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Garden room foundations: which base is best?
The base is the part of a garden room you'll never see again, and the part that's hardest to fix if it's wrong. Here's how the main options compare.
The short answer: ground screws are quicker, cheaper and cause far less disruption, at around £30 to £50 per m². A concrete slab costs around £80 to £120 per m² and suits heavier buildings and some difficult ground.1
The options compared
| Base | Typical cost | Good for | Watch out for |
|---|---|---|---|
| Ground screws | £30 to £50 per m² | Most timber rooms; sloping gardens; tree roots; poor access | Very stony ground; ask for a load test |
| Concrete slab | £80 to £120 per m² | Heavy or brick-built rooms; level sites | Digging, mess, curing time, and access for a mixer or barrows |
| Timber frame on pads | Varies | Small, light rooms and kits | Needs good ventilation and treated timber |
Costs: MyBuilder price guide, October 2026.1
Ground screws
Ground screws are large steel screws twisted into the ground, with a timber or steel frame on top. They can go in within a day, with very little digging, and they cope well with slopes because each screw is set to its own depth. They're now the most common base for timber garden rooms.
Concrete slab
A concrete slab is the traditional choice. It's very stable and suits brick-built and heavier rooms. The downsides are cost, disruption, more spoil to remove, and the time it takes to set before building can start. Sloping, clay or difficult ground can push the price up.1
Questions to ask
- Is the base included in the price, and who's responsible if it moves?
- How do you deal with a slope, clay soil or tree roots?
- How is the floor insulated, and is there airflow under the room?
- How will materials get into the garden?
Questions people ask
Are ground screws good for garden rooms?
For most timber garden rooms, yes. They're quick, cheaper than concrete and handle slopes well. Ask the installer how they test the ground first.
Do I need a concrete base for a garden room?
Not usually for a timber room. Concrete is mainly needed for heavier, brick-built rooms or particular ground conditions.
Related guides
Sources
- MyBuilder, Garden room cost price guide, updated 21 October 2026. UK price ranges for garden rooms, foundations, electrics, plumbing and fees.