What should my shed stand on?
A level, free-draining base that matches the building's footprint. Get that right and almost nothing else can go seriously wrong. Get it wrong and no amount of timber quality or treatment will save you.
Nearly every premature rot claim we see traces back to the base.
What the base has to be
Level. Not nearly level. A twisted base gives you doors that won't shut, windows that crack, and joints that slowly pull apart.
The right size. The same footprint as the building, or very slightly smaller โ never larger. A base that sticks out past the walls collects rainwater and holds it against the timber.
Free-draining. Water must run away from the building, not pool underneath it.
Off the wet. Timber in permanent contact with soil or standing water will rot regardless of how it's treated or what guarantee it carries.
The usual options
| Base | Good for | Notes |
|---|---|---|
| Paving slabs on compacted hardcore | Sheds and summerhouses | The common choice. Needs proper preparation underneath or it settles unevenly. |
| Timber bearer frame | Lighter buildings | Quick, but must sit on something solid and stay clear of wet ground. |
| Plastic grid system | Sheds, bike stores | Fast, permeable, good on reasonably level ground. |
| Poured concrete slab | Log cabins, garden rooms, anything heavy | The gold standard. Worth it for anything you'll spend real time in. |
Leave room around it
Allow at least 300mm (1ft) clear on every side you'll need to treat or maintain. Two feet is better. You'll be glad of it the first time you have to paint the back.
Some manufacturers set their own minimum โ commonly 600mm (2ft) clearance โ before they'll send an installation team at all.
Hot tubs are a different matter
A filled hot tub with people in it can exceed 1,500kg. That needs a properly specified reinforced concrete base. Do not put one on slabs or decking without checking the load rating first.
Not sure what you've got? Send us a photo of the spot and your postcode and we'll tell you honestly whether it's ready.