Ground Screws vs Slab
Every SFS building needs a foundation. For garden buildings, outbuildings, and low-rise extensions, the choice usually comes down to two options: a concrete slab, or ground screws. Both work. Both have advantages. This guide compares them directly, so you can choose the right foundation for your project.
What are ground screws and concrete slabs?
Concrete slab
A concrete slab is a poured concrete foundation — typically 100–150mm thick, reinforced with mesh or rebar, laid on a compacted sub-base. It provides a solid, level, and permanent base for the building.
Concrete slabs are the traditional foundation for garden buildings, garages, and extensions. They're strong, stable, and durable. But they require excavation, formwork, and time to cure (typically 7–28 days before loading).
Ground screws
Ground screws are steel piles that are screwed into the ground — typically 76mm diameter, 1–2m long, with a helical flight at the base. They're installed using a handheld driver or a mini-digger attachment, and they support the building through a bracket system that connects to the SFS base track.
Ground screws are a relatively new foundation system (in widespread UK use for about 10 years). They're fast to install, require no excavation, and can be used in most ground conditions.
Installation compared
| Factor | Concrete Slab | Ground Screws |
|---|---|---|
| Excavation required | Yes — typically 150–300mm depth plus sub-base | No excavation |
| Time to install | 3–7 days (plus curing 7–28 days) | Half a day to a day |
| Weather dependent | Yes — rain and cold affect curing | Minimal |
| Skilled labour | Concreting experience needed | Specialist installer (but fast) |
| Ready for loading | 7–28 days after pour | Immediately |
| Site disruption | High — excavation, muck away, deliveries | Low — no muck away |
Ground screws win on installation speed and site disruption. A ground screw foundation can be installed and loaded in a single day, while a concrete slab takes weeks before the building can start.
Cost compared
| Factor | Concrete Slab | Ground Screws |
|---|---|---|
| Materials (concrete, mesh, sub-base) | £80–£150/m² | £40–£80/m² |
| Labour (excavation, formwork, pour) | £50–£100/m² | £20–£40/m² |
| Muck away | £20–£50/m² | £0 |
| Curing time (cost of delay) | Significant | None |
| Typical total | £150–£300/m² | £60–£120/m² |
Ground screws are typically 30–60% cheaper than concrete slabs for small to medium garden buildings, particularly when you account for the time saved and the muck-away cost avoided.
For very small buildings (under 10m²), the cost difference narrows. For larger buildings (20m²+), ground screws become significantly cheaper.
Environmental impact
| Factor | Concrete Slab | Ground Screws |
|---|---|---|
| CO₂ footprint | High (cement production, transport, muck away) | Low (steel manufacture, minimal transport) |
| Ground disturbance | High — permanent change to ground | Minimal — ground recovers if screws removed |
| Water runoff | Reduced (impermeable) | Natural (permeable ground maintained) |
| Material recyclability | Concrete not easily recyclable | Steel fully recyclable |
| Tree root impact | Significant excavation damages roots | Minimal — screws can be positioned around roots |
Ground screws are significantly more environmentally friendly than concrete slabs. Concrete production accounts for around 8% of global CO₂ emissions, and a garden building slab contributes to that. Ground screws use far less material and can be removed cleanly.
For sites with trees, ground screws are often the only viable option — a concrete slab would require significant root damage that could kill the tree or destabilise it.
Performance and longevity
| Factor | Concrete Slab | Ground Screws |
|---|---|---|
| Load capacity | Very high — suitable for any garden building | High — suitable for most garden buildings |
| Longevity | 50+ years | 50+ years (galvanised steel) |
| Movement resistance | Excellent | Good, but more sensitive to ground conditions |
| Level tolerance | Excellent (achieved during pour) | Good (±5mm achievable) |
| Water management | Requires drainage consideration | Naturally drains |
| Frost heave | Resistant | Resistant if installed to frost depth |
Both foundations perform well for garden buildings. A concrete slab is more rigid and offers the most straightforward load capacity. Ground screws perform excellently when installed correctly and can match the load capacity of a concrete slab for most garden buildings.
The main caveat for ground screws: they must be installed to the correct depth (below the frost line) to avoid frost heave. In the UK, frost depth is typically 450–600mm, and most ground screws are installed to 1–2m depth, which is well below frost.
Ground conditions and suitability
| Ground Type | Concrete Slab | Ground Screws |
|---|---|---|
| Firm, level ground | ✓ Suitable | ✓ Suitable |
| Sloping ground | Requires retaining/stepped slab | ✓ Easily adjusted — screws can be different lengths |
| Rocky ground | Hard to excavate, may require breaking | Difficult — screws can't penetrate rock |
| Soft/clay soils | Requires deeper sub-base | Requires longer screws |
| Sandy soils | Suitable but requires compaction | Usually suitable |
| Waterlogged ground | Requires drainage work | ✓ Suitable |
| Contaminated soil | Requires disposal of spoil | ✓ Suitable (no spoil) |
| Tree roots | Damaging | ✓ Suitable if positioned around roots |
| Wetlands / flood zones | Problematic | ✓ Suitable if raised above flood level |
Ground screws are more adaptable to difficult ground conditions — slopes, trees, waterlogged areas, contaminated soil, and wetlands. Concrete is more straightforward on flat, firm, dry ground.
The main ground condition where concrete wins: solid rock. Ground screws can't penetrate rock, so concrete is often the only option.
Removal and relocatability
| Factor | Concrete Slab | Ground Screws |
|---|---|---|
| Removal difficulty | Hard — requires breaking up | Easy — screws can be unscrewed |
| Ground restoration | Slow — leaves broken concrete and rubble | Fast — ground recovers quickly |
| Reusability | Not reusable | ✓ Screws reusable |
| Moving building | Not moveable | ✓ Can be relocated with screws |
Ground screws win decisively on removability and relocatability. If you might ever move or remove the building, ground screws are the obvious choice — you can unscrew them, relocate the building, and the ground is virtually untouched. A concrete slab requires breaking up (hard, slow, costly) and leaves the ground permanently altered.
For rental properties, temporary installations, or any building where you want to preserve the future use of the site, ground screws are the clear winner.
Decision guide
Choose concrete slab when:
- You need maximum load capacity (e.g. for a heavy workshop or one with heavy equipment)
- The ground is solid rock
- Budget is not the priority and long-term permanence is
- The building will never be moved
- You want the most straightforward load path (some clients prefer concrete for structural simplicity)
Choose ground screws when:
- You want a fast installation (days instead of weeks)
- Cost is a consideration (30–60% cheaper)
- Environmental impact matters (much lower carbon footprint)
- The ground is sloping, rocky, waterlogged, or has trees
- You might relocate the building in future
- The site has limited access (no room for concrete lorries or excavation)
- You want to preserve the ground for future use
Summary
Ground screws and concrete slabs are both valid foundations for SFS garden buildings. Ground screws are faster, cheaper, more adaptable to difficult ground, more environmentally friendly, and relocatable. Concrete is stronger, more rigid, and more traditional — better suited to large buildings, rock ground, or situations where permanence is the priority.
For most garden buildings, ground screws are the better choice in 2026. For specific applications, concrete may be preferred. Always get quotes for both before committing, and check the ground conditions for suitability.
Key Takeaways
- Ground screws — faster (1 day vs 3–7 days + curing), cheaper (30–60% less), less ground disturbance
- Concrete slab — stronger, more rigid, traditional, better for rock ground
- Ground screws win on environmental impact, removability, and adaptability to difficult ground
- Concrete wins on load capacity and long-term rigidity
- Ground screw viability depends on ground conditions — check before committing
- Both last 50+ years when installed correctly
- Get quotes for both — costs vary by location and installer
- For garden buildings up to ~30m², ground screws are usually the better choice
Designing a garden building?
Our Building Kits configurator lets you choose foundation type, roof style, openings, and cladding — and gives you a full materials list and build guide.