Following recent decisions by some Building Control authorities to introduce a blanket ban on approving screw pile foundations, it’s a timely moment to pause and examine what’s really going on.

In a recent discussion with John Staves, Chartered Structural Engineer and the UK’s screw pile specialist, one thing became immediately clear:

Building Control concerns are justified, but the terminology is muddying the waters.

The Root of the Problem: Terminology Confusion

The phrase “screw pile” is being used too loosely.

In practice, it’s often incorrectly applied to two very different systems:

  • Ground screws (lightweight, shallow, friction-based systems)
  • Helical piles (engineered, deep, end-bearing systems)

This confusion is not just semantic it has real structural consequences.

ground screws

Image: Lux Garden Rooms


What Is a Ground Screw?

Ground screws are typically:

  • Up to 2m in length
  • Installed from the surface (handheld or small machinery)
  • Variable in form, ranging from large threaded screws to twisted square bars


How Ground Screws Work

Ground screws rely primarily on:

  • Shaft friction
  • Resistance from the surrounding shallow soil

This means their performance is entirely dependent on the condition of the soil along their full length.

The Critical Weakness

Ground screws are often used in unsuitable conditions, especially:

  • High shrinkability clay
  • Areas within the zone of influence of trees
  • Sites requiring deeper, stable bearing strata

If the top 50–100cm of soil dries and shrinks (common in clay), you lose capacity immediately.

A recent example:

We were approached by a homeowner who had installed a garden room using ground screws (1.2m deep) in high shrinkable clay, located 5m from an oak tree, and he was experiencing seasonal movement.

As moisture levels changed, the clay expanded and contracted, causing the structure to rise and fall, just like a shallow foundation.

It was suggested an attempted fix would be to excavate around the ground screws and backfill with concrete – this would only make matters worse, creating an irrecoverable and poorly performing shallow pad foundation.

A more appropriate fix would have been helical piles to 4m depth.


What Is a Helical Pile (True “Screw Pile”)?

Helical piles are a completely different technology.

They consist of:

  • A central steel shaft
  • Discrete helical plates (helices) welded at intervals
  • Modular extensions to achieve depth


How Helical Piles (Screw Piles) Work

  • End-bearing system
  • Load is transferred through the helices into deeper, more stable strata
  • Not reliant on shallow soil conditions

Unlike ground screws, they are engineered foundation solutions.

Why Helical Piles Perform Differently

  1. Load Transfer Mechanism
  • Helical piles: End-bearing through helices
  • Ground screws: Shaft friction in upper soils

This is the fundamental difference.

screw piles on site


  1. Depth and Stability

Helical piles are installed in sections, allowing them to:

  • Reach deeper competent strata
  • Avoid influence zones (e.g. tree roots, shrink/swell zones)

Ground screws cannot achieve this in any meaningful way.


  1. Torque = Capacity (A Critical Advantage)

One of the most powerful features of helical piles is:

Installation torque directly correlates with load capacity

  • Higher torque = stronger ground = higher capacity
  • Measured in real time during installation using calibrated equipment

This gives Building Control something rare: on-site validation of performance as the foundations are installed. No waiting for concrete to cure. No waiting for testing.

  1. Engineered Design vs “Off-the-Shelf”

  • Ground screws:
    • Typically selected from catalogues
    • Rarely designed for site-specific soil conditions
  • Helical piles:
    • Designed using:
      • Site investigation data
      • BGS records
      • Trial installations (torque testing)


screw piles log cabin


Installation and Design Detail (What Good Looks Like)

Helical pile helices are:

  • Circular steel plates
  • Cut and formed into a spiral
  • Welded at specific angles and spacing

Spacing is critical:

  • Typically 3x the diameter of the helix
  • Ensures efficient load transfer and avoids interaction between plates

These aren’t lightweight components they are:

  • Thick-walled steel shafts
  • Designed to withstand high installation torque (often the maximum stress they will ever experience)

Why Building Control Is Right to Be Concerned

The issue is not that “screw piles don’t work.”

It’s that:

Ground screws are being used where engineered deep foundations are required.

They may perform adequately in the short term, but:

  • They remain vulnerable to shallow ground movement
  • They behave like shallow foundations
  • They do not address geotechnical risks

Where Ground Screws Do Work

To be fair, ground screws have a place:

  • Lightweight structures
  • Stable, granular soils
  • Situations without shrink/swell risk

But they are not a universal foundation solution.

screw piles sloping site

How Building Control Can Move Forward

Rather than a blanket ban, a more robust approach could be:

  1. Demand Engineered Solutions

    • Require site-specific design
    • Distinguish clearly between ground screws and helical piles

  1. Require Torque Verification

    • Calibrated torque heads
    • Digital readouts
    • Data logging of installation

  1. Encourage Validation Testing

    • Trial installations to confirm design assumptions
    • Adjust depth based on achieved torque

The Case for Helical Piles

When properly designed and installed, helical piles offer:

  • No spoil removal
  • Immediate load-bearing capacity
  • Suitability near tree roots (displacement installation)
  • Adaptability to variable ground conditions
  • Real-time verification of capacity

Conclusion

The current concern from Building Control authorities is both understandable and justified.

What’s being challenged is not the principle of screw pile foundations but the misuse and misunderstanding of two very different systems.

Ground screws and helical piles are not interchangeable. One relies on shallow soil conditions and is highly susceptible to environmental changes; the other is an engineered, verifiable deep foundation solution designed to perform reliably across a range of ground conditions.

For Building Control officers, the key lies in clarity and specification ensuring that what is being proposed is appropriate for the ground conditions, properly designed, and capable of being verified on installation.

We’ve recently been approached by several Building Control officers, planners, and architects asking for our perspective on screw piles and their appropriate use.

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Related Blog;  Ground screws vs helical piles – what’s the difference?

Ground Screws vs Helical Piles

Ground Screws

Ground screws are often marketed as an alternative to traditional concrete foundations and in some situations, they’re a perfectly reasonable choice. But it’s worth being clear about what they are from an engineering point of view.

ground screws

Image credit: Lux garden rooms


A ground screw is essentially a proprietary product.

It’s usually selected from a manufacturer’s range using standard load tables and basic assumptions about the ground conditions, rather than being designed specifically for the structure or the site.


There is usually:

  • Limited or no project-specific design
  • No verification of load capacity during installation
  • An assumption that the ground conditions are suitable and consistent

This makes ground screws ideal for:

  • Lightly loaded structures
  • Temporary or non-critical applications
  • Situations where speed and minimal disruption are priorities

From an engineering standpoint, they are a convenient solution but not a fully verified one.

Ground Screws vs Helical Piles

Helical Piles

Helical piles might look similar at first, but they’re a different thing altogether.

They’re not just selected from a range they’re designed to suit the structure and the ground they’re going into.


Each pile is:

  • Engineered to suit the load requirements of the building
  • Designed based on site-specific ground conditions
  • Installed using controlled torque, which provides real-time verification of capacity


The helical plates (or flights) are not just there to “screw it in” they are critical structural elements that:

  • Transfer load efficiently into competent strata
  • Control settlement
  • Provide predictable performance

This makes helical piles suitable for sites where:

  • Poor or variable ground conditions
  • Restricted site access
  • Tree roots nearby
  • High water tables
  • Sloped or uneven site
  • Retrofitting or underpinning

The Key Difference Between Screw Piles and Helical Piles

The distinction is straightforward:

  • Ground screws are selected from standard manufacturer data
  • Helical piles are designed to suit the structure and the ground conditions
difference between screw piles and helical piles

Why This Matters

The issue arises when the two are treated as interchangeable.

Using a ground screw in place of a designed foundation introduces uncertainty:

  • Settlement behaviour is less predictable
  • Load capacity is assumed rather than demonstrated
  • Long-term performance depends heavily on ground variability

With helical piles, the approach is different:

  • Capacity is derived from design and verified during installation
  • Load transfer is taken into competent strata
  • Performance is more predictable and measurable

Final Thought

For lightly loaded structures, ground screws can be a practical solution.

But once you’re dealing with a building, the foundation becomes a structural element.

At that point, it’s no longer about selecting a product it’s about designing a foundation system with known and verifiable performance.

Related blog: Why Building Control is raising concerns about screw pile foundations

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