Bored Piers vs Screw Piles: Which Foundation Method Suits Your Site?
When a site can’t simply support a slab on the ground, it needs to be founded on something deeper and more stable. Bored piers and screw piles are the two most common ways of doing that in and around Melbourne, and while they solve the same basic problem, the process, disturbance and cost involved are quite different.
What Are Bored Piers?
Bored piers are deep concrete footings formed by drilling (boring) a cylindrical hole into the ground, placing a reinforcement cage inside it, and filling the hole with concrete. The pier transfers the structure’s load down past the reactive or unstable surface soil layer to firmer material or bedrock further down, effectively bypassing the problem soil altogether.
They’re a long-established, highly reliable method for founding slabs, retaining walls and structures on sites where the near-surface soil simply isn’t capable of supporting the loads involved — whether that’s because of deep reactive clay, fill, or a sloping or unstable site.
What Are Screw Piles?
Screw piles are galvanised steel shafts with helical (screw-shaped) flights welded along their length, which are mechanically screwed into the ground using hydraulic equipment rather than drilled and poured. Once installed to the required depth and torque, a bracket or cap is fixed to the top of the pile to connect it to the structure above.
Because there’s no excavated spoil and no concrete curing time involved, screw piles are a faster, lower-disturbance alternative to bored piers for many lighter structures — though they’re not a direct substitute in every situation, which is where load capacity and site conditions come in.
When Each Method Is Used
Bored piers are typically specified where higher load capacity is required — under a full house slab on a difficult site, under retaining walls, or where an engineer needs to found the structure at a specific, often considerable, depth to reach suitable bearing material. They’re also generally the preferred method where the site has already been confirmed to require deep footings for structural reasons.
Screw piles are commonly used for decks, verandahs, carports, smaller extensions, boundary and lightweight retaining walls, and situations where minimising ground disturbance matters — for example, close to existing structures, services, or trees, or on a site with restricted access for larger drilling equipment.
Installation Process Compared
A bored pier installation involves positioning a drill rig, boring each hole to the specified depth and diameter, placing the reinforcement cage, and pouring concrete — followed by a curing period before the piers can be loaded. Spoil from the boring needs to be managed and removed from site.
A screw pile installation is mechanical rather than wet trade: the pile is screwed into the ground to a specified installation torque (which correlates to its load capacity), cut to height, and capped — often ready to be built on the same day, with minimal spoil and no curing wait. This is a large part of why screw piles are popular for time-sensitive or access-constrained projects.
Cost and Timeframe
As a general rule, screw piles are faster to install and involve less site disruption, which can make them more cost-effective for lighter structures where they’re a suitable engineering solution. Bored piers involve more time, more equipment and wet trade curing, but they remain the go-to method where higher loads or greater depths are required and a screw pile simply isn’t rated for the job.
Neither method has a single “right” price — the real cost drivers are depth, load capacity, ground conditions and access, which is why our house slab pricing guide and a proper site assessment matter more than a generic rate per pier or pile.
Choosing the Right Method for Your Site
The decision ultimately comes down to what your structural engineer specifies for the loads and soil conditions on your particular site — it isn’t a straight lifestyle or budget choice between the two. What we can do is talk you through why one method has been specified over the other, get you an accurate quote for the method that’s actually appropriate, and manage the installation from start to finish.
If you’re comparing quotes and one contractor has priced screw piles while another has priced bored piers for the same job, that’s worth querying — it usually means the engineering brief wasn’t identical, which makes the quotes impossible to compare fairly.
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Frequently Asked Questions
Are screw piles as strong as bored piers?
Screw piles can carry significant loads and are rated by installation torque, but for very high loads or specific depth requirements, bored piers are often the specified solution. It comes down to what your engineer certifies for the structure and site.
Which method is faster?
Screw piles are generally faster to install since there’s no concrete curing time involved — many projects can be built on the same day the piles go in. Bored piers require time for the concrete to cure before they can be loaded.
Can screw piles be used under a full house slab?
They can be used in some engineered slab systems, but bored piers are more commonly specified for full house slabs on difficult sites, particularly where higher loads or greater depths are required.
Do bored piers create a lot of mess on site?
There is spoil generated from the boring process that needs to be managed and removed, which is more disruptive than a screw pile installation. We manage spoil removal as part of the process.
How deep do bored piers or screw piles typically go?
Depth is entirely site and engineering specific — it depends on the soil profile and the depth required to reach adequate bearing capacity, which is determined by your soil report and engineer.
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