Your local building codes may specify this based on the size of your shed. If not, a general rule is one shed foundation pier at least every 8-10 feet along the width and length of your shed. For example, you would need 6-9 piers for a 10×12 shed. You would need 15-18 piers for a 16×40 shed.
So, how do you build a pier foundation for a shed? Although there are several steps, it’s a relatively straightforward process overall.
(If you plan to combine your shed foundation piers with a gravel shed foundation, it will be easiest to build the gravel pad as a second part of the project, after the piers are in place. To get the best overview, it may be helpful to read our guide to building a gravel shed foundation before starting either part of the process.)
Here are the steps for building shed foundation piers:
1. Mark shed pier locations
Once you decide on the location for your shed, mark lines at each of the shed corners. It’s a good idea to double check that there are no tree roots or utility lines in the area where you’re planning to dig.
If your shed will be next to a fence or driveway, it’s a good idea to use that as a starting point and make sure the first side of your shed foundation is parallel. Once you’ve marked all four corners, take diagonal measurements as well. The diagonal measurements should be equal in each direction to ensure that the shed base is square.
If you will have multiple rows of shed piers, mark each row across both the length and width of the shed. You will want to end up with an X marking the spot where you will set each pier for the shed.
An important note: Depending on how it’s constructed, the runners beneath your shed may be inset from the sides of the shed by up to 12”. You will want your shed piers to be approximately centered beneath the runner, rather than centered on the exact corner of the shed. Be sure to find out where the runners will be on your shed and mark your pier placement lines accordingly.
2. Determine grade/site slope
If your site has a slope, you’ll need to measure it. It’s important to determine the grade exactly since you will pour the shed foundation piers to compensate for it and level the shed. It’s easiest to use a laser level, but you can also use a string line level or a stick level and straightedge to get the job done.
To measure the slope with a laser level, place the laser at the highest point of your site. From there, move around the site and use the laser receiver to take readings where each of your shed foundation piers will be. By moving the receiver up or down the transit rod, you can find the exact height difference between the highest pier location and every other pier. You may want to draw a simple diagram of all the pier locations and their respective height differences. You can refer to this diagram when placing your pier forms.
Our gravel shed foundation guide gives additional details on measuring shed site slope here. You can also find laser level tutorials here and here. The video below gives a helpful overview of the general process to find the slope of a site.
Keep in mind that if your site has a slope of more than a few inches, it will be easiest to access your shed if the door is placed on the uphill side. It’s certainly possible to dig out the site so the door is level with the downhill side of the slope, but it’s a lot more work. If a downhill door is your only option, you may want to consider hiring a professional shed foundation company to prepare the site.
3. Excavate the pier holes
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It’s easiest to dig the shed pier holes with a power auger. When we install shed foundation piers, we dig the holes with an auger attached to a mini skid steer. As mentioned above, there are a number of auger types that will do the job.
Of course, you can also dig the footings by hand with a post-hole digger. (If you dig by hand, you can probably also cancel your gym membership! 😉)
Pier footings are measured by diameter in 2” increments. While there are many sizes available, the most common shed foundation pier diameters are between 12” to 16”. Check local code to see what’s required in your case.
Dig the footing holes to whatever depth is required by your municipality or the International Residential Code. If not otherwise specified, it’s good to go at least 12” below the local frost line. For instance, 36” is the standard depth for shed foundation piers here in the northeast USA.
Some municipalities require shed foundation pier holes to be inspected before the concrete is poured. You’ll want to check ahead of time if this is required in your area. If so, try to schedule the inspection for the end of the same day when you’re excavating, or for the day after. That will keep your project from being held up while waiting on inspection.
Once the footing holes are at the proper depth, insert the pier forms. Sonotube® is the most well-known brand, but they are also made by many of the ready-to-mix concrete companies. You should be able to find them at any large home improvement store by searching for “concrete form tubes”.
You don’t necessarily need to insert the tube the entire way to the bottom of the hole. We often cut the tube forms to extend about 12” below ground. That keeps the visible part of the shed pier looking nice and lets the concrete completely fill the rest of the footer hole. Make sure the top of the hole is tight enough to hold the form in place if you do this.
Shed pier forms come in 48” sections. You can cut them to length with a handsaw, chainsaw, circular saw, reciprocating saw…basically any kind of saw!
If your site is on a slope, remember to extend the forms far enough above ground on the downhill side to level the shed. It’s best to have the top of the forms almost exactly where the top of the finished pier will be. However, it’s better to extend it a little higher than to have it too low.
5. Pour the shed piers
For larger projects, consider buying the concrete premixed and having it delivered by truck to your site. You can typically purchase concrete by the cubic yard, though you may need to pay a convenience fee if you order less than a full truckload (10 cubic yards).
If you’re only pouring a few shed footings, you can mix up your own concrete by hand. Just follow the mixing instructions on the concrete bags when you purchase them. Generally, you’ll add about 1 gallon of water per 80 lbs bag of concrete mix. (As an example, you can see the instructions for Sakrete® concrete mix here.)
The best ways to mix concrete for your shed piers are:
Using a concrete mixer – This will give you the most thorough and consistent mix. It’s also the least strenuous! Make sure to use a mixer that’s designed for concrete specifically. (Some are intended only for mortar without stones or aggregate.) Mixing by hand in a wheelbarrow – If you don’t have a concrete mixer, you can pour your ingredients into a wheelbarrow and mix them with a shovel. Mixing by hand in the pier hole – This is the quickest way. It won’t result in as thorough of a mix, but it will save you time. This may be sufficient if the piers will be combined with a gravel pad. The gravel pad will bear much of the building load while the piers simply provide an anchor point.
The video below gives a good, quick overview of how to mix small batches of concrete in a mixer.
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If your piers will be supporting a large load, you can add rebar for extra strength. To do this, add up to 4 lengths of vertical rebar in each pier. (This is generally not required for most average-sized sheds.)
To prevent concrete honeycombing, it’s a good idea to tap the sides of the form with a hammer or other tool. This releases air bubbles and shakes the concrete into every part of the form.
Use a concrete float (magnesium floats are ideal) to finish off the tops of each shed foundation pier. You’ll want to use a float that’s shorter than the diameter of your pier. Check the height of the concrete in each form with the laser level to make sure everything is level. If needed, you can add or remove concrete to bring it to level, then refinish the top of the pier with the float. The following video gives an overview of concrete float types and how to use them to finish concrete.
6. Cure the shed piers
If your piers will be bearing most of the structural load of the building (i.e., not combined with a gravel pad) you should let them cure for 3-7 before placing the building on them. It actually takes concrete about 28 days to fully cure, but it has much of its structural strength within the first week.
For highly technical, load-bearing applications, it’s recommended to “wet cure” concrete by keeping it covered and damp for the first 3-7 days or coating it with a curing compound. However, this is unnecessary for shed pier applications in almost every case.
Once the concrete is cured, you can use a utility knife to cut and remove the visible parts of the form. Backfill dirt around the shed piers and make sure it’s tamped down well.
7. Install anchors
Technically, the order of this step depends on what type of shed anchors you use.
We recommend simple L-brackets, installed with a concrete bolt or large Tapcon® into the shed pier and a lag into the shed runners. This style of anchor is installed after the shed is in place.
Alternately, you can embed concrete anchor straps into the shed piers during pouring as part of step 5. However, this requires you to know exactly where the shed runners will fall in relation to the piers (to an accuracy of about ½”).
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Photo: Egor Komarov
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