Knowing how to accurately square a building’s footing or posts is one of the most important techniques in construction. The more precise your foundation is laid out, the easier the rest of your building project will be.
Materials & Tools
Rebars or stakes
8 or more 24″ pieces of lumber
Long measuring tape
Step 1: Getting a rough square
This is a way to mark out your corners. They will not be exact, but it’s a good starting point.
- Place a stake or rebar in the center of one corner. We’ll call this your northeast corner.
- Measure away from this corner the distance you want to the northwest corner and drive in a stake or rebar. This one line determines the orientation of the building, so
adjust it now if you wish, moving the NW corner a little north or south.
- Tie a string between the two corners and put a stake in the line for any other intersecting walls.
- From the NW corner, you’ll be putting in the SW corner. You want to get the corner roughly square, though at this point it doesn’t have to be perfect. To do so, we
will be using the 3:4:5 rule: in a right angle triangle (which is perfectly square), when one side (A-B) is a multiple of 3 and the other (A-C) is a multiple of 4, the diagonal (B-C) is a multiple of 5.
- So, take a piece of non-stretching string, make a loop on one end and put it around the NW corner’s stake. Then mark the string 9 feet (this is 3x 3, but you can use any multiple of 3 you want, so long as you multiply the 4 and 5 by the same number) from the loop.
- From the NW corner, measure 12 feet (3x 4) along the NW to NE line, and put in a stake or rebar.
- Take another piece of string and make a loop in it. Put the loop over the stake you’ve just put in. Make a mark 15 feet (3x 5) from the loop.
- Take both pieces of string in your hand and find where the two marks meet and put in a stake or rebar. This line is square to the NW-NE.
- Measure along this line to your SW corner.
- Repeat Step 4 and 5 for the NE corner to get the location of SE corner. The distance between the SE and SW corners should be the same as between the NE
and NW. If it’s off a little (an inch or so), don’t worry, we’re about to fix that.
- Tie a string between the SE and SW corners and put a stake in the line for any other intersecting walls.