Underpinning, party walls and the neighbour's structure

A party wall notice is required before underpinning a party wall or excavating close to a neighbour's foundations, and it has nothing to do with planning permission. The Party Wall etc. Act 1996 is a separate statutory regime with its own notices, its own periods and its own dispute procedure, and a council will not enforce it or advise on it. Basement and underpinning work on a terraced or semi-detached house almost always engages the Act, often under two sections at once, and the notice periods are long enough to derail a construction programme that ignores them.

Serve early. The Act is one of the few parts of a build where time cannot be bought back.

Where the Act applies to basement and underpinning work

Three situations arise on a typical house project.

Work directly to a party structure, such as cutting into a party wall, underpinning it, raising it or rebuilding it, falls under the party structure provisions. Underpinning a party wall to form a basement is the clearest example.

Excavation near a neighbour's building falls under the adjacent excavation provisions. There are two limbs: excavation within three metres of a neighbouring structure that goes deeper than the bottom of its foundations, and excavation within six metres of a neighbouring structure where the excavation cuts a line drawn downwards at 45 degrees from the bottom of those foundations. The six metre limb catches deeper basements that people assume are far enough away.

Building a new wall at or astride the boundary falls under the line of junction provisions, which matter where a basement wall is being constructed on the line itself.

A single basement project frequently triggers all three. Each has its own notice.

The notice types and their periods

The periods are set by the Act and cannot be shortened by agreement to any useful degree.

An adjacent excavation notice has to state whether you propose to underpin or otherwise strengthen the neighbour's foundations, and it must be accompanied by plans and sections showing the site and the depth of the proposed excavation. A notice without those documents is defective, and a defective notice does not start the clock.

The adjoining owner then has 14 days to respond. Written consent ends the matter for that notice. Dissent, or simply no reply within 14 days, puts the parties into dispute for the purposes of the Act, and surveyors are appointed. Silence is the most common response, and it is not a problem, merely a step.

Schedules of condition

A schedule of condition is a dated record, usually photographic with written notes, of the state of the adjoining property before work starts. Cracks, movement, finishes and any existing defects are recorded in detail.

It protects both sides and it is the document that decides most later arguments. Without one, a neighbour who notices a crack in month six has no way to show it was not there before, and the building owner has no way to show that it was. With one, the question takes ten minutes.

Get access for the schedule early and treat it as a courtesy visit rather than a legal formality. A neighbour who has met the surveyor and understands the process is far less likely to dissent aggressively or to make a claim later.

Awards and surveyor appointments

Once the parties are in dispute, either a single agreed surveyor acts for both, or each owner appoints their own and those two select a third surveyor who resolves any deadlock.

An agreed surveyor costs less and moves faster, and works well where the neighbour is comfortable. Two surveyors is the norm where the work is substantial or relations are strained, and it is the route most neighbours choose once they take advice.

The output is a party wall award: a document setting out the works permitted, the method and sequence, hours of working, access arrangements, the schedule of condition and the allocation of costs. The building owner normally pays the surveyors' fees on both sides, which is the point at which the cost becomes visible.

Awards take time. Appointments, an inspection, an exchange of drafts and service of the award can run to several weeks even when everyone cooperates, and an award covering a basement with a detailed structural methodology takes longer. Either owner can appeal an award to the county court within 14 days of service.

How this sits alongside the planning application

Planning permission and a party wall award answer different questions. Permission deals with the public interest in the appearance and effects of the development. The award deals with the private rights of the two owners.

Neither depends on the other. You can obtain an award before permission is granted, though it wastes money if the scheme changes. You can obtain permission with no award in place, and that permission gives you no right to touch your neighbour's structure.

The practical sequence is to secure permission, settle the structural design at a level the surveyors can work with, then serve notices once the drawings are stable. Serving notices on a design that is still moving produces an award that no longer matches the works, and a variation requires an addendum award.

Where the project involves a basement, the structural and ground evidence prepared for the planning application does double duty. A Basement Impact Assessment and the ground investigation behind it give the party wall surveyors the information they need about ground conditions, and a Structural Survey of the existing house tells everyone what they are underpinning.

Objections at planning against dissent under the Act

Neighbours regularly object to a planning application on the ground that the works will damage their house. That objection has very little planning weight.

Structural stability, damage to adjoining property and construction methodology are controlled by the Building Regulations and by the Party Wall etc. Act, and officers will generally say so in the report. What is material at planning is the effect of the finished development: its appearance, its effect on amenity, the traffic and disturbance during construction where a construction management plan is needed, and the drainage and ground water consequences.

So the same neighbour has two separate opportunities, and they work differently. A planning objection can be answered by the officer. A dissent under the Act cannot be answered at all: it simply moves the matter to the surveyors, where the question is not whether the work happens but on what terms.

Explaining that distinction to a worried neighbour early, in plain words, defuses more disputes than any amount of correspondence later.

Sequencing notices with the construction programme

Work back from the date the machine arrives.

1. Finalise the structural design and the temporary works principles.
2. Identify every adjoining owner, including freeholders, long leaseholders and, in a converted house, the owners of other flats.
3. Serve the notices, and count two months for any party structure notice.
4. Allow four to eight weeks beyond the response date for appointments, inspection and the award, longer for a basement.
5. Build the schedule of condition visit into that period rather than after it.
6. Keep 14 days clear after service of the award for the appeal period.

The commonest programme failure is discovering a second adjoining owner late. In a terrace, a basement can engage both immediate neighbours and sometimes the property behind, and in a converted house every flat owner with an interest in the structure may be an adjoining owner. Check the title before serving anything.

Starting work without a valid notice exposes you to an injunction, and courts do grant them. That is the practical reason to treat the Act as a programme item rather than paperwork. If you want a view on which reports your own scheme will need alongside it, enter your postcode on PlanScope.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.