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The right way to cut a basement window in a foundation wall

Updated: Feb 17, 2021

There is only one way to properly cut a basement window in a concrete foundation and that is with a wall mounted concrete saw. A wall saw is an important tool for cutting basement windows, as it produces straight and level cuts, which is a precursor to a properly waterproofed window. Since the window is secured to a pressure treated wood frame that lines the inside of the concrete cut-out, the wood must fit snuggly against the concrete. With the addition of construction glue and caulking, a wall saw ensures that there is no gaps or spaces between the substrates at the respective junction.

Additionally, the concrete should never be overcut in the corners. One often notices that many basement window installations have an extra 6 inches of cutting in all directions at the corners of the window opening. This is due to the size of the round blade that is used to cut the foundation, as in order to completely penetrate through the foundation wall (usually 8 inches) the saw must overrun the desired cut length. This leaves a characteristic cross pattern in the corners that in many cases, travel right into the joist space.

Overcuts can lead to many issues with waterproofing and structural integrity. 1) The overcuts are effectively channels that allow water to pass in behind the window. 2) There is a far greater risk of crack formation at the corners of overcut windows, which can lead to structural issues and waterproofing issues. 3) Overcuts can destroy the structural integrity of the joist systems above the window, by severing the structural supports. and 4) they look awful.

To eliminate the overcuts, we at True North Concrete Cutting use a specialized saw called a ring saw. The unique design of a ring saw holds the blade by the side, rather than at the middle. This design allows the blade to be completely inserted into the wall and finish the cut from the inside out. This saw produces a true 90 degree corners, rather than the cross pattern.

If overcuts are bad, but preventable, why do so many companies overcut the corners? The answer is simple, it takes more time to eliminate the overcuts, ring saws are expensive and ring saws are hard to maintain in the wrong hands. We at True North have embraced the ring saw and use it on every single window that we cut. We take pride in the finished product and would never hesitate to take the extra time to do the job properly.

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