Sinking foundation: causes and how it's fixed

A sinking or settling foundation sounds alarming, and left alone it does get worse. The good news is that it's one of the more solvable foundation problems, because the fix goes straight at the cause: getting the foundation back onto ground that can hold it. Here's why foundations settle, how to recognize it, and what a repair actually involves.

Why foundations sink

A foundation settles when the soil beneath part of it can no longer support the weight. Around Frederick County that usually comes down to the soil and the water moving through it:

• Clay soils that shrink and swell. Our Piedmont clay expands when wet and shrinks when dry. Years of that cycle can leave voids under a footing and let it drop.
• Poor drainage. Water that pools against the foundation, from short downspouts or ground sloping the wrong way, softens and washes out the supporting soil.
• A plumbing or gutter leak. A slow leak eroding soil under one spot can settle a single corner.
• Poorly compacted fill. On newer homes, backfill or fill soil that wasn't well compacted keeps settling for years after the house is built.
• Drought and big trees. A long dry spell, or large tree roots pulling moisture from the soil, can shrink clay enough to drop a footing.

How to tell a foundation is settling

Settlement shows up as one part of the house dropping relative to the rest. Common signs:

• Stair-step cracks in exterior brick or block, often wider at the top.
• Gaps opening where interior walls meet the ceiling.
• Floors that slope toward one wall or corner.
• Doors and windows that suddenly stick or won't latch.
• Cracks fanning out from the corners of windows and doors.

If several of these cluster in one area of the house, that's the classic pattern of a settling section. Our signs guide covers each in more detail.

How a sinking foundation is fixed

Steel piers to stable soil

The standard repair is underpinning with steel piers. The contractor installs piers under the footing and drives them down until they reach soil or rock strong enough to carry the load, bypassing the weak soil that let the foundation drop. There are two main types:

• Push piers are driven straight down using the weight of the house for resistance, which suits heavier structures.
• Helical piers screw into the ground like a large screw and work well for lighter loads and softer soils.

See piering and underpinning for how the type is chosen.

Stabilize first, then lift

Once the piers reach stable soil, the immediate goal is to stop the settling. From there the contractor can often lift the dropped section back toward its original position. How much lift is safe depends on the structure, so a good contractor recovers as much elevation as the house allows without forcing it and causing new cracks.

Fix the water, too

Because drainage is so often part of the cause, a lasting repair usually pairs piers with better grading, gutter extensions, and sometimes waterproofing to keep water from undermining the soil again.

Don't wait it out

Settlement is progressive. The cracks widen, the slope increases, and a repair that needed a few piers can grow into a bigger job. If you're seeing the signs, an inspection now tells you how far it's gone and what it takes to stop it.