Basement & Underpinning Party Wall Surveyors

Grey & Associates are party wall surveyors for basement and underpinning schemes in London. We act for owners digging out under their own house and for the neighbours whose foundations the excavation comes close to. Basements have been part of our caseload since the practice opened in Hammersmith in 2008, and they are the part of the Party Wall etc. Act 1996 that leaves the least room for a thin Schedule of Condition.

Key takeaway

Three things separate a basement from every other party wall job. The excavation reaches the neighbour's foundations, which brings section 6 into play — and section 7 puts the building owner under a duty to compensate the neighbour for loss or damage caused by the work, regardless of fault. The works run for months, so the case has to be managed and not merely notified. And the damage, when it comes, is structural: cracked walls, dropped floors, movement in the neighbour's own basement. That is why the Schedule of Condition taken before the first shovel matters more here than anywhere else.

If you have received a basement notice from a neighbour, you are in a stronger position than most people expect. In a dispute the building owner pays the reasonable fees of both sides' surveyors, and the record of your property is taken at their expense.

Why a basement is the hardest party wall job there is

A loft conversion involves the roof. A side-return extension involves the ground and the wall. A basement involves the ground beneath the neighbour's foundations — and everything that sits on top of it. Four things make the difference.

You cannot dig without affecting what is next door. In a London terrace the neighbour's foundations are typically shallow, often no more than a metre or so of brickwork stepping out at the base. A basement that gains usable headroom is far below that. The excavation is therefore working at a level the neighbouring structure has never had to tolerate, and the Act treats that as a distinct category of risk rather than as ordinary building work.
The works run for months, not weeks. A rear extension can be notified, begun and finished inside a single notice period. A basement is a season-long programme of excavation, temporary works, piling or underpinning, damp-proofing and concrete. That duration is what turns a small amount of movement into an argument, because the neighbouring building is exposed to the excavation for the whole of it.
The engineering is part of the notice. Basements are built behind secant or contiguous piles, propped by temporary works, and often require the neighbouring foundations to be underpinned before the dig reaches them. Those operations are themselves notifiable, and the award has to describe them accurately enough that the contractor can work to it and the neighbour knows what to expect.
The claims arrive late. Movement from a deep excavation often shows up in the neighbour's decoration, thresholds and floors after the dig is finished — sometimes after the basement is occupied. By then the only thing that decides the claim is whether a dated, photographic Schedule of Condition was taken beforehand. There is no second chance to take it.

What the Act requires before you excavate

Basement projects around London almost always engage more than one section of the Act at once. The ones that matter:

Section 6 — adjacent excavation. Notice must be served at least one month before excavation begins where the dig is within three metres of a neighbouring structure and goes deeper than that structure's foundations, or within six metres where the excavation would cut a line drawn downwards at 45 degrees from the bottom of the neighbour's foundations. Section 6 also gives the building owner the right to underpin or strengthen the neighbour's foundations where it is necessary to do so. The duty to compensate the neighbour for loss or damage caused by the work sits in section 7, alongside the section 7(1) duty not to cause unnecessary inconvenience.
Section 2 — work on the party wall itself. Cutting a beam or padstone into a party wall, underpinning it, rebuilding or thickening it are all section 2 works. Almost every basement does at least one. The notice period is two months, and where the wall separates two buildings the schedule has to record both sides.
Section 1 — building on the line of junction. Where the scheme puts up a new wall on the boundary line rather than alongside it, section 1 applies and the notice is one month.
Section 8 — the right to inspect. The surveyors are entitled to enter to inspect and record the neighbouring property. That right is exercised on proper notice; it is a statutory right and not a favour to be negotiated.
Sections 10 and 11 — when the neighbour objects. If the adjoining owner dissents, the surveyors are appointed under section 10 and the case is resolved by an award under section 11. The award is what binds the parties and governs how the basement is actually built.

The one-month and two-month periods run in parallel, and the longer of the two governs when the project can start. On a basement programme, a notice served late is the most expensive mistake available — a wasted month at the start is a month at the end.

The Schedule of Condition is the evidence, not the paperwork

On a light structural job a Schedule of Condition is a sensible precaution. On a basement it is the case. We take it before the first shovel, and on a basement scheme it records considerably more than the usually expected list:

Crack mapping across the neighbouring property, photographed with a scale and keyed to a plan, so a crack that widens later can be measured against a known starting width rather than described from memory.
Levels at thresholds, door heads and floor plates, because that is where a neighbour notices settlement first, and it is where a claim is easiest to prove or disprove.
Doors, windows and joinery that already bind or stick — recorded before the dig, so that pre-existing faults cannot be attributed to it.
The neighbour's own basement, if they have one: tanking, sump, pump, drainage and the condition of their retaining structure. A neighbouring basement is the most common source of a water-ingress claim after an adjacent excavation.
The outside: paving, garden walls, boundary walls, steps, drains and gullies, all of which are disturbed by a basement site whether or not the award covers them.

Where the basement affects two neighbours — the usual situation in a terrace — both properties are recorded. On a deep scheme we also agree a monitoring position, so that any movement is measured on an agreed basis rather than detected by a neighbour who notices a new crack one morning.

What we do on a basement case

Read the drawings before setting the programme. The fee is fixed and published, but how far the Schedule of Condition has to reach, whether temporary works are needed and whether the award carries a monitoring regime all follow from the design. We read the structural drawings and the method statement before the notice goes out.
Establish every interest. Where the neighbouring building is a converted house or a mansion block, the adjoining owners may include the freeholder, a management company and one or more leaseholders. Basements in London are served on titles, not on occupiers.
Serve in time for the programme. We work backwards from the excavation date, and we tell you at the outset which of the one-month and two-month periods applies.
Put the operating rules in the award. Working hours, access arrangements, protection of the neighbouring property, temporary works, making good and the position on monitoring belong in the award. An award that only describes the work leaves the contractor and the neighbour to argue about everything else on site.
Stay on it. A basement runs long enough that the award needs administering. We deal with the neighbour's questions, the contractor's variations and any claim that arises during the works.

For the statutory background, the Party Wall Act explained sets out how the sections fit together. Where a deep dig raises questions about the condition of the structure itself, telling rising, penetrating and condensation damp apart explains what a survey can and cannot attribute to a neighbour's work.

Fees for basement and underpinning schemes

Basement and underpinning schemes are priced as a fixed package, per adjoining property. The figures are published rather than quoted by the hour:

Serving notice — £250 + VAT per adjoining property.
Schedule of Condition — £1,100 + VAT per adjoining property. The dated photographic record of the neighbouring property, taken before the excavation starts.
Award — £1,050 + VAT per adjoining property, acting for the Building Owner.
Total — £2,400 + VAT per adjoining property, covering the three stages above.

All prices exclude VAT, charged at 20%: the £2,400 package carries £480 of VAT, so £2,880 including VAT. Each of the three figures is per adjoining property, so a scheme with two neighbours is priced at £2,400 + VAT for each of them.

Basement work costs more than standard notice work, and deliberately so. A two-storey basement in Kensington is not a loft conversion and is not priced as one. The scheduling runs through more of the neighbouring property, the engineering input is heavier, the works last far longer and the exposure to a claim is greater. Where a scheme goes beyond a single adjoining property — several interests, a mansion block freeholder and its leaseholders, or works that need access across a third property — we quote in writing before anything is agreed or any notice is served. Dispute and non-compliance work is charged separately at £185 per hour plus VAT.

Nothing in this section is an offer. The fixed figures apply to straightforward notice, Schedule of Condition and award work; anything that falls outside the scope is quoted in writing first. The full breakdown, including the statutory position on who pays for both sides' surveyors, is on our London party wall surveyor page.

Basement party wall questions

Do I need a party wall award to dig a basement under my own house?

In most London cases, yes. Section 6 of the Party Wall etc. Act 1996 requires you to give notice before excavating within three metres of a neighbouring structure and deeper than that structure's foundations, or within six metres where the excavation would cut a line drawn downwards at 45 degrees from the bottom of the neighbour's foundations. Almost every basement that gains headroom is deep enough to meet one of those tests. If the dig also cuts into, underpins or alters the shared wall, section 2 applies as well and the notice period is two months rather than one.

How does the party wall process change as a basement goes deeper?

The legal tests do not change with depth — section 6 applies as soon as the excavation passes below the level of the neighbouring foundations. What changes is the engineering and the evidential burden. A two-storey basement usually means temporary works to hold up the neighbouring structure, a wider Schedule of Condition covering more of the neighbouring property, and often a monitoring regime. The deeper the dig, the further the six-metre and 45-degree tests reach, which is why the basement package is priced above the standard notice work rather than by the hour.

My neighbour already has a basement. What does that mean for my own basement or extension?

Their basement changes the datum. If their basement runs under the shared wall or close to it, your excavation is likely to be within three metres of their structure and deeper than their foundations, which puts you squarely inside section 6. Their tanking, sump, pump and drainage also need to be recorded in the Schedule of Condition before you start, because water ingress and movement in an existing basement are the two claims that follow a neighbouring dig most often, and the only defence is a dated record showing the condition beforehand.

How much does a party wall surveyor cost for a basement project?

Basement and underpinning work is priced as a fixed package per adjoining property: £250 to serve notice, £1,100 for the Schedule of Condition and £1,050 for the award acting for the Building Owner — £2,400 in total. All figures exclude VAT at 20%, which adds £480 on a one-neighbour scheme. Where a scheme goes beyond a single adjoining property we quote in writing before any notice is served. Dispute and non-compliance work is charged at £185 per hour plus VAT. Nothing on this page is an offer.

Talk to a basement party wall surveyor

Grey & Associates have worked on basement and structural schemes under the Party Wall etc. Act 1996 since 2008, acting for owners digging out and for the neighbours next door. The first conversation is free.

Schedules of Condition written to survive a structural damage claim two years later.
Experience of temporary works, underpinning, piling and monitoring regimes.
Awards that set out access, hours, protection and making good — not just the work.
Fixed fees for the standard notice work, agreed before anything starts.

Call 020 8150 3762 or email info@greyandassociates.co.uk.

Where our basement work is concentrated: Kensington, Chelsea, Knightsbridge, Hammersmith, Chiswick and Ealing, with the wider picture on our West London page.

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