The slab downstairs isn't holding up your house
Start with the reassuring part. In nearly every Thornton home, the basement floor is a separate pour that sits inside the foundation walls without carrying them. The walls bear the house; the slab just gives you something flat to stand on. So when the floor drops a half inch along one side, or a crack at the expansion joint widens and one edge sits lower than the other, you're usually looking at a floor problem, not a structural one. That distinction is worth real money, because floor problems have a floor-priced fix.
Clay plains, indoor edition
The clay under Thornton doesn't stop being clay just because there's a house on top of it. In dry summers, with the open-plains wind pulling moisture out of the ground and little tree cover to slow it, the soil shrinks, and that shrink reaches under the footprint of the home. The slab loses bedding a little at a time. Then the wet cycle comes back, spring melt or a string of hail-track downpours, the soil around the perimeter recharges, and the drying repeats the next summer. A few decades of that pumping action and the middle of a basement floor can sit noticeably lower than the edges, or the reverse.
Homes in the 1960s core have run the most cycles, which is why so many of the settled basement floors in this city sit under its oldest houses. The 2000s houses up north show a different cause, fill settlement, but the symptom looks identical from the top of the stairs.
How do you spot it early? A gap opening under the baseboard, interior doors in the basement swinging on their own, tile grout lines cracking in a line across the room, or a floor drain that's become the high point instead of the low one. None of those mean emergency. All of them mean measure it now and again in six months.
Melt season and the perimeter puddle
If water shows up along the basement wall every March, take it seriously before calling us. Flat Thornton lots let snowmelt and storm water linger against foundations instead of draining off, and a slab we lift over wet, moving soil won't stay lifted. Fix the grading or the gutters first, or alongside the lift. We're happy to look at both during the estimate and tell you the right order. Mudjacking is not waterproofing, and we won't pretend otherwise.
What we check before drilling a single hole
Every basement estimate starts with the foundation walls, not the floor. Stair-step cracks at wall corners, doors upstairs that won't latch, windows racking out of square: those point to wall movement, and lifting the slab under a moving wall just hides the evidence. If we see it, we'll tell you to bring in a structural engineer before spending anything with us. Most of the time we don't see it, and the job is straightforward:
- Drill 1-1/2" holes through the slab, one every 4 to 6 feet across the lift area.
- Pump the sandy loam slurry until the slab returns to grade.
- Patch the holes flush, ready for carpet, tile, or epoxy.
The slurry is inert when cured. No foam chemistry, no solvents, nothing to smell through the HVAC.
The bill, next to the alternatives
Thornton basement lifts are priced by lift area and void volume, quoted free and in person. Breaking out and re-pouring a basement floor means jackhammers inside your house and rubble carried up the stairs by the bucket, at a multiple of our price. Underpinning costs more still and is the answer to a different problem. How long we need depends on access; Trevor covers that at the estimate. You can see finished examples from around the metro on our completed work page.
Finished basement? Bring it on
Drywall, trim, and built-ins can all stay. Our hole pattern stays off the perimeter, and we tarp and protect the room before the drill comes out. AAA has been quoting these jobs in person since 1988, and the estimate is free whether you book or not. Call (303) 526-2222 and let's find out what your floor actually needs.