Guide
Pier types, wall repairs and the drainage fix that comes first
Updated
Underpinning is the expensive answer. Sometimes it is the right one. Here is how the methods differ, and what should be ruled out before you buy any of them.
Start with water, because it is cheap
In a clay soil, most seasonal foundation movement is a moisture story. Roof water dumped at the wall, ground sloping toward the house, a leaking supply line, a downspout discharging into a flower bed. These change the moisture content of the soil carrying your footing, year after year.
Correcting them costs a fraction of underpinning and sometimes stops the movement. It also earns a repair contractor very little, which is why it is under-recommended. Ask any contractor proposing piers what drainage correction they considered and why they ruled it out.
The three main underpinning methods
- Steel push piers (resistance piers)
- Steel sections hydraulically driven into the ground using the weight of the structure itself as the reaction. They go until they meet resistance, so they suit heavier structures and situations where competent bearing is deep. Because the house provides the reaction, they work best where there is enough structural load to drive against.
- Helical piers (screw piles)
- Steel shafts with helical plates that are screwed into the ground with a torque motor, where installation torque correlates with capacity. They do not need the building's weight to install, so they suit lighter structures, additions, porches and new construction as well as underpinning. Often preferred where the structure is too light to drive push piers against.
- Concrete pressed pilings
- Precast concrete cylinders pressed into the ground in segments. Common in some markets and generally the lower-cost option, but with less control over depth and no torque or resistance measurement of capacity, so its suitability depends heavily on soil profile.
The choice between them is a design decision driven by soil profile, depth to competent bearing, structure weight and access, not a matter of brand preference. A contractor who installs only one method will recommend that method. This is another reason the engineer comes first: see why the engineer comes before the contractor.
Basement wall repairs are a different family
- Wall anchors, tying the wall back to a plate set in stable soil out in the yard, tensioned over time. Needs yard access and space.
- Steel I-beam bracing, fixed to the floor slab and the joists to resist further inward movement. Intrusive in a finished basement but does not need exterior access.
- Carbon fiber straps, bonded to the wall to resist further bending. Suitable for walls that have moved only slightly, and generally not a way to straighten a wall that has already bowed significantly.
- Rebuilding the wall, where deflection is severe. Expensive, and the honest answer in some cases.
- Relieving the load, by correcting exterior drainage and sometimes excavating and replacing saturated backfill, so the pressure that bent the wall is reduced.
Lifting versus stabilizing
Two different outcomes are sold under the same heading. Stabilization stops further movement. Lift attempts to return the structure toward its original level. Lift sounds better and sometimes is, but it can open cracks elsewhere, disturb plumbing, and is not always achievable.
Ask which you are buying, how much lift is expected, and what the contractor will do about drywall, tile and trim that lifting cracks. Get that answer before signing: it is a common source of disputes afterwards.
Interior pier work means breaking and reinstating basement floor slab. Exterior work means excavation past patios, decks, landscaping and buried utilities. Reinstatement is where quotes quietly diverge, so get it itemized on every bid.