Underpinning means extending or strengthening a building's foundations so that they carry its load down to firmer or deeper ground. It is real engineering, and when a foundation genuinely cannot do its job it is the right answer. It is also expensive, disruptive, stays on a property's history for good, and is recommended far more often than it is needed.
We do not carry out underpinning or any other repair, and we take no commission from anyone who does. That is the point of this guide: to set out, from the side that does not sell it, when underpinning is justified and when it is not.
What underpinning is for
Foundations fail to do their job for a short list of reasons: the ground beneath them has lost support, the ground has changed volume, the foundation was too shallow or too small for what it carries, or the load on it has increased. Underpinning addresses the foundation. It does nothing about the cause unless the cause is the foundation itself.
That is why the order of work matters. If a leaking drain has washed fines out from under a footing, or a tree is drying a clay subsoil, underpinning that part of the house while the drain still leaks or the tree still drinks treats the symptom and leaves the cause in place.
Why most movement does not need it
- Historic settlement that stopped long ago is common in older houses and needs no foundation work - the cracks are repaired and the house is left alone
- Movement caused by a leaking drain often stops once the drain is repaired and the ground has recovered
- Seasonal movement on shrinkable clay can often be controlled by managing the vegetation responsible, once the cause is confirmed
- Cracking from thermal movement, wall tie corrosion, lintels or an unsupported alteration has nothing to do with foundations at all
Most subsidence cases, including those handled through buildings insurance, are resolved without underpinning: the cause is found and removed, the building is monitored until it is stable, and the superstructure is repaired.
When underpinning is the right answer
- The cause cannot be removed - for example, a tree that cannot be felled for legal or practical reasons, or ground that will keep moving
- Movement continues after the cause has been dealt with and the ground has had time to recover
- The existing foundation is genuinely inadequate for the ground or the load - very shallow footings on soft or made ground, for instance
- New work changes the loads or the ground - a basement, a lowered cellar floor, or excavation for a new foundation next to an old one
The methods, briefly
Traditional mass concrete underpinning excavates beneath the existing footing in short sections and fills each with concrete, taking the foundation down to firmer ground. Beam and pile, and mini-piled systems, transfer the load to piles where firm ground is too deep to reach economically by digging. Resin injection, marketed as a form of underpinning, injects an expanding resin into the ground beneath a footing; whether it suits a particular case depends on the ground and the cause, and it should be specified on the evidence like any other method.
Partial underpinning - one corner or one wall - needs particular care. A building that is founded at two different depths can move differently either side of the junction, and the junction itself becomes a place where cracking appears. A design that only addresses the visible crack can create the next one.
Approvals and neighbours
Underpinning is building work under the Building Regulations and needs Building Control approval. Where the excavation is close to a neighbour's foundations, the Party Wall etc. Act 1996 is likely to apply, and notice has to be served before work starts. A semi-detached or terraced house almost always involves a neighbour.
What to do if you have been told you need it
- Ask what the cause is, and what evidence establishes it
- Ask whether the movement is still active, and how that has been measured - one visit cannot tell you
- Ask whether the cause has been removed and the building monitored since
- Ask who is recommending it, and whether they are also the firm that would carry it out
If the answers are thin, an independent engineer's diagnosis before you commit is a sensible and common instruction.
How we would investigate it
Inspection of the whole building with the cracking recorded and classified, a look at the drains, vegetation, ground and history, a check of the mining record where it is relevant in Yorkshire, and monitoring where the question is whether movement is still active. The report says what is causing the damage, whether it is still moving, and what - if anything - actually needs doing. Where foundation work is justified, we design and specify it; we do not carry it out.
A structural survey and report is a fixed £580 + VAT, with the report inside 10 working days of the inspection, guaranteed.
Frequently asked questions
Does subsidence always mean underpinning?
No. Most subsidence is dealt with by finding and removing the cause - commonly a leaking drain or vegetation on clay - then monitoring until the building is stable and repairing the damage. Underpinning is for cases where the cause cannot be removed or the foundation itself is inadequate.
Can a house be underpinned in just one corner?
It can, but it needs careful design. A building founded at two different depths can move differently either side of the junction, and that junction becomes a likely place for new cracking.
Do I need Building Control approval for underpinning?
Yes. Underpinning is building work under the Building Regulations. If the excavation is near a neighbour's foundations, the Party Wall etc. Act 1996 is also likely to apply.
Is resin injection as good as traditional underpinning?
It depends on the ground and the cause. Resin injection suits some situations and not others. Like any method, it should be chosen on the evidence for the specific building, ideally by someone who is not selling it.
Will underpinning affect selling my house?
Underpinning is usually something a buyer's conveyancer will ask about, and the paperwork - the design, Building Control completion and any guarantees - matters when you sell. That is one more reason to be sure it is needed before it is done.
Do you carry out underpinning?
No. We investigate, diagnose, and design and specify foundation work where it is justified. We do not carry out repairs and take no commission from anyone who does.