Underpinning Cost

How Much Does Underpinning Cost?

Underpinning a house typically costs between £6,000 and £21,000 in the UK. The average cost is £13,500, based on the traditional mass concrete method for a standard 3-bedroom semi-detached home.

The final price depends on the underpinning method used, the size of the property, and the complexity of the job. A structural engineer is required for all underpinning work and their hourly rate is typically £50 to £90, or £200 to £2,000 for a fixed-price inspection.

As a rough guide for individual cost elements: initial excavation at 1m deep costs around £120 per m², removing existing foundations runs approximately £45 per metre length, and installing reinforcement rods to address wall cracking costs around £400 per metre length.

Why Would Underpinning Be Required?

Underpinning may be necessary when a property shows signs of subsidence, when a new floor is being added or removed, or when existing foundations are too shallow to support structural changes. To fix subsidence, costs can increase significantly depending on the cause and extent of the damage. In older properties, shallow foundations are common and may need reinforcing before any significant building work can begin.

It's not a DIY job. Incorrectly underpinning a property can compromise structural integrity and create serious safety risks. Work typically takes 3 to 6 weeks to complete and requires a qualified structural engineer and experienced building contractor at minimum.

Depending on the cause, you may also need a tree surgeon, plumber, or legal support for planning permission and Party Wall Agreement documentation.

For any finishing touches, you may need to factor the plastering an indoor wall cost into your budget, or the need to hire painters and decorators to complete the job.

If the underpinning relates to an extension, planning permission may also be required. In England and Wales, you must serve a Party Wall Act notice for underpinning a shared wall or qualifying excavation near a neighbour's foundations, with legal documentation costing up to £1,000 per neighbour.

Underpinning Costs by Property Size and Method

The cost of underpinning varies depending on the type and size of your property. Prices are lower for flats and bungalows, and higher for larger detached homes, particularly where deep foundations or challenging ground conditions are involved.

Location also plays a role. Properties built on slopes, or in densely built-up areas where access is restricted, can cost more. A structural engineer may need to carry out trial pit tests before work begins, adding to the overall cost.

The figures below show indicative costs for underpinning a single wall using each method. For whole-house underpinning, multiply by the number of walls involved:

• The average cost for the traditional mass concrete method of underpinning is £1,500 per m².
• The average cost for the mini-piling method of underpinning is £2,600 per m².
• The average cost for the resin injector method of underpinning is £1,200 per m².

2-Bedroom Terrace House Underpinning Costs

The table below shows underpinning costs for a single wall in a 2-bedroom terraced property (4m), based on a job taking 3 weeks to complete.

3-Bedroom Semi-Detached House Underpinning Costs

The table below shows underpinning costs for a single wall in a 3-bedroom semi-detached property (5m x 4m), based on a job taking approximately 4 weeks to complete.

4-Bedroom Detached House Underpinning Costs

The table below shows underpinning costs for a single wall in a 4-bedroom detached property (8m x 6m), based on a job taking around 6 weeks to complete.

Cost Breakdown for Underpinning Work

The following is a breakdown of individual steps and what you are likely to pay for a straightforward job:

Additional Costs

Some of the additional costs you may face during the underpinning work include:

You may need to hire an additional tradesperson to complete remediation work after your underpinning.

Along with decorators for any internal work, you may also need a gardener due to the additional cost of laying garden turf or someone to help build a garden brick wall to replace any damaged areas that have occurred during the foundation work.

Labour Costs and Timescales

For the average mass concrete underpinning job, labour and materials combined typically cost £13,500 and take 3 to 5 weeks to complete. Prices vary depending on location and the extent of work required.

Builders are not involved in planning permission or legal documentation. You'll need to hire additional professionals for those aspects before work begins. For jobs involving adding or removing a floor, a structural engineer will carry out periodic inspections, soil tests, and prepare design paperwork for building control. All of this must be completed before any physical work starts.

Additionally, for older properties, the foundations are often shallower so the tradesperson may have to dig a lot deeper or use an alternative underpinning method to the more traditional ones available.

The most common method is mass concrete, carried out by hand without specialist machinery. For older properties with shallower foundations, however, an alternative such as resin injection may be more appropriate, a less invasive option that avoids the need for deep excavation.

How Long Does Underpinning Take?

Most underpinning jobs take 3 to 5 weeks to complete, with 4 to 5 weeks being typical for a standard mass concrete job on a 3-bedroom home. The method used has the biggest impact on timescale.

Mass concrete underpinning is the most time-consuming approach. Concrete must be allowed to fully cure between each excavation stage before the next section can begin. Resin injection is significantly faster and can often be completed in a matter of days, as there is no curing time involved. Mini-piling falls between the two, with timescales depending on the depth of foundations and site accessibility.

For jobs involving planning permission, building control applications, or a Party Wall Agreement, the overall project timeline can extend considerably (sometimes by several months) before physical work even begins.

Underpinning Cost Factors

The South East and London are considered the most expensive locations, so expect to pay more if you live there. However, another important point worth noting isn't just which city you reside in but whether you live in a built-up area or not.

The countryside is traditionally much cheaper due to the area of space available, but in terraced locations, there is less room to move. On top of that, there are legal complications if you share a wall with a neighbour(s).

A structural engineer's presence is crucial. Their design calculations provide the dimensions and materials needed to complete the work, and these designs must be submitted to the Building Control department before work can start. Hourly rates typically range from £50 to £90, while a full property survey costs from £200 for a smaller home up to £2,000 for a larger detached property.

Before work starts, you need to notify your local Building Control office as it is classed as notifiable work under Building Regulations. It isn't a simple case of letting them know as you have to make an application, which could potentially be denied, plus there is a fee.

The fee differs depending on your location so you will need to contact them first. Although councils publish their building control charges, the amount you pay depends on the work involved and the inspections needed.

In England and Wales, underpinning work covered by the Party Wall Act requires written notice to your neighbour, normally at least 2 months before work on a shared wall or 1 month before qualifying excavation. Work must begin within a year of the notice.

If your neighbour refuses or does not consent in writing within 14 days, you'll need an agreed surveyor or one each to arrange a party wall award setting out how the work will proceed and who pays. It is also worth taking photos of the affected areas before work begins and checking that your contractor has suitable insurance.

• The cost of legal documents needed for the party wall agreement can total up to £1,000 per neighbour.
• When satisfied with the underpinning work, the structural engineer will issue a Certificate of Structural Adequacy (this, in turn, assists with applying for suitable insurance).

With the proposed work, the cost for the actual underpinning will vary based on the method used (the width and depth of excavations, determined by the structural engineer).

What Is Underpinning a House?

Underpinning is the process of strengthening the existing foundations of a property to extend it further, such as adding a new floor or to reinforce the structure where the materials may not have been adequate when initially built. If left alone, the structure can be dangerous.

Another reason to underpin your home will be a pre-emptive response if your neighbours have recently had to treat a subsidence issue as this could have a knock-on effect on other properties within the area especially if it is a common soil issue due to excess water or lack of moisture due to tree roots, which could cause the property to sink.

A large-scale example of underpinning is the result of subsidence. Still, not all cases of subsidence require underpinning. You can save yourself a significant amount with the correct approach by identifying whether it is an issue you can correct yourself such as cosmetic cracks in the wall or with maintenance carried out by a tradesperson such as a tree surgeon if necessary.

What's Involved in Underpinning a House?

Structural Engineer

The initial step with underpinning your home is to instruct a structural engineer. They will determine the safety of the structure and what materials are required to correct the issue. In cases of subsidence, this process can potentially take a long period from weeks to even years. The cause of subsidence is identified, and the correct method applied to resolve the matter.

The structural engineer will ascertain whether underpinning is needed, carry out soil and structural tests if required, decide on the most appropriate underpinning method, and provide design calculations and submit the necessary applications. Their hourly rate is typically £50 to £90.

Builder Costs

The role of a builder is to carry out the underpinning work, including the following tasks:

• Manually digging holes under the existing structure — costing on average £220 for first and second excavations.
• Filling holes/cracks and cement rendering, or in some cases, by injecting a resin mix. £150 to £250 is the average cost for a day's work.
• Replacing beams where necessary, working with existing structures to help strengthen them — on average costing around £190 in total (providing there's no additional brickwork required).
• Renewing defective bricks as a cost of approximately £120 per m² or £15 per individual brick.
• As well as underpinning the house, a builder will also need to repoint brick walls on a house where needed.
• The removal of any debris and make good after completion.

Tree Surgeon Costs

For subsidence related matters, if the property is too close to the trees, a tree surgeon may be needed to either remove them, or prune them to prevent future complications or create root barriers, an additional trench between the roots and the property to stop the roots removing any moisture from the soil or causing any further movement to the foundations.

The cost of having a tree trimmed or pruned varies on its size, type of tree and location (tree surgeons are likely to charge more in London and the South East).

• The average cost to remove a problem tree — £200 to £300.
• Pruning back a tree costs — £100 for an average-sized tree.
• Removal of debris approximately — £100.
• Investigation into whether roots are causing an issue — £200 to £300.

The 5 Stages of Underpinning

In summary, the bulk of the underpinning process is made up of the following steps:

• Excavation — the digging of trenches for the concrete to be poured into and any reinforcing of beams.
• Reinforcement — concrete is poured into each area strategically and allowed to cure to monitor both the existing structures and soil.
• Infilling — all excavated soil is replaced.
• Repair Work — the reinforcement or replacement of wall cavity ties and removal of any defective brickwork.
• Make Good — the removal of any defective material and components that needed replacing, and to leave the property in a presentable condition.

Benefits of Underpinning

The immediate benefits of underpinning a property have two main areas. The first area would be the safety of the structure. If left as is, while the property may be stable, it could deteriorate over time. Carrying out works earlier as a pre-emptive matter would alleviate any future costs or perhaps even any insurance claims.

If you are looking to sell the property in the future, you will need to declare that the property has had subsidence (if applicable) and this can put off potential buyers. Correcting the work will offer peace of mind, but you have due diligence to divulge this information.

For older properties, the foundations can be shallower. By reinforcing the existing foundations, this can increase stability and longevity but at a fraction of the cost should it be left as is.

Underpinning Methods

There is a range of underpinning methods available, each with their pros and cons, plus an alternative approach to underpinning which involves resin injections. In almost all situations, the structural engineer can advise on the most suitable method for your property.

Mass Concrete

This is traditional, and the most common and straightforward method. Holes are dug around the existing foundations by hand and concrete is poured into strategic locations to provide additional strength to pre-existing footings.

This method is the most common, and therefore the most cost-effective. Works well with shallow foundations as long as they are accessible. No specialist tools or machinery are required, so it is ideal when time isn't a factor and when on a budget.

Average cost for this option is £1,500 per square metre.

Pros

• ✔ Very cost-effective
• ✔ No need for heavy machinery
• ✔ Retains the original foundations and improves upon them
• ✔ Sometimes, the structure can be used while being repaired

Cons

• ✖ Time-consuming
• ✖ Limited depths
• ✖ Before each new pin area is excavated, the concrete must be allowed to cure

Beam and Base

In this scenario, the existing footings are entirely replaced or fortified with a concrete beam. This, in turn, disperses the weight of the structure on the new concrete beam. Each of these new beams is strategically placed to offer the most robust footings for the property. It is essentially a further advanced option of the mass concrete method.

An advanced approach that offers more stability than mass concrete, but with increased costs due to the method applied. The average cost for beam and base underpinning is £2,000 per m².

Pros

• ✔ Can be placed above or below the existing beam or outright replace it.
• ✔ A more advanced method.
• ✔ Increases strength and stability.

Cons

• ✖ The base size and depth are limited to ground conditions.

Mini-Piled

When deep foundations are needed for more than 16ft, piling is best suited. It needs specialist equipment and is suited to deeper foundations with variable conditions, which makes it the most expensive option. Structural engineers are also able to use bespoke rigs to get into more challenging locations.

It is suited when transferring foundations to more suitable soil and for foundations that need to be dug further for additional support. Due to the depths involved, the use of a rig significantly adds to the cost of this process.

An average cost for this option is £2,600 per square metre.

Pros

• ✔ For variable ground conditions
• ✔ Useful for areas that are restricted
• ✔ Less disruptive

Cons

• ✖ The most expensive method.
• ✖ The installation of mini-piles requires a lot more work than the traditional method and requires specialist skills and machinery.

Resin Injection Underpinning

Resin injection underpinning involves mixing a resin with a hardener and injecting it into the ground beneath the existing footings. A chemical reaction causes the mixture to expand, filling voids, compacting loose soil, and hardening the surrounding ground. Repeated injections can gradually raise the structure, allowing it to be levelled.

The average cost of resin injection underpinning is £1,200 per m², making it the most affordable method. As a rough guide, costs typically run to around £4,800 for a 2-bedroom terraced house, £11,000 for a 3-bedroom semi-detached, and £17,000 for a 4-bedroom detached property, based on a single wall.

It's worth noting that while resin injection is faster and less disruptive than traditional methods, it may not be suitable for all ground conditions or levels of structural movement. A structural engineer should confirm whether it's appropriate for your property before proceeding.

Pros

• ✔ Clean
• ✔ Fast and efficient
• ✔ Non-disruptive

Cons

• ✖ While a cheaper option, it doesn't offer the same stability as other methods.

Cantilever Needle Beam

This method is an external approach. Work is carried out at the exterior of the property, without the need for the removal of fixtures inside. Another cost-effective strategy that is less disruptive as work can continue outside the property and needs less preparation inside.

Cantilever needle beams are best suited when space isn't an issue, and the tradespeople can access the property externally. Interior work will still need to be completed, but as the bulk of the work is external, it is one of the least disruptive methods.

An average cost for this option is £2,000 per square metre.

Pros

• ✔ Less excavation required than conventional methods
• ✔ Faster method
• ✔ Has high load capabilities

Cons

• ✖ Requires substantial working space to the exterior of the property.

Things to Consider When Underpinning a House

A key factor to consider when underpinning a house is whether it can be covered by your insurance, as this will keep the costs down. When underpinning is required for strengthening existing structures, it's vital to get work completed sooner rather than later as this could potentially affect you getting adequate insurance cover in the future, or perhaps you wish to sell your home.

Equally important is to instruct the right contractors for the job. Price is always a decider, but do they have suitable qualifications and experience, a portfolio you can request to see and are they adequately covered in terms of the insurance?

Another important thing that shouldn't be overlooked is whether you feel you can communicate with them properly. Are you comfortable in their presence? Underpinning work takes a good deal of time and you will be in contact with them frequently.

Does My House Need Underpinning?

Not every property showing signs of movement will need underpinning. However, the following warning signs may indicate a more serious structural problem that warrants a professional inspection:

• Bowing of walls, either inwards or outwards
• Uneven floors
• Unable to open/close windows or doors without some realignment
• Cracks located around windows
• Wallpaper ripping
• Existing cracks in walls and ceilings are becoming more prominent, or new ones are occurring
• Neighbouring homes also being in need of underpinning work

Two additional causes are worth investigating separately, as they don't always lead to subsidence but should be assessed by a professional:

• Leaking drains, which can cause deterioration to footings.
• Tree roots, which can damage foundations directly or dry out the soil by absorbing moisture.

If trees near your home may be contributing to subsidence, it's best to get professional advice before pruning, removing them or installing a root barrier. Removing trees can cause clay soil to swell, so the best approach depends on an assessment.

You may also need permission before carrying out tree work. Trees protected by a Tree Preservation Order (TPO) need council consent, while work to trees in a conservation area may need to be reported in advance.

Can I Claim Underpinning on My House Insurance?

Most insurance providers will cover the cost of underpinning in cases of subsidence, but there's usually an excess that applies, and the average is £1,000. As long as you can provide adequate evidence, it should be covered by your home insurance policy but does not apply for new properties as they are still covered with the new building warranty.

In most cases, they will send a surveyor to your property to further inspect as there is a high percentage of claims being cosmetic and not needing any underpinning treatments.

In many cases, underpinning may not be necessary, but after a structural engineer has surveyed the property, the insurance company will be able to pay out. This may not apply if the property has a history of subsidence. Insurers are sometimes reluctant to cover a building already affected unless it is work they have actioned themselves. Check with your insurer beforehand to confirm your level of cover.

What Should I Do if I Suspect My Home Is Affected by Subsidence?

In all cases, a structural engineer will be able to inspect and evaluate whether your property has been affected by subsidence. A call-out typically costs £200 to £600. More often than not, factors that appear to indicate subsidence can be remedied with simple maintenance and preventative measures.

Many homeowners see a crack appear and assume the worst, but all properties experience some movement over time, particularly older ones. Calling in a professional for an initial inspection can offer peace of mind and help determine whether any further action is needed.

In the event of having to start damp proofing a wall, costs can reach around £1,250 depending on the extent of the issue and size of property.

Before carrying out any work, however, check with your insurance provider beforehand as underpinning can be covered by buildings insurance, but the insurance company is most likely to send out its surveyor to verify.

What Causes Subsidence?

Various points can affect your property with subsidence. The most common cause in the UK is the shrinkage of clay soil beneath the house foundations which can be caused by tree and plant roots searching for moisture and drying out the soil. The roots can also get underneath your home, causing additional pressure and weakening of the foundations.

Other typical causes include softening of the foundation soil due to water because of leaking drains or flooding.

New developments such as new homes or a new building can disrupt your foundations, and properties built on clay soil can create an issue too. If water can penetrate metal parts in a structure (rainwater or a leaking drain, for example), this can cause rust and force the surrounding area to move. Rust is also the cause of some issues with cavity wall ties. A common sign is horizontal cracks in mortar joints.

Preventing Subsidence

If nearby trees are contributing to subsidence, a professional assessment can help determine whether pruning, removal or a root barrier is the best option. Avoid removing or heavily cutting back trees without advice, as this can cause clay soil to swell and lead to further movement around the foundations.

You should also check with your local council before carrying out work to any tree protected by a Tree Preservation Order (TPO) or located in a conservation area.

Another way of preventing subsidence is by being proactive. Check with your neighbours whether they had any underpinning in the past or if there is a history of it locally. Properties built on clay soil are notorious for this and it is more prominent in the South of England.

If you have an older property, you can reinforce the walls that may be a result of old age or shoddy building work by renewing beams and cavity wall ties in a less invasive way than underpinning can be. This is an excellent opportunity to monitor for doors or windows sticking as well as uneven floors. This pre-emptive approach can reduce the chances of subsidence in the future.

Building Regulations for Underpinning

Underpinning your home does not usually need planning permission, but you will need to apply for Building Regulations approval. This can cost upwards of £750, depending on the work involved. Check with your local council before starting if your home is listed or in a protected area, such as a conservation area or national park.

The work must also comply with the Construction (Design and Management) Regulations, which cover health and safety during construction. Your structural engineer and contractor can help you understand the requirements for your project.

Can I Underpin a House Myself?

Underpinning your house is a substantial job and wouldn't be classed as a DIY job. Everybody wants to cut down on costs, but the amount of work involved is labour intensive, and unless you have the skills and experience, you will need to instruct specialists to complete the job.

Besides, a structural engineer will need to inspect the property beforehand and be able to provide a Certificate of Structural Adequacy that you can forward to your insurance provider. The insurance provider may not accept any work you have carried out, even if you are capable of completing the work.

Additionally, as structural design calculations are required for all underpinning work, you will have to satisfy your local Building Control department as well.

Checklist: Hiring an Underpinning Contractor

As touched upon earlier, an area often overlooked is whether you can get on with the contractors, so when you speak with them, ensure you feel comfortable and able to ask any questions, and happy with their answers. More importantly, there are a few points you need to tick off as you go along:

• Regardless of how appealing a quote is, get at least 2 of them before you commit.
• Get any quotes in writing and get receipts for everything.
• Don't pay the full amount upfront.
• Ask your builder for proof of public liability insurance and check that your structural engineer has professional indemnity insurance.
• Look up testimonials and a portfolio of work to see if they're right for you.
• Check their qualifications and professional memberships. Reputable underpinning contractors are often members of the Association of Specialist Underpinning Contractors (ASUC), whose members can offer a 10-year latent defects insurance policy. Membership of the National Federation of Builders is also a good sign.

FAQs