Ground Screws, Gravel Pads and Timber Rafts: Five Garden Builds That Skip the Concrete

Pouring concrete has become the reflex answer to almost any garden question. Shed base? Concrete. Bench platform? Concrete. Small pergola? Concrete, and probably too much of it. It's heavy, it's permanent, it destroys the soil underneath, and it usually arrives in a wheelbarrow on the wettest Saturday of the month.

The fear driving all that concrete is real enough: frost heave, settlement, and the fact that a British garden can sit on shrink-swell clay that moves like a slow tide. But a slab isn't the only way to deal with any of that. There are five methods worth knowing, each suited to different structures, soils and budgets. None of them is right for everything. All of them are lighter on the ground than a slab, and all of them need you to do the checks before you start.

1. Helical ground screws

A ground screw is a galvanised steel shaft — typically 76mm to 100mm in diameter, 550mm to 1,600mm long — with a helix at the base. It's wound into the soil with a torque driver, either handheld for small jobs or on a mini-excavator for bigger ones, and it isn't finished until it reaches a specified torque reading. That reading is the point: it tells you the ground is actually holding the shaft, not just letting it slide in.

Where it works: almost anywhere with enough depth of soil and no buried services. It's excellent on clay, because the screw resists uplift and lateral movement without needing a mass of concrete. It's also removable, which matters if you might move the shed in five years or sell the house to someone with different plans.

Where it doesn't: shallow ground over rock, fill sites with rubble and unknown voids, and anything within a metre or so of a drain you can't verify. Screws can also be pulled up by wind on a tall, lightweight structure, so the fixing detail at the head — brackets and bracing — needs to be designed, not improvised.

Practical notes: a ground screw installer will usually do a site visit and size the screws to the load. DIY versions exist and are fine for a bench or a small planter, but a 3m shed with a heavy roof is not a DIY screw job unless you enjoy doing the same task twice.

2. The gravel-and-sleeper raft

Strip the turf, dig out 100–150mm, lay a woven geotextile, then fill with compacted MOT Type 1 in layers of no more than 75mm, wetted and whacked properly. On top of that goes a raft of pressure-treated sleepers or 100mm bearers, set level and squared diagonally, and the structure is built off that. The raft spreads load and lifts the timber clear of the soil, which is the single most important thing you can do for the lifespan of any garden building.

Where it works: lightweight sheds, bike stores, log stores, bench platforms and small summerhouses on reasonably free-draining ground.

Where it doesn't: heavy structures, steep slopes, and soft silt or peat, where the whole raft will simply settle unevenly. It also needs a genuinely flat, well-compacted base — the compactor hire is not optional.

Practical notes: use timber rated for ground contact (UC4), not ordinary UC3 decking board. Keep the bottom of the structure at least 150mm above ground level and leave an air gap underneath. Ventilation is what stops a shed rotting from the floor up, and a raft makes that easy; a slab makes it impossible.

3. Gravel pad with dry-laid slabs

A cheaper, more forgiving cousin of the raft. Excavate 100–150mm, geotextile, compacted Type 1, then a 20–40mm bed of sharp grit with paving slabs or concrete block pavers dry-laid on top, adjusted with a rubber mallet until each one rings solid and the whole array is level. Build a timber frame across the slabs, or set posts on individual pads.

Where it works: small sheds up to roughly 2.5m square, bin stores, and platforms under benches. It's also the easiest method to remove, since every component lifts out.

Where it doesn't: heavy loads and any building with a floor that needs to be perfectly rigid. Gravel beds can migrate if the edging isn't restrained, and weeds will find the gaps unless you keep on top of them.

Practical notes: set the pad with a fall of about 1:80 away from the house, not perfectly flat, so water leaves rather than pools under the frame. Edge it with timber or a row of setts.

4. Deck blocks and adjustable pedestals

Precast concrete deck blocks — the ones with a moulded cradle on top — are widely sold and widely misused. Used properly, as isolated piers sitting on a compacted sub-base, they'll carry a low deck or a small outbuilding frame perfectly well. Plastic and adjustable pedestals do the same job for decking, letting you fine-tune height to the millimetre and keep the timber well clear of wet ground.

Where it works: low-level decks, step-down platforms, and frames that can tolerate a series of point loads rather than a continuous bearing.

Where it doesn't: heavy roofs, anything on a slope without proper restraint, and sites where the blocks will sit on soft topsoil and rotate under load. Each block is a point load, so the sub-base under each one has to be genuinely good.

Practical notes: never lay them straight onto bare soil or grass. Dig out, compact, and set them on a 100mm pad of Type 1 at minimum. On any deck more than 300mm above ground, check the height and guardrail rules before you build.

5. Dry-laid brick piers on a hardcore bed

Traditional, cheap, and underrated. Excavate a shallow trench, fill with compacted hardcore, then build small piers of engineering bricks in lime mortar or — for a genuinely concrete-free build — bed them on a compacted grit base and rely on the structure above to tie them. Bearers span between piers, and the building sits on the bearers.

Where it works: sheds and outbuildings on clay where you want the load spread across several points, and where you want a bit of height under the floor.

Where it doesn't: it's slow, and a poorly built pier will crack and settle. It's also the least removable of the five.

What British weather does to all five

The enemies are the same in every case. Water, which rots timber that sits in it; frost, which lifts anything with moisture underneath; and movement, which is worst on shrink-swell clay — the stuff that cracks in summer and swells in winter across large parts of the south-east and Midlands.

All five methods deal with this by keeping the timber out of the ground, allowing drainage, and spreading load. What none of them can do is fix bad ground. On soft silt, made-up ground, or a site that visibly holds water in February, get advice before you build rather than after.

Before you dig

Check for buried services first — there's a free national service for plans, and it takes minutes. Check whether you need permission: most small outbuildings fall under permitted development, but height limits, distances from boundaries, and conservation areas all change the rules. Check where the tree roots are, since foundations near mature trees are their own specialist subject. And check the ground itself: dig a test hole a spade deep and see what comes out.

If it's dark, crumbly, and smells of soil, almost any of the five will work with care. If it's grey clay that smears, plan for movement. If it's rubble and old brick, plan for something else entirely — or a slab, honestly, and no shame in it.