What the Building Code asks
Clause B2 of the Building Code says parts of a building that keep it standing, or that are hard to reach or replace, must last at least 50 years. Foundations are in that group, so the piles must do their job for at least 50 years in your ground.
Hot-dip galvanising
Our piles are hot-dip galvanised: the finished steel is dipped in molten zinc, which bonds to its surface. The zinc protects the steel in two ways. It keeps moisture off it, and where the coating is scratched, the zinc around the scratch corrodes first and protects the bare steel.
What happens underground
Steel in undisturbed soil usually corrodes slowly, because there's little oxygen once you're a short way down. Most of the attack tends to happen near the surface, where air and water come and go.
Sites that need more
Some ground is harder on steel, and the engineer allows for it:
- Coastal sites and sea spray
- Acidic ground, such as some peats
- Fill with rubbish or industrial waste in it
- Ground that's wet and dry in turn
How it is allowed for
For consented work, the engineer checks the soil and the exposure, then specifies the steel thickness and coating so the piles meet the 50-year requirement. That can mean a thicker shaft wall, which leaves extra steel to spare, or extra protection where the pile meets the surface.
If your site is near the sea or has unusual ground, tell us early.