Most homeowners never choose their foundation. The engineer specifies it, usually concrete, because that’s what’s always been used. It’s not a bad decision. It’s just not always the right one for the site.
Concrete is the incumbent for a reason. It’s familiar to engineers, straightforward for building surveyors to sign off, and it performs well across a wide range of ground conditions, including sites with shallow rock, where a bored pier remains the correct engineering choice. Screw piles aren’t a replacement for concrete everywhere. They’re a different tool, suited to a different set of conditions, and the job is to choose correctly, not to default to whichever one is more familiar.
What actually decides it
Four things determine which foundation is right for a given site, and none of them is “which one is newer” or “which one is cheaper on paper.”
Ground conditions
Screw piles can extend past weak surface soils and perform well in reactive clay, with installation torque providing a real-time read on capacity as each pile is driven. Where rock sits close to the surface, though, a bored pier is generally the more reliable option, and pre-drilling or a site-specific assessment may be needed before screw piles are viable at all.
Timeline
Concrete needs to cure before it can carry load. Screw piles can generally take load as soon as they’re installed and verified, which matters most when a build date is fixed or site access is limited.
Site access and disturbance
Screw pile installation requires no excavation or formwork, making it well-suited to tight urban blocks, sloping sites, or situations where the existing landscaping and services need to remain intact. Concrete’s larger footprint and spoil removal can be a bigger factor on constrained sites.
What happens at the end of the building’s life
Steel screw piles can be removed and recycled. Concrete generally can’t be recovered in the same way.
Where this shows up in practice
For a straightforward residential build on reasonable ground, either system can do the job well, and the decision often comes down to program and site access rather than engineering necessity. For restumping and underpinning existing homes, where excavation around an occupied building is a real constraint, screw piles tend to be the more practical choice. For sites with reactive clay or difficult access, the same applies. For sites with shallow rock, concrete usually wins.
The point isn’t picking sides
The right question isn’t “which foundation is better.” It’s “which foundation suits this site, this timeline, and this build.” A foundation contractor who only offers one answer isn’t giving impartial advice; they’re giving you whatever they happen to install.
