If you’re going to be spending a lot of money on building a shed, then you will want to have a good foundation that will last for years. If you’re wanting to have a shed that is portable, then using a permanent foundation is not a good idea.
Unless you intend to have a small shed that is portable, a permanent foundation is a great idea. The more permanent the foundation in general, the sturdier the foundation for the shed. Also, the more work that goes into the foundation, the more likely your shed will be protected from damage from moisture, insects, shifting and weather.
What is a Permanent Foundation for a Shed?
A permanent foundation for a shed is one that cannot be removed without a lot of work. It is designed to be permanent. These include concrete slabs, block or poured concrete walls, and concrete piers.
What is Considered a Permanent Foundation for a Shed?
Basically, anything that involves concrete can be considered a permanent foundation. These foundations cannot be moved or removed without a lot of work and digging or excavation. Some people also differentiate between on-grade foundations that sit on the surface of the ground and those that require excavation and are partially below ground when making the distinction of a permanent foundation. For more information on other types of shed foundations read my article What’s The Best Shed Foundation Option For You?
How Do I Attach My Shed to the Foundation?
Many sheds are not actually attached to a foundation, but are set on top of it, be it a concrete slab, paving stone, gravel or plastic base. In addition, attaching the shed is not possible with many popular foundations, such as gravel or paving stones.
It is a good idea to anchor your shed to the foundation in some way to keep it from being affected by high winds and the ground shifting from freezing and thawing. Your local building authority may require that your shed be anchored to the ground or a firm foundation as well.
If you intend to have a concrete slab foundation, the easiest way to attach your shed to it is to sink anchor bolts right into the concrete. Wait until it has started to set and is not so soupy. Insert your anchor bolts, moving them slowly up and down a bit to encourage the concrete to flow around the bolts firmly. Make sure they are all even and level, then let them dry right into the concrete.
If your slab and shed have already been put into place, you can get some sleeve anchors. Figure out how many you’ll need to put a bolt in every three to four feet all the way around. You’ll need to drill the bottom plate of the shed and down into the slab, with a hammer drill and concrete/masonry bit. Insert the sleeve anchors. Use the included washers and nuts to bolt down the shed.
Another way is to use foundation anchor plates. These are shaped like a “T” and have pre-drilled holes. The T shape is placed upside down and attached to the side of the concrete pad through two holes drilled into the concrete and secured with bolts. The upright part is attached to the shed frame.
Will I Need Plans and a Permit for a Permanent Foundation?
Unless you live in a fairly rural area, you probably will need a building permit for the shed, including the foundation. You’ll need plans to submit to the building authority, along with a site plan showing the location of the shed relative to other things such as other buildings, the property lines, any utility lines above or below ground, and perhaps other things. You need to follow zoning regulations even if you don’t need a building permit.
Even if you plan to have a movable shed, such as a small plastic shed, you may need a permit or at least an inspection. Many localities have codes governing the allowance and placement of outbuildings, whatever the size and purpose, with or without a building permit. You’ll need to make sure that you are allowed to have a shed and to place it where you want it.
In addition, you may need to satisfy other regulations such as securing your shed to the ground or a foundation. If you live in a homeowner’s association, there may be other rules, such as size, placement, visibility from the street, color, and other things. Check out my article Do You Require a Building Permit For a Storage Shed? for information on permits and plans.
What is the Best Permanent Foundation and Why?
Concrete slabs are generally considered to be the best and most stable permanent foundation. It’s the most durable foundation you can have. It provides a good, stable base for your shed, whatever type you want. Having a slab means that your shed can be fairly close to the ground even allowing for raising it above the slab allowing for airflow.
This makes it easy to keep your lawn tractor or ATV stored in the shed with a minimal ramp. Your slab can be used as the flooring for your shed, saving you some steps and materials. The slab is the firmest base you can have for attaching your shed and keeping it from being damaged by wind.
Any moisture problems caused by dampness seeping through the concrete can be addressed by installed a vapor barrier on the ground before the concrete is poured. An additional benefit is that the vapor barrier actually helps the concrete cure evenly instead of curing around the edges first, potentially causing curling.
The next best permanent foundation is the concrete pier system. The number of piers you will need will depend on the size of your shed and the type of joists it has, but they are usually placed every three to four feet around the perimeter and through the interior.
Round holes are dug to six inches below the frost line, or at least four feet deep. Six inches of gravel is put into each hole for drainage. Tube forms, usually made of cardboard, are set into the holes with the tops at least six inches above ground level. Once the tube tops are level, concrete is poured into them. Anchor ties are set into the concrete to allow the shed to be attached to the piers. For more details read my article How Do You Build a Concrete Pier Foundation for a Shed?
When considering a shed foundation, remember that your shed is no more stable or solid than the foundation below it. If the foundation is well planned and built, you have built-in peace of mind.