A Guide to Helical Piers

Here’s a scenario no homeowner wants to face: Sticking windows and doors or cracks in the walls that suggest foundation problems. Closer inspection reveals settling soil and erosion have undermined the foundation, leading to cracked concrete and/or foundation piers and footings that lean.

Now what?

One increasingly common solution, according to Mike Powell, owner of Tampa-based Red Flag Home Inspection, are helical piers. Powell calls them “a proven and effective solution for foundation construction and repair that have been used since the 1800s.”

But Aaron Goucher of Olshan Foundation Repair says they aren’t the only solution, and certainly not the cheapest. “As far as a repair pier to existing structures, a helical pier is a good repair,” he says. “However, there are other types of support systems that can perform just as well at a much lower cost to the consumer.”

What Are Helical Piers?

A type of deep foundation system that supports various structures. Helical piers (aka helical piles, screw piles and ground anchors) are screwed into the soil, instead of being buried or rammed in like concrete piers.

Think of helical piers the way you compare screws to nails. As any carpenter knows, a screw’s threaded shanks provide more holding strength than the smooth shanks of a nail. The same is true of helical piers.

A helical pier is basically a steel shaft usually galvanized to prevent corrosion with one or more attached metal spirals (helices) that resemble a large screw. The length and diameter of the shaft vary according to the soil conditions and intended load. The above-ground termination may be a flat base to support a post or a screw plate that can be connected to a foundation.

Helical piers are hard to drive into rocky soil. Goucher says pressed piles, which are pounded into the ground, are often more cost-effective. Helicals work best in loose and water-saturated soil and can be installed with minimum impact to the landscape.

Helical piers are becoming common in new construction of residential and commercial buildings, decks and outbuildings. Some contractors even use them to support posts for fences and solar panel arrays.

What Are the Advantages of Helical Piers?

According to Powell, helical piers work well in unstable soil conditions. They install quickly with minimal disturbance.

• Installation: Unlike buried concrete footings, helical piles require no excavation, and there’s no concrete to cure. You simply apply torque to the shaft using a drive head attached to an impact wrench or, for large piers, an excavator. They’re ideal for projects where preserving existing landscaping or structures is a priority. “These piers provide immediate load-bearing capacity, allowing for prompt continuation of construction or repair work,” Powell says. “Other options tend to require curing or stabilization periods.”
• Stability: Powell says helical piers prevent settlement issues and offer long-term structural support.
• Cost: “Helical piers are more cost-effective than end bearing pile, auger cast, and drilled concrete piles,” says Powell. The flange allows them to gain strength with much less material cost. Installing them can often be done with smaller equipment.

However, Powell says helical piers may not be suitable for heavy structures or extremely rocky soils. He advises consulting with a structural engineer to determine their viability for a specific project.

Do Helical Piers Really Work?

Yes. Patented by Alexander Mitchell in the mid 1800s, engineers have reinforced foundations with helical piers all over the world. They’re especially effective in loose and water-saturated soils because of their ability to transfer loads directly to the bedrock.

However, Goucher adds, “As a company that does both helical and pressed piling, Olshan believes that a pressed pile system is a better system for the consumer in most markets.”

How Many Helical Piers Do I Need?

“The number of piers will depend on the building components being supported,” Powell says. “A typical residential building may require one every six to nine feet, whereas a four-story building may need them every four feet to get the required Factor of Safety.” For engineers, that means providing more support than the structure actually requires.

How Far Down Can Helical Piers Go?

The depth of installation depends on the load and soil conditions. Most helical piers are 10 to 25 feet deep, but some may go as deep as 100 feet. There’s no maximum depth, according to Powell. Basically, they go as deep as necessary to support the structure.

“They are installed to get foundation loads beyond near-surface issues, like organics, or very loose soils,” he says.

How Much Do Helical Piers Cost?

Between $10 and $30 per linear foot, with most ranging from five to 20 feet in length. Goucher puts the average cost per pier between $900 and $1,300.

It’s possible to DIY the installation of smaller piers for deck, stair and fence footings. But you’ll need heavy equipment for large foundation piers, and that can drive the cost to $2,000 to $3,000 per pier.

Most residential foundations need five to 10 piers, depending on the square footage. So a foundation repair can cost from $5,000 to $30,000.

Are Helical Piers Cheaper Than Concrete?

No. One helical pier is generally more expensive than a comparable concrete footing. But because helical pier installation requires less labor, costs may even out on large projects.

Where Can I Buy Helical Piers?

Purchase helical piers for fence and deck posts at building and landscaping supply outlets, as well as online at Amazon and other sites. Helical piers for supporting foundations must be sized for the load and soil conditions; they’re best purchased from the contractor you hire to install them.

About the Experts

Mike Powell is a professional engineer and certified home inspector who owns Red Flag Home Inspection in Tampa, Florida. He’s been a forensic engineer for buildings and building components for more than 20 years.

Aaron Goucher is a structural technician for Olshan Foundation Repair in Denver, Colorado. He offers advice on structural and waterproofing issues to television, podcasts and local media outlets.

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