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Colorado and Texas--what do they have in common? Unfortunately, they're the biggest two problem states in the country when it comes to expansive soil. Expansive soil is usually clay or shale (or a combination of both) that swells when wet and contracts when dry. Build a house on it with the wrong foundation or poor drainage and you're asking for trouble.
Expansive soils cause cracked foundations, damage to basement and interior walls and ceilings, even plumbing pipe breaks. Over time, the repeated swelling and shrinkage can make a house unliveable.
What's a homeowner to do? Educate yourself about expansive soils, of course. Here are few tips to get you started.
- Read the soil conditions report.
Before you buy a new house or a lot in a new subdivision, ask to see the soil conditions report. In the mid-80s Colorado passed a consumer protection law requiring one for all new construction.
- Ask about the type of foundation.
Expansive soils require special foundations. The old standard slab-on-grade won't do. Instead, pier and beam foundations are the new standard in Colorado. Basically, concrete pillars are set down onto bedrock. Then concrete beams are placed atop the piers. A thick cardboard spacer can be placed under the beams so that if the soil heaves, the spacer will be crushed but the floor won't move. The walls, especially in finished basements, are separated by 2-4 inches from the concrete slab with small spikes for the same reason.
- Learn about these techniques before finishing your basement.
To save money, homeowners often finish their own basements. That's fine, but if your house if built on expansive soils, you'd better incorporate the above-mentioned construction techniques or you'll end up with cracked basement walls or floors.
- In older homes, look for wide or uneven foundation cracks.
If your home was built before the soils testing requirements of the '80s and you're concerned about expansive soils, you probably only need to worry if you find wide (a quarter inch or more) or uneven (one side higher than the other) cracks. Hairline cracks are usually caused by normal settling. If you're unsure, call in a professional inspector or soil engineer for his analysis.
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- Ensure proper drainage away from the house.
Expansive soil conditions are made worse when water collects around the home's foundation. Rainfall should run off the property as fast as possible following a storm. Rain gutters and downspouts should direct water away from the house, discharging it no closer than 3 feet from the foundation.
- Plant trees AT LEAST 10 feet away from the house.
Tree roots take in water from the soil around them, causing expansive soil to shrink. So when tree roots grow into the perimeter of a home's foundation, the expansive soil in that area will shrink while rootless soil in other areas may expand, causing the foundation to crack. Shrubs and other small plants that require a lot of moisture are also not good foundation plantings in expansive soils.
Expansive soils are so prevalent in Colorado, in fact, that the University of Colorado at Denver has an Expansive Soils Research Laboratory. Their mission is to study expansive soil and design ways to keep construction damage to a minimum. If you've got a tough question about expansive soils, you might give them a try. Their phone number is (303) 556-2362.
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