What underpinning a house involves and when it is needed

Underpinning a house means extending or strengthening its existing foundation so it rests on deeper, more stable soil. A simple cosmetic patch fills a crack but leaves the footing resting on soft ground. Underpinning aims to carry the load past the weak soil to help stop the structure from sinking.

What underpinning does that a simple crack repair cannot

A foundation holds up your home, and the dirt holds up the foundation. When the dirt fails, the concrete cracks and drops. Patching visible cracks with epoxy or mortar can seal out water, but it does not add support under the footing.

Underpinning creates new structural legs beneath the old footing. These new supports reach down to firmer soil layers or bedrock.

The weight of the house shifts off the failing surface dirt and onto these deeper foundations. Understanding how slab, crawl space and basement foundations carry a house makes it clear why a surface patch is useless. The support under the footing has to be addressed before any wall repair.

The soil problems that usually lead to it

Footings can drop when the earth beneath them shrinks, washes out or compacts.

Expansive clay soil can cause substantial foundation damage. Mequon, Wisconsin's foundation repair standards say these soils absorb water and swell. Repeated movement can crack or shift a footing.

Poor soil compaction can cause gradual settling. Sometimes a builder places a house on loose fill dirt instead of undisturbed earth. Over the years, gravity and the weight of the house compress the loose soil. The foundation simply drops with it.

Erosion can wash away the earth supporting a footing. A broken underground water pipe, a damaged sewer line or poor yard drainage can carve hollow pockets in the dirt.

A homeowner must learn to read the walls. Knowing which foundation settling cracks are normal and which are not tells you when to call a professional. Minor shrinkage cracks are often harmless, while wide or jagged cracks are a reason to call a structural engineer, who decides whether underpinning is needed.

Push piers and helical piers and how each reaches firmer ground

Foundation contractors often use steel piers, which can reach deeper soil without digging up the whole yard.

Push piers are smooth steel tubes. Builders also call them hydraulically driven pipe piles. Workers dig small pits outside your house to expose the sinking footing. They bolt heavy, galvanized steel brackets directly to the concrete base.

Hydraulic rams attach to these brackets. The rams use the massive weight of the house to push the steel pipes straight down into the earth. The pipe sections interlock as they go deeper.

Pushing stops when the pipe hits bedrock or a soil layer dense enough to resist the pressure. Push piers rely on the weight of the house for resistance, so an engineer decides whether they suit a given house.

Helical piers do not depend on the house's weight in the same way. These shafts have large steel plates welded to them, shaped like the threads of a heavy screw. Hydraulic motors rotate these engineered helical pier anchors deep into the earth.

As the shaft turns, the steel plates pull the pier downward. It works just like driving a wood screw. The contractor monitors the torque required to turn the steel shaft.

High turning resistance usually points to denser soil. Because they screw themselves in, helical piers do not need the house weight to push them down. They are often considered for lighter structures such as single-story homes, additions and porches, and the engineer decides what suits your house.

Concrete piers and mass concrete underpinning

Concrete provides massive load-bearing capacity. Contractors use it in several ways to support a failing foundation.

Drilled caissons are deep, vertical shafts dug into the earth. Workers use heavy machinery to drill down to firm, stable soil. They lower a cage of steel rebar into the hole and fill it to the top with wet concrete. Once it cures, the caisson acts as a solid concrete pillar holding up the house.

Contractors also install support pads attached to the footing. Workers excavate beneath the sunken foundation section. They pour new, much wider concrete pads directly under the old footing. The larger surface area spreads the weight of the house over more dirt, which cuts down the pressure per square foot on the soil.

Mass concrete underpinning is a traditional, labor-intensive method. It requires no heavy steel piers but demands careful digging by a licensed contractor working to an engineer's plan. Workers excavate the dirt directly below the existing footing. They dig in small, separated sections to keep the wall supported.

They fill these pits with concrete, building a new, deeper footing directly underneath the old one.

The dry pack is meant to transfer the weight without shrinking. Once the first sections cure, the crew digs out the remaining soil in between and pours the rest. This method steps the foundation down to reliable ground.

Where lifting a settled house fits in and why it is done slowly

Installing piers stops the house from sinking further. The next step may involve pushing the foundation back toward its original, level height. The building trades call this jacking.

Hydraulic jacks sit on top of the newly installed steel or concrete supports. A central pump manifold controls multiple jacks simultaneously. The crew raises the entire side of the house off the sunken soil in small, controlled steps.

Lifting a house is slow work and never a do-it-yourself job. A house is a stiff box of lumber, rigid plaster and fragile glass. Pushing one corner up faster than the rest twists the framing. A twisted frame can cause damage right away.

Interior doors can jam, drywall can crack and windows can bind or break. Slow, synchronized jacking gives the structure time to adjust.

A house may not return perfectly to level. Framing that has sat crooked for years can resist being lifted, and forcing it flat might damage it, so the engineer sets how far the house is lifted and the contractor locks the brackets in place at that point.

Why an engineer's report and a permit come before any digging

You cannot look at the ground and guess how much weight a footing can take, so a foundation repair like this needs site specific engineering. A structural engineer calculates the heavy loads of your roof, walls and floors. They dictate exactly how many piers you need and how far apart they must sit. A homeowner should learn the 8 things a structural engineer checks in a foundation inspection.

Many city building departments have specific rules for foundation repairs, and yours may differ. A foundation repair permit application in Mequon, Wisconsin requires a statement of the defects, an analysis of their cause and a plan with specifications. Mequon's municipal standards list engineered helical pier anchors, hydraulically driven pipe piles, drilled caissons and support pads attached to the footing as standard repairs for a settled footing. All of them require site specific engineering.

Texas offers another example. A residential foundation repair permit in Sachse, Texas requires a pier layout plan, an engineer's letter and pier specifications stamped and signed by a Texas licensed engineer.

In Sachse, the engineer of record must inspect the foundation repair and give the city a copy of the report before the final inspection. Never allow a crew to dig out your foundation without an engineered plan and an active permit.

Questions to ask a foundation contractor about their plan

A licensed foundation contractor takes the engineer's plan and turns it into physical work. Ask detailed questions about their process before signing a contract.

• Ask if the underpinning requires interior work. If the house sank in the middle, exterior piers may not reach the problem, and workers may need to break through your basement slab or crawl space floor to install interior supports. That can mean heavy dust and noise and damage to finished flooring.
• Ask how they adjust for underground obstacles. A large, buried boulder or an old construction debris pit can stop a push pier or a helical pier from reaching the engineer's target depth. Ask how the contractor and engineer would handle an obstruction.
• Confirm who pulls the building permit and coordinates the engineer's inspections. Ask whether the contractor files the permit paperwork and schedules the required inspections.
• Ask how they will manage water control after the job. Poor yard drainage may have contributed to the soil failure. Fixing the footing without moving gutter water away from the foundation can leave the soil exposed to the same washout, so ask whether the plan covers drainage and regrading around the new piers.