How to Make a Fence Corner Square

Written by c.l. rease
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An important part of installing a fence is having square corners. You can use a framing square to get a corner close to 90 degrees, but the framing square will not be 100 per cent accurate. Lumber that is bent (crowned) can throw off the accuracy of the framing square. To ensure a true 90-degree corner, math has to be put to work. Laying out a 90-degree triangle at each corner of the fence will result in square corners every time.

Skill level:

Things you need

  • Landscaping stakes
  • Hammer
  • String line
  • Tape measure
  • Soapstone
  • Permanent marker
  • A helper

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  1. 1

    Determine the length and width of your fence. Pound a landscaping stake in the ground where the fence post closest to the house will be located. Tie one end of the string line to the landscaping post. Stretch the string line perpendicular to the house. Measure out the distance required to the first 90-degree corner of the fence.

  2. 2

    Secure the string line to another landscaping post. Do not place the landscaping post into the ground. Back at the house, measure 3 feet from the landscaping stake and place a mark on the side of the house with the soapstone. Measure out 4 feet from the landscaping stake and place a mark on the string line with the permanent marker.

  3. 3

    Have a helper hold the loose landscaping stake near the ground, with the string line pulled tight. Measure the distance between the 3-foot mark on the house and the 4-foot mark on the string line. Tell the helper which way to move until you have exactly 5 feet in between the two marks. When the measure is 5 feet, have the helper pound the landscaping stake into the ground with the hammer.

  4. 4

    Stretch the string line to the next dimension that the fence makes a 90-degree turn. Attach the string line to the landscaping stake. Measure 6 feet from the first corner stake and place a mark with the permanent marker on the string line. On the string line on the other side of the corner, place a mark 8 feet out from the landscaping stake. Have the helper pull the string line tight while the landscaping stake is near the ground. When the distance between the 6- and 8-foot marks equals 10 feet, have the helper pound the landscaping stake into the ground.

  5. 5

    Perform the same operation at each 90-degree corner. The 3-4-5 triangle you lay out at each corner will ensure that the corners are 90 degrees. Where you have the room, extend the length of each leg of the triangle. A triangle with larger legs will provide you with a more accurate corner. Use the largest triangle possible to square the corner. For example: if you have the room, multiply each leg of the triangle by four and use a 12-16-20 triangle instead of a 3-4-5. As long as each leg is a multiple of the 3-4-5 triangle, the corner will be square.

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