How to Replace Windows in a Concrete-Block Home

Measure across the width of the window opening, from inside the tracks of the sashes, at several points, moving the sashes up or down as needed to get at the sides. Measure the height of the opening in the same manner. Order your replacement windows based on the measurements.

Receive the new window and check the dimensions to ensure they're correct.

Remove the existing window by prying out the border of trim from around the interior edge of the window opening using your prybar and hammer. Don't break the trim as you remove it. Set it aside.

Stand the new window in the window opening, bottom first. Push the top back into the opening until it comes to rest against the trim border around the exterior edge of the opening.

Put a level alongside the window unit. Shim the unit around the sides and bottom until it's level all around.

Drive galvanized mounting screws outward through the sides of the window unit, through the screw holes, into the surrounding frame of the opening. Note that even though there is concrete block on the outside of the house, the space just inside the concrete, on the sides of the window opening, are wood.

Push fiberglass insulation in around the perimeter of the window unit, into the gaps at the edges, filling them completely.

Reinstall the trim around the inner perimeter of the opening using a trim nailer. Seal the joints around the trim with caulk.