Squaring a Building

Squaring a building properly is the best way to begin your building project.

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

Non-stretch string

8 or more 24″ pieces of lumber




Long measuring tape

Spirit level



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.

  1. Place a stake or rebar in the center of one corner. We’ll call this your northeast corner.
  2. 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.
  3. Tie a string between the two corners and put a stake in the line for any other intersecting walls.
  4. 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.
  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.
  6. From the NW corner, measure 12 feet (3x 4) along the NW to NE line, and put in a stake or rebar.
  7. 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.
  8. 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.
  9. Measure along this line to your SW corner.
  10. 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.
  11. Tie a string between the SE and SW corners and put a stake in the line for any other intersecting walls.


Step 2: Perfect square

Now that you know roughly where all your corners are, we’re going to lay out where the footing will go, while also making sure that it’s all exactly square.

At each corner, you are going to construct something that’s kind of difficult to explain, so look at the diagram.

  1. square-2iPlace a 24″ board on the ground, about 12″ or so (it needs to be clear of where the foundation will be) east of the NE corner. The board should run parallel to the NE-SE line, with it’s center positioned roughly 12″ east of the NE corner.
  2. Place another 24″ board on the ground at right angles to the first, so that it runs parallel to the NE-NW line about 12″ away from it.
  3. Screw or tie the two boards together at the corner and then raise them up on legs (stakes), so that the top of the boards are at about the height you want the top 
of the foundation to be. You can use a water (spirit) level to level across to each of the other corners.
  4. Do the same for each corner.
  5. For any places where there’s an intersecting wall, put one board 12″ away and parallel to the line.
  6. Attach four strings – one for the north, south, east and west lines – to the boards. Each string should touch two corners and there is a corner at the intersection of 
two strings.
  7. You can now remove the stakes that you placed to mark the actual corners.
  8. square-2jMeasure the two diagonals, one between the NE and SW corner, the other between the NW and SE corner. They should be exactly the same if the corners are all 
square. Move the strings until the diagonals are the same.
  9. Now that you have the exact location of the corners, put a screw in the boards to mark where the strings go. By using the string and the screws, you can now 
relocate the position of your corners even if you dig up the actual ground.
  10. The strings mark the center line of your foundation, so measure off each side of the string to find the location of outside of the foundation. For example, if your 
foundation is 12″ wide, make a line 6″ above the string and 6″ below it.
  11. Look at the plan of your building and put markers around the area that will help you remember things that need to be added at this level of the building.