Swelling Soils: Foundation Care on the Front Range

Much of the Front Range sits on clay soils and claystone bedrock that swell when they get wet and shrink when they dry out. The Colorado Geological Survey (CGS) calls swelling soil a geologic hazard and a common, sometimes serious problem in Colorado, capable of causing severe damage to houses. It also notes that the damage may occur slowly over time, and that houses in the same neighborhood may be affected at different times.

The good news is that most of what protects a house is ordinary maintenance: keeping water away from the foundation.

How swelling soil damages a house

Clay minerals absorb water and expand. When soil next to or under a foundation gets wetter than the rest, it pushes up unevenly. When it dries, it shrinks. Repeated cycles can crack slabs and foundation walls, lift basement floors, make doors and windows stick, and crack drywall. Builders on the Front Range use foundation designs and floating basement floors to handle it, but those designs assume water is kept away from the house.

CGS publishes a homeowner's guide, A Guide to Swelling Soils for Colorado Homebuyers and Homeowners (SP-43), which it says satisfies part of Colorado's disclosure requirements for new houses built on swelling soil. If you bought a newer home, you may have received it at closing. CGS also maps potentially swelling soil and rock across the Front Range Urban Corridor.

Keeping water away: the essentials

Grading. The ground should slope away from the house on all sides. Settled backfill often creates a low spot right against the foundation that collects water. Fill and regrade so water runs away.

Gutters and downspouts. Clean gutters at least twice a year, especially after spring tree seeds and fall leaves. Extend downspouts well away from the house and onto ground that slopes away. A downspout dumping next to the foundation is one of the most common causes of trouble.

Landscaping and irrigation. Avoid planting thirsty lawns, flower beds or trees right against the foundation. Point sprinkler heads away from the house and check for leaks. Drip irrigation for nearby plants puts water where you want it. If you're converting a lawn, see water-wise yard rebates.

Window wells. Keep them clear of debris, and consider covers. Make sure the well bottom drains.

Patios and walks. Cracked or settled concrete sloping toward the house sends water to the foundation. Repair or replace it with a slope away.

Inside the house

Floating (slip-joint) walls. Many Front Range basements have a floating slab and interior partition walls with a gap at the bottom so the slab can move without lifting the framing above. If you're finishing a basement, your contractor should build new walls the same way. See our basement finishing guide.

Don't fill the gaps. Leave the slip-joint gap at the bottom of floating walls open. Filling it can transfer movement into the floor above.

Warning signs

• New or widening cracks in foundation walls or the basement slab
• Doors and windows that start sticking or won't latch
• Drywall cracks above doors and windows
• Gaps between walls and ceilings or floors
• Water in the basement after storms or watering

A single hairline crack is often normal shrinkage. Changes over time matter more. Mark the ends of cracks with a pencil and date to track them.

Repair costs

HomeGuide's foundation repair guide (updated February 6, 2026):

When to call an engineer

Call a licensed structural engineer, not just a repair contractor, if you see significant movement or before major projects like a basement finish in a house with past problems, a pop-top or addition, or removing a load-bearing wall. An engineer's independent assessment helps you avoid buying a repair you don't need. Older and newer suburbs alike, from Centennial to Highlands Ranch, sit on these soils.