A pier foundation is a concrete block that serves as a foundation point for a timber or steel structure. Instead of a continuous strip of concrete (strip foundation), individual piers are placed at strategic points — usually under the corners and intersections of the structure. Pier foundations are the most commonly used foundation for garden buildings, covered structures, decks, and lightweight sheds.
How does a pier foundation work?
A pier distributes the weight of the structure over a larger ground area:
The post or column stands on the pier (or is anchored into it)
The pier spreads the point load over its full surface area
The ground carries the weight
The principle is the same as snowshoes: the larger the contact area, the less the structure sinks.
Types of pier foundations
Precast concrete pier
Ready-made concrete blocks available at building merchants. Available with and without a hole or socket for the post.
Type
Dimension (indicative)
Application
Small pier
30x30x30 cm
Decks, light pergolas
Medium pier
40x40x40 cm
Garden buildings, covered structures
Large pier
50x50x50 cm
Sheds, carports
Self-poured pier
For heavier structures or when you need to go deeper, you can pour piers yourself:
1. Dig a hole below the frost line (60-80 cm)
2. Compact the base
3. Build formwork
4. Add reinforcement if needed
5. Pour concrete (minimum C20/25)
Screw pier (ground screw)
A steel screw that is turned into the ground. Quick installation, no excavation needed. Suitable for light to medium-weight structures.
Placing pier foundations — step by The six-step sequence for setting piers correctly.
step
1. Set out — Mark the exact positions with stakes and string line. Check the cross measurement (diagonals must be equal).
2. Dig — Dig a hole per pier. Depth: minimum 30 cm for light structures, 60-80 cm where frost is a concern.
3. Compact — Compact the base with a hand tamper.
4. Gravel bed — Lay 5-10 cm of gravel as a drainage layer.
5. Place the pier — Set the pier level. Check with a spirit level or laser that all piers are at the same height.
6. Mount the post bracket — Fix an adjustable post bracket on the pier (keeps the timber away from the concrete).
Common mistakes
Piers not level with each other — The entire structure will then be skewed. Use a line laser or straight edge with spirit level.
Placed too shallow — In frost, the pier can be pushed upward. Minimum 30 cm deep, preferabl Key dimensions for digging and bedding a pier.
y 60 cm.
Timber directly on concrete — Moisture wicks from the concrete into the timber. Always use a post bracket or lead strip as a barrier.
Cross measurement not checked — The structure will then be out of square.
