By Craig Davison, Director, Lichfield Garden Buildings
Quick answer: Every shed or log cabin needs a base that is flat, level, solid and the right size. For most sheds a pressure-treated timber base or paving slabs on a compacted sub-base works well. Log cabins and garden rooms need something stronger and perfectly level, such as a concrete slab or a ground screw base.
In 14 years of selling garden buildings, I've seen more problems caused by poor bases than by anything else. Doors that stick, windows that won't open and floors that rot early can nearly always be traced back to the ground underneath. Get the base right and the building will last.
What a good base must do
- Be level. If the base is out, the frame twists. Doors and windows stop lining up.
- Be the right size. Most makers want the base the same size as the floor, or slightly smaller, so rainwater runs off and doesn't sit under the walls. Check the base size on the product page.
- Stay dry. Water sitting against timber causes rot. Airflow under the floor helps.
- Carry the weight. A log cabin full of furniture weighs far more than a garden shed.
Many makers make a proper base a condition of their guarantee, so check the guarantee terms for your building before you choose.
The main types of base compared
| Base type | Best for | Pros | Cons |
|---|---|---|---|
| Concrete slab | Log cabins, garden rooms, workshops, metal and concrete buildings | Strongest and longest lasting. Perfectly flat if laid well. | Most work and cost. Permanent. Needs time to cure. |
| Paving slabs | Sheds, summerhouses, smaller cabins | Good value. DIY friendly. Solid. | Must sit on a compacted sub-base or slabs can sink. |
| Plastic grid | Sheds and greenhouses on fairly level ground | Light, quick, drains well. | Needs well-prepared ground. Not ideal for heavy cabins. |
| Timber base or bearer frame | Sheds and summerhouses | Quick to fit. Lifts the floor for airflow. Easy to level on small slopes. | Timber needs to be pressure treated. Not for the biggest buildings. |
| Ground screw base (steel screws plus timber frame) | Sloping or awkward ground, cabins, garden rooms | No concrete or digging out. Adjustable. Can be removed. | Higher upfront cost than timber. |
Concrete bases
A concrete slab is the gold standard for log cabins, garden rooms and anything heavy. It should sit on a compacted hardcore layer and be laid dead level. Many builders add a damp-proof membrane underneath. A typical domestic slab is around 100mm thick (always follow your building's base specification). Ask your installer to follow the maker's base plan exactly, as log cabins in particular need a perfectly square, level surface.
Paving slabs
Slabs are a popular choice for sheds and summerhouses. The secret is the sub-base. Dig out the turf, lay and compact hardcore, then bed the slabs on sand and cement. Slabs laid straight onto soil will move over the first winter.
Plastic grid bases
Interlocking plastic grids are filled with gravel. They are light and drain well, which suits greenhouses and smaller sheds. You still need to remove the turf and level the ground first. For heavy log cabins, I'd choose concrete or a ground screw base instead.
Timber bases
A pressure-treated timber frame is the quickest option for most sheds. It lifts the floor off the ground for airflow and can be packed level on a gentle slope. We sell timber bases sized to match buildings from several of our ranges, including:
- Timber shed base from £52
- Timber base for Sheds DIY buildings from £60
- Shed base kit for Power Sheds buildings from £89
- Pressure-treated timber base with adjustable ground spikes from £89
- Tanalised airflow base from £95
- Timber base range for Sovereign buildings from £99
Prices were correct at the time of writing and depend on size. Choose the base made for your building's range where one exists. Want to know why "pressure treated" matters? Read pressure treated vs dip treated timber.
Ground screw bases
Ground screw bases use galvanised steel screws twisted into the ground, topped with a pressure-treated timber frame. There's no concrete and no digging out. The screws adjust, so they cope well with slopes and uneven ground. The frame keeps the building off the ground for airflow and drainage, and the whole thing can be removed later if your garden changes.
We sell the Gorilla Base system in two forms:
- Ground screw base DIY kit, from £482.30, for frames from 1.2m x 1.2m up to 4.8m x 6.0m.
- Ground screw base PRO, professionally installed, from £1,899.99.
Both work with any make of garden building.
Which base for which building?
- Small shed (up to about 8x6): timber base, slabs or plastic grid.
- Larger shed or summerhouse: slabs on a sub-base, a timber base, or ground screws.
- Log cabin or garden room: concrete slab or ground screw base.
- Metal shed: a solid, level surface such as concrete or slabs, so it can be fixed down.
- Concrete garage or store: usually a concrete base to the maker's plan.
- Greenhouse: a matching greenhouse base on slabs or a level, firm surface.
Still choosing a size? See what size shed do I need. Comparing materials? Read metal vs wooden vs concrete sheds. You'll find our base products in Accessories & Extras.
Base and the planning height limit
A base adds height. If your building is within 2m of a boundary in England, the total height usually needs to be no more than 2.5m. A tall timber or ground screw base on a slope can tip a building over the limit. Our planning permission guide explains the rules. Scotland, Wales and Northern Ireland have different rules.
FAQs
Can I put a shed straight on grass or soil?
No. The floor will sit in the damp, rot early and move out of level. Every shed needs a proper base, even a simple timber frame or slabs.
Should the base be bigger than the shed?
Usually no. Most makers want the base the same size as the floor or slightly smaller, so rain runs off rather than collecting under the walls. Check your building's base size before you build.
What is the best base for a log cabin?
A level concrete slab or a ground screw base. Log cabins are heavy and the logs settle over time, so the base must be perfectly flat and square.
Is a ground screw base as good as concrete?
For most garden buildings, yes. Ground screws give a strong, level base without concrete, cope with slopes, and lift the building off the ground for airflow.
Can I build a shed base on a slope?
Yes. On a gentle slope a timber base can be packed level. On steeper slopes, a ground screw base or a stepped concrete base works best.
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