Are you planning on building a shed, but can’t decide on what would be good foundation for it? Or maybe you do have some ideas, but you can’t make up your mind because of the ground moisture or the slope it should be placed on?
Well, I have some good news for you if you’re tilting on choosing a pier foundation. It doesn’t loose to a regular poured slab and in some conditions it might even be better.
A precast concrete pier foundation is the most stable foundation you can have besides a concrete slab. It is much more stable than skids and you can be sure your shed will be stable for years to come. There are also solutions to protect concrete pier foundation against frost heaving if that is a problem that might happen.
The precast concrete piers are embedded in the wet concrete footings and support 4×6 pressure treated timbers. That will lift it off the ground and protect against moisture that comes from the ground and depending on height, also against the snow.
The pressure treated beams on top of piers will support the shed. Once you have laid out your shed, excavate it to a depth of 3 to 4 inches. Then dig holes 10 inches below the frost line for footings. This will help protect against frost heaving.
Pour the concrete for the footings and then set the precast piers in the wet concrete. It’s good to check with laser or level that all the precast concrete piers are on the same level, this will make it easier to continue with the 4×6 beam.
Once the concrete cures, lay down landscape fabric and a gravel drainage bed, then install the beams. If the ground drains well and stays frost-free all year round, you will not need to make the gravel drainage bed. If you don’t have good drainage you will need to do this and I will explain how later in this article.
Start by laying out the concrete pier foundation design
In the beginning, we need to layout our project, as we have done already. Then we remove the sod and 3 to 4 inches of soil from the site. This will help us to install the drainage later.
Use your batter boards and string line and put masking tape or some kind of mark every 4 feet to help layout where your piers will go. It’s important to get it right as no one wants to move the piers and footings once they are done. So take your time measuring everything correctly.
Run string lines across the taped points. Square the lines by applying the 3:4:5 triangle rule. If you don’t know it, every triangle with 3:4:5 sides is a right triangle. This way you can make your shed any rectangle shape.
With a plumb bob and powdered chalk, mark the locations of piers on the ground where the lines intersect.
Dig holes for concrete footings
Next, we need to dig some holes for the concrete footings. These need to be 12 to 14 inches square and 10 inches below the frost line. We shovel 4 inches or so of gravel into the holes for drainage and tamp it down with a 2×4 or something similar. Just have the bottom level so it’s easy to set form on top of it if we use one.
Let’s assume you do want to make your own concrete forms. We build square forms or of 1×6 material for the top of the footings and seat the forms over the holes and level the forms on all sides and with each other. If necessary we should use stakes to hold the form in place on the bottom.
Another pro move here would be to measure the distance between the top of our form to the supposed 4×6 beam height. That helps us a little with setting the precast concrete pier foundations to the correct height.
Finally, we mix concrete and shovel it into the forms and holes. We move the shovel up and down in the concrete to help eliminate air pockets or use a vibrating tool for the same purpose. With a straight edge scrape the concrete even with the top of the form.
Attach concrete pier foundations on the footings
Next, it is time to install the precast concrete pier foundation on the footings, we need to do this before the concrete dries. This way the cement in concrete adheres to the precast concrete piers as well as it does to aggregates in it.
We can align the piers by placing a straight board across them with the board lying horizontally. Then put the straight board on the edge next and sit a level on top to level the anchors from end to end.
We should let the concrete set for at least 24 hours before removing the forms. After we remove them, we can shower the footings with little water so it will harden some more. It will also prevent possible cracks.
If necessary, we should place landscape fabric and gravel for drainage. If the drainage is already good, this is unnecessary. When in doubt, it’s better to be safe than sorry.
At last, we place 4×6 beams into the anchors on the piers. We can level the beams from end to end, side to side, and with each other by slipping shims under them if needed. Next, we can attach the anchors to the beams with nails or screws.
Now we have the precast pier foundation ready for the shed. This is a good way to do a shed foundation; it’s very stable and will work in most applications. It’s good for wet ground, uneven ground, frost heaving ground, etc.
Precast concrete pier foundations have their own place in building houses and sheds. It’s a good way to get the building of the ground if there’s a problem with ground moisture for example.
It’s also a good way to build on uneven ground and you might have seen some precast concrete piers on hill houses etc. There is more here if you want to read more about concrete foundations.
Personally, I would lift most of the storage and other kinds of buildings of the ground I have at home. When it is lifted off the ground, the floor gets to breathe and you might even plan for that quality.
Raise the structure enough and you don’t have to worry about sinking anymore. I had a kids playhouse build on piers and when it started to slowly sink all I did was raise it back up by some leverage and concrete pads. For my defense, I have to say that it wasn’t built by me.
If you’re interested in ways to support concrete foundations, here is an article about precast concrete piles that support the foundations underground.