Building Surveying
Apr 30, 2024

Underpinning Guidance

Your mortgage lender will normally have an issue with movement at a property you are looking to purchase, as it will...

Banks

Your mortgage lender will normally have an issue with movement at a property you are looking to purchase, as it will affect the value of their collateral if the issue has not being dealt with. Once underpinned by a qualified company, the lender should no longer have those issues.

Foundations

What needs to be taken into account is the condition of the property. If it has been neglected for so many years, then it is hard to tell whether any cracks and sagging have appeared recently. There may be no surefire way of putting a timeline on structural events, so a surveyor might have to assume that the building, similar to Victorian properties, will never be safe from further subsidence, as these retrofit properties normally have shallow foundations.

Historical v Progressive

The problem with surveying a dilapidated house is that it is impossible to see whether cracks or sunk areas have recently occurred or are progressing. 

With a house in good condition, fresh cracks obviously indicate recent movement. Otherwise, for retrofit properties, cracks may be 1 month old, a year or 50 years. It is very difficult to tell. 

Property surveyors have to pick up on the above and emphasise the risks, as playing them down could backfire on them. So, by nature, property surveys always sound somewhat negative. Surveys generally never state that a wall is in “excellent condition”, but a crack here and a bulge there must be mentioned.

Further Investigation

To obtain a conclusive answer on whether the movement has settled or not, the property should be inspected by an independent structural engineer, who will be establishing the status of subsidence by means of digging inspection holes and applying tell-tale gauges. These gauges will display any widening of cracks over time. This will take months though. This activity is referred to as monitoring

Therefore, the only way to test this is by tell-tale gauges and/or instructing an engineer who can physically inspect the structure and loadbearing capabilities of the soil on which the house stands.

Old v New Build

Every new building has settlement which is caused by compacting of the new soil. 

Older buildings subside only as a result of changes in the soil (or the load at the house, such as extensions). This could be by the raising of the water table, flooding, nearby excavation works, tree roots, large broken sewer pipes buried in the soil and so on.

If the age of the property is fairly old and there are no immediate nearby trees or excavation works, you have a fair chance that the movement has stabilised. 

Taking into account the abovementioned, you must instruct a good subsidence surveyor to obtain a definitive answer. Do not instruct any structural engineer/surveyor, because underpinning is very different from assessing the condition of or calculating the loadbearing abilities of a beam. 

Remedy

For a conclusive and rather quick decision on the degree of ongoing subsidence, we strongly recommend the services of a structural engineer.

The engineer will also be able to give you the exact method of underpinning, if required. There are many and very different ways of underpinning, such as the mass concrete method, the pile driving method or mini pile casting method to name a few.

Insurance

As far as insurance is concerned, we all know too well that an insurance company, at the time of a claim, may attempt to avoid payout if they find that they have been insuring against any pre-existing subsidence. 

With an engineer's report presented to them, an opinion may be given on how recent the defect arose. 

Certification

The completion/sign-off certificate of the repair works will also be a required document for resale in the future.

Lastly, please be advised that underpinning usually requires Building Control to be notified with the relevant certificate also provided.

Builder Quotation

We would not ordinarily recommend asking for initial advice from an underpinning company, for it will be likely that they will persuade you into giving them business, even if it is not necessary. 

Armed with an engineer's report, you can then confidently approach various underpinning companies for the most suitable quotation. Approach 2 -3 specialist underpinning contractors and demand a very detailed quotation explaining exactly which method they are going to use.

Then, ask the structural engineer if he/she would be happy to sign off the works for Building Control, which is extremely important when you instruct a particular contractor. Better still, let the engineer decide which contractor they prefer, particularly as they would need to sign off. 

Method

Underpinning involves excavation below the sunken wall and pumping in large volumes of concrete. Local underpinning should be carried out as a last resort, particularly with older properties, because the part that has not been underpinned will continue to naturally move in tune with ground conditions, setting up stresses with the newly rock solid underpinned length of wall. 

It is therefore prudent to conduct soil inspection (with inspection holes) as to what the exact depths and condition of the existing foundations of the entire house are and what the composition of the soil underneath the foundations is. 

Underpinning Risks

The main problem with local underpinning is that, if there is continuing subsidence, the rest of the property may continue to sink and will therefore cause cracks at the transition to the solid areas, hence why you may consider underpinning all around the house. 

The upfront costs are higher, but it may save on further works and might be considered the safest solution to recommend. Notwithstanding, there is still a chance that movement may have settled, in which case you do not need underpinning. 

Action

You then have two choices: 

  1. Contractor Managed: you instruct a professional contractor with the benefit of having their warranty. Note: before instruction, demand to be sent a copy of their liability insurance policy, should their works fail in the future, which you must check is still active.
  2. Self-managed: alternatively, you get a few reliable workmen together via, say, CheckaTrade, who can do the underpinning based on the specifications that you provide them with. You might miss out on having a warranty, but you may save roughly 50% of build costs. The down side is that you have to check yourself (or instruct an independent approved inspector for Building Regulations) that the workmen are conducting the works as agreed. 

Our recommendation, however, is option 1. This may be more costly from the outset, but it is a safer option with a warranty, which can save you if the underpinning fails. First, instruct a structural engineer as per above.

Costs

The costs vary greatly. 

Victorian properties with shallower foundations move more than most, as they adjust to seasonal changes in ground conditions or new loadings, particularly in regions with clay subsoils.

Regardless of the precise cause of movement, the big question to answer in all cases is whether the movement is historical or “progressive”, and whether it is likely to move more in the future. 

The possible presence of roots, water logged soil, deteriorated foundations, restricted access, etc. will affect the price. As a ballpark figure, considering that underpinning might be required on all sides of a house, as well as crack repair (HeliFix bars embedded in resin mortar) average pricing is often a minimum £20,000. Prices by different contractors vary tremendously. Retail prices could be significantly more. As a guide, see below for a rough price per m, m2 or m3 of items which are standard in today’s market.