Foundation For A Shed Or Tiny Home

Wondering what type of foundation is best for a self-built shed, tiny home, or shabin? Here are some things to consider, along with a review of the four main types of shabin foundations.

This is part of a series of blog posts on our self-built shabin. You can find all of the posts here.

Foundation Considerations

There are a number of considerations when thinking about a foundation for a small shed, tiny home, or shabin. I’m only an amateur, so this outline of the different foundation options should really be discussed with local planners and builders in your area. Each unique topography will have its own building requirements.

Regardless, here are a few things to consider when deciding what type of foundation to use:

• Services: Will you have electricity, water, or a small fireplace in your shed? Any of these items will require a more structurally supportive foundation in order to pass a building or wiring inspection.
• Frost line: Foundations need to account for the frost line (depth of the frost). It’s important for foundations to extend below the frost line otherwise you will have shifting with the freezing and thawing each year.
• Topography: While having a relatively level bit of ground to build on is handy, it’s also important to know what is underground. Is the ground soft, and likely to shift over time? Or is it bedrock? Getting a geological survey might be an important first step, especially if you live in an earthquake zone.

Four Options for a shed foundation

Here is an overview of the 4 main options for a self-build shed or shabin foundation.

1. Skid foundation

A skid foundation involves using either several large pieces of lumber as the foundation or in an even simpler form, using floor joists for the foundation.

We made a super simple skid foundation for our composting toilet. It was the perfect option for a tiny building that needed to be built relatively quickly.

1. It’s important to start with a good base of gravel to prevent the wood from rotting. The gravel should be at least 4-inches deep and you’ll need to use 1-inch crush.
2. To prevent rotting, use treated lumber. For a more eco-friendly option, we used cedar that we further protected with a solid stain on our outhouse.

Pros:

• The building can be moved. (After 2 years of use, we moved our composting toilet to a more private location).
• Simple to build.

Cons:

• They are not very long-lasting. Wood foundations are prone to rot and pests.
• The ground needs to be level.

2. Concrete block foundation

We used a concrete block foundation for our shabin foundation. Here are a few notes on how to set up a concrete block foundation:

1. Either use a whole gravel pad, then place the concrete blocks on top. Or make gravel pads underneath each of the concrete blocks. Either way, the gravel needs to extend below the frost line to prevent shifting.
2. Use solid concrete blocks, not cavity blocks.
3. You can even get blocks (like deck blocks) that allow you to anchor your shed to the blocks.
4. Here’s a good guide on how to level a concrete block foundation.

Pros:

• Best for small buildings that don’t have any electricity or plumbing.
• As simple to build as a skid foundation, but longer-lasting.
• Allows you to move the building without too much effort.
• The ground doesn’t need to be perfectly level.

Cons:

• Prone to settling, however, you can use a jack to relevel the building.
• You’ll have to keep the grass and weeds from growing up around the outside which would encourage critters to move in under the shed.

3. Poured concrete slab

Our friends built a shabin that doubles as a utility shed. So they used a poured concrete foundation that doubles as the shed floor. It’s sturdy enough to allow them to add electricity and plumbing to their shabin.

Pros:

• It’s heavy-duty. You could drive a truck or a tractor into the shed.
• Anchoring the shed to the foundation creates a really strong structure that will stand up better in an earthquake.
• Durable and pest-resistant.

Cons:

• Requires really level ground.
• It’s more complicated to build and takes longer than the other options.
• Since it’s not elevated, there is a risk of flooding.
• Concrete floors are cold.

4. Pier and beam Foundation

My dad made a number of bunkhouses, cabins, and swing sets during my childhood. Building those sorts of things was a bit of a hobby of his… and all of them were made using a simple pier and beam foundation.

If you’re building a house with a pier and beam foundation, then you’ll need concrete forms, rebar, etc. However, my dad had a simple pier and beam foundation method that he used for smaller structures:

1. Dig holes that extend below the frost line at each of your support points.
2. Pour in the mixed concrete. Then either set it with an adjustable fastener (which I would recommend). Or do what my dad did, and put the posts right into the concrete.

Pros:

• The ground doesn’t need to be level.
• You can decide how high you want to elevate your shabin. So you can have a crawl space or storage underneath.
• Much simpler than a concrete slab and more secure than a concrete block foundation.

Cons:

• Prone to settling (which is why you need to have the concrete extend below the frost line.)
• You’ll have to keep the grass and weeds from growing up around the outside which would encourage critters to move in under the shed.

Have you built a shed, tiny home, or shabin? What type of foundation did you use?