A strip foundation is a continuous strip of concrete beneath the load-bearing walls of a building. It is the most common form of shallow foundation: an uninterrupted concrete beam that distributes the weight of the walls evenly across the ground.
How does a strip foundation work?
The strip foundation follows the exact line of the load-bearing walls. Wherever there is a wall, there is a concrete strip beneath it. The weight of the wall is distributed over a larger ground area via the strip, preventing the structure from settling.
The strip is always wider than the wall above — typically 20-30 cm wider on each side. This increases the bearing area.
When do you use a strip foundation?
| Suitable for | Not suitable for |
|---|---|
| Garages with masonry walls | Soft peat soil |
| Sheds with single- or half-brick walls | Ground with variable bearing capacity |
| Garden buildings on firm subsoil | Very heavy structures (multiple storeys) |
| Garden walls and boundary walls | Areas with high water table |
Construction
A standard strip foundation for a garage or shed:
| Layer | Description |
|---|---|
| Subsoil | Load-bearing, undisturbed ground |
| Sand bed | 5-10 cm of poured and compacted sand as a levelling layer |
| Concrete | Reinforced concrete strip, minimum 20 cm high |
| Plinth masonry | Damp-proof masonry from foundation to ground level |
| Wall | The actual wall of the building |
Dimensions (guidelines)
| Application | Width | Height | Depth (below ground level) |
|---|---|---|---|
| Garden wall | 30 cm | 15 cm | 60 cm |
| Shed (half-brick) | 35 cm | 20 cm | 60-80 cm |
| Garage (single-brick wall) | 45 cm | 20-25 cm | 60-80 cm |
| Dwelling | 50-60 cm | 25-30 cm | 80 cm (structural engineer calculation) |
Building a strip foundation yourself
1. Set out — Stretch lines between profile boards to mark the exact position
2. Excavate — Dig the trench to the correct depth and width. Keep the sides as clean as possible
3. Compact the base — Firmly compact the bottom of the trench
4. Apply sand bed — 5-10 cm of sand, levelled
5. Place reinforcement — Minimum 2 bars diameter 10 mm at the bottom, on spacers (cover 3 cm)
6. Formwork — Only needed if the soil is crumbly. In firm clay, the trench itself can serve as formwork
7. Pour concrete — C20/25 concrete, poured in one go (not layer by layer)
8. Curing — Minimum 7 days, cover in hot weather to prevent drying too
quickly
Strip foundation vs. pier foundation
| Strip foundation | Pier foundation | |
|---|---|---|
| Shape | Continuous strip | Separate concrete blocks |
| Suitable for | Masonry walls | Timber post structures |
| Material use | More concrete | Less concrete |
| Load distribution | Even under entire wall | Point load per pier |
| DIY | More work, but feasible | Simpler |
Related terms
- Shallow foundation
- Piled foundation
- Reinforcement
- Concrete slab (floor slab)
- Damp-proof course
- Frost line