Concrete block walls are generally used in basements, though some houses and buildings are built completely of concrete block. Putting a window in a concrete block wall is more complicated than installing one in other types of walls because you have to cut through the concrete block. Although this project can take several days to complete, with proper planning a do-it-yourself homeowner with some experience in home renovations can handle this project.
Prepare for Installation
Determine where you want to place the window. Determine if the joists run parallel or perpendicular to the wall. A small window in a wall that runs parallel to the joists may not need a header, or lintel, for support above the window, but if the wall runs perpendicular to the joists, you will almost certainly need to build a header. Consult an architect or structural engineer about your project and to determine the size of header you need.
Add the width of your header plus 1 3/4 inch to the rough opening height of the window. Add 3 1/2 inches to the rough opening width of the window. These additions will allow room for your framing and header.
Mark the outline of the window on the concrete block wall with masking tape. Hang plastic sheeting from the ceiling surrounding the area where the window will be installed to help contain the dust.
Cut and Remove the Concrete Block
Drill through the entire wall with a hammer drill and a masonry bit that is longer than your wall is thick at each lower corner of the window. This provides location points for the outside cuts. Mark the dimensions of the window on the wall's exterior using the drilled holes as a guide.
Cut a groove in the interior wall that is 1/2-inch deep, using a concrete saw and diamond blade or a handheld cutting tool with a diamond blade. Cut to the full depth of the blade on a second pass. Repeat for each side of the window and on the exterior of the wall to complete the cut through the wall.
Knock out the concrete blocks with a 4-lb. hammer. Start with the top center block and work out and then down. Be careful around the edges so that you do not loosen blocks that will remain in place.
Chip the cut sides smooth with a brick chisel and hammer. Fill the holes in the interior of the concrete blocks with quick-setting concrete. Cover the wet concrete with plastic sheeting. Screw in 3-inch deck screws partway into the bottom sill and press the screws into the concrete to anchor the sill. Allow the concrete to dry.
Install the Window
Build the header as specified by your architect or engineer. Screw this to the floor joists or use concrete screws to anchor it to the top of the window opening.
Cut and install the side framing so that it fits tightly between the header and sill. Screw the side at an angle to the header and sill, and then screw in two concrete screws to each side. Seal the window frame with exterior caulk.
Place the window in the frame and level it with wooden shims. Tack the shims in place and remove the window. Apply a bead of caulk around the frame to seal the window and replace the window. Screw or nail the nailing fin in place as directed by the instructions with the window.
Tips & Warnings
- Use a grinder or rotary tool with a masonry wheel or attachment to smooth and add a finished look to any exposed edges of the concrete block around the new opening.
- Make sure the building load above the window area is fully supported with temporary supports before cutting into the block wall. Wear safety glasses, work gloves and a respiratory mask when cutting concrete. A simple dust mask is not sufficient; you need a filtrated mask.
Things You'll Need:
- Safety glasses
- Work gloves
- Respiratory mask
- Masking tape
- Plastic sheeting
- Hammer drill
- Masonry bit
- Concrete saw with diamond blade
- Handheld cutting tool with diamond blade
- 4-lb. hammer
- Brick chisel
- Quick-setting concrete
- 3-inch deck screws
- Concrete screws
- Exterior caulk
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