What would cause foundation to crack on a house?

Most foundation cracks come from soil pressure and water around the house. The dirt packed back against your foundation when the home was built drains slowly and holds water. That water adds weight and pressure against the wall. In New Hampshire, winter frost in that wet soil pushes the walls inward, and the foundation cracks. Settling, poor drainage, and tree roots add to it.

Here is what is going on under your house.

When a foundation goes in, the crew digs a wide hole, pours the wall, then pushes the dirt back. That pushed-back dirt is called disturbed backfill. It is looser than the packed ground around it. It drains slowly and holds water. So water pools right against your wall. That is why the soil next to the house is the wettest spot on the lot.

Then NH winter shows up. Wet soil freezes. Frozen soil swells. Swollen soil pushes against the wall. We call it frost heave, and around here it pushes basement walls inward year after year. You will see a horizontal crack partway up the wall. Sometimes the whole wall starts to bow. That one is structural, and it needs attention.

Not every crack is a crisis. A thin vertical crack in a poured wall is often just the concrete curing and shrinking in the first year or two. Common. Usually fine on its own, though it can let water in. If you see a hairline vertical line and a dry basement, you do not need a structural fix yet. You might just need that crack sealed.

The cracks we watch closely:

A horizontal crack means the wall is taking side pressure from the soil. That is the frost-heave one. Stair-step cracks in a block wall point to settling, where one part of the footing has sunk. Cracks that widen at the top or bottom, doors that stick, floors that slope. Those say the foundation is moving.

Why foundations move:

Settling, when soft or uneven soil under the footing gives way. Water, the big one, washing out or softening the ground. Frost heave, our New England special. Poor grading or gutters that dump right at the foundation. Big tree roots pulling moisture out of the soil so it shrinks. Old age on a sill or fieldstone wall.

How we fix it depends on what we find. We start with a free inspection so we know which problem you actually have.

For a simple crack that is not moving, crack injection with epoxy or polyurethane seals it from the inside and keeps water out. That runs $1,000 to $3,000 and carries a 10-year warranty. For a wall that is bowing from soil pressure, carbon-fiber straps lock it in place. Those are $850 each with a 25-year warranty. A power brace is another way to stop a bowing wall, priced at $1,300 per brace. When a footing has settled, helical or push piers go down to solid ground and lift the foundation back. Helical piers are $2,700 per pier for the first three, then $2,200 per pier after that with a 25-year engineered warranty. Sagging floors over a weak beam often need lally columns or floor support, at $1,300 to $2,500. A failing sill or beam gets sill and beam replacement, $7,000 to $40,000. A wall too far gone for straps may need an auxiliary wall built beside it, about $1,350 per linear foot.

Some jobs we do not price over the phone. A full foundation-wall rebuild, wall anchors, or steel I-beams. We price that after we see it. And if you are asking about a brand-new foundation, we repair foundations, we do not pour new ones.

One more thing. If your cracks are letting water into the basement, the lasting fix is interior, not exterior. We do not dig up the outside of the house to waterproof it. In our field experience that fix fails in about two to three years. Interior perimeter drainage that sends water to a sump holds up. That is the Forever Dry System, and it is 100% guaranteed to be dry for life!

We self-perform the structural lifting and helical work in-house, so the crew at your house is our crew.

Want to know what your crack is telling you? Call us at 603-610-1770 or book your free inspection. Free inspection, free estimate, and a quote within 24 hours.

See the structural and foundation repair hub, the foundation repair page, helical piers, sill replacement, supplemental support, and the 603 guarantee.

For general guidance on home settling and what insurance does and does not cover, the Insurance Information Institute is a neutral place to start [verify].

Related questions

Is a vertical crack in my foundation serious? Often not. A thin vertical crack in a poured wall is usually shrinkage from the concrete curing. It can still let water in. Crack injection seals it at $1,000 to $3,000 with a 10-year warranty. A horizontal crack is the one to worry about.

What does a horizontal foundation crack mean? It means soil and frost are pushing the wall inward. That is a structural sign. Carbon-fiber straps at $850 each or a power brace at $1,300 per brace stabilize the wall, both with strong warranties. Get it inspected before it bows further.

Will fixing the crack stop my basement from leaking? A sealed crack stops water at that crack. If water is finding other paths, you need full interior drainage. The Forever Dry System handles the whole perimeter and is guaranteed dry for life. We do not waterproof from the outside, since that fix tends to fail in two to three years.

Does homeowners insurance cover foundation cracks? Usually not for settling or normal soil movement, though it depends on your policy and the cause. Check with your carrier. The Insurance Information Institute (iii.org) explains what is typically covered.