FOUNDATION ENGINEERING

How Does Screw Piling Work?

At Dawson Foundation Engineering, we regularly design and install screw piles for a wide range of applications, from residential structures and lift pits to temporary installations such as walkways and staging. This guide explains how screw piling works, where it’s typically used, and when it may not be the right choice — for full technical specifications and to discuss your project, visit our screw piling service page.

What Are Screw Piles?

Screw piles, also known as helical piles, are steel foundation elements comprising a central shaft and one or more helical plates, usually two or three, welded to the shaft. They’re installed by rotating them into the ground using handheld equipment or machine-mounted hydraulic drive systems. For pile sizes, load capacities and commercial details, see our screw piles service page. For depth-specific guidance, read how deep screw piles go.

How Are Screw Piles Installed?

Installation is monitored against one of two criteria, and understanding the difference matters for anyone assessing whether a screw pile design is appropriate for their site: Target torque — the pile is installed until it reaches a torque value that correlates with the required load capacity for the ground conditions encountered. This method relies on real-time feedback during installation rather than a fixed depth, so the pile is effectively self-verifying against the ground it actually meets. Design length — used where torque correlation is less reliable, such as in very soft or highly variable ground, the pile is instead installed to a pre-calculated depth based on site investigation data. Installation equipment ranges from handheld drive heads, suited to confined or low-headroom sites, through to excavator-mounted hydraulic systems for larger commercial schemes. The choice of equipment affects achievable torque, and therefore which of the two methods above is used to verify capacity.

Where Can Screw Piles Be Used?

Common applications include:

House extensions and small residential developments
Lift shafts and plant room bases
Temporary walkways, platforms and event staging
Decking and garden structures
Solar panel foundations
Projects with limited access
Sites where low ground disturbance is required
Projects within root protection zones

For residential projects specifically, read our guide to screw piles for house extensions.

When Screw Piling May Not Be the Right Choice

Screw piling isn’t suitable for every site, and it’s worth understanding the limitations before assuming it’s the default option:

Ground with significant obstructions — cobbles, boulders or made ground containing debris can prevent piles reaching design torque or length, or damage the helical plates during installation.
Very high load requirements — beyond a certain capacity, larger-diameter bored or driven pile systems become more practical than adding multiple screw piles.
Highly variable ground conditions — where torque readings can’t be reliably correlated to capacity across a site, design-length verification or an alternative piling method may be more appropriate.
Corrosive ground conditions — unprotected steel shafts may require additional coating or an alternative pile type where soil chemistry increases corrosion risk over the design life.

A proper assessment of ground conditions is essential before ruling a method in or out — see our guide to why site investigation is important for pile design.

How Is Screw Pile Suitability Assessed?

The assessment typically considers:

Ground conditions and available site investigation information
The required compressive, tensile or lateral capacity
The target installation torque or design length
Access for handheld or machine-mounted installation equipment
The required pile diameter and shaft specification
The proposed connection between the piles and supported structure
Whether the installation is permanent or temporary

Screw Piles for Restricted Access Projects

Handheld or compact machine-mounted installation equipment can make screw piles suitable for rear extensions, garden developments, existing buildings and other confined working areas. Access must still be assessed carefully to ensure the equipment, pile sections and installation process can be safely accommodated. Read more in our guide to restricted access piling.

Screw Piles vs Mini Piling

Screw piling is a specific method using steel shafts fitted with helical plates. Mini piling is a broader term covering several bored, driven, drilled or screwed systems installed using compact equipment. Our screw piles vs mini piling comparison explains the differences in full.

Costs and Advantages

For a full breakdown of pricing factors, see screw pile costs in the UK. For a complete assessment of the benefits and limitations of the system, see our guide to the advantages and disadvantages of screw piling.

More Screw Piling Guides

If you have a project that may be suitable for screw piling, contact our team to discuss the ground conditions, structural requirements and available installation options. Call 0333 224 5196 or send us an enquiry to arrange a free site visit and no-obligation quotation.