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Do you need a concrete slab for a plastic shed?

The only time you wouldn't need some sort of foundation is if you have a very small 6×6 or 8×8 shed that is made out of rubber or plastic. And even in that case, we still highly recommend a gravel foundation to keep that little plastic shed from sinking into the ground or experience moisture problems as time goes on.

siteprep.com - Do You Need A Foundation For A Shed? - A Guide For 2022 - Site Prep
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Like many good things in life, such as romantic relationships and bowling alleys, most sheds need a foundation! That’s the short answer anyway. There are a few exceptions (which we’ll talk about), but a foundation is generally required when building or buying a shed. In this article, we’ll discuss a whole range of common shed foundation questions and help you prepare for that new backyard building!

Is a foundation required for a shed?

It depends on the size of your shed. As mentioned above, most sheds require a foundation. However, some very small sheds may not need a foundation. The best way to answer the question “Do you need a foundation for a shed?” is to check with your specific shed manufacturer and your township or homeowners association (HOA) to find out exactly what is required for the shed you’re planning for. 3 key factors to consider when deciding whether or not to put your shed on a foundation are size, weight, and shed floor.

What shed size needs a foundation?

The size of your shed is often what determines whether or not you need a foundation. Typically, any shed larger than 6×8 or 8×8 is going to require a foundation. However, a foundation is a good idea even for small sheds, because the right foundation, installed correctly, will protect your shed and extend the life and useability.

What shed weight needs a foundation?

In general, if the total weight of your shed is over 300-500lbs, it’s a good idea to place it on a foundation. It’s not only about the exact weight of your shed alone, but also about what you’ll be storing in your shed and the weight of those items that factor in here. If you’re going with a garage shed for storing farm tractors or cars and trucks, then you may want to go with a concrete pad. If you will be storing things like ATVs, lawn mowers, and motorcycles, then a gravel pad is usually fine. For very small sheds, like those made by Rubbermaid, Lifetime, and similar brands, you may still want a gravel shed foundation if the total weight of the shed and contents is over 300-500lbs.

Does a shed with a built-in floor need a foundation?

Generally, any shed that comes with a floor should get a gravel pad 12” larger in each direction than the corner to corner exterior dimensions of the shed itself. Any shed that comes without a floor should get a concrete pad the same size as the corner to corner exterior measurements. We’ll go into more detail later about how to figure out what size of gravel pad you should use and why concrete pads should not exceed the size of the shed resting on them. For now though, just remember that sheds with floors get oversized gravel foundations and sheds without floors get same-size concrete pads.

What do you put under a shed?

Although there are many possible shed foundations, the main options for under a shed include a gravel shed foundation, a concrete pad, a post-and-beam shed foundation, or a plastic grid shed base (for smaller sheds). Like we said earlier, you will most likely want to install a foundation for all but the smallest sheds. The question is which foundation is best for your shed? Here are the best options for what to put under your shed:

Crushed stone shed foundation

If your shed comes with a floor built in, then a gravel shed foundation will be best for you. The crushed stone that makes up the gravel foundation allows water to drain through the stone and away from your shed foundation. This prevents rain from pooling around or under your shed. When water pools around or under your shed, rot or rust can set in and begin to destroy the foundation and the siding of your shed. Crushed stone or gravel foundations work so well because they allow all water to drain away from your shed. Your shed will stay level and dry on a gravel foundation. It is one of the easier and more affordable options as well. Additionally, crushed stone pads are a relatively affordable options in terms of shed foundation costs. (This style of foundation can also serve purposes, such as a gravel hot tub pad.) You can learn how to build your own gravel shed foundation here. (Or just hire a professional shed foundation company to do it!)

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Concrete shed foundation

If you’re getting a shed without a built-in floor you’re going to need a concrete pad. The walls of your shed will actually get anchored to the concrete pad and that will provide a lot of stability that you would have otherwise gotten with a built-in floor. It’s important to make sure that the concrete pad your shed is built on is exactly the same length and width as your shed. This is so water cannot pool around the back or sides of your shed. For more details on concrete shed foundation options, check out our full guide to shed footings.

Nothing (no shed foundation)

Wait, really? Yes, sometimes you don’t need a shed foundation.

For instance, if you have a small plastic shed that is under 8×8, you could potentially get away with not having a foundation. One of the things that gravel and concrete foundations do for sheds is protect them from water damage. Your small plastic shed won’t be affected structurally from a little water around the base. (*Little water* is the key; if your shed is in a location that gets wet, you’ll want to think about putting it on a base that allows drainage and keeps moisture out of the inside of the shed.) PC: Wayfair The risk with putting no foundation under your shed is that your shed could settle over time. Settling is when one or more corners of your shed begin to sink into the ground due to the ground compacting or eroding. Putting a shed on some kind of foundation will prevent settling and keep the structure you’ve invested in level. So, while you can get away with not putting smaller plastic sheds on a foundation, we don’t recommend it. In a perfect world every shed would have a well built foundation (and we would all be able to eat fast food whenever without health consequences)!

Which shed foundation is right for your shed?

If your shed comes with a built-in floor (most likely pressure-treated wood), a gravel/crushed stone foundation that is 12” larger than your shed’s length and width dimensions will be best. This allows proper water drainage that will prevent premature weathering and damage of your shed. If your shed comes without a floor (as some sheds do), a concrete pad with the same dimensions as your shed will be best. This way it will have a solid, level foundation and water will not have extra room to puddle up on the concrete sticking out past the outside edge of your walls. (Check out this article for a full comparison of concrete vs. crushed stone shed foundations or this article for a detailed comparison of shed foundation options.)

How high should a shed be off the ground?

Generally speaking, you will want the floor of your shed to be 4”-6” inches off the ground. Again, this is to prevent moisture accumulation around the bottom of the structure. Both a crushed stone pad and a concrete pad will allow for this slight elevation. This added height will allow water runoff and drainage while protecting your shed in the process. It’s especially important if your shed is on a concrete pad because the elevation will keep water from pooling where the shed walls meet the concrete.

What is considered a permanent foundation for a shed?

Concrete pads are most commonly considered permanent shed foundations. Poured concrete cylinders called “piers”, buried 32”-36” ft deep in the ground would also be considered permanent foundations because they extend below the frost line in most parts of the United States. Keep in mind that a “permanent foundation” could refer to either 1) a frost-proof foundation or 2) a method of anchoring your shed to its foundation. Local municipalities may require your shed and foundation to meet one or both of these requirements. Gravel shed foundations (our recommendation for most sheds with built-in floors) can be either permanent or non-permanent, depending on how they are installed. To meet local frost-proofing requirements, a gravel shed pad can be combined with concrete shed foundation piers to add the benefits of footers without the cost of pouring a full concrete pad. For anchoring a shed on a gravel pad, options include pound-in stake anchors driven through the gravel and fastened to the shed or anchors embedded in the concrete piers.

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Sheds placed on foundation blocks (which we never recommend) and skid foundations (also not recommended for direct ground contact) are all in the category of “on-grade” foundations. These are easier to install and uninstall and don’t involve pouring concrete. Shed foundation blocks and wooden skid shed foundations are NOT considered permanent foundations.

What dimensions should a shed foundation be compared to the shed?

This is a really common question and one that is worth digging into a little bit. If your shed has a built-in floor, you want the gravel foundation to be 2ft longer and 2ft wider than your shed wall dimensions. If your shed does not have a floor, you want the concrete foundation pad to be exactly the same length and width as the walls of your shed. A shed with a floor needs a larger, gravel foundation that will keep water away from where the walls meet the foundation. If water is allowed to pool and sit there for lengths of time, it will cause rot or rust and eventually ruin your shed. Gravel foundations prevent water from accumulating because any rain water is able to immediately drain through the stone. Water never pools, your shed retains its integrity, and your things stay dry. Pop Quiz: If you have a 10×12 shed, what size should your foundation be? 12×14, that’s right! If you have a 10×20 shed what size should your foundation be? 12×22, exactly. Ok, so why does your shed with no floor need a concrete foundation and why can’t the concrete foundation be any bigger than the footprint of your shed? Generally, sheds without floors are designed with the intention that they’ll be anchored to a concrete foundation. The issue with concrete is that water will collect on concrete and not drain like it does through gravel. Just think about all the parking lots and sidewalks that you’ve seen big puddles of water just sitting in waiting for the sun to dry them out. Sometimes it takes days for those puddles to go away. If your concrete shed foundation is larger than the corner to corner exterior dimensions of your shed, you could end up with puddles like that around the base of your shed. That standing water will cause problems as time goes on.

Let’s Recap…

So, do you need a foundation for your shed?

Yes! Almost always. The only time you wouldn’t need some sort of foundation is if you have a very small 6×6 or 8×8 shed that is made out of rubber or plastic. And even in that case, we still highly recommend a gravel foundation to keep that little plastic shed from sinking into the ground or experience moisture problems as time goes on. There’s definitely a lot to figuring out what kind of shed foundation you need. And installing it is a whole different story! Remember, we’re here to help, whether that’s providing information or actually doing some work! If you’re interested in how to build your own shed pad, check out the article we put together on installing gravel shed foundations. If you’re not ready to tackle the project yourself, find a well-reviewed, professional shed foundation company to assist you with the job. If you’re in the Mid-Atlantic US, we’d be happy to give you a free quote for your shed foundation and advise you on what foundation is best for your specific structure.

siteprep.com - Do You Need A Foundation For A Shed? - A Guide For 2022 - Site Prep
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