Helical Piers: Foundation Underpinning on Expansive Soil

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A diagonal crack over a basement window, a door that suddenly drags on its threshold, a floor that slopes toward one corner of the house: these are the symptoms that send many Front Range homeowners searching for foundation repair, and helical piers are one of the first solutions they encounter. A helical pier is a steel shaft with one or more screw-like plates welded near the tip. It is twisted into the ground below the house until it reaches soil firm enough to carry the load, then bracketed to the footing so the house rests on the piers instead of the soil that moved. This guide explains how helical underpinning works, why Colorado’s expansive clays complicate every foundation decision, how helical piers compare with push piers and mudjacking, what a structural engineer should evaluate first, and how permits, warranties and costs typically work. It is general guidance, not an engineering opinion for any specific house.

Part of our Structure & Exterior guide — start there for the full picture →

What Helical Piers Are and How They Underpin a Foundation

Helical piers, also called helical piles or screw piles, are manufactured deep-foundation elements. The shaft is usually round or square steel, often galvanized, and the helix plates are sized and spaced to the load the pier must carry. The installer uses a hydraulic drive head, typically mounted on a mini-excavator or a handheld torque motor in tight spaces, to rotate the pier into the soil much like driving a screw into wood.

The key engineering idea is torque correlation. As the helix plates bite into denser soil, the torque needed to keep turning the pier rises. Manufacturers publish relationships between installation torque and expected capacity, so the installer monitors torque continuously and keeps advancing until the reading indicates the target capacity has been reached. Extension sections are bolted on as needed, so a pier may stop at 12 feet in one corner and 25 feet in another.

Once the pier reaches its target, a steel bracket is fastened to the foundation footing or grade beam. Depending on the plan, the contractor then does one of two things:

• Stabilize. The bracket is tightened so the house is held where it currently sits, preventing further settlement without trying to undo what has already happened.
• Lift. Hydraulic jacks at several piers raise the structure in small, coordinated increments toward its original elevation, after which the brackets are locked off.

Lifting sounds like the obvious choice, but it is not always wise. A house that settled over many years may have drywall, plumbing, door frames and finishes that adjusted to the new position. Lifting can reopen old cracks, crack tile, or bind doors that were fine. A structural engineer usually decides how much recovery, if any, is reasonable.

Where helical piers are used

Helical piers are common for underpinning existing homes that have settled, for new additions and porches, for decks and sunrooms built on poor soil, and for new construction where a conventional footing would sit on weak or expansive ground. Because they can carry tension as well as compression, they are also used to resist uplift. Light equipment lets crews work inside a basement or on tight lots in Denver, Boulder or Fort Collins.

Why Expansive Soil Makes Front Range Foundations Different

Much of the Colorado Front Range is built on clay-rich soils and claystone bedrock that swell when wet and shrink as they dry. The U.S. Geological Survey has mapped swelling clays across the country, including its 1989 Swelling Clays Map of the Conterminous United States, and local geologic reports in counties from Douglas to Larimer describe the same behavior. When these soils take on water from a downspout, a leaking sprinkler line or snowmelt that ponds against the foundation, they can lift slabs and footings. When they dry during a long summer, they can shrink away and let the structure drop.

That two-direction movement is the reason foundation repair in this region is not as simple as “the house sank, so push it back up.” Some cracks come from settlement, some from heave, and some from both at different times of year. Signs of heave include basement slabs that dome upward, interior partition walls that push into the floor joists above, and cracks that are wider at the bottom than the top. Signs of settlement include stair-step cracks in block walls, a corner that dips and gaps between the foundation and exterior trim.

How this affects pier design

On expansive soil, the goal of a deep foundation is to bypass the active zone, the upper layer of soil whose moisture content changes seasonally. A pier that stops inside the active zone can be pushed up or dragged down along with the soil around it. Engineers therefore specify a minimum depth or require the pier to reach bedrock or a dense stratum, and helical systems sometimes need to resist uplift forces from swelling clay gripping the shaft. Many older Front Range homes already sit on drilled piers or caissons for exactly this reason, and repair plans need to account for what is already there.

Moisture management matters as much as steel. Even a well-designed underpinning job will not fix a basement floor that is heaving from below, and gutters that dump water at the foundation can keep the problem going. Grading, downspout extensions and keeping irrigation away from the foundation are usually part of any sensible plan. For more on reading the cracks themselves, see our guide to foundation cracks, and for floor slabs specifically, basement floor cracks.

Helical Piers vs. Push Piers vs. Mudjacking

Homeowners usually see three or four options in their quotes. They are not interchangeable, and the right one depends on the soil, the type of foundation and what actually moved.

Helical piers

Helical piers are screwed into the ground independently of the structure’s weight. That makes them useful for lighter structures, such as single-story homes, porches, additions and garages, that may not weigh enough to drive a push pier deep. Capacity is verified by torque during installation. They can be installed in many soil types but may struggle where cobbles, rock fragments or very dense layers stop the helix before reaching the design depth.

Push piers (resistance piers)

Push piers are steel pipe sections hydraulically driven straight down, using the weight of the house as the reaction force. The installer keeps adding sections until the pier hits refusal on bedrock or a very dense layer. They suit heavier structures and situations where competent bearing exists at reachable depth. On lighter homes, the structure may begin to lift before the pier reaches good bearing, which limits how deep the pier can go.

Mudjacking and slab lifting

Mudjacking pumps a cement-based slurry, and polyurethane foam lifting injects expanding foam, under a concrete slab to fill voids and raise it. These methods are generally used for slabs such as driveways, sidewalks, patios, garage floors and sometimes interior slabs, not for underpinning a bearing footing. They rely on the soil directly beneath the slab, so they do not bypass expansive or weak soil the way a deep pier does. See our mudjacking guide for how slab lifting works and where it falls short.

Wall repair is a separate problem

A basement wall bowing inward from soil pressure is a lateral load issue, not a settlement issue, and piers do not straighten it. Wall anchors, steel beams, carbon fiber straps or excavation and rebuild address bowing walls. Many houses have both problems, which is why a single quote that bundles piers and wall braces deserves careful review. Our guide to foundation wall repair covers those methods.

Have a Structural Engineer Evaluate the Foundation First

Many foundation repair companies offer free inspections, and many of their staff are experienced. The person writing the quote, however, also sells the repair. An independent licensed structural engineer, paid by the homeowner, can tell the difference between a cosmetic shrinkage crack, ongoing heave and active settlement, and can design a repair rather than accept a contractor’s standard package.

A typical engineer’s evaluation includes some combination of the following:

• A walk-through of the interior and exterior, noting crack locations, widths and patterns.
• A floor elevation survey with a digital level or manometer to map how far each area has moved.
• Review of drainage, grading, gutters and irrigation around the house.
• Review of any available soils report, original foundation plans or prior repair records.
• A written letter or report with findings and, if needed, a repair design with pier locations, depth or capacity requirements and bracket details.

Engineers frequently recommend monitoring before repair. Measuring the same cracks or floor points over a few months can show whether movement is seasonal or ongoing, which may change the plan entirely. After the work, a final engineer’s letter confirming the repair was completed as designed is valuable when the house is sold.

What a home inspector does and does not do

A home inspection is often where foundation concerns first surface during a sale. The ASHI Standard of Practice directs inspectors to inspect structural components, including the foundation and framing, and to describe the foundation, floor, wall, ceiling and roof structure. The same standard says inspectors are not required to provide engineering or architectural services or to offer an opinion about the adequacy of structural systems. In practice, a home inspector documents symptoms such as cracks, displacement and sloping floors and refers the buyer to a structural engineer when the pattern warrants it. Our structure and exterior inspection hub explains how that referral process typically fits into a purchase timeline.

Permits, Installation Day and What to Expect

Most Front Range building departments treat foundation underpinning as structural work that requires a permit, typically supported by engineered drawings or an engineer’s letter. Requirements vary by city and county, so the contractor or engineer should confirm with the local building department before work starts. A permitted job usually ends with an inspection or an engineer’s sign-off, and that paperwork matters at resale.

Exterior installations require excavating a small pit at each pier location to expose the footing. Interior installations involve cutting the basement slab at each pier, then patching it afterward. The work itself often takes a day to several days depending on the number of piers. Homeowners should expect:

• Utility locates. Colorado 811 must be contacted before digging, and private lines such as sprinklers and landscape lighting may need marking separately.
• Landscape disruption. Shrubs, rock beds and sprinkler heads near the foundation may be removed and replaced.
• Excavation safety. OSHA identifies trench collapses, or cave-ins, as the greatest risk to workers in trenching and excavation, and calls for sloping, shoring or shielding trench walls. Deep pier pits next to a foundation deserve the same respect, and children and pets should stay well away from open excavations.
• Interior effects. If the plan includes lifting, cracks may close, open or shift, and doors may need adjusting afterward.
• Records. A pier log showing each pier’s depth and final torque or load, the bracket type and the lift achieved.

Homes on a pier-and-beam foundation or with a crawl space follow a somewhat different process, since the repair may involve new interior supports and shimming rather than brackets on a perimeter footing.

Warranties, Costs and Questions to Ask Contractors

Foundation repair companies often advertise long or “lifetime” warranties on their pier systems. The details vary widely, and the fine print deserves careful reading. Some warranties cover only the piers that were installed, not other parts of the foundation. Some cover settlement but not heave. Some are transferable to a future buyer, sometimes for a fee, and others end when the house changes hands.

Questions worth asking

• Was the repair designed by an independent engineer, or by the contractor?
• How many piers, at what spacing, and what capacity or depth is required for each?
• Will the house be stabilized only, or lifted, and by how much?
• Who pulls the permit, and who provides the final engineer’s letter?
• What does the warranty cover, is it transferable, and what voids it?
• What drainage changes are included or recommended?
• Does the quote include slab patching, landscape restoration and interior repairs?

Typical cost ranges

Costs depend on the number of piers, depth to suitable bearing, access, whether lifting is included and local labor rates. As a rough 2026 guide, contractor quotes for helical piers commonly fall somewhere in the low thousands of dollars per pier installed, and many residential underpinning projects that cover one side or one corner of a house land in a range from several thousand dollars to the low tens of thousands. Whole-house underpinning, difficult access, deep bedrock or extensive interior work can push totals higher. An independent structural engineer’s evaluation usually costs several hundred dollars or more, and a repair design or final letter may add to that. Collecting at least two or three quotes built on the same engineered plan makes them easier to compare.

Drainage corrections such as regrading or longer downspout extensions usually cost far less than piers and may matter more where soil moisture drives the movement.

Buying a House With Helical Piers Already Installed

A history of foundation repair is not automatically a reason to walk away. A well-documented, engineered and permitted underpinning job can leave a house more stable than its neighbors. What buyers want to see is the paper trail:

• The original engineer’s evaluation describing what was wrong.
• The repair design and the contractor’s pier log.
• The permit and final inspection or engineer’s completion letter.
• The warranty document and any transfer requirements.
• Any monitoring results after the repair.

During the inspection, signs of continuing movement, such as fresh cracks that are clean-edged and free of paint, doors that bind again, or new gaps at trim, suggest the repair did not address the cause or covered only part of the foundation. In that case, a follow-up visit from a structural engineer before closing is reasonable. Buyers comparing several older homes can use our home inspection hiring guide to plan who to bring in and when.

Concrete patches in the basement slab at regular intervals along a wall are a common clue that interior piers were installed. Cosmetic crack repair with a concrete crack filler can be fine once the structure is stable, but filling cracks before understanding them can hide useful evidence.

References

• Swelling Clays Map of the Conterminous United States (IMAP 1940) — U.S. Geological Survey
• ASHI Standard of Practice for Home Inspections — American Society of Home Inspectors
• Trenching and Excavation Safety — Occupational Safety and Health Administration

Seeing new cracks or sloping floors in a house you are buying? Reach out to us to schedule a Front Range inspection that documents foundation symptoms before you decide on next steps.