Our Screw Pile Underpinning Process

 

Every foundation repair project is different, but the principle behind screw pile underpinning is straightforward: identify the problem, determine the loads and ground conditions, install piles into suitable ground and transfer the structure's load onto the new foundation system.

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1. Assess the Foundation Problem

 

The first step is understanding what has moved and why.

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Existing foundation construction, ground conditions, structural loads, access and the extent of movement can all affect the proposed solution.

 

Where subsidence is suspected, a structural engineer, insurer or other relevant specialist may already be involved in investigating the property.

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2. Determine the Underpinning Design

 

Once the problem and project requirements are understood, the screw pile system can be designed around the loads that need to be supported.

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Pile type, installation position, required capacity, termination details and installation equipment all need to be considered.

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This is particularly important on existing buildings because access around the foundations may be restricted.

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3. Expose the Existing Foundation

 

The affected foundation is carefully exposed.

 

Rather than excavating continuously beneath the entire building, localised pockets can be formed beneath the existing footing at the required centres.

 

ABC Anchors' current system typically uses pockets at approximately 0.8–1 metre centres, subject to the project design.

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4. Install the Screw Piles

 

The screw piles are installed through the weaker near-surface soils and into suitable ground using specialist screw pile installation equipment.

 

Installation torque is monitored during this process. This provides important information about the resistance being achieved as the pile advances.

 

The final depth is therefore not simply an arbitrary measurement that is the same on every project. It depends on the design and actual ground conditions encountered.

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5. Connect the Piles to the Existing Foundation

 

Once the required installation criteria have been achieved, the piles are connected to the structure using the specified underpinning bracket, jacking plate or termination.

 

This creates the connection through which the structural load can be transferred to the new deep foundation.

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6. Preload and Stabilise the Structure

 

Hydraulic jacks can be fitted to the underpinning system.

 

The piles are preloaded in a controlled manner so that the building's load is supported by the new foundation system.

 

Depending on the condition of the structure and the engineering requirements, it may sometimes be possible to lift an affected area towards its original position.

 

However, lifting is not automatically appropriate on every property. Stabilisation is the primary objective.

 

7. Complete and Reinstate the Area

 

Once the underpinning system has been installed and the structure stabilised, excavated areas can be backfilled and the site reinstated as required.

 

Structural cracks and other damage can then be repaired at the appropriate stage of the wider remediation project.

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Screw Pile Underpinning vs Traditional Concrete Underpinning

 

Both methods are designed to provide additional support to an existing foundation, but they achieve it differently.

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Traditional mass concrete underpinning normally requires sections to be excavated beneath the existing foundation and filled with concrete to create a deeper or larger foundation.

 

It remains an established solution and may be appropriate for some buildings.

 

Screw pile underpinning instead uses steel piles to transfer structural loads through unsuitable ground to stronger material at depth.

 

One of its principal advantages is that it can reduce the amount of excavation required compared with extensive mass concrete foundation works. Screw pile installation also produces relatively low levels of vibration and can be particularly useful where access is restricted.

 

Another important difference is installation control.

 

The resistance encountered while a screw pile is installed can be monitored through torque. The pile configuration and depth can therefore be developed in response to the actual ground conditions and the engineered requirements of the project.

 

For more detail on how the system works, see our guide to what screw piles are and how they work.

 

The right option depends on the structure, loads, soil, access and cause of movement. Underpinning should therefore be specified for the individual project rather than selected simply because one method is described as newer than another.

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How Much Does Screw Pile Underpinning Cost?

 

There is no meaningful fixed price for underpinning without first understanding the property and the extent of the foundation problem.

 

The cost of screw pile underpinning can be affected by:

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• the number of pile positions required

• required pile capacity

• installation depth

• soil and ground conditions

• access around the property

• whether handheld or excavator-mounted installation equipment is required

• excavation needed to expose the foundations

• underpinning bracket and termination requirements

• structural engineering requirements

• whether controlled lifting is required and

• the amount of reinstatement and associated repair work

 

For context, RICS states that underpinning generally can cost approximately £10,000 to £75,000 for a typical house, with larger properties potentially costing more. 

 

Our quotations for screw pile underpinning needs are based on the actual design and site conditions.

 

For contractors, engineers or property owners with an identified foundation problem, we can discuss your project requirements and help determine the screw pile system you need.

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How Long Does Screw Pile Underpinning Take?

 

Installation time depends heavily on the size and complexity of the project.

 

A small conservatory or extension requiring a limited number of piles is very different from underpinning a complete property with dozens of pile positions.

 

Timescale can be affected by:

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• the number of piles

• required pile depth

• access

• excavation requirements

• ground conditions

• installation equipment

• structural connections

• whether lifting is required and

• other remedial works taking place at the same time

 

Screw piles themselves can be installed efficiently because there is no requirement to wait for large volumes of newly poured mass concrete to cure before the foundation system can perform its intended role.

 

However, the whole subsidence repair programme may take considerably longer than the pile installation itself, particularly where movement has to be investigated or monitored before remedial work is authorised.

 

We can provide a more realistic installation programme once the scope of the foundation repair is understood.

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Underpinning Conservatories

 

Conservatory subsidence is a common reason for investigating foundation repairs.

 

A conservatory may begin moving independently from the main house if its foundations are not adequate for the ground conditions beneath it.

 

Signs can include:

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• cracks developing around the conservatory

• separation between the conservatory and house

• doors becoming difficult to open or close

• visible distortion of frames or

• an uneven or dropping floor

 

At ABC Anchors, we have worked with window companies to support and lift subsiding conservatories using screw pile underpinning.

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The affected foundation can be exposed and screw piles installed at designed positions beneath it. The piles provide deeper support, while the underpinning connection transfers the conservatory load away from the failing foundation.

 

Where conditions allow, controlled hydraulic jacking may also be used as part of the stabilisation process.

 

For property owners worried about underpinning a conservatory, the important point is that the entire structure does not necessarily have to be removed simply because part of its foundation has moved. The appropriate solution depends on the extent and cause of the movement.

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Underpinning Extensions

 

Extensions can also experience differential movement, particularly when the extension and original house have different foundation designs, depths or ground conditions.

 

Movement may become visible where the extension joins the original property.

 

An extension built on inadequate foundations or unstable ground may require additional support beneath its existing footing.

 

Screw pile underpinning can provide that support without relying on the weak ground immediately below the original foundation.

 

This can make the system suitable for both relatively small residential extensions and larger structural foundation repair projects.

 

As with any subsidence problem, the cause of movement should be established first. Repairing visible cracking without dealing with continuing foundation movement can leave the underlying problem unresolved.

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Foundation Problems Near Trees

 

Trees can become an important consideration when investigating subsidence, particularly where buildings are founded on shrinkable clay soils.

 

Tree roots draw moisture from the surrounding ground. During prolonged dry conditions, moisture loss can cause clay soils to shrink. If that shrinkage occurs beneath part of a foundation, differential movement may result.

 

Removing a tree is not automatically the correct solution.

 

The relationship between the tree, soil, building and observed movement needs to be investigated. Other factors such as leaking drains, poorly compacted ground or inadequate original foundations may also be involved.

 

Where deeper structural support is required, screw piles can be designed to transfer building loads beyond unsuitable near-surface ground.

 

This can be particularly useful where the existing shallow foundation can no longer provide dependable support.

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Real Subsidence Project: 108 Screw Piles Installed to 14 Metres

 

A recent ABC Anchors project demonstrates the scale of foundation problems that screw pile underpinning can address.

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Working with Opus Construction & Civils, ABC Anchors was involved in stabilising a bungalow suffering from significant subsidence and foundation movement.

 

The project required:

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• 108 screw pile positions

• 60R screw piles

• installation depths of up to 14 metres

• both handheld and excavator-mounted installation equipment and

• rebar terminations to transfer the building loads into the new pile system

 

Restricted sections of the property were installed using an Autoguide Equipment 400H handheld torque head, while accessible areas could be completed using the 500X excavator-mounted system.

 

Using both installation methods meant the solution could adapt to different access conditions around the same property.

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Torque was monitored as the piles were progressively installed. Once the required piles had been completed, rebar terminations connected the structure to the deep foundation system.

 

The result was a stabilised residential structure supported by 108 deep screw pile positions extending as far as 14 metres below ground.

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Read the full subsidence case study and see how 108 screw piles were used to stabilise the bungalow.

 

For homeowners, engineers and contractors considering screw pile underpinning, this provides a real example of how the system can be adapted to significant structural movement, deep installation requirements and restricted site access.

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What Happens If My Subsidence Repair Is an Insurance Claim?

 

If you believe your home is suffering from subsidence and you intend to make an insurance claim, contact your buildings insurer before arranging substantial remedial work yourself.

 

Depending on the circumstances, the insurer may appoint a loss adjuster, structural engineer or other specialist to investigate the damage and determine its cause.

 

Some properties require a period of monitoring before the appropriate repair can be confirmed. In other cases, the cause can be established more quickly.

 

Importantly, not every subsidence claim results in underpinning.

 

Where foundation stabilisation is required, the engineer and insurer will normally need to agree the remedial design and scope of work before it proceeds.

 

Buildings insurance usually includes cover for subsidence damage, subject to the wording and exclusions of the individual policy. Subsidence claims also commonly carry a higher excess than other types of household claim.

 

If ABC Anchors' screw pile system is being considered as part of an insurance repair, we can work with the relevant contractors and project professionals to establish the pile and installation requirements.

 

For homeowners who are still at the investigation stage, our guide to fixing subsidence without traditional excavation explains what to establish before remediation is agreed.

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Why Use Screw Piles for Foundation Repair?

 

Screw pile underpinning offers several practical characteristics for existing buildings.

 

Reduced excavation

The system uses localised pile and underpinning positions rather than relying solely on large volumes of mass concrete beneath the structure.

 

Low vibration installation

Screw piles are rotated into the ground rather than driven using impact piling equipment, helping to minimise vibration around an already vulnerable structure.

 

Suitable for restricted access
Different screw pile installation equipment can be used depending on available space, including handheld systems where larger machinery cannot reach the pile position.

 

Installation torque can be monitored
Torque provides measurable information during pile installation and forms an important part of confirming the required installation criteria.

 

Deep foundation support
Pile sections can be extended where necessary to reach the depth required by the design and ground conditions.

 

Immediate structural support

Once correctly installed and connected, screw piles can be loaded without waiting for a large mass concrete foundation to cure.

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Suitable for different structures
The system can be used for houses, conservatories, extensions and other structures requiring foundation stabilisation.

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Talk to ABC Anchors About Your Foundation Repair

 

Foundation movement needs a solution based on what is happening beneath the building — not simply a cosmetic repair to the cracks above it.

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ABC Anchors designs and manufactures screw pile systems for foundation and ground engineering applications and provides underpinning solutions for structures affected by subsidence and foundation failure.

 

Whether you are dealing with a subsiding house, conservatory, extension or another structure, we can discuss the site conditions, loads, access and installation requirements with you and the professionals involved in your project.

 

Contact us today to discuss screw pile underpinning and foundation repairs.

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Frequently Asked Questions About Screw Pile Underpinning

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1. What is screw pile underpinning?

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Screw pile underpinning is a foundation repair method that uses steel helical or screw piles to support an existing foundation. The piles are installed through weaker ground to the required depth and resistance before being connected to the existing structure using an engineered underpinning system.

 

2. Are screw piles and helical piles the same thing?

 

The terms screw pile and helical pile are commonly used for piles that incorporate one or more helical plates and are rotated into the ground. Terminology and individual pile designs vary, but both terms describe the same broad foundation principle.

 

3. Can screw piles repair subsidence?

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Screw piles can be used as part of an engineered subsidence solution where an existing foundation requires deeper support. They transfer structural loads away from unsuitable near-surface soil and into more competent ground. Whether underpinning is necessary should first be established through appropriate investigation.

 

4. Can you underpin a conservatory with screw piles?

 

Yes. Screw piles can be used for underpinning a conservatory where the existing foundation requires additional support. ABC Anchors has worked with window companies on subsiding conservatories and extensions, including projects where the affected structure has been supported and, where appropriate, lifted.

 

5. Can an extension be underpinned without underpinning the whole house?

 

Potentially. If movement is localised to an extension, the remedial design may focus on that affected area rather than the entire property. The cause and extent of movement must first be investigated so the appropriate repair can be designed.

 

6. Can a subsiding building be lifted back into position?

 

In some circumstances. Our underpinning system can incorporate jacking plates and hydraulic jacks, allowing piles to be preloaded and potentially enabling controlled lifting. However, not every structure should or can be returned fully to its original level. The primary requirement is safe stabilisation.

 

7. How deep do screw piles need to go for underpinning?

 

There is no standard depth suitable for every property. Required depth depends on ground conditions, structural loads, pile design and the resistance achieved during installation. We can explain these variables in more detail in our guide to how deep screw piles need to go.

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8. Is screw pile underpinning cheaper than traditional underpinning?

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It depends on the project. Costs are affected by the number and depth of piles, access, structural loads, ground conditions and associated works. Screw piling can reduce excavation and avoid some of the processes associated with mass concrete underpinning, but a project-specific assessment is needed before costs can be compared accurately.

 

9. How much does underpinning cost?

 

RICS gives a broad guide of approximately £10,000 to £75,000 for underpinning a typical house, with larger or more complicated projects potentially costing more. A project-specific quotation is needed once the required foundation solution has been established.

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10. How long does screw pile underpinning take?

 

The installation period depends on the number of piles, their depth, access, ground conditions and the work needed to connect them to the existing structure. The pile installation itself can be relatively quick, but an insurance-led subsidence project may take considerably longer because investigation and monitoring can be required before repair work begins.

 

11. Will my buildings insurance pay for underpinning?

 

Many UK buildings insurance policies cover damage caused by subsidence, subject to the policy terms, exclusions and excess. However, underpinning is only used where investigation shows that foundation strengthening is required. Contact your insurer before commissioning substantial repairs if you intend to make a claim.

 

12. Should I remove a nearby tree if my house is subsiding?

 

Not automatically. Trees can contribute to movement where roots remove moisture from shrinkable clay, but other causes of subsidence include leaking drains, inadequate foundations and poorly compacted ground. The cause should be investigated before trees or major vegetation are removed.

 

13. What is the difference between repairing cracks and repairing subsidence?

 

Crack repair addresses damage visible above ground. Subsidence repair addresses the movement that caused the damage.

 

Where foundations are continuing to move, repairing cracks alone does not stabilise the structure. The underlying cause needs to be identified and, where necessary, the foundations stabilised before permanent cosmetic repairs are completed.