Why Your Gravel Shed Foundation should be 12″ Wider than Your Shed

gravel shed foundation
gravel shed foundatoin

12″ Wider All Around

One important question many folks have when planning for their new shed or storage building is: “How wide should my shed foundation be?” Thankfully, it’s one question with a pretty simple answer. 

Your gravel shed foundation should be 12″ wider than your shed, all the way around the building. That means if your shed measures 8’x12′, your foundation should measure 10’x14′. There are good reasons for this which we’ll explain below.

In cases where your shed has an extra large overhang, you may want to make your foundation big enough so that the water that runs off the roof runs onto the stone pad. Of course, you always have the option to add a gutter and downspout to control the runoff.

Gravel or Concrete: Which Makes a Better Shed Pad

There are a variety of shed foundation options available, but gravel and concrete are two of the most popular. We cover the different situations where each is preferable in the article “Gravel vs. Concrete: Which Shed Base is Best for You?“. We’ll cover it briefly here, but we won’t go into too much detail.

The basic idea is that if your shed comes with a floor, you should choose a gravel foundation. If your shed doesn’t have a floor, you should choose concrete. 

With a concrete foundation, your shed foundation should not be wider than your building; you will want to make it exactly the same size. As stated before, with a gravel pad, you will want to make your shed foundation 12″ wider than your shed on every side.

gravel shed foundation gravel vs concrete

4 Reasons to Make Your Gravel Foundation Wider than Your Shed

Protects the Wood Siding

gravel shed foundation prevent rot

Making your gravel shed foundation wider than your shed helps to reduce the amount of water that splashes up against your shed. Repeated contact with a significant amount of moisture over the course of several years is what causes the siding to rot around the bottom (see photo).

You’ll notice that if you pour water into a bucket of gravel, it splashes less than if you pour it into an empty bucket. The same thing happens when water runs from the roof onto a gravel pad. It splashes less than if the building was surrounded with concrete or another hard surface. This keeps your shed dryer.

Keeps Your Shed Cleaner

Another benefit of making your gravel foundation wider than your shed is that it keeps your your shed cleaner. If rain water splashes into the dirt and up against your shed it will make your shed look like it took a mud bath.

If you allow grass to grow around your shed you may keep the mud from splashing up but then you’ll have another problem which we’ll address below.

Diagram of a shed in the mud with no gravel foundation
gravel shed foundation grass

Blocks Grass and Weeds

Grass and weeds growing up against the sides of your shed is a problem because it traps moisture after a rain fall. Your shed won’t dry out as quickly which can cause problems in the long run.

Another problem is that you may need to weed whack around your shed which can scuff the paint or scratch the vinyl siding. Eliminate this with a wider stone pad.

Reduces Water Runoff

A gravel shed foundation acts like a basin that collects rain water under your shed. This allows the water to soak into the ground instead of running off and causing other possible issues.

If you live in an urban area, your township may require you to put in a deeper stone base so that it can hold more water. This is one way to control water runoff issues that can be created by installing a shed.

Diagram of a shed foundation with water runoff

A Gravel Shed Foundation: Better All Around

A gravel foundation is your best all-around option when installing a shed or garage that comes with a floor. It will help your investment last longer and you’ll have fewer issues down the road that might come from your building settling. Making your foundation 12″ wider all around the building is another way to maximize the benefits you’ll get from installing your shed on a gravel shed base.

You may also be interested in our complete step-by-step guide for how to install a gravel shed foundation.

40 thoughts on “Why Your Gravel Shed Foundation should be 12″ Wider than Your Shed

  1. Callum Bonsall says:

    Do you mean 12” plus the width of the timbers or is the 12” taking into the account for the width of the timber perimeter already? Thanks.

  2. Site Preparations LLC says:

    The perimeter can be included in the 12″ measurement. We use 4×6 lumber turned on edge for our shed foundations, so that would still leave 8″ of exposed stone.

  3. Serena says:

    This is a great post. I am getting a 16′ x 26′ shed in my backyard that I’ll use for a workshop. I got a quote for a 6″ gravel foundation with 6×6 pressure treated posts, plus drainage built into the back corner, and 1’6″ of extra gravel extended on the sides. We haven’t submitted the permit yet, but my worry is that a shed that size, I worry that the county will require a concrete footing below the frost line. I know this is county specific, but do you know if 16′ x 26′ sheds fair well on a gravel foundation? (FYI, the pre-fab shed I am ordering has metal floor joists and rim joists). Would love to know your feedback on gravel foundations for larger buildings. Thanks!

  4. Site Preparations LLC says:

    Hi Serena, we’ve built gravel pads for buildings of all sizes, so it shouldn’t be an issue from that perspective (if installed properly). A lot of folks even put in gravel foundations for doublewide garages! However, it’s really up to what your township requires. If you do need to go with concrete footers, you may be interested in a combination gravel/concrete pier foundation like these:
    https://www.siteprep.com/recent-projects/gravel/ken-c-gravel-shed-foundation-in-warminster-pa/
    https://www.siteprep.com/recent-projects/pennsylvania/michael-l-gravel-shed-foundation-in-philadelphia-pa/
    Hope that’s helpful!

  5. David says:

    Hi great info. Can I ask how high the gravel should be above grass or ground level. Also what is your opinion on the plastic trays sold for use with gravel shed bases?

    Thanks Dave

  6. Site Preparations LLC says:

    Hi David, we usually construct our shed foundations so the top of the gravel is at least 2″-4″ above the surrounding grade. We don’t have a lot of firsthand experience with plastic/gravel shed foundations, but from what we’ve seen, they may be suitable for smaller sheds (especially plastic sheds, like Lifetime or Rubbermaid brands). For a larger shed, we’d recommend a compacted stone (gravel) shed base like what’s shown in this article.

  7. Hal says:

    I’m buying a galvanized metal shed 10 by 16 how large should the pad be,will 4 mil plastic be ok and what gravel should I use.

  8. Site Preparations LLC says:

    Hi Hal,
    Your shed pad should be 12×18 in that case. You don’t want to use plastic under your shed foundation as it won’t allow water to drain through properly; we recommend a permeable stabilization fabric. Use ‘3/4″ clean’ crushed stone for your shed foundation. You can see a full shed foundation building guide here.

  9. Steve says:

    We’re getting a 8’x10′ shed. The shed will have 6″ eaves. Will a 10’x12′ gravel foundation using 6×6 lumber suffice?
    Depth of gravel would be 6″. We’re also getting a 4’x4′ wood ramp with it. The shed floor joints will have 4×4 PT ground contact runners underneath. What’s the different benefit of the top of gravel being 2″ vs 4″ above grade? If we only go with 2 inches above grade, that may work better with the ramp. Won’t be as steep an incline. Thank you for the wealth of information that you provide on your website. Much appreciated.

  10. Site Preparations LLC says:

    Hi Steve,
    Those foundation specs sound quite adequate. Going 2″ above grade with the foundation is fine and, as you mentioned, won’t leave your door ramp as steep.

  11. Emma says:

    Can you breakdown what “Steve says” on the following in laymens terms.
    He said …The floor joints will have 4×4 PT ground contact runners underneath. What’s the different benefit of the top of gravel being 2″ vs 4″ above grade? If we only go with 2 inches above grade, that may work better with the ramp. Won’t be as steep an incline..
    I want to purchase a 12×12 or 12×16 storage shed but was giving up on the idea because I couldn’t decide on the type of foundation. Your advise and straight answers to those seeking it has given me hope and confidence. The information you provide is simply awesome. Wow.
    Yep. And I’m back in the saddle again. Thanks for being available,,,,,!!!!!!

  12. Site Preparations LLC says:

    Hi Emma,
    Steve is referring to the 4″x4″ pressure-treated lumber runners (or skids) that support many prefab shed floors. He also asked about how high the lumber perimeter of the shed foundation should extend above the surrounding lawn…2″ or 4″. The answer is that either is fine…usually the step up to the shed foundation should be as low as possible on the end where the shed doors will be located, for easy entry/exit.
    Hope that makes sense!

  13. Trace says:

    Can’t a small shed with a framed floor be placed on concrete blocks which have gravel underneath each block only? Also, how necessary is placing weed fabric underneath the gravel?

  14. Site Preparations LLC says:

    Hi Trace,
    Shed foundation blocks aren’t ideal due to the structural strain they can place on the building; this article gives more detail on that. The geotextile fabric we use in our gravel shed foundations not only prevents weeds but also adds to the overall stability and durability of the foundation.

  15. Matthew T Gulley says:

    I am wanting to put in a shed that is 12′ x 16′ but can’t find 4×6 that is 18′ to give the extra 2 feet. What is the best way to accomplish this?

  16. Site Preparations LLC says:

    Hi Matthew,
    You can join multiple shorter pieces of lumber together by toe-screwing the ends and drilling+staking through each piece so it doesn’t shift. This article gives more details.

  17. Ryan says:

    I have purchased a Mini-O prefab shed (the model is The Twelve, which is a 12’x8′ shed) that will be delivered already assembled. They are going to crane it into place once it arrives. I need to have the site prepped before delivery happens. I was wanting a DG (decomposed granite) look around the perimeter of the shed (I think it looks better than just gravel). Would this be a sufficient enough foundation? Or should I have a slab put in, and then just do the DG around the perimeter? Thanks for your insight!

  18. Site Preparations LLC says:

    Hi Ryan,
    We don’t use decomposed granite and we would have some concerns about how well it would support the shed structurally. One idea is to install a pad with crushed limestone (as detailed here) and then add a layer of DG around the shed once it’s in place to give the desired aesthetic.

  19. Britt says:

    Hello. The article says 12″ wider than shed dimensions but all your replies are for 24″ wider. Can you please clarify?

  20. Site Preparations LLC says:

    Hi Britt, the pad should extend 12″ past the shed on all 4 sides, meaning the pad needs to be 24″ larger than the shed in both length and width.

  21. Rick Bourque says:

    I have ordered a 12’ x 8’ all wood shed that comes with a 2 x 4” framed wooden floor, that will sit on quantity four 8 foot long, 4” x 4” runners. I plan on using a 14’ x 10’ gravel base, as described herein and I plan to remove some of the topsoil so that the gravel is only slightly above grade. That way, the step-up to the shed will be about 7.5” which is about the height of a standard step.

    My Question: I’ve had to dig down to remove a number of shrubs from the area and I’m concerned that some of the roots may take hold and start to grow underneath the foundation gravel and the shed. Should I put down some ground cover below or on top of the gravel ?

  22. Deb says:

    Is a gravel base the same as a gravel base with concrete slabs on top? Do I still need to make the base 2 feet past the shed?

  23. Site Preparations LLC says:

    Hi Deb,
    A gravel pad is different than a concrete pad, even though the concrete pad is poured over the top of a gravel bed. The main difference is the drainage provided by a gravel pad.
    A concrete pad should be the same size as your building dimensions; otherwise water can puddle on the concrete and cause moisture damage to the building frame over time.

  24. Matt Fedorczyk says:

    Hey, I already have a 9 7/8 by 9 7/8 concrete pad in my yard. 2 questions for you. 1) am I able to still put up a 10×10 shed on it (I could possibly surround the concrete pad with an extra inch or two of gravel to increase its total area to slightly over 10×10. 2) if I’m buying a shed from HD that doesn’t come with a floor, should I install my own or just use the concrete as the floor?

  25. Site Preparations LLC says:

    Hi Matt,
    To take your questions in order:
    1. You can use the concrete, but make sure it’s draining well. The last thing you want is water sitting under your shed.
    2. For sheds without a built-in floor, it’s great if you can build directly onto the concrete pad. Back to point 1, if you do build on the concrete it’s especially crucial that water not be able to run across the concrete and under the edge of the shed. So you’ll want to consider ways to drain the pad and seal the bottom of the shed if you go that route.
    Good luck with the project!

  26. Buzzy says:

    I just purchased a 10 x 8 Shed (Vynal) how big should my foundation be ? and what size gravel do you recommend for the foundation?

  27. Site Preparations LLC says:

    Hi Buzzy,
    An 8×10 shed should have a foundation of approximately 10×12 (12″ extra on each side). We recommend 3/4″ clean crushed stone.

  28. Corrina says:

    Hi I was wondering how you would build a shed and level it on uneveb concrete its going to be 7x7ft

  29. Site Preparations LLC says:

    Hi Corrina,
    It’s hard to give a specific recommendation without having seen the site. You may be able to pour enough concrete on top of the existing concrete to level the area for the shed.

  30. Chuck says:

    Can I build a garage on perimiter footings like 12×12 inches the building sits on? And the middle will be gravel.

  31. Site Preparations LLC says:

    Hi Chuck,
    Based on what it seems you’re asking, yes. You could technically pour perimeter footings but leave gravel on the inside and not pour any flat concrete. You can see how we install concrete garage foundations here (including pouring the concrete floor).

  32. Paul Findlay says:

    Hi, I am about to build a 12′ x 3′ shed. I have restricted enclosed space and wondered if allowing 6″ either side would still work. Also, I am planning on using old pallets as the base foundation, filled with pea gravel to just before the top of the pallet. Should I dig the pallets down to ground level and build shed on that or should these be slightly raised above ground level, if so, by how much? Also, do you think this method will be ok?

  33. Site Preparations LLC says:

    Hi Paul,
    You should be fine with 6″ on each side, though you may get slightly more dirt splashing up on your shed.
    As far as the pallet building method…Pallets are not necessarily made with treated lumber, meaning they are more prone to rotting when exposed to the elements. We would recommend building on something a bit more durable. We have a detailed how-to guide here that covers our recommended method for building a shed foundation. Hope that helps!

  34. Robert Chaplik says:

    Can I dig a two foot trench around my shed that is on dirt gravel and compact 12”deep with large washed stone ?

  35. Site Preparations LLC says:

    Hi Robert,
    Not sure exactly what you’re trying to accomplish, but that should be fine.

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