What is a pier (foundation pier)?
A pier 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. Piers are the most common foundation for garden sheds, shelters, decks and light sheds.
How does a pier 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 distributes the point load across its full 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 piers
Prefabricated concrete pier
Ready-made concrete blocks you buy at the building supplies store. Available with and without a hole or sleeve for the post.
| Type | Size (indicative) | Application |
|---|---|---|
| Small pier | 30x30x30 cm | Decks, light pergolas |
| Medium pier | 40x40x40 cm | Garden sheds, shelters |
| Large pier | 50x50x50 cm | Sheds, carports |
Cast-in-place pier
For heavier structures or when you need to go deeper, you can cast piers yourself:
- Dig a hole below the frost line (60-80 cm)
- Compact the base
- Build formwork
- Add reinforcement if needed
- Pour concrete (minimum C20/25)
Screw pier (ground screw)
A steel screw that is driven into the ground. Quick installation, no excavation required. Suitable for light to medium structures.
Placing a pier — step by step
- Set out — Mark the exact positions with stakes and string. Check the diagonal measurement (diagonals must be equal).
- Dig — Dig a hole per pier. Depth: minimum 30 cm for light structures, 60-80 cm in frost-prone situations.
- Compact — Tamp the base with a hand tamper.
- Gravel bed — Lay 5-10 cm of gravel as a drainage layer.
- Place pier — Set the pier level. Check with a spirit level or laser that all piers are at the same height.
- Mount post bracket — Attach an adjustable post bracket to the pier (keeps the timber clear of the concrete).
Common mistakes
- Piers not level relative to each other — The entire structure will be skewed. Use a line laser or long spirit level.
- Placed too shallow — Frost can push the pier upward. Minimum 30 cm deep, preferably 60 cm.
- Timber directly on concrete — Moisture wicks from the concrete into the timber. Always use a post bracket or lead strip as a separator.
- Diagonal measurement not checked — The structure will not be square.
Related terms
- Concrete pier
- Post bracket
- Shallow foundation
- Strip foundation
- Diagonal measurement
- Spirit level