Site Excavation Suggestions
DEAR TIM: My husband and I are getting ready to build a new home. We are worried about all the digging that will happen at the site. What should we be concerned with? How do we know that the hole will be correct in both size and depth? What happens if the excavator runs into water? I’m filled with anxiety that there will be problems. Will my house lot look like a wasteland for years because of the heavy machinery? Amber D., Plano, TX
DEAR AMBER: I can understand your apprehension. Backhoes, excavators, track loaders with toothed buckets are not too far removed from prehistoric dinosaurs. The giant yellow machines can tear into soil and some animals shred flesh with their talons and sharp teeth. A giant gash in your lot where trees and bushes used to be can absolutely shake you to your core.
A smaller backhoe like this can be used to dig small basement and cellar holes but don’t use them for big holes. These machines are really made for digging trenches. PHOTO CREDIT: Tim Carter
The good news is that with a little water, sunshine and a great landscaper at the end of the project, your lot, with the new home, will look fantastic. Don't be too concerned now, just try to look at other completed homes that have finished landscaping and imagine that's where you'll be soon enough.
That being said, your excavator can make some mistakes. In my opinion, the worst one would be digging the hole too deep. All too often I see houses where the top of the foundation is just inches away from the ground or grade level around the home.
The building code has strict guidelines for how high the foundation must protrude above the ground and how much slope there needs to be to the ground falling away from the house. Do the math and you'll often discover that the top of the foundation should be at least 14 inches above the highest point within 10 feet of the house line.
Keep in mind that you need to have the ground slope away from the house on every side of the house. Where a house is built into a hillside, you have to create a drainage swale on the uphill side of the house. This usually means constructing some sort of retaining wall above the house to create this drainage feature.
I always took precise measurements with my builder's transit and drew a picture showing how deep the basement hole should be. I didn't guess. I was there constantly monitoring the depth of the hole.
You also need to be concerned about reaching good soil. Some lots are comprised of fill dirt and others even have buried vegetation. I'll never forget acting as a consultant in a lawsuit about a home that was built directly on top of an old stream bed that the developer bulldozed trees into and then covered with soil. The house eventually started to crack in half as the vegetation rotted and the soil dropped.
A good builder and excavation contractor can almost immediately spot fill dirt. If you have access to old topographic maps of your area, you can often see the old valleys that got filled in by developers.
If you do run into the water table and your lot has a slope to it, you can dig a trench leading from the hole in the ground until the trench daylights. The ground water will drain naturally through this trench. A pipe can be installed in the trench and connected to a foundation drain system around the house so this water permanently has a pathway to the surface.
If you have a nice wooded lot and want to preserve the trees, you need to make sure the construction equipment doesn't drive over the soil under the trees as well as a decent distance away from the trees. This may mean creating just one pathway for ingress and egress to the basement hole. It's well worth the money to hire a certified arborist that will develop a plan to protect the trees. In almost all cases, you have to erect sturdy fencing to keep all construction traffic away from the trees.
Rock can be an issue in many parts of the nation. In the worst cases, you have to blast through the rock to create the needed hole for the job. This can be very expensive.
You also want to be aware of future settlement issues. It's important to only dig about 3 feet away from the edge of the outer foundation wall. This usually gives the workers plenty of room.
Be aware of where sidewalks, driveways, patios, etc. will be when the home is finished. You don't want the basement hole to be any bigger than it needs to be in these areas. When the foundation is backfilled the soil either needs to be compacted, or you fill these areas against the foundation with a granular fill material that will not settle.
Be sure that the excavator skims off all the fertile and rich topsoil as he starts to dig. Stockpile this material on the job site someplace where it can be easily accessed at the end of the job. You can use it in your landscaping and realize a decent savings by doing so.
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