Gravel vs Concrete Shed Base

Most people assume a concrete slab is the serious option and gravel is the budget compromise. For a timber shed it is very often the other way round. A compacted gravel pad drains, breathes, costs a fraction as much, tolerates ground movement and can be built in a weekend with hand tools. A slab is flat, permanent, rodent-proof and strong — and it will hold water against the bottom of a wooden shed for the rest of its life if you set the shed straight onto it.

The real decision comes down to what the shed is made of and what is going inside it. Wood floor on skids, garden tools, a mower: gravel. Concrete-block or steel building, or a floor that has to take a vehicle, a lathe or a heavy workbench anchored down: slab. Everything else is detail.

Drainage Is the Whole Argument

A gravel pad built from compacted crusher run is not a sponge, but it is porous enough that rain hitting the ground beside the shed keeps moving down and away instead of pooling. Set a timber shed on skids or blocks over that pad and there is an air gap under the floor with dry stone below it. The underside of the joists stays ventilated, and ventilated wood does not rot.

A concrete slab is the opposite: an impermeable plate that water runs across and then sits on at the edges. Bolt a wooden sill plate flat to that slab without a capillary break and you have created a permanent damp reservoir at exactly the point where the building is most vulnerable. Slabs for timber buildings need a vapour barrier underneath, pressure-treated sill plates, sill sealer and a slab surface raised above the surrounding grade — all of which are doable, and all of which are steps a gravel pad simply does not require.

	Gravel pad	Concrete slab
Cost, 10 x 12 ft	$150–300	$700–1,400
Material	4–6 in crusher run	4 in concrete over 4 in base
Drainage under floor	Free-draining	None — sheds water sideways
Wood rot risk	Low, with an air gap	Moderate without detailing
Frost movement	Moves and resettles	Cracks or heaves as one piece
DIY difficulty	Weekend, hand tools	Forms, rebar, timed pour
Reversible?	Yes — rake it away	No — demolition job
Permit often needed?	Rarely	Frequently

Frost, Settling and Cracking

In freezing climates the ground under a shed lifts and drops every winter. A slab is a single rigid plate, so when the soil beneath it moves unevenly the slab either cracks across the middle or tilts and takes the whole building with it. Preventing that properly means digging footings below the frost line, which turns a cheap outbuilding into a foundation job.

A gravel pad has no rigidity to lose. Individual stones shift, the pad heaves slightly and settles back, and if a corner does drop over a few years you shim the skids or add a bucket of stone and re-level in an afternoon. That forgiveness is why gravel is the default for sheds in frost country, and it is the same reason a gravel driveway shrugs off a winter that destroys asphalt.

When Concrete Is Genuinely Required

• Masonry or steel buildings. A block or steel structure has no floor of its own and needs a rigid slab to sit on and anchor into.
• Vehicles. A garage, tractor bay or anything driven in and out needs a slab, or at minimum a much deeper compacted base.
• Fixed heavy machinery. A lathe, mill or large compressor that has to be bolted down and stay in plane.
• Workshops you will finish out. If the shed becomes an office or studio with insulation and drywall, a slab plus vapour barrier makes sense.
• Code or HOA rules. Some jurisdictions require a permanent foundation above a certain footprint, or for anything with power run to it.
• Serious rodent pressure. A slab is the only base that genuinely seals the underside.

Note what is not on that list: shed size on its own, or a heavy load of stored goods. A well-built 6-inch compacted crusher run pad carries far more than a garden shed will ever hold. If you do pour, remember the slab still sits on 4 inches of compacted dense-graded base — concrete over bare soil is how slabs crack — so you are buying stone either way.

Building a Gravel Pad That Lasts

1. Size the pad 12 in larger than the shed on every side. The overhang catches roof drip and keeps splash-back off the walls. A 10 x 12 shed wants a 12 x 14 pad.
2. Strip turf and topsoil. Excavate 6 to 8 in. Anything organic left underneath will decompose and drop a corner.
3. Compact the subgrade and lay woven geotextile. Fabric stops the stone sinking into the soil, which is what quietly loses you an inch a year.
4. Frame the perimeter. Pressure-treated 4×4 or 6×6 timbers, staked and levelled, contain the stone and give you a straight edge to work to.
5. Fill with crusher run in 2-inch lifts. Compact each lift with a plate compactor. Do not dump 6 inches and roll it once — you get a crust over loose fill.
6. Level the top dead flat. Screed with a straightedge and check both diagonals. Unlike a driveway, a shed pad gets no crown.

For volume: a 12 by 14 ft pad at 5 inches compacted is 168 sq ft ÷ 65 = 2.6 cubic yards, roughly 4 tons of crusher run at 1.55 tons per yard, plus a compaction allowance of about 25 percent on top. Run your own dimensions through the shed base calculator or the crusher run calculator, and follow the full levelling method in how to level a shed base.

Bottom Line

Gravel is the right base for a timber shed roughly nine times out of ten: five times cheaper, self-draining, frost-tolerant, repairable and reversible. Build it 4 to 6 inches deep in compacted crusher run, extend it a foot past every wall, contain it in treated timber, and keep the shed floor up off it on skids or blocks. Save the concrete for masonry buildings, vehicles, bolted-down machinery and anything the building department insists on — and even then, budget for the compacted stone base underneath it, which you can price with the gravel calculator. If the site is wet to begin with, fix the drainage first with a French drain or trench drain; no base survives standing water.