Checking corners

Whether you lay out your project with simple stakes or use batter boards, you'll want to be sure that any corners are exactly square before proceeding. Use a simple geometric formula.

As you probably recall learning in school, the square of the hypotenuse in a right triangle equals the sum of the squares of the two shorter sides. This means that if one leg of a triangle measures 3 feet (3 squared = 9) and the other 4 feet (4 squared = 16), the diagonal hypotenuse must be exactly 5 feet (square root of 9 + 16).

T One way to position posts on a slope; Mark 1-foot intervals on a 2x4. Butt this against the starting stake at the slope top. Level the board, drop a plumb bob, then drive a stake at that point. (See also pages 74-75.)

► Use the principle of the 3-4-5 triangle to assure that a corner is square. First, mark a spot 3 feet over from the corner. Extend a tape measure 4 feet along the string line. The diagonal between these points must be 5 feet.

Using the principle of the 3-4-5 triangle, you can check a corner for square as shown at upper right. If necessary, adjust strings and remeasure.

After you turn a second corner and plot locations for a third run of posts, as you would with a square or rectangular structure such as a deck, measure diagonally from both sets of opposite corners; these measurements must be equal.

• Marking for digging

For patios and other projects requiring excavation, once you know the corners are at right angles, sprinkle powdered chalk, lime, or sand along the strings, as shown opposite. These marks will guide you as you dig. Also adjust the string to the proper grade so you can use it as a reference when determining how deep to dig.

For projects that require posts, measure along the strings, drop a plumb bob, and drive stakes.

A. Tlx sides of a triangle with a square corner always relate to each other the same way. You also can use multiples of 3-4-5 (6-8-10, 9-12-15).

MMake batter boards by nailing crosspieces to stakes. You 7/ need two assemblies for each corner, situated a foot or so beyond the corner. Stretch strings, square them, and drop a plumb bob to position each corner stake.

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