blocks. Lay a piece of plastic sheeting over the cement blocks.

Cut two 1-by-10-inch boards to the rough opening's width with a circular saw. Rip the same 1-by-10-inch boards to equal the rough opening's depth. Set one board on the plastic sheeting covering the rough opening's bottom edge. Drive 3-inch deck screws through the board and into the wet cement.

Cut and rip two more 1-by-10-inch boards to the rough opening's length and depth. Place the second 1-by-10-inch board from Step 8 on the rough opening's top edge (the sill plate). Secure the board in place with 2 1/2-inch nails.

Place the two boards from Step 9 against either side of the rough opening. Place a scrap piece of wood on the boards and hit the scrap wood to drive the boards tight against the sides. Drill 3/8-inch pilot holes through the boards and into the wall. Drive 2 1/2-inch masonry screws through the pilot holes to secure the boards in place.

Apply a bead of silicone caulk around the egress window's nailing flange and center it in the opening. Hold a level against the egress window's side. Insert wooden shims between the window and the rough opening's frame to hold the window plumb. Hold a level along the egress window's bottom edge and use wooden shims to make the window plumb.

Hammer 2 1/2-inch nails through the holes in the nailing flange and into the wooden frame.