Back in 1173, an Italian architect from Pisa named Frank Lloyd Wright (name changed to protect identity) got up one morning, dusted off his drafting table, and set to work on a new project. The history books neglect to mention this, but he may have been suffering from a slight hangover (that part of Italy is famous for its wines), because he designed a tower 180 feet high and weighing an estimated 14,500 tons — with a foundation only 3 meters deep.
It was a remarkable lack of foresight. In fact, tourists have been remarking at the sight of it ever since the tower began to shift in 1178–only 5 years after construction started.
You are fortunate for two reasons. First, portable storage sheds are only about 10 feet high, and many weigh less than a ton (1/14,500th of the infamous Tower). Second, and consequently, they need less of a foundation.
But it’s a great lesson for us all. The foundation matters. You don’t want to have your shed sitting on the ground, or it will rot from the moisture. And you do want it stable, so that it doesn’t lean (sound familiar?), and so that the doors and windows work properly.
With that introduction, let’s look at your options for a shed foundation.
This is the easiest and most common way of building a shed foundation. At Bylers we use cement blocks for the majority of our shed sets (FREE delivery and setup for many sheds, up to a foot out of level!), and have found them to be very satisfactory. Shea (delivery driver) tells of having moved one of our sheds that was 30 years old, well-maintained, in beautiful condition, and still sitting level on its cement blocks. For block sets it is best if the shed site is not more than 2 feet out of level. It’s possible that you may want to build your own block foundation — here’s an article to help you.
Cement blocks are built in piers (think mini-towers–but they don’t lean) 3-5 feet apart. If the sheds are built like they should be, the structure of the shed easily spans the piers–unless you’re parking the car in it, in which case you’ll want to consider a gravel pad.
Gravel pads are useful if you are parking heavy equipment (like a car or tractor) inside your shed or garage. A gravel pad is one way of leveling out ground that is more than 2 feet out of level. Another advantage of gravel pads is that unlike block piers, the shed skids (supports under the floor) are in continuous contact with the gravel pad. Parking your tractor in the same place for 10 years will not result in a drooping floor. And you may be able to build your own gravel pad. The disadvantage of gravel pads is that they are more expensive and take more time.
Concrete pads function almost identically to gravel pads, except for a few obvious differences: they are more expensive, and they are more permanent. But as with gravel pads, they have the advantage of full load contact–allowing the shed floor supports to be in continuous contact with the foundation, rather than spanning as with blocks or concrete piers. This option is only necessary if you are storing heavy equipment in your shed. One other reason to consider a concrete pad is if you have an extra-heavy building, such as a 1.5- or a 2-story building.
This may surprise you, but if you decide to build a concrete pad, you should construct it to the length and width of the shed skids, not to the nominal size of the building itself (eg. 10×12 or 12×20). If the pad is too large, it will catch water run-off from the roof, allowing it to puddle on the slab. This leaves the building skids sitting in water, which promotes rotting.
Post and Beam (cover photo)
These aren’t common–we only set buildings on them occasionally. A Post and Beam structure is used when the slope is way out of level; it’s cheaper than excavating, and may be done by a homeowner. It’s built of pressure-treated lumber, in which posts are buried in the ground, and beams span from posts to post. The shed is set on the beams.
Be sure to use a set of engineered drawings, however, since . . . well, let’s just remember the lesson from the Leaning Tower. You wouldn’t want to have a tourist attraction called the Collapsed Shed of YourTown.
Be careful about another factor: the Post and Beam structure must be close to the ground on one side, or the trailer (which is not capable of catapulting a shed up into the air) will not be able to set the shed down on it. The maximum height at the end where the trailer backs up to place the shed cannot be higher than 32 inches.
As with post and beam, concrete piers are fairly rare. You may recognize how concrete piers look from seeing the design of many bridges, which span from one set of round concrete piers to another. Concrete piers for sheds may be necessary if the shed site has considerable slope. Unlike setting a shed on blocks, which are also built in piers, concrete piers go fairly deep into the ground, and are a permanent foundation.
Concrete piers are built by digging holes, inserting tubes (called Sonotubes), and pouring them full of concrete.
Should you decide to go with concrete piers, Bylers has a set of engineered drawings that will show your contractor how to build them.
Your Shed Foundation
As you can see, you have a lot of options for your shed foundation. The majority of our portable sheds, however, go onto blocks; gravel pads are another fairly popular option. You will need to choose what will work well for you and your shed. Using this information, you should be able to construct a shed foundation that won’t become the next local tourist “detraction” getting you strange looks from strangers.
Your turn! What advice or experience with a storage shed do you have? Give others a helping hand by leaving a comment below. Tell us what worked (or didn’t work!) for your shed foundation.
Source for Tower facts: www.towerofpisa.org
Shed Delivery Video (watch a block set)