Make the 3-4-5 Square
Step1
Find the exact location for left outside wall of the room addition. Drive a 1x3 stake at that point. Mark an "X" in the center of the stake so you have an exact point from which to work. Drive a number 7 sinker nail into the center of the "X" and tie a dryline (or string) on it.
Step2
Use the 3-4-5 method of finding the square for the other corners. To do this, find the multiple closest to your measurements using the size of the room edition. For example, if you're making an 8-x-10 addition use the 9-12-15 measurements. This number was found by multiplying each number in the sequence by 3.
Step3
Measure along the wall of the foundation from the nail toward the inside of the room, using the first multiple you located. Mark the foundation at that point. Use the dry line attached to the stake, pulling it at a right angle from the building. Making certain that you use the same side of the tape measure (because using different sides can skew the results), measure 12' on the dryline and put a piece of masking tape on that spot. Mark the tape with a pencil hash for precision. You will now need a second person to hold the dryline taut as you, measure from the hash mark from your first multiple on the side of the foundation to the second multiple mark on the dryline, using the same side of the tape. Keep moving the string until the measurement is exactly your third multiple.
Step4
Drive a stake and attach the dryline. Remeasure for the 3-4-5, to make certain that it is still in square.
Step5
Find the width of the rooms outside walls along the foundation. Put another stake in the ground. Connect another dryline and again do the 3-4-5 method as you did in Step 2.
Step6
Measure from the left corner against the foundation to the right corner away from the foundation and write the number down. Measure the opposite corners from point to point (if you were laying lines you would have formed an X). These two measurements should be exactly alike. If they aren't, your foundation may not be straight and you'll need to make adjustments.
Making and Installing Batter Boards
Step1
Create 4 batter board by starting with ten 1-x-4-x-3 stakes and six 4 to 5' horizontal pieces to attach with drywall screws.
Step2
Connect two of the boards with the horizontal piece. Use the same measurements and do the same process three more times.
Step3
Set 2 of the wooden forms aside. They are complete and will be used against the foundation. On the remaining two forms attach an additional 1-x-4 stake with a horizontal board, at a right angle to the original form.
It should look like an L. For extra insurance do the 3-4-5 technique to check the square.
Step4
Locate the stake against the foundation for the outside wall and measure 3' to the left. This will be away from the outside wall marker. Place a stake and put a 2 stake batter board in the ground so that the stake is in the middle. Measure at a right angle from the stake the length of the room addition plus 3' and place a stake. You will place one of the L-shaped batter boards so that side of the L goes toward the building and the center of bottom of the L is right above the stake. Attach a line to the batter board from the stakes below.
Step5
Repeat the step above on the other side of the addition form.
Setting the Lines for Digging
Step1
Transfer the lines marking the outside wall, done in Section 1, to the batter board. Do this by having someone dropping a plumb line next to the first dryline and attaching a new line to the batter board at one end. Moving to the opposite side, do the same.
Step2
Complete the other side so that you now have the markings for the outside walls with dryline on the batter boards.
Step3
Extend a line marking the end of the wall parallel to the foundation by connecting a dryline to the stakes marking it. Transfer to the batter boards.
Step4
Measure for the 16" footing. You will need to go 4" from the outside wall and mark. Then measure 12" toward the center and mark. This allows 8" for the wall and 4" beyond. You are now prepared to dig.
