What are expansive soils, and should Colorado Springs buyers worry about them?

Expansive soils are clay soils that swell when they get wet and shrink when they dry, and they're common along Colorado's Front Range. They're worth understanding, not fearing. The key is telling the difference between the foundation, which holds up the house, and concrete slabs like a basement floor or driveway. A cracked slab is often unsightly or a trip hazard without being a structural problem. Movement in the foundation is the part to take seriously. Your inspector will usually call out what they see.

What expansive soils are

Some clay soils absorb water and swell, then shrink as they dry out. The Colorado Geological Survey calls swelling soil a common and sometimes serious problem in Colorado that can cause severe damage to houses, and notes the damage may happen slowly over time, with homes in the same neighborhood affected at different times.

Water is usually what sets it off. Poor drainage, downspouts that empty next to the house, sprinklers or plantings watered right against the foundation, and water that ponds near the walls can all change the moisture in the soil and lead to movement. Water flowing under concrete can also wash out the soil beneath it.

Foundation versus slab: the part people confuse

This is the distinction that matters most, and it's where people tend to get confused.

• The foundation is what holds up the house: the foundation walls and what they sit on. On expansive soils, many homes are built on drilled piers that reach down to more stable ground, with beams spanning between them. Movement here is the part to worry about, because it can affect the whole structure.
• Slabs, such as a basement floor, garage floor, driveway, sidewalk, or patio, are typically concrete poured on the ground. In many Colorado homes, the basement floor is designed to move separately from the foundation, and interior basement walls are often built with a gap at the bottom so the floor can rise or settle without pushing on the framing above.

You want slabs to look uniform, and nobody likes a heaved driveway. But if a slab shifts, it usually isn't a structural concern for the house. It's unsightly, and it can be a trip hazard. One caution: in a finished basement, a floor that moves a lot can still affect interior walls, doors, and plumbing, so it's worth having it looked at.

Signs to watch for

The Colorado Geological Survey lists cracked and heaved sidewalks, patios, and driveways as common signs of expansive clay. Other things an inspector may note:

• cracks in foundation walls, especially wide, stair-step, or uneven ones;
• doors and windows that stick or no longer latch;
• drywall cracks above doors and windows;
• a basement floor that has heaved or cracked, or interior walls with no remaining gap at the bottom;
• grading or downspouts that send water toward the house.

What to look for during a home inspection covers how inspectors weigh findings like these. If a crack is in the foundation itself, which foundation cracks are serious explains how to tell.

How it gets fixed

The repair depends on what moved and why.

• Slabs: a sunken slab can sometimes be lifted with mudjacking or foam injection, or replaced. That fixes the concrete, not the cause.
• Water: fixing the water flow is often the most important step, so the problem doesn't come back. That can mean regrading, extending downspouts, or moving sprinklers and plantings away from the foundation.
• Foundation: foundation movement calls for a structural engineer's evaluation, and repairs such as piers or wall bracing should follow the engineer's design.

The goal is to make sure the whole thing is fixed, not just the visible crack.

How it comes up in a sale

It depends on the severity. The inspector will usually call it out. A cracked driveway or basement slab may be something you note and live with, or negotiate a small credit for. A foundation concern is different: I'd recommend bringing in a structural engineer during the inspection period, before you decide what to ask the seller for. What contingencies to consider covers those deadlines.

Sellers are expected to disclose what they know about soil, foundation, and structural issues, including past repairs. What disclosures Colorado sellers need to think about covers the form.

New construction in Colorado

Colorado law requires a builder or developer selling a new home to give the buyer a summary of the site's soils report and recommendations at least 14 days before closing. If the site has significant potential for expansive soils, the builder must also provide a publication explaining the problems these soils cause, how the home was built to address them, and how to care for it. Read it; it's one of the best guides you'll get to the home you're buying. Getting an inspection on a newer home covers the rest.

What could change the answer

• Whether the movement is in the foundation or only in slabs.
• The type of foundation and whether it was engineered for expansive soils.
• Drainage, grading, and irrigation around the house.
• A finished basement, where floor movement affects more than concrete.
• Past repairs and whether an engineer documented them.

When to talk with a professional

Your home inspector can flag signs of movement. For anything involving the foundation, hire a licensed structural engineer before you decide what to do. For drainage fixes, a landscaping or grading contractor can help, and for concrete slabs, a concrete or slab-lifting contractor. Your real estate agent can help you fit those evaluations into the contract deadlines.

Sources

• Colorado Geological Survey, Expansive Soil: https://coloradogeologicalsurvey.org/hazards/expansive-soil/
• Colorado Geological Survey, SP-43, A Guide to Swelling Soils for Colorado Homebuyers and Homeowners: https://coloradogeologicalsurvey.org/publications/swelling-soils-guide-colorado-homebuyers-homeowners
• C.R.S. § 6-6.5-101, soils report disclosure for new residences: https://colorado.public.law/statutes/crs_6-6.5-101
• Colorado Division of Real Estate, Contract to Buy and Sell Real Estate (Residential), CBS1, and Seller's Property Disclosure: https://dre.colorado.gov/real-estate-broker-contracts-and-forms