The right foundation ensures that your shed will last a lot longer and save you money and labour in the long run. But what is the right shed foundation for you?
The best shed foundation is a concrete slab. Concrete slabs can support a lot of weight, so you can use it with a permanent shed of any size. But when building a temporary shed, you can go with the less expensive gravel base.
Pros and Cons of a Concrete Slab Shed Foundation
Concrete slab foundations are permanent, frost-proof foundations. Frost-proof means that you have to dig down below the frost-line for construction, which means it won’t break or shift from seasonal weather shifts. Once they’re in place, you can’t move them without a jackhammer.
Concrete Slab Foundation Pros:
- Supports greater weight without shifting or cracking, so can support large sheds, anything larger than 160 square feet. You could even build a two-story shed on top of one of these.
- A permanent foundation that will last for decades when properly installed. It won’t shift or crack as the seasons change.
- Suitable for sheds with or without a floor.
- May be required by local ordinances for permanent structures.
Concrete Slab Foundation Cons:
- More expensive than other types of foundations.
- Concrete slabs are more prone to cracking from seasonal changes in temperature when not installed properly. If water gets into a crack and freezes, it can create potholes. You need to dig below the frost line to pour the concrete to reduce this risk. A better option (although more expensive) is a combination of concrete piers and a lumber frame.
- If the ground shifts underneath, the concrete will crack.
- The ground needs to be even, and may need a retaining wall.
- More difficult to build. Experienced DIYers could tackle this project themselves, but otherwise, it’s best to hire contractors.
- May need a drainage ditch to prevent flooding.
- Any water that gets inside the shed will stay there until it dries, unless you installed a drain.
- You’ll need to get a local permit before construction starts. A contractor may handle this for you.
How much does a Concrete Slab Foundation Cost?
A 300 sq. ft. concrete slab foundation costs between $2500 and $4500. The cost depends on how big of an area needs to be paved.
Pros and Cons of a Gravel Shed Foundations
Gravel foundations are a type of on-grade foundation, which basically means it sits on the ground and when you remove the shed, you can easily remove the base.
Since ideally, you’ll have 6-inches of gravel (4-inches minimum), you’ll need to install a frame with pressure-treated wood. A cloth barrier like landscaping fabric will make the foundation more stable, since it’ll keep the gravel from mixing with the dirt below, as well as keep weeds from growing inside your shed.
Gravel Foundation Pros:
- Less expensive than other types of foundations, costing around $300.
- Suitable for small to medium-sized sheds, anything 160 square feet or smaller.
- Quick and easy to install. Leveling the timber frame and squaring the corners is the most difficult part, so most DIYers can tackle this project themselves.
- A great choice for temporary sheds. Once you take down the shed, you can just shovel up the gravel and use it for another yard project.
Gravel Foundation Cons:
- Can’t support the weight of sheds over 160 square feet.
- The ground needs to be even, so if you have inclines or bumps, you’ll have to grade the spot.
- If the soil is often wet, the foundation will sink over time. You may need to add a drainage ditch.
- Easier for moisture to seep into the shed through the gravel.
- Outdoor cats might use the gravel as a litter box.
- If you’re building a permanent shed, local zoning ordinances may require you to use a concrete slab or other permanent bases.
- Erodes over time as the gravel shifts or washes away.
How much does a Gravel Shed Foundation Cost?
A gravel shed foundation will cost between $200 and $400. The price depends on the cost of gravel, if you hire someone to build it for you and the size of the base you need. You can save money by finding garden cloth on sale.
Shed Foundation FAQs
What type of gravel is used for a shed base?
The best choice of gravel for a shed base is ¾-inch drainage stone. The right size of gravel allows for enough compaction to make a firm base, while also allowing water to soak through to avoid both runoff and puddling.
Can I build a shed foundation on deck blocks?
Yes, you can also build a shed foundation on deck blocks. Deck blocks are best for places where mixing concrete is difficult or for freestanding structures.
Do not use deck blocks for:
- Permanent structures that have frost protection requirements.
- High-wind or high-uplift situations.
- If someone is going to be living in the shed.
How to anchor a shed to a gravel foundation?
You can anchor a shed to a gravel foundation by using auger anchors. Auger anchors can hold up against 1500lbs of force and are easy to install.
To install auger anchors, you simply:
- Insert cables under the roof,
- Feed the cable over the roof beams,
- Attach the cable to the clamps, and
- Twist the augers into the ground.
Should a shed base be bigger than the shed?
If you’re using a concrete shed base, the concrete slab should be the same size as the shed. If you’re using a gravel base, then the gravel base should be 12” wider on all sides.
A 12” lip on a gravel base:
- Protects wood siding from puddling or splashing water, extending its life.
- Keeps your shed cleaner as soil can’t splash onto it.
- Keeps grass and weeds away from the shed walls, so you’re not denting the walls with a weed whacker or mower.
- Allows the shed to dry faster, since there’s no grass or weeds holding the moisture.
- Reduces water runoff, as water can drain through the gravel and into the ground.
What’s the Verdict?
A concrete slab shed foundation is best for large-sized or permanent sheds, although you may also want to check out concrete pier and timber frames and soil-concrete.
But if you have a small-sized shed and/or just need something temporary for storage or while waiting to put up a permanent shed, then go with a gravel base.
Jamie is the founder of The Backyard Pros. When he was 15 years old he started working at a garden centre helping people buy plants, gardening products, and lawn care products. He has real estate experience and he is a home owner. Jamie loves backyard projects, refinishing furniture, and enjoys sharing his knowledge online.