How to Build a Garden Shed Foundation: Gravel vs Concrete

A garden shed is only as good as what it sits on. I learned this the hard way with my first shed — a perfectly nice 8x10 kit that I set directly on bare ground because the instructions said I could. Within two years the floor joists had wicked moisture from the soil, the door frame racked out of square as one corner sank into soft ground, and the whole structure listed visibly to the south. Fixing the foundation after the fact cost more in time and frustration than building a proper one from scratch would have.

The foundation is the least glamorous part of a shed build and the most important. It keeps the structure level, dry, and stable for decades. Our DIY project guides cover everything from raised beds to trellises, and this guide tackles the critical first step for any outbuilding: getting the base right.

Three Foundation Types Compared

Every shed foundation serves the same basic functions: distribute the shed's weight across the ground, keep the floor above standing water, prevent settling and shifting over time, and provide a level plane for the structure. How they accomplish this differs significantly in cost, effort, and permanence.

When a Gravel Pad Makes Sense

A gravel pad is the right foundation for most residential garden sheds up to about 200 square feet. It is forgiving of imperfect ground, drains beautifully, and requires no specialized skills or equipment. If your soil is reasonably stable (not pure clay that turns to soup in rain, and not fill dirt that has not fully settled), a gravel pad handles the load of a standard wood-frame or metal shed without any issues.

Gravel pads work especially well in areas with freeze-thaw cycles because the gravel does not heave. Water drains through the gravel instead of pooling underneath the shed, which means ice does not form in a solid sheet that could lift and shift the structure. This is why gravel pads are the default foundation for sheds in the northern half of the country.

When Concrete Is Worth the Cost

A poured concrete slab makes sense for large sheds (over 200 square feet), structures that will hold extremely heavy contents (a workshop with a table saw, a riding mower storage bay), or situations where you want the shed floor and the foundation to be one and the same. A concrete slab also makes sense if you are building on a slope — the forms can accommodate grade changes that would require an impractical depth of gravel.

The downside is cost and permanence. A concrete slab is a permanent modification to your property. It requires forms, rebar or wire mesh reinforcement, a proper sub-base, and either a concrete truck delivery or a lot of bag mixing. For most garden sheds, this is overkill. Save concrete for garages, workshops, and structures you know you will never want to move.

When Pavers Work Best

A paver foundation — typically concrete pavers or solid concrete blocks laid on a compacted gravel base — splits the difference between gravel and concrete. You get a solid, level surface without the permanence or cost of a poured slab. Pavers work well for sheds with built-in floors because the floor frame sits on the pavers and the pavers prevent any direct ground contact.

Pavers are also the best choice when drainage is poor and you need to create a completely flat, elevated platform. The paver surface sheds water to the edges where the gravel base handles drainage below. The tradeoff is more material and more labour than a simple gravel pad — you need to level every single paver, which is tedious work even on a small pad.

Step-by-Step: Building a Gravel Pad Foundation

This is the foundation I build for every shed project and the one I recommend for most homeowners. The process is straightforward, the materials are inexpensive, and the result is a rock-solid base that lasts for decades. Here is the full build for an 8x10 shed.

Materials Needed

• Six 4x6x8-foot pressure-treated timbers (for the perimeter frame)
• 12-inch timber screws or 10-inch structural screws (8 per corner, plus every 24 inches along the sides)
• Landscape fabric (woven, commercial grade — not the thin stuff)
• 3/4-inch crushed stone, approximately 2 to 3 cubic yards for a 10x12 pad (make the pad 1 foot wider and longer than the shed on all sides)
• Stakes and string for layout
• A plate compactor (rent from any equipment rental shop for $80 to $100 per day)
• A long straight 2x4 and a 4-foot level

Step 1: Mark and Excavate

Mark a rectangle 2 feet wider and 2 feet longer than your shed (10x12 for an 8x10 shed). This extra border prevents weeds from growing against the shed walls and gives you a gravel apron that sheds water away from the base. Remove all sod and topsoil within the marked area to a depth of 4 to 6 inches. If you hit clay, go deeper — 8 inches is not overkill in heavy clay. The goal is to remove any organic material that could decompose and settle, and to get below the topsoil into stable subsoil.

Step 2: Compact the Subgrade

Run the plate compactor over the exposed subsoil in overlapping passes. This is the step most DIYers skip, and it is the step that determines whether your shed stays level. Loose subsoil settles unevenly under weight, creating dips and tilts. A compacted subgrade settles as a unit, keeping the pad flat. If the soil is very dry, dampen it lightly before compacting — moisture helps soil particles lock together.

Step 3: Build the Perimeter Frame

Lay the 4x6 timbers on edge around the perimeter of the excavated area, creating a rectangular frame. Check for square by measuring diagonals — when both diagonals are equal, the frame is square. Secure the corners with timber screws driven through the end of one timber into the face of the adjoining timber, two per joint. Level the frame in both directions. If the ground slopes, stack a second timber on the low side to bring it level. Stake the outside of the frame with rebar driven 18 inches into the ground to prevent the timbers from shifting outward under the weight of the gravel.

Step 4: Lay Landscape Fabric

Roll commercial-grade woven landscape fabric across the entire interior of the frame, running it up the inside faces of the timbers. Overlap seams by 12 inches. The fabric prevents gravel from migrating down into the subsoil and keeps weeds from growing up through the pad. Use landscape staples every 24 inches along the seams to hold the fabric in place while you fill.

Step 5: Fill and Compact Gravel

Fill the frame with 3/4-inch crushed stone (also called "crusher run" or "process gravel" — the angular, self-compacting kind, not round pea gravel). Add gravel in 3-inch lifts, compacting each lift with the plate compactor before adding the next. This sounds tedious, but it is the difference between a pad that stays level and one that develops ruts and dips. After the final lift, screed the surface flat using a straight 2x4 dragged across the top of the perimeter timbers like rails. Check level in multiple directions. Add or remove gravel and re-compact until the surface is flat and level to within 1/4 inch over the full span.

Step 6: Set the Shed

Position the shed on the gravel pad. If your shed has a built-in floor frame (floor joists and plywood or OSB), it sits directly on the gravel. If you are building a floor separately, lay pressure-treated 4x4 or 4x6 skids on the gravel running parallel to the short dimension of the shed, spaced 4 feet on centre, and build the floor frame on top of the skids. The gravel drains so freely that the skids will stay dry even in heavy rain, but pressure-treated lumber adds a belt-and-suspenders layer of rot protection.

Drainage and Levelling Tips

• Grade the surrounding ground away from the pad. The area around your gravel pad should slope away at 1 inch per foot for the first 4 to 6 feet. This directs rainwater away from the shed rather than pooling against the foundation.
• Never skip the compaction. Renting a plate compactor costs $80 to $100 for a full day. It is the single most important step in the entire build. A hand tamper works for very small pads (4x6 or smaller) but is not adequate for anything larger.
• Use angular crushed stone, not pea gravel. Angular stone interlocks under compaction and stays put. Round pea gravel shifts and displaces under load like ball bearings — it looks nice in a garden path but makes a terrible shed foundation.
• Check level after loading the shed. The weight of the shed will cause very slight settlement in the first few weeks. Recheck level after a month and shim if needed. A well-compacted pad typically settles less than 1/8 inch.

If you are also building raised beds near your shed, our guide on how to build a raised bed covers the same principles of level foundations and rot-resistant materials that apply to any outdoor structure.

Frequently Asked Questions

Do I need a building permit for a shed foundation?

In most jurisdictions, sheds under 120 or 200 square feet do not require a building permit — but the rules vary widely by municipality. Some areas require a permit for any permanent structure regardless of size. Check with your local building department before you start. The foundation type does not usually affect permit requirements; it is the shed itself that triggers (or does not trigger) the permit.

Can I put a gravel pad on a slope?

Yes, but you need to terrace the site first. Excavate into the high side and build up the low side with additional perimeter timbers stacked to create a level frame. For slopes greater than 12 inches of drop across the pad, a concrete slab with stepped forms or a pier-and-beam foundation is more practical than gravel.

How long does a gravel pad take to build?

One person can build a gravel pad for a standard garden shed in a single day, assuming the materials are already on site. The longest part is the compaction — each lift takes 10 to 15 minutes to compact properly. Budget a full weekend if you are also handling excavation with hand tools rather than a small skid steer. Having the gravel delivered and dumped as close to the pad site as possible saves enormous time and back strain.

Will weeds grow through a gravel pad?

Not if you use commercial-grade woven landscape fabric under the gravel. The cheap, thin fabric sold in home centres degrades within 2 to 3 years and weeds punch through. Commercial woven fabric (3 to 4 ounce weight) lasts 15 to 20 years and blocks root penetration completely. It costs about $0.10 to $0.15 per square foot — a trivial expense for a huge difference in longevity.