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In this video, I want to explain how to use a simple mathematical trick for laying out partition walls
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so they're square, either to perimeter walls or other partition walls that are in place
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This illustration, we're looking from the ceiling down. So this is a top view. This is one perimeter wall, or the exterior wall of your basement
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And then this is another one over here. And the question becomes, where do I place the end of this partition wall so that the corners are 90 degrees
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so it's square to the existing walls? You might think that's a fairly simple thing to do if you've never tried to do it before
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and a lot of people might be tempted to use a carpenter's square in the corner and hope that that works
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That's a no-no, and the reason is because a carpenter's square isn't really long enough to give you an accurate reading
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The wall can seem to be tight to the square here and here
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but even a small deviation here is going to result in a fairly significant out-of-square orientation when you get to the end
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So this is where a little simple high school geometry comes in
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This is finally that time when the teacher's told you someday you're going to use this
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Well, this is that day. And it's the 3-4-5 trick, and it makes use of the Pythagorean theorem
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So you're essentially using math to create a larger reference square for yourself
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So if you put the partition wall against the perimeter wall where you want it
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and you could even anchor this end down if you wanted to
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but the first step is to measure over 3 feet and then mark that spot there
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and then measure up here, 4 feet. Now, when the wall is positioned, you know, when you move it from side to side, move the end from side to side
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when the wall is in such a position that it is 5 feet from this spot down here up to this spot up here
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measured diagonally, then you can be sure your wall overall is square to the perimeter wall
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So the partition wall will be square, and that's good. That's what you want
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The nice thing about this is that it sidesteps any minor deviations
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You know, maybe the wood is a little bit warped. You know, there are a bunch of things that can throw the whole carpenter's square method off
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But this sidesteps all that. You do this, it only takes a minute or two, and then you can plunk that wall down with confidence and fasten it
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Now, there is another way. It's a bit more cumbersome. I don't really like it
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But if you have a sheet of plywood with all the factory edges on it, at least North American plywood
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has corners that you can count on to be square. So you could lay down a full sheet or even half a sheet with one side against the perimeter wall
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and then that other adjoining side is going to be square. So that could be kind of a large-scale reference for you, but that's kind of the process in a nutshell
