Building a deck creates outdoor living space for the whole family to enjoy. There are different ways to support decks, such as concrete, masonry, or wooden piers, or you could consider helical piles for decks. If you’re wondering what helical piles are, we’re here to help!
Helical piles have load-bearing steel blades for foundational support. They can be quickly screwed into the ground in any season and don’t require any excavation, so there’s minimal impact on the surrounding landscape. They’re great for tight spaces and work in most types of soil conditions. Plus, they have a 30-year warranty and are removable and reusable too!
In this article, we’ll explain what helical piles are, the different types, and their pros and cons. We’ll discuss their lifespan, depth, spacing, the number required, where to buy, and their cost. We’ll also explore DIY vs professional installation including the cost, and look at the differences between screw piles and concrete piers. Our aim is to provide you with the information to make the best choice for your project.
- What Are Helical Piles?
- Types of Helical Piles
- Pros and Cons of Helical Piers
- What Is the Lifespan of a Helical Pile?
- How Deep Should Deck Footings Be?
- How Much Do Screw Piles Cost?
- What Is the Maximum Spacing Between Helical Piers?
- How Many Helical Piers Do I Need for a Deck?
- DIY Helical Piles Installation
- How Much Do Helical Piers Cost to Install?
- What’s the Difference Between Screw Piles and Concrete Piers?
- Where to Buy Helical Piles?
- Are Helical Piers Good for Decks?
What Are Helical Piles?
A helical pile or pier has spiraling Grade 50 steel blades or plates welded to a solid Grade 80 steel square shaft or hollow pipe for strength and durability. It may also be a combination of both square and round styles too. The blades or plates form a standard 3” to 8” pitch of one screw thread for a diameter of 6” to 16”.
The blades range from 3/8” to 1” in thickness depending on loads. They are often interspersed along the shaft length to provide individual bearing support independent of and uninfluenced by the plates above or below. They are used to anchor or stabilize a multitude of small and large structures.
In some helical footing styles, only the lead end of the shaft has helical blades, in others, they are spaced along the shaft at set distances. Most systems have extendable lengths with modular sections of square and/or round shaft lengths being bolted together. This allows for adjustments in depth depending on load-bearing strata depths as identified by the installer using torque readings – the greater the soil-bearing capacity, the higher the torque reading.
Helical piles are engineered deep foundation solutions that are screwed or rotated into the ground for minimal vibration or soil disturbance to form prefabricated foundations. They aren’t augered in, so the soil is not removed or drawn out, leaving an open hole. The piles transmit the loads deeper into the ground to load-bearing soils.
Helical piers for decks are ideal for unstable, weak, or expansive soils where a shallow foundation may not be acceptable. It forms a displacement foundation due to the blades since the shaft diameter isn’t great enough to generate the contact required for a friction foundation.
Helical piles form long-lasting, stable, no-dig foundations that can be ready for deck construction in a couple of hours. They don’t require heavy equipment for installation, just a small hydraulically equipped tractor, skid-steer, or backhoe. The piles can be screwed into most soil conditions or types, including sand, glacial till, bogs, and swamps.
Helical deck footings are ideal for locations with poor access, tight or restricted space, rough terrain, and flood plains, as well as open easy access spaces. However, installation and use must be code compliant.
Types of Helical Piles
Helical piles have been used since the 1830s and were originally made of cast or wrought iron. They were mostly used to shore up existing buildings and lighthouses. Since their invention, they have undergone improvements in design and metal. Today there are four main types of helical piles in use for a multitude of foundation and anchoring purposes.
Round shaft helical piles are greater in diameter than square shafts, so sturdier and are more resistant to buckling. They are commonly used to support heavier structures due to the broader diameter providing more support. Unfortunately, the greater diameter makes it difficult to screw into rocky soils, so it is better used in softer soils.
Square shaft helical steel piles have a narrower width and are easier to screw into rocky soil. They have greater penetrating ability. They catch less soil pressure and rely on the rocky soil to support the helical blades or plates. The smaller diameter makes them less sturdy and poorly suited for softer soils.
Grouted shaft helical piles are round or square posts fitted with steel or PVC grout or displacement plates that remove or displace the soft soil around the upper section. The upper section of the shaft is encased in a steel or PVC pipe, or uncased which leaves the upper shaft and displacement plates exposed. The encased or uncased section is then filled with grout mixed onsite. The grout improves the support for larger structures or those in softer soils and helps prevent buckling.
Combination helical piles use both the square shaft for its penetrating abilities and the round shaft for its sturdiness. Combo pipes are best for locations with soil layers of different hardness, low laying areas where the water table is high and the soil softer, or near sea level. They capitalize on the strengths of both shaft types, so they aren’t used where either square or round shaft would be more suitable.
Pros and Cons of Helical Piers
The use of helical footings, piles, or piers has grown significantly in the past 50 years. They are versatile and flexible deep foundations used to support or anchor decks, sheds, houses, retaining walls, bridges, large multistory buildings, and communication towers. But like everything, there are pros and cons to consider.
- Easy to transport
- High load-bearing capacity
- Multiple installation methods
- Can be installed in all seasons
- Ideal for both tension and compression
- Don’t require heavy equipment to install
- No wait or cure time, can be instantly loaded
- Quick installation between 30 and 60 seconds per foot
- Installation torque related to load capacity performance
- The piles are modified for load-bearing soil depths and structural loads
- Can be used in most soil conditions, including glacial till, sand, clay, wet, swampy, and silt
- Screwed in so easier penetration through wet, sloughy, poor-bearing soil layers
- Minimal disturbance or damage to the surrounding area, no tailings or debris
- May be installed in confined or difficult-to-reach spaces
- Can be galvanized or treated to be corrosion resistant
- Excellent resistance to frost movement and heaves
- No disruptive noise or vibration during installation
- Multiple caps or connection brackets available
- Can be removed, reused, or recycled
- Long-lasting and durable
- Not an option for shallow foundations
- Expensive compared to some options
- May require maintenance or adjustments
- Load-bearing capacity affected by soil conditions
- Structural performance hinges on the ability and ethics installer
- Installation requires skill, knowledge, qualifications, experience, and ethics
- Helical piles require deep penetrable ground strata, not bedrock or dense soils
- Other types of piles or anchors generate market confusion
- Require universally accepted engineering principles
- May require load testing which can cause delays
- Mill-grade steel and certified welds required
- Some shafts are susceptible to bending
What Is the Lifespan of a Helical Pile?
The lifespan of helical piers depends on the type of metal used, the design and quality of the pile and installation, the acidity of the soil, humidity, salinity, soil conditions, frost issues, and ground movement potential. Steel can be galvanized or protected from corrosion, but stones and abrasive soils can damage the coating. Aluminum is less vulnerable to corrosion, but often more bendable, so may be less structurally sound.
A properly installed code-compliant helical pier, whether steel or aluminum, has an estimated life expectancy between 75 and 350 years. However, 150 years is the most common lifespan estimate. Much depends on the soil and climatic conditions, soil movement caused by a variety of factors, including earthquakes, and the quality and care of the installer.
How Deep Should Deck Footings Be?
The depth of the footing depends on the size of the deck, its elevation above grade, loads, the load-bearing capacity of the soil, and whether it is attached or freestanding. A freestanding 200 sqft or less deck with its surface no higher than 20” off the ground measured 36” horizontally anywhere from its perimeter, can sit on deck blocks on the ground.
For larger decks or those higher off the ground, or those of any size and attached to a structure, the footing must be 12” below the surface of undisturbed soil and the bottom at least 6” below the frost line.
Helical pile deck footings also need to be code compliant, so they must be below the frost line and secured in undisturbed load-bearing soil. Since most helical piles are available in 24” to 240” modules, their length can be adjusted to meet local soil and frost conditions. Helical pile installation must meet local building codes and may require an engineer’s stamp in some jurisdictions.
The drive torque identifies the load support strength of the soil, and thus, the depth required. The installation must meet the minimum embedment length as well as the torque criteria. The pile may be cut or screwed deeper to meet the specified end reveal too. In most situations, a 7-foot pile will do the task, but the uppermost blade or plate must be a minimum of 6” below the soil surface.
How Much Do Screw Piles Cost?
The material costs of helical screw piles depend on a variety of factors, including the type screw, metal, coating, blade or plate size, length, diameter, corrosion-resistant coating, couplings, saddle fittings, and other accessories. It also depends on load requirements and deck size too.
Depending on all variables, expect to pay between $15 and $30 per linear foot with brackets, caps, and accessories adding to that cost. A 32” adjustable screw with beam or post saddle at my local box store is $52US and a 50” is $66US.
What Is the Maximum Spacing Between Helical Piers?
The maximum spacing depends on the load strength of the soil, the pier’s load rating, the beam or foundation wall load factors, and the maximum structural settlement allowable. The spacing is also affected by live and snow loads too, which can range from 40psf to 90psf depending on location.
Piers should be 24” or less from the end of the beam or frame, and 48” OC to 120” OC depending on structural framework dimensions, tributary loads, and all other variables. In many areas, an engineer must determine the size, spacing, and depth in conjunction with the manufacturer’s information.
How Many Helical Piers Do I Need for a Deck?
The size of the deck and type of materials used affect the loads and the spacing of the screw in deck footings, and thus the number of piers needed. A freestanding deck will also require more helical metal deck footings than an attached deck too. The larger the beam depth and width, and diameter of the pier, the fewer required.
The number usually depends on the load values, so if properly sized and installed, a 12’x12’ attached deck will require 3 piers and a freestanding one of the same size will need 6 helical piers. A 20’ x 12’ garden shed typically requires three rows of four piles, so 12 piers in total.
DIY Helical Piles Installation
The type and magnitude of the project often determine if it is possible for a DIYer. Plus, much depends on the skillset of the DIYer. It is possible to manually screw some types of helical piers into the ground, provided there is enough depth of load-bearing soil near the surface.
Identifying the pier location is similar to determining the location of a concrete pier or post. However, instead of digging holes, helical pile installation requires the piers to be turned into the ground. Rocky ground can be problematic for manual installation, while the use of hydraulic-assisted equipment has its own issues.
It is recommended that a chat with a local certified installer may identify the geotechnical soil conditions as well as the appropriate shaft size and blade diameter. They may even provide a location plan based on your design specs.
Ensure you get the right sized pier and compatible bracket for your project, and check with your local building department too. You may decide, that while you could do the installation, having certified pros with an engineer involved is better.
How Much Do Helical Piers Cost to Install?
The cost of installed helical piles depends on the type, diameter, length, metal, and protective finish of the piles. New construction versus remedial applications also affects the cost, as does soil type and type of cap required. The magnitude of the project affects the costs as does the travel distance too. Some installers, though, do provide discounts based on the number of metal deck footings installed.
Piers cost between $15 and $30 per foot and installation can double the cost every 7 feet. So, a typical deck requiring 7-foot helical piers will run between $105 and $210 per pier with anappropriate cap plus an equal amount for installation, for a total of between $210 and $420 per pier. However, as the length increases, so does the labor costs.
A 21-foot pier has a base cost between $315 and $630, but the labor costs are often doubled, tripled, or quadrupled. The price per installed 21-foot pier can range from $630 to a whopping $3150 depending on all factors.
What’s the Difference Between Screw Piles and Concrete Piers?
There are several key differences between helical piles and concrete piers. Helical pile installation is a no-dig foundation that can be done in any season, including winter. It causes minimal disturbance to the surface and can be accomplished with a small hydraulic-equipped tractor or skid steer. Once the screw pile is in place, it is ready to use. There’s no drying or cure time required.
A concrete pier needs to be augered or dug out so it is below the frost line and typically requires temperatures above freezing and with limited precipitation. The excavation requires a post-hole auger or shovel and leaves a pile of dirt that needs to be dealt with.
The auger may be a gas-powered or manual one or two-person operated tool or one attached to a small tractor or skid steer. Once the holes are prepped, they need to be filled with concrete, and a post or beam saddle aligned and set in the concrete. The concrete then has to cure for 24 or more hours before construction continues.
Both screw piles and concrete piers require earth resources and thus have an environmental impact. The two materials have similar lifespans, but helical piles can be more easily removed and reused or recycled. Plus, there is less on-site waste too.
The cost factor for a helical pier foundation is also considered less than a concrete foundation. The concrete itself may be less expensive per pier, but the excavation, formwork, rebar, equipment, curing time and removal of debris make a concrete pier foundation comparably more expensive.
Where to Buy Helical Piles?Helical piles can be purchased at many home building supply stores, online from various suppliers, or check out community resale boards like Craig’s List or eBay. The selection online is significantly better than what is available at your local home improvement box store, though.
It’s a good idea to check with your local building department before purchasing helical piers for decks to ensure they are acceptable. Another suggestion is to check if there are any local installers and see about getting a quote or some suggestions if you’re planning a DIY installation.
Are Helical Piers Good for Decks?
Helical piers are ideal screw-in deck footings for attached or freestanding decks. They are quick and reasonably easy to install with the right equipment and are ready to build on immediately. Once the helical deck footings are installed and the beam or post saddle bracket attached and leveled, you’re ready to build.
There’s no cure time delay, no pile of excavated material to remove, no frost heave worries, and the cost isn’t budget-breaking. Plus, they can be installed in the rain or into frozen ground, so you don’t have to wait to build your deck. Are you ready to get started?