Q: I am going to attempt to build my home myself, using some subs to do various work. I am going to do the footing and foundation. How do I lay out my batter boards with a string line to make sure the piers are all straight and in line?
A: You’ve asked a great question, but you didn’t touch on how important it is to set the foundation correctly first. Let’s discuss the process of laying a foundation, and along the way I’ll share some common mistakes I’ve seen builders make.
The height of a house’s foundation is one of the most important things to consider. When I help homeowners who are having water-infiltration issues, they’re often caused by the top of the foundation being too close to the ground surrounding the house. In many older neighborhoods, you can see the tops of foundations 30 inches or more above the ground, but that’s rarely the case with new construction.
Building codes commonly require that the top of a foundation must be at least 4-6 inches above the ground that touches the foundation. The ground must then slope away from the foundation a minimum of 6 inches within the first 10 feet of horizontal distance from the foundation.
This means that your foundation should mimic the top of a hill, with the ground around the foundation sloping away so surface water doesn’t flow toward the house. Remember, these are minimum requirements: You can create more slope if you want.
It’s also important to make sure the house’s rectangular foundation slab has corners that are perfectly squared. We were taught how to do this in high school geometry class, but you don’t actually need to know any math to create square corners. After all, a rectangle is simply two identical right triangles sandwiched against one another.
To give a foundation’s batter boards — or form boards — square corners, start by making sure the measurements of the opposites sides of each leg of the rectangle are the same. If a house’s foundation is going to measure 45 feet by 28 feet, for example, then two opposing form boards must both measure 45 feet, and the other two need to be 28 feet.
After creating a rectangle with the four boards, stretch a tape measure diagonally in both directions, crisscrossing the rectangle you’ve created. If they measure the same distance, it means you’ve got two identical right triangles and the form is perfectly square.
If the diagonal measurements do not match, pull one side of the form to shorten its diagonal measurement. (You’ll need to have someone hold the opposite side of the form so it doesn’t move while you pull.) As you pull, the short diagonal measurement will automatically lengthen. Continue adjusting and remeasuring until your lengths match. You can do this trick with frame walls, decks or anything else to make them square.
Next, you’ll want to make sure the top of the foundation is level. This can be done using a laser level or a traditional builder’s transit.
As for your question about getting the piers in line, you’ll want to stretch a mason’s string tightly across boards set away from the foundation corners. Be sure to place the string where the outer face or center of the piers will be, and use a level to plumb down to ensure the pier forms are where they need to be. I’ve got much more information about this project on my website, AsktheBuilder.com.
Tim Carter has worked as a home improvement professional for more than 30 years. To submit a question or to learn more, visit AsktheBuilder.com.