A friend of mine wanted to build a shed in the backyard of the home he recently bought. The problem was that he didn’t want to ruin his new landscaping digging holes for concrete piers. He opted for a screw pile shed foundation, which he could install himself without ruining his lawn.
Screw piles are popular because you don’t need special tools or a machine to use them. All you need are some 2 x 4s and some elbow grease. Once the piles are twisted into the ground, they are as strong as any concrete pier and more resistant to frost heaving.
- What Is a Screw Pile?
- Screw Helical Pile Design and Components
- Why Build a Shed on Screw Piles?
- How to Install Screw Piles for Sheds
- How to Build Screw Pile Shed Foundation
- Screw Piles Foundation Cost
What Is a Screw Pile?
A screw pile is a galvanized pole with a flat pile head at the top and a helical “plate” at the bottom. The helical plate at the bottom acts like a screw, and the entire screw pile is driven into the earth just as a screw is driven into wood. This can be done either manually or with a machine.
Once the pile is driven into the ground, the structure rests on top of the flat plate that protrudes from the ground. Screw piles come in a variety of diameters for both the pole and the helical plate. The larger the diameter, the more weight it will support.
Screw piles exist largely because they can be cheaper options than using concrete piers. While the piles themselves are expensive, they are quick and easy to install. As well, there is minimal impact on the surrounding areas and you can start building your structure immediately after installation.
Screw Helical Pile Design and Components
The design of the screw pile is simple, which is what makes it a great option for many DIYers. My friend was able to pick up some screw piles at a local Home Depot and install them himself the same day. Granted, it required some elbow grease, but he figured he saved himself at least a day’s work and some money, as well.
Let’s take a more in-depth look at the parts of a screw pile:
The head of a screw pile is either flat or u-shaped. Many store-bought DIY versions of the screw pile, such as the Pylex helical screw piles, offer u-shaped heads that can hold a 4×4 or 6×6 wood post. The vertical part of the u-bracket is usually around 2 ¼” high. Many commercial piles will feature flat heads, which allow for the user to either add their bracket or simply support a lateral beam.
Store-bought brands also offer adjustable height heads. That means that the head sits on a threaded rod, which is adjusted with a large nut at its base. Simply turning the nut can raise and lower the height of the head by up to 3”.
It is important to note that many of these store-bought screw piles are not galvanized. Instead, they are painted with anti-rust paint and have a powdered coating. Other versions offered by contractors are completely galvanized. I highly recommend using only galvanized posts. The paint can chip during installation, resulting in rust, rot, and pile failure over time.
The central shaft of a screw pile comes in a variety of diameters. Obviously, the smaller the diameter the less weight it can hold. The most common diameters for sale are from 1 ¼” to 3 ½”. Keep in mind that all piles come with technical bulletins, which clearly outline the amount of weight it is designed to hold.
While all shafts are cylindrical, some top-out with a square shaft which is designed to sit above the ground. This allows the nut and pile head to sit more squarely atop the shaft. Often this is only found on smaller diameter shafts bought from home reno stores.
Of course, the length of shafts vary. Since shafts are designed to be installed below the frost level, there are 10’ options for really cold regions. As well, Pylex and a few other manufacturers sell screw piling extensions. These sit on top of the existing screw pile to elongate the existing pile.
Be sure to consult your local building code to find out what the frost line is in your area. To be safe, many contractors argue that 2’ below the frost line is ideal. That way you ensure that even in the dead of an ultra-cold winter, your shed won’t move a muscle.
The helix plate is a helical piece of metal at the bottom of the pile. It is what gives the pile the “screw” name. This plate allows the pile to be driven into the earth using a screwing or twisting motion. The diameter of the screw plate varies. Just like the shaft, the larger the diameter of the plate, the more weight it will hold.
The diameter of the helix plate is not necessarily dependant on the size of the shaft. However, a smaller shaft limits the diameter of the helical plate. For instance, you won’t get much larger than a 6” helical plate from a 1 ¼” diameter screw pile shaft.
The helical plates are welded to a shaft. If you don’t have a galvanized shaft, then you better believe that the first place your cheap screw pile will rust will be at the welds connecting the helix to the shaft. That means screw pile failure.
Why Build a Shed on Screw Piles?
The number one reason is the ease of installation. Once you have your deck or shed plan and you mark where on the ground you want your piles, then all you have to do is purchase them and start screwing. While that requires some effort if not using a machine, this can be accomplished far more quickly than doing concrete piers.
As well, you can install these piles in nearly any type of weather – unless the ground is completely frozen (but who wants to work outside then, anyway?) Once your piles are installed, you can begin building your structure on top of them immediately. No waiting for the concrete to dry.
There is absolutely zero, or very little, mess to clean up afterward. If you want to protect your nicely landscaped lawn, then the screw pile is the only way to go. Many Kubota’s come with large track wheels that barely impact the ground beneath. Alternatively, you can use a long 2×4 as a lever to drive screw piles into the ground without any impact whatsoever.
The reason screw piles work is their narrow shaft. As the earth moves and freezes, the small profile of the shaft provides an extremely small surface area. This means it is more apt to resist movements in the soil as opposed to the surface area of a concrete pier.
While screw piles are extremely stable, they also offer flexibility in that the pile head can be adjusted. This added 3” is useful when leveling support beams for decks or sheds.
Guaranteed Weight Capacity
Each screw pile comes with a technical bulletin outlining exactly the maximum amount of weight it is designed to hold. Since the pile is so stable, you can be assured that it will hold exactly what it was designed to hold.
Since there are various versions of the screw pile, it is adaptable to any type of deck or shed size. Whether you have an 6’x6’ shed for your lawnmower or a 24’x30’ man cave in your backyard, there is a screw pile to support all manner of structures.
Removable and Reusable
While this might not be a selling feature to most, these posts can be re-used. For shed owners, this should be a huge plus. If you use sonotubes to build your shed, then moving it five years later would be a massive pain. Concrete means it is there for life.
On the other hand, using screw piles for your shed means that you can move your shed. Let’s say you install a shed with screw piles. Then five years later you want to add a garage to your house, but the shed is in the way. Read my article about how to move your shed, then remove the piles, re-install elsewhere in the yard, and you’ve moved your shed with excavating concrete.
The cost of a 4’ screw pile with a 1 ¼” diameter shaft is extremely cheap and can be had for under $20 on sale. This is for a cheap, made in China pile. Galvanized screw piles of a larger diameter in both shaft and helix can run closer to $200 per pile.
However, you pay for what you get. Look for domestically made piles that are galvanized – these are the ones you want. If you opt for quality piles, then you can save money by installing them yourself.
Image courtesy technometalpost.com
How to Install Screw Piles for Sheds
Below we’ll go over the steps for installing a screw pile shed foundation. Naturally, hiring a contractor is always easier. However, not everyone has a couple of extra thousand dollars lying around. Instead, I’ll show you that you can install ground screw foundation yourself quickly and without any special tools or machines.
Let’s look at some of the technical aspects of the project that you should consider before you start screwing piles in your backyard.
What Kind of Shed?
The type of shed you are building will dictate the number of screw piles you’ll need and the type. If you have a shed that will be supporting heavy objects like a wood stove, large compressor, or even a classic car, then you’ll need wider diameter shafts and helix plates.
It’s important to note that building a shed on screw piles can imply any type of shed, it’s just that some sheds don’t necessarily require screw piles. Small, plastic tool sheds will do just fine up on 4 cinder blocks. But if you’re like me, then you want something solid and permanent. Therefore, screw piles are essential.
Where is the Shed Located?
Screw piles can go into most soils, whether clay, sand, or silt. Gravel presents more problems, particularly if it is a coarser grade with larger stones. In some cases, mixed soils with large stones beneath must be excavated first.
Pylex recommends purchasing ⅜” rebar called a reinforcement rod to use as a pilot spike to probe for rocks as well as to keep the screw straight during installation. Probing with the rebar can inform you of any large rocks that might present problems.
Understand that one of the great parts about screw piles is that wet locations are not an issue. Even snow or semi-frozen ground can accept screw piles. Your primary concern is large rocks, so use the rebar to assist you. If there are huge boulders, then you can adjust your footing plan or you’ll need to consider a different foundation option.
How Big is the Shed?
Consult a technical sheet, which will help you determine the weight capacities of various sizes of screw pile. A 50” Pylex foundation screw for a shed is designed to hold about 6000 lbs of weight if installed in sandy soil. Clay tends to allow structures to sink under very heavy loads, so the capacity for the same pile in clay is only about 4000 lbs.
I can’t say how many screw piles you’ll need for your shed. It depends on how big your shed is and the material used to construct it. If you used lumber, then it’ll be heavy. But again, it also depends on what you put in your shed, too. Use virtual constructor tool to help guide you when choosing the number of piles you’ll need.
Bigger manufacturers will claim that 8 to 10 feet between screw piles is standard. But they are taking into account using larger diameter shafts and helical plates. Since the Pylex screw piles are smaller, you’ll likely need to put them closer together.
Type of Floor
A screw pile has either a flat plate or a u-bracket for a head. Both are intended to be used in conjunction with a wood beam. Typical shed floor construction would then have joists running perpendicular atop the beams, with a plywood floor on top of that.
Remember, consult your local building code for information about where the frost line is and how deep a pile must go into the earth. If you don’t go deep enough, you risk damaging your shed structure resulting in an uneven floor.
How to Build Screw Pile Shed Foundation
Let’s take a look at how to install screw piles yourself. We’ll use a typical 50-inch Pylex screw pile as an example.
Remember, consult your building code first and understand how deep your screw piles need to go. The helical plate must be below the frost line.
Once you have the location for your screw pile planned out, you are going to bang into place a piece of rebar called a reinforcement rod. You will hammer this into place with a 5 or 8 lb. hammer. Take the time to ensure it is perfectly vertical. Hang a plumb bob next to your rod to make sure it’s straight.
Hammer the rod until it is protruding a few inches above the ground.
With the rod in the ground, you know have a guide for your pile. Remove the top plate or u-bracket from the top of the pile. Remove the threaded rod and nut. Re-insert the bracket back into the top of the pile. The square end of the bracket will fit snugly into the square top of the pile shaft.
To start, you can simply grasp the edges of the u-bracket firmly and twist. It will get difficult quickly, and you’ll be forced to use some more leverage.
When twisting with your hands becomes too difficult, grab a 2×4 about 2’ long. Center it, laying flat, inside the u-bracket. Grab either end and continue twisting. Now you will start to see some progress. As the pile gets closer to the ground, you will find it difficult to twist further.
Ditch the 2’ 2×4 and grab a longer one – a 6’ piece will do. Lay one end flat within the bracket and grab the other end. Slowly walk the lever so that the screw pile reaches its final resting place about 6” above the soil.
Using the hammer, pound the pile into place with several hard blows. This will compact the pile firmly into place. Remove the bracket and put the threaded rod with nut back into the top of the shaft. Re-install the bracket atop the threaded rod.
The bracket should now be 6” above the ground if you are installing in clay – it can be 4” if installing in sand or silt. You can now install your 4×4 post in the u-bracket. Use structural wood screws to attach the bracket to the post.
Adjust the adjustable top plate using the nut on the threaded rod to achieve a level post and beam. Pylex mandates that you need at least 3” of the threaded rod below the shaft height to ensure stability.
Using a Contractor to Install Screw Piles
There are several reasons to opt for a contractor as opposed to doing the job yourself.
First, they have access to better quality screw piles. Many installers purchase their piles directly from the manufacturers, which use domestic steel. Also, these piles are galvanized. Pylex only coats their piles with anti-rust paint. Galvanization is a much more reliable option as it theoretically resists rust forever barring any major abrasions.
Second, contractors have access to are up to 10’ long and much wider in diameter than the piles Pylex offers. If you are installing a shed that will be holding lots of weight, or that will be large, you’ll need a bigger diameter pile shaft and helical plate. Stores don’t sell 3” diameter shafts or 14” helical plates.
Lastly, contractors will install the piles faster and more accurately than you likely can, mostly because they have a machine that will put them in perfectly straight and torqued exactly to specifications.
Screw Piles Foundation Cost
A 50” Pylex screw pile costs around $40. Ten piles would therefore run you about $400 plus tax. All in all you could spend under $500 for your shed screw pile foundation. These could be installed in a morning, by you, and you could be constructing your shed by lunchtime.
Now, if you hire a contractor, he’ll install a much higher quality screw pile, but at the cost of at least $200 per pile. With ten piles, you are looking at four times the cost of doing it yourself, likely at a minimum.
It is possible to purchase commercial screw piles, although many are not designed to be installed manually. The square base of the Pylex bracket and square top of the shaft allow it to be turned manually, whereas commercial piles do not have the squared off shaft, making manual twisting impossible. Some commercial piles do have pre-drilled holes where you can mechanically attach a 2×4.
When installing a screw pile shed foundation yourself, remember that the most important part is planning. If you accurately plot out your pile locations and properly account for weight displacement and beam positioning, then your shed structure will be stable.
Also, be sure to install the screw piles below the frost line. The helical plate should be entirely below the frost line to ensure your shed foundation doesn’t shift or heave.
Thanks for taking the time to read this article on screw piles. I hope you find it helpful when it comes time for you to install screw piles for your next project. As always, if you have any comments or questions about the article, be sure to leave feedback below.