Technical Installation · 7 min read
How to Prepare a Shed Base: Options, Steps & Mistakes
Concrete, paving slabs, plastic grids or a timber frame — how to choose and build a level, free-draining base for your garden building.
Groundwork
A good shed starts with a level base
The base decides whether your doors close, whether the floor stays dry and how long the building lasts. Here's how to get it right.
Your building needs a base that is firm, level and lets water drain away. It must be at least the building's external size — shown on every product page — not just the nominal size. Many people make it 50–100mm bigger all round, so rain drips clear of the walls rather than onto the base.
Your four main options
Concrete slab
The most solid and long-lasting. 75–100mm of concrete on compacted hardcore. Best for large buildings and workshops, but the most work.
Paving slabs
Slabs laid on a sand and cement mix over compacted hardcore. Good for most sheds and easier to do yourself.
Plastic grid
Interlocking grids filled with gravel. Quick, free-draining and good on slightly uneven ground.
Timber base frame
A pressure-treated timber frame on level ground or pads. Fast to fit — our pressure-treated timber base is available as an upgrade on every building.
Step by step: a paving-slab base
1. Mark out
Mark an area slightly bigger than the building's external size with pegs and string. Check the diagonals match so it's square.
2. Dig and level
Remove turf and topsoil to around 100–150mm deep. Level the bottom and compact it.
3. Sub-base
Add around 75mm of hardcore or MOT Type 1 and compact it well with a plate compactor or a heavy tamper.
4. Lay the slabs
Bed the slabs on a sand and cement mix, tapping each one down and checking it with a spirit level in both directions. Keep the joints tight and even.
5. Let it set
Leave the mortar to cure for at least a couple of days before putting the building on it.
Before delivery day
- ✓The base is level in both directions
- ✓It is at least the building's external size
- ✓Water drains away from it, not onto it
- ✓There is a clear path at least 600mm wide around it for assembly
- ✓You have checked whether you need planning permission
Base questions
Can I put a shed straight onto grass or soil?
No. Damp ground rots floors and lets the building move. Even a simple timber frame or plastic grid makes a big difference.
How level does it need to be?
As level as you can get it — use a long spirit level. A slope of more than a few millimetres across the base will make the doors stick.
Does the base need to be bigger than the shed?
It must be at least the external size. A little larger is fine, but not so large that rain collects on it around the walls.
Ready to build?
Once the base is down, assembly takes two people half a day to a day.
Read the assembly guideReady to put it into practice? Every building is in stock, flat-packed and delivered free to the UK mainland the next working day.
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