Building Concrete Foundations--Laying Out the Site

Site layout refers to the process used to determine precisely where the outside edge of the foundation will be located. This is done primarily through the use of batter boards.

The structure should be roughly positioned first with a stake at each corner. Stretch a string from stake to stake. Use a carpenter’s square to roughly determine each right angle. Then, see how close to square it's by measuring the diagonals. A building layout is square when the diagonal measurements are equal. Move the stakes until the measurements fall within a couple of inches of being square. The actual squaring occurs with the batter boards.

Constructing Batter Boards

Batter boards are located at all four corners and consist of 2 by 4 stakes connected by 1 by 4 boards. Use a framing square to construct the batter boards at 90-degree angles, but don’t waste hours being exact. How ever, make sure the stakes are driven firmly into the ground so the boards are stable. You will be pulling twine on the batter boards, and if they wobble or shift, your work will be inaccurate.

Two things are important about batter boards: where you position them and how you level them. On a small job, where you will be digging the footing ditch by hand, place the batter boards 4 feet out from the rough perimeter strings. If you are going to dig your ditches with a backhoe, either set them 2 feet back so the backhoe operator can reach over them or set them 10 feet back so the operator can maneuver inside them.

Leveling Batter Boards

For an accurate layout, the tops of the crosspieces on the batter boards should all be the same height. On small jobs, such as a 12-foot by 16- foot workshop, the tops can be leveled with a line level. Build one batter board, then stretch twine to the other stakes and make a pencil mark on them where level. Nail the cross- pieces to the stakes.

On larger jobs, twine can't be stretched tight enough for accurate leveling. Here you can quickly and efficiently find the level with a transparent plastic hose or a hose leveling attachment found in most large hard ware stores. This consists basically of some clear plastic tubing that fits over each end of a hose. To use it, first build a batter board at one corner, using a level to make sure both crosspieces are level. For a poured perimeter foundation, the tops of crosspieces should be the same height as the top of the foundation wall. Build this first batter board at the highest corner of ground when working on sloping terrain. Fill the hose with water—in fact, let it overflow to make sure no air bubbles are trapped in the hose—then hold one end so the water line is level with the top of the crosspiece. Have a helper take the other end of the hose to the stakes driven at the other corners. Mark each stake at the water line, then nail the tops of the crosspieces flush with these marks.

80 Laying out the site: Diagonals measure the same if your strings are square. 3-4-5 method tests right angles. Line level establishes batter boards at the same level on jobs of 20 feet or less. If a backhoe will be used to dig the footing, set the batter boards at least 10 feet from the corner stake to give room to maneuver.

Faster and more accurate than the hose device is the transit. This is basically a small telescope that re mains perfectly level as you move it. Set the tripod far enough back from the low corner of the building site so that you can see all four corners when you move the transit. Use the bubbles on the sight to level the transit. Move it back and forth and double check that it's still level. Now set the batter-board stakes at all four corners, but don't put on the cross- pieces. Starting with the stakes at the highest corner of the site, center the transit sight on one of the stakes. Have a helper mark the stake where the cross hairs are centered.

Turn the transit to each succeeding corner and repeat this process. Nail the crosspieces to the stakes with the tops flush with the lines, and they will all be level.

81 Leveling batter boards... With a hose level; With a transit: To use a transit, find a spot from which you can see all the batter boards clearly. Level the transit and rotate it so you can tell your helper where to mark. Stringing the perimeter: Twist the string a half-dozen times; put a loop over a nail and pull the string tight. Save kerfs in batter board at edges of footing and foundation for accurate replacing of string when it has been removed for digging.

Stringing the Perimeter

Once the batter boards are in place, stretch twine between the batter boards to mark the outside edge of the foundation. Stretch the first string above the rough string layout you have on the ground for the south side of the building. Everything else must be square with this line. Drive small nails in the top of the crosspieces and attach the string to the nails.

The twine must be pulled extremely taut to eliminate any sags. To tie off twine on nails in a crosspiece, use the technique shown; then, with out cutting the twine, cross over to the other crosspiece, tie it around the nail, and string the next leg.

Pull the next leg at right angles to the first by using the 3-4-5 method. Do the same on the succeeding legs. Now, to check your work, first mea sure the building dimensions, then measure the diagonals. Adjust the strings until the diagonal measurements are equal.

Once you have squared the building, cut a shallow notch with a saw underneath each string where it crosses the top of the batter board. This is more accurate than trying to rely on nails, which may bend or come loose. When the strings have to be removed for digging the footing ditch, they can be quickly restrung over the notches.