How do you build a functional wooden shed for garden storage?
The Wood Guide · Do it yourself
Building guideBuilding a wooden garden shed
Tools, bikes and firewood kept dry and in their place. Seven steps, and one decision that sets how long it lasts.
- 3 × 3 m is the usual size
- The foundation decides everything
- Pressure-treated or Douglas fir
What makes or breaks it
A shed that rots away at the bottom after eight years was almost never built with the wrong wood. It was simply set on the wrong base.
Moisture comes from below. A timber wall that touches the ground, or stands on a base that holds water, soaks it up — and then no wood species will help. That's why the foundation isn't a preliminary chore but the most important decision of the whole project.
The rule of thumb: the timber starts at least ten centimetres above ground level, sits on a free-draining base, and the bottom rail is always pressure-treated to use class 4. Do that, and you can build the rest in ordinary garden timber.
A 3 × 3 metre shed holds garden tools, a lawnmower and a few bicycles. List what needs to go in before you decide on the size — extending later costs more than building half a metre bigger straight away. Also check how much floor area your local council allows without planning permission.
- Usual size
- 3 × 3 m for tools, mower and bicycles
- Foundation
- concrete slabs, pad footings or a concrete base
- Ground clearance
- timber at least 10 cm above ground level
- Frame
- pressure-treated spruce or Douglas fir
- Walls
- feather-edge, board-on-board or planed boards
- Roof pitch
- at least 5 degrees for drainage
To be honest: don't underestimate the time. For two people with basic tools, a 3 × 3 metre shed is a project of three to four full days, spread over several weekends — concrete has to cure and paint has to dry. If you want it done in one weekend, you'll cut corners on the foundation or the finish, and those are exactly the two places where it comes back to bite you.
Not the wrong wood — the wrong base
A shed that rots away at the bottom after eight years was almost never built with the wrong wood. Moisture comes from below: timber touching the ground soaks it up. So the timber starts at least 10 cm above ground level, on a free-draining base.
Click a chapter or use the arrows · 3 × 3 m shed to scale, details enlarged where marked.
Seven steps
- 1 · Planning and designDecide what the shed is for and list what needs to go in — that determines the size. Choose a level, well-drained spot with room all around for access and maintenance. Draw out the layout, including doors, windows, shelving or a workbench.
- 2 · FoundationConcrete slabs on a bed of sand-cement mix for small sheds, concrete pad footings or a poured slab for larger ones. Getting it level is crucial here: every millimetre out multiplies as you build upwards.
- 3 · Floor and bottom railA frame of pressure-treated joists on the foundation, with the bottom rail always in use class 4. On top of that, a floor of moisture-resistant plywood or OSB/3.
- 4 · FrameStud framing for all four walls, with studs at 60 centimetre centres. Assemble each wall flat on the floor and then stand it up — much easier than building it upright.
- 5 · RoofTrusses or a simple mono-pitch roof with a pitch of at least five degrees. Roof decking, covered with roofing felt, EPDM or shingles, with an overhang of at least ten centimetres so water drips clear of the walls.
- 6 · Cladding the wallsFeather-edge, board-on-board or planed boards on ventilated battens, so air can circulate behind the cladding. See feather-edge cladding for the profiles and which way to fit them.
- 7 · Doors, windows and finishingDoors with enough clearance for the wood to move, windows with a sill that sheds water. Treat all end grain before fitting.
Which wood for what
| Component | Recommended | Why |
|---|---|---|
| Bottom rail and joists on the foundation | Pressure-treated, use class 4 | Close to the ground; this is where every rot problem starts |
| Frame and battens | Pressure-treated spruce, class 3 | Affordable, strong, strength-graded |
| Wall cladding | Larch, Douglas fir or pressure-treated spruce | Class 3 is enough above ground; larch weathers to a handsome grey |
| Floor sheet | Moisture-resistant plywood or OSB/3 | Ordinary board swells with rising damp |
| Roof decking | OSB/3 or plywood | Carries the roof covering |
| Doors | Planed softwood or afzelia | Dimensional stability matters most here |
The bottom rail (ground contact), the end grain of the wall boards (moisture soaks in ten times faster there) and a roof edge without overhang (water runs down the wall). Solve those three and the rest follows naturally.
What you still need to do afterwards
Walk round it once a year
Especially the bottom thirty centimetres and the end grain. That's where you'll spot problems first.
Keep the gutter and overhang clear
Leaves holding water against the wall are the quietest cause of rot.
Keep plants away
Ivy and shrubs against the wall trap moisture and stop the wood from drying. Keep at least thirty centimetres clear.
Check the ventilation
Air must be able to pass at the bottom and top of the cladding. Blocked openings mean moisture that stays put.
Frequently asked questions about building a garden shed
Which wood should I use for a garden shed?
Pressure-treated spruce in use class 4 for everything close to the ground, class 3 for the frame, and larch or Douglas fir for the wall cladding.
Do I need planning permission?
That varies by local authority and depends on floor area, height and position on the plot. Check with your council before you start — getting approval afterwards costs more than asking beforehand.
What foundation do I need?
Concrete slabs on sand-cement mix for small sheds, concrete pad footings or a poured slab for larger ones. The key requirements: level, free-draining, and the timber at least ten centimetres above ground level.
How long does it take to build?
For a 3 × 3 metre shed with two people and basic tools: three to four full days, spread over weekends because concrete has to cure and paint has to dry.
Get started
Start with the foundation and the rest will follow.
Have a question about your project? Just ask — we're happy to help.
Photos via Wikimedia Commons: Treated floor bearers on a gravel bed with a base grid — Guywall, CC BY-SA 4.0 · Hautes-Pyrénées, Frankrijk — Florent Pécassou, CC BY-SA 3.0
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