How to Put a Window in a Block Foundation

What You'll Need
A tape measure
Sledge hammer
A masons chisel
Concrete saw
Wooden window frame
Window bucks
The window glass block
Safety gear {eye goggles & face shield}

Block foundations are building foundations made out of concrete blocks rather than poured concrete. Windows are for no other greater purpose than the provision of light and air if the area within the block foundation is one you use often. As with the installation of door frames into block foundations, this project is relatively easy and is one that you can partake yourself. If you do not already have an existing opening on your block foundation and you are unsure about going about it yourself, then contact an experienced repair person to do the heavy lifting. Otherwise, the following steps should act as a general guide.

Step 1 - The Opening

Given that most block foundations run deep into the ground, you would want to install your window higher up to serve the purpose of a window. There should be minimal shoveling in this instance.

Step 2 - Cutting

Use the tape measure to determine the area of your window. These measurements should be inclusive of the window frame, bucks and sills. Keep in mind that all these measurements are subject to the size of your window. Purchase your window according to the measurements. Ask a sales assistant at your glass block vendor to help you with the specifics.

Use the sledge hammer and mason chisel to cut the area you marked out on the blocks. You can also use a concrete saw for this task although this option is a noise pollutant and dangerous to observers. Remember that these cuts are to be made from the outside and not from the inside as the window fitting will be done from the outside.

Once you are done, ensure that the edges of your rough opening are even. If not, fill in these hollows with sludge, mortar or wood.

Step 3 - Fitting

Using a level to test for accuracy, fit the window frame into the opening. Secure a sub frame 1/2 inch from the window frame to create a buck, which is a pressure treated lumber that will attach the window to the opening. Use tapcons to secure both fastenings. Tapcons are hard masonry nails that are preferred to ordinary nails as they are sturdy and can withstand high winds. Choose these tapcons according to the thickness of your frames and bucks.

Get an extra pair of hands to help you fit in the window from the other side. Use a pry bar or level as you go along to secure it into the space between the frame and the buck. Use the caulk outside the edge of the window bucks. Place screws into the screw holes to hold the window permanently.

Test the window then follow the manufacturer’s instructions on how to go about fitting the screen.


Due to fire safety concerns, the type of window to install into your block foundation should be an egress window. Your building code area office should advice you further.