Ask the Builder: Getting your building foundation right

A 75-year-old man recently submitted a question on the Ask Tim page at askthebuilder.com. I get quite a few each week and answer each one. This particular question put a huge smile on my face because it screamed “attitude.”

Connie – yes, it can be a name for a man – wrote: “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 my piers are all straight and in line?”

Can you imagine the excitement he’s feeling about starting this project? Don’t you love a positive attitude like this? To be sure, it needs to be mixed with realism as to what he can do physically.

I was immediately reminded of Harry Andrews, who built the one-of-a-kind Loveland Castle along the banks of the Little Miami River in a suburb of Cincinnati. Andrews set a goal in 1927 nearly a decade after serving in World War I. He decided to build the massive castle and continued to add stone after stone until his death in 1981.

While Connie’s house dream is much more modest, I admire people who set goals and do their best to achieve them. We should all take a lesson from Connie and Harry!

Connie asked a few of the right questions, but he didn’t touch on a few really important ones about what needs to be done when you decide to build a foundation.

Let’s start to unpack the process, and I’ll share some of the common pitfalls I see many professional builders make.

The height of the foundation is perhaps one of the most important things to consider. All too often, I do autopsies on water-infiltration issues homeowners suffer because the top of their foundation is too close to the ground surrounding the house.

Drive through older neighborhoods near you, and you’ll see the tops of the foundations typically 30 or more inches up out of the ground.

The building code – which happens to be a set of minimum standards – states that the top of the foundation must be no less than 4 or 6 inches above the ground that touches the foundation.

But wait, there’s more! 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. Confused?

What this means is that your foundation should simply mimic the top of a hill where all the ground around the foundation slopes away so you have great water drainage and surface water doesn’t flow toward the house. Remember, the numbers above are minimum requirements. You can create more fall if you want.

The next most important step is to make certain that the foundation is square. Connie didn’t mention this, but I’m sure he’s aware of it. You were taught how to do this all those years ago in high school geometry class.

Remember when you grumbled under your breath sitting at your desk saying, “When am I ever going to use this silly formula about right triangles?” Well, today is the day.

The really amazing thing about this is you don’t need to know any math at all to get a rectangle square. After all, a rectangle is simply two identical right triangles smashed up against each other.

Here’s what you need to do to get the batter boards or form boards for a foundation square. The first step is to make sure the measurements of the opposites sides of each leg of the rectangle, or even a square, are the same.

For example, if Connie’s house slab measures 45 feet by 28 feet, then he needs to make sure the two opposing form boards do measure 28 feet and the other two are exactly 45 feet. That’s easy to check.

You then make sure all four sides are straight. Now you stretch a tape across the diagonals of the rectangle and see what the measurements are. If you’re lucky, they’ll measure exactly the same. This means the form is perfectly square, as you’ve got two identical right triangles.

But if the diagonal measurements are different, you need to pull one side of the forms so the one diagonal measurement shortens. Have someone hold the opposite side of the forms so they don’t move while you pull.

As this happens, the short diagonal measurement will automatically lengthen. You don’t need to have a calculator or know any algebra. It’s magic! You can do the same thing with frame walls or decks or anything else to make them square.

Connie needs to make certain the top of his foundation or piers is level. This is accomplished using a traditional builder’s transit or a newer fancy laser level.

As for getting piers in line, stretch a mason’s string tightly across boards set away from the foundation corners. Be sure the string represents the outer face or center of the piers, and use a level to plumb down to ensure that the pier forms are where they need to be.

I’ve got more about all this in past columns at askthebuilder.com. Go check them out for more hidden building secrets.

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