A pile extension piece (in Dutch foundation jargon ‘hoerenjong’) is a concrete cap placed on the head of a timber driven pile, which keeps that pile head below ground level and out of sight. The concrete piece effectively extends the pile “invisibly” upwards.
Why below ground?
Timber piles last for centuries, but only as long as they stand permanently below the water table. If the timber head dries out, fungal pile rot begins. By keeping the timber head low and setting a concrete piece on top, the wood stays wet and protected while the foundation still reaches the required level.
Where is it found?
- In timber pile foundations under older buildings
- In foundation repair, where the connection between old timber piles and new concrete has to be made
- Related to the extension piece and the “sacrificial head”, other ways of forming the transition between pile and superstructure
Points of attention
- The water table must not fall; lowering it (for example by dewatering) can still cause pile rot
- When buying an old building, a foundation survey is advisable to assess the state of timber piles and heads
Related terms
- Driven pile
- Pile foundation
- Pile rot
- Sacrificial head
- Foundation repair
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