Screw Pile Foundations vs Concrete Strip Foundations: How Much Do They Cost?

Most people compare the wrong numbers. Here’s what a genuine cost comparison of screw piles vs. concrete strip foundations actually looks like.

Ask a builder to quote for foundations and you’ll almost certainly get a concrete strip price back first. It’s the default. It’s what groundworkers know, what estimators price in their sleep, and what most structural engineers draw without a second thought.

So how much do screw pile foundations cost compared to concrete? Less straightforwardly than most quotes suggest. When people look at screw pile foundations cost vs concrete, they typically compare headline figures that don’t include the same scope.

This matters. On many projects across London and the South East, screw piles, also known as helical piles, are faster, less disruptive, and more cost-effective overall. 

 

Why Direct Price Comparisons of Screw Pile vs. Traditional Concrete Foundations Don’t Work

The instinct is to compare like for like. What does a concrete strip foundation cost versus screw piles for the same extension?

The problem with a direct comparison is they’re different systems with different costs, different timelines, and different knock-on effects across the rest of your project.

A concrete strip quote typically covers excavation, concrete, reinforcement, and backfill. It rarely includes skip hire and spoil disposal, concrete pump hire on tight sites, the 28-day curing period sitting idle in your programme, or extra groundwork if conditions are worse than expected once digging starts.

A screw pile quote covers the full pile design, supply, installation, and preformed concrete ground beams, ready for your builder to start the next day. 

 

The Real Screw Pile vs Concrete Strip Foundation Price Comparison: A Typical SE England Rear Extension

The figures below are based on a single-storey rear extension, perimeter of around 16 linear metres, on London Clay, with access via a side gate. 

All figures are indicative 2026 market rates. Every project is different.

 

A few things to note. The programme delay line is the most variable: it depends on your contractor’s prelims and whether a four-week wait has real knock-on costs for your project. The concrete figures also assume restricted access – on an open site costs can come in lower.

 

What Affects the Final Price of a Piled Foundation the Most

Not all screw pile jobs cost the same, and not all concrete jobs do either. These are the variables that move the needle most, roughly in order of impact.

Ground conditions. This is the biggest single factor for both systems. London Clay requires deeper piles to get below the active zone. Made ground needs a Ground Inspection to establish what’s underneath. Chalk can be variable near the surface. Poor or unpredictable ground adds cost to both systems, but the risk lands differently. With concrete, bad ground can mean a redesign mid-dig. With screw piles, the pile goes deeper until it hits the required torque. You pay for extra depth, not a redesign.

Depth. Helical pile depth drives cost directly. A 2m pile costs less than a 4m pile. Depth is determined by ground conditions and the required load, so it can’t be fixed until the ground is understood. Any quote given before a ground investigation is an estimate, not a price.

Number of piles. A small single-storey extension might need 6 piles. A larger L-shaped or two-storey structure could need 14 or more. The structural engineer’s layout drawing determines this, which is one of the main reasons costs vary between projects of similar footprint.

Access. Restricted access adds significant cost to concrete: pump hire, manual labour, logistics. For screw piles the impact is smaller. 

Pile diameter. Larger diameter piles carry higher loads but cost more per pile. The structural engineer specifies the required diameter based on load at each pile position. For most domestic extensions, standard diameters are sufficient.

 

Does a Ground Investigation Add Cost or Save It?

A ground investigation (GI) is one of those line items that gets cut from budgets and then regretted on site. Here’s the honest picture.

A basic GI for a domestic extension typically costs between £500 and £2,000, depending on the number of trial pits or boreholes, the tests required, and the site location. It feels like an extra cost at the outset. In practice, it almost always pays for itself.

Without ground information, a pile contractor is designing blind. Depths get estimated conservatively, which means you’re likely quoted for more pile than you need. If conditions are worse than assumed, there’s a risk of additional cost on site when the pile needs to go deeper than designed. If conditions are better, you’ve overpaid.

A GI gives the structural engineer what they need to design the pile correctly: depth, diameter, helix configuration, and ground beam specification. The quote you receive based on that design is accurate, not padded with contingency.

There’s a compliance angle too. Your structural engineer will often require ground data before signing off a foundation design, and Building Control may ask for it as part of the approval process. 

For sites with a complex history – made ground, previous demolition, proximity to old drainage or buried structures – a GI is the difference between a project that runs smoothly and one that stops on day one when the pile hits something unexpected.

 

Where Screw Piles Cost More 

There are cases where concrete strip foundations are the better value choice vs. helical pile foundations.

Good ground, easy access. Where bearing strata are close to the surface, ground is consistent, and there’s no programme pressure, strip foundations can be cheaper on a straight cost basis.

Very high loads. Large commercial structures with heavy loads need bigger, deeper piles. At that scale, the cost per pile rises and the programme saving narrows.

Sites with buried obstructions. Old concrete, flint beds, or buried services can slow or stop screw pile installation. On urban sites with an uncertain below-ground history, this risk needs pricing in.

 

Want a Quote on a Screw Pile Foundation? Get in Touch

The only way to compare foundation costs fairly is to price both systems on equal terms considering all the factors that influence your project.

Preformed Substructures offers free, no-obligation quotes across London, Surrey, Kent, Hertfordshire, East Sussex, and West Sussex. We’re one of the South East’s specialist screw pile foundation contractors. Get in touch with your plans and ground conditions and we’ll give you an accurate figure based on the actual design.