Settlement is what happens when the ground under part of a house loses the ability to carry the load above it, and that part of the house goes down. It is the most common structural problem in the Birmingham metro, and it is almost always uneven — one corner, one wall, one addition — which is precisely why it causes damage. A house that sank evenly by two inches would show almost nothing.
Why It Happens Here
Three causes account for most of what we see locally.
Clay shrinkage during drought. When Birmingham clay dries out it contracts and pulls away from footings, leaving them spanning a void. The house drops into it.
Poorly compacted fill. On a hillside lot, the downhill side is often built up with fill. If that fill was not compacted properly — and on older builds it frequently was not — it consolidates for years afterward.
Water in the wrong place. A downspout discharging at the corner of the house, a driveway pitched back toward the slab, a plumbing leak under a bathroom. Water repeatedly wetting one spot changes that soil and not the soil next to it.
How It Is Repaired
The principle is the same in every case: get the load off the failing soil and onto something that will not move.
Push piers are steel tubes hydraulically driven through the unstable layer to bedrock or refusal, using the weight of the house itself as the reaction. They suit heavy loads and are common on full masonry homes.
Helical piers are screwed into the ground with a torque motor rather than driven. They can be installed where there is less structural weight to push against, which makes them useful for porches, additions, stoops and lighter framed sections.
Crawl space jacks and new footings handle the very common Birmingham case where the perimeter is fine but interior masonry piers have settled or failed, leaving the floor sagging through the middle of the house. This is a much smaller job than perimeter underpinning and is often what people actually need.
Lift Versus Stabilize
Once piers are in, there is a choice. You can stabilize — hold the house exactly where it is and stop further movement. Or you can attempt lift — jack the settled section back up toward its original elevation.
Lift is satisfying and closes cracks. It also risks new damage, because plaster, tile, brick and trim have spent years adjusting to the settled position and do not always enjoy being moved back. On an older Birmingham home with original plaster, a cautious partial lift is usually wiser than chasing level.
A contractor who promises full lift on every job, without looking at what the finishes will tolerate, is overselling.
What This Costs, Roughly
Pier work is normally priced per pier, and the number of piers depends on the length of the affected footing rather than the size of the house. A short run on one corner is a very different job from underpinning two full walls. Crawl space support work is usually a fraction of the cost of perimeter piering.
Nobody can price this honestly from a phone call. What can be done on the phone is telling you which category you are probably in, and what would move the number up or down.