Helical Piles (Helical Piers): What They Are, How They Work, Cost
Helical piles (helical piers) defined: parts, how bearing and torque prove capacity, square vs round shafts, uses, pros and cons, cost, codes and history.
Helical piles, also called helical piers or screw piles, are steel foundation shafts with one or more screw-shaped plates (helices) near the tip. A hydraulic motor screws them into the ground until they reach soil strong enough to carry the load, and the torque measured at final depth confirms their capacity. They support new decks, homes and commercial buildings, and they lift and stabilize settling foundations.
Key takeaways
- Definition: a manufactured steel deep foundation with a shaft and helical bearing plates, installed by rotation.
- Same product, several names: helical pile, helical pier and screw pile mean the same thing; a helical anchor is built for tension.
- How capacity is checked: final torque times a factor (Qult = Kt × T) estimates each pile's capacity.
- Two main families: new construction piles with direct-load caps, and repair piers with side-load brackets.
- Typical cost: about $350 to $1,200 per pile for decks, additions and light commercial work, and about $3,000 per pier for foundation repair.
- Code status: IBC Section 1810 covers helical piles, and ICC-ES AC358 sets the product testing rules.
What is a helical pile?
The International Building Code defines a helical pile as a manufactured steel deep foundation element with a central shaft and one or more helical bearing plates, installed by rotating it into the ground, with each plate formed as a screw thread of uniform pitch (Ram Jack IBC guide). In practice, a crew screws a steel shaft down like a large wood screw instead of pouring concrete, and the helix plates carry the load into firm soil below the soft or frost-prone surface layers.
Because there is no concrete to cure, framing or lifting can start as soon as the piles are in. For each step on site, see the helical pile installation process and how long it takes to install a helical pile.
Helical piles vs helical piers vs screw piles vs helical anchors
The four terms overlap far more than they differ:
| Term | Where you hear it | What it usually means |
|---|---|---|
| Helical pile | Engineers, the IBC, evaluation reports | The formal name for the foundation element, carrying compression, tension or lateral load |
| Helical pier | U.S. foundation repair contractors | The same element, most often used to underpin or lift an existing foundation |
| Screw pile | Canada and the U.K. | The same element, common for decks, homes and additions. See our screw piles guide |
| Helical anchor | Utilities, retaining walls, towers | The same hardware designed mainly for tension (pullout), such as guy wires and wall tiebacks |
Canadian makers such as Postech and Almita say screw pile, while U.S. repair brands such as Ram Jack say pier. Our guides to helical anchors vs helical piles and helical ground anchors cover the tension side in more depth.
A short history of helical piles
Screw piles are nearly 200 years old. The blind Irish engineer Alexander Mitchell patented the screw pile in 1833 (Wikipedia), used it for ship moorings in 1836 and for a lighthouse foundation in 1838. In 1907 A.B. Chance began holding utility pole guy wires with helical anchors (Hubbell). The company developed the torque-to-capacity relationship in the late 1950s and early 1960s, and Hoyt and Clemence published it in 1989 from nearly 100 load tests at 24 sites (Hubbell). Helical piles were then written into the 2009 International Building Code (Ram Jack).
The parts of a helical pile
AC358 describes a system as a central shaft with one or more helical bearing plates, extension shafts, couplings and a bracket that attaches to the structure (ICC-ES AC358).
| Part | What it does | Typical specs |
|---|---|---|
| Lead section | The first section into the ground. It carries the helix plates and a cut or pointed tip. | Smallest helix at the bottom, larger helices above it |
| Helix plates | Pull the pile down during installation and bear on the soil afterward. | 8 to 14 in. diameter, 3/8 to 1/2 in. thick, 3 in. pitch |
| Extensions | Bolted on to reach deeper bearing soil. They may be plain or carry extra helices. | Added until depth and torque targets are met |
| Couplings and bolts | Join sections into one continuous pile. | Integral sleeves or welded couplers with through-bolts |
| Shaft | Carries load from the structure down to the plates. | Solid square bar or hollow round pipe |
| Bracket or cap | Connects the pile to the structure. | New construction cap, deck post saddle, or repair bracket |
Those helix numbers come straight from the code criteria. To use the standard torque factors, AC358 requires true helix plates 8 to 14 inches across and 3/8 to 1/2 inch thick, a 3-inch pitch (plus or minus 1/4 inch) that is the same on every plate, spacing of 2.4 to 3.6 times the helix diameter, and the smallest helix on the leading end (AC358, Table 3). For shaft dimensions by brand, see the helical pile shaft sizes chart, and for layout rules see how far apart helical piers need to be.
How helical piles work: bearing and torque
A hydraulic drive head on a skid steer or excavator turns the pile slowly, advancing it about one pitch per turn. AC358 conformance assumes the pile advances at least 85% of the helix pitch per revolution at final torque and turns at less than 25 rpm (AC358, Table 3). As the plates reach denser soil, the pile gets harder to turn and torque rises. The crew stops only when both the design depth and torque are met.
End bearing on the helix plates
Each helix acts like a small buried footing, pushing on the soil below in compression and the soil above in tension. Under IBC 1810.3.3.1.9, the allowable load is half of the ultimate capacity, and the ultimate capacity is the least of four values: the helix area times the bearing capacity of the soil or rock, a torque correlation, a load test, and the structural strength of the shaft (Ram Jack). Our guide to how much weight a helical pile can hold works through typical numbers.
Torque to capacity
The ultimate capacity is estimated as Qult = Kt × T, where T is final torque in ft-lb and Kt is an empirical factor that falls as the shaft gets larger. AC358 assigns these default factors to conforming systems (AC358, Section 3.13.1.1):
| Shaft | Default Kt (ft-1) | Ultimate capacity at 4,000 ft-lb |
|---|---|---|
| 1.5 in. and 1.75 in. square | 10 | 40,000 lb |
| 2.875 in. round | 9 | 36,000 lb |
| 3.0 in. round | 8 | 32,000 lb |
| 3.5 in. round | 7 | 28,000 lb |
With the factor of safety of 2, a 2.875-inch pile finished at 4,000 ft-lb has an allowable load of about 18,000 lb. The IBC also caps installation torque at the pile's rated maximum (Section 1810.4.11). The research behind the method cautions that torque should be used alongside other capacity methods, not as the only one (Hubbell). The helical pile torque to capacity chart has more sizes.
How deep do helical piles go?
As deep as it takes to reach the design torque. CHANCE's rule of thumb is a minimum of 5 times the largest helix diameter below the bottom of the foundation, or 3 times that diameter below the zone of seasonal change such as frost (Hubbell). See how deep helical piles go for typical ranges, and helical piles in rocky soil for what happens when the pile meets cobbles or bedrock.
Types of helical piles
Square shaft vs round shaft
Square shafts are solid steel bars. CHANCE says they have the highest torque correlation factor of any shaft type, are the easiest to install with small equipment and give the lowest cost per unit of capacity for loads of 50 kips or less. They resist little lateral load and should not carry compression in very soft soils. Round hollow-pipe shafts resist lateral load and buckling far better, so they suit soft clays and heavier structures (Hubbell).
New construction piles vs repair brackets
AC358 sorts brackets by how the load reaches the pile. Direct-load (Type B) brackets sit on top of the shaft, so load runs straight down its axis. These are the caps used under new decks, additions, grade beams and steel columns. Side-load (Type A) brackets bolt to the side of an existing footing, so the load is off-center. These are the repair brackets used to stabilize or lift a settled house, and AC358 allows them only on structures that are braced (AC358, Section 3.10). Learn more in helical piers for foundation repair and helical piers vs push piers.
Compression piles vs tension anchors
The same hardware can carry weight vertically or resist pulling at an angle. Angled helical tiebacks hold back bowing basement and retaining walls, and tension anchors secure guy wires, towers and boat moorings.
Uses, pros and cons
Where helical piles are used
- Decks, porches and sunrooms: see helical piles for decks and DIY helical piles.
- Additions and new homes: often tied into a grade beam.
- Foundation repair and underpinning: stabilizing or lifting settled footings and slabs.
- Commercial and infill buildings: where vibration or tight access rule out driven piles, as in this Jersey City underpinning project.
- Solar and utility structures: fast to install and strong in uplift. See helical piles for solar.
- Boardwalks, docks and sensitive sites: small machines, little disturbance.
Advantages and limitations
| Advantages | Limitations |
|---|---|
| Installed in hours or days with no concrete to cure | Cobbles, boulders, debris fill and shallow rock can stop a pile |
| Capacity is checked on every pile through torque | Results depend on calibrated torque equipment and a careful operator |
| Small machines fit backyards, side yards and basements | Heavy loads or very soft soils need larger shafts, which raises cost |
| Little spoil, noise or vibration | Steel needs galvanizing or a corrosion allowance in aggressive soils |
| Can be installed in winter and in high groundwater | Square shafts have limited lateral and buckling resistance |
AC358 handles corrosion by deducting a sacrificial steel thickness over a 50-year service life: 0.013 inch for zinc-coated steel and 0.036 inch for bare steel (AC358, Section 3.9). See do helical piers rust? for more. For head-to-head comparisons, read helical piles vs concrete and helical piles vs drilled piers.
How much do helical piles cost?
Price depends on job type, depth, shaft size and access:
| Application | Typical installed cost | Source |
|---|---|---|
| Deck, porch or accessory structure | $350 to $700 per pile | Helical Anchors Inc. |
| Addition or light commercial | $500 to $1,200 per pile | Helical Anchors Inc. |
| Marine, dock or boardwalk | $2,500 to $3,500 per pile | Helical Anchors Inc. |
| Foundation repair pier | About $3,000 per pier; $15,000 to $30,000 for 5 to 10 piers | Today's Homeowner |
| Engineer inspection / soil report | $300 to $600 / $1,000 to $2,000 | Today's Homeowner |
Depth is the biggest swing factor; extensions beyond the quoted depth add about $20 to $25 per linear foot (Helical Anchors Inc.). For state-by-state pricing and what drives a quote, see the helical pier cost guide. If you are buying hardware only, start with helical piers for sale.
Codes and approvals: IBC 1810 and AC358
The IBC covers helical piles in Section 1810. Section 1810.3.3.1.9 sets how capacity is found, and 1810.4.11 requires installation to the depth and torque set by a registered design professional (Ram Jack). The code also calls for continuous special inspection during installation, except on small accessory structures such as sheds unless the building official requires it.
Products earn recognition through an ICC-ES evaluation report (ESR) issued under AC358, which covers load testing, torque correlation, corrosion and brackets. Homes under the IRC usually rely on an ESR or an engineer's design; Canadian screw piles use CCMC evaluations. Details are in helical pile permits and building codes.
How to find a helical pile installer
Hire an installer certified on the system they use who can show you the evaluation report and a sample torque log. See how to hire a helical pile contractor for questions to ask, and helical pile drivers explains the equipment you will see on site. You can compare brands such as CHANCE, Techno Metal Post and Magnum Piering in the helical pile manufacturer directory. Then find a helical pile installer in your state or province.
Frequently asked questions
What are helical piers used for?
Foundation repair (supporting or lifting a settled footing) and new decks, additions and homes. They also anchor walls, solar racks and towers.
Is a screw pile the same as a helical pile?
Yes. Screw pile is the common Canadian and U.K. term for the same foundation, and helical pier is the common U.S. repair term.
How long do helical piles last?
They are permanent foundations. Code-evaluated systems are designed with a corrosion allowance for a 50-year service life.
Who invented helical piles?
Irish engineer Alexander Mitchell patented the screw pile in 1833 and used it for moorings in 1836 and a lighthouse in 1838.
Do helical piles need an engineer?
Commercial projects do. For homes, many building departments accept an evaluation report for decks, but additions and repairs usually need an engineer.
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