Party wall and underpinning alongside a basement plan

Planning permission and the Party Wall etc. Act 1996 are two independent regimes, and a basement under an existing house almost always engages both. Permission deals with whether the development is acceptable in planning terms. The 1996 Act deals with your right to carry out work to a shared structure or to excavate near a neighbour's building, and it gives the adjoining owner rights you cannot override by obtaining permission.

Homeowners discover this in the wrong order with some regularity. The council grants permission, the contractor arrives, and a neighbour's solicitor writes.

Two regimes running at once

The council has no role under the 1996 Act and will not ask whether notices have been served. Equally, an adjoining owner cannot use the Act to stop a scheme the council has approved; the Act regulates how the work is done, not whether it happens.

What the Act gives the adjoining owner is a say in the method, a right to have a surveyor appointed at the building owner's cost in most cases, a schedule of condition recording the state of their property before work starts, and a mechanism for compensation if damage occurs.

So the two processes should run in parallel rather than in sequence, with the structural approach settled early enough that it does not have to change after permission.

Which notices a basement triggers

Three sections generate notices, and a basement commonly engages two or three of them.

Section 1 applies where you build on the line of junction between two properties where no wall currently exists. Less common for a basement under an existing house, more common for a new side infill.

Section 2 applies to work to an existing party wall or party structure, including underpinning it, cutting into it, raising it, or inserting a damp proof course. Underpinning a party wall to form a basement is squarely within section 2, and the notice period is two months before the work starts.

Section 6 applies to excavation. Section 6(1) covers excavation within 3m of an adjoining owner's building or structure where the excavation goes deeper than the neighbour's foundations. Section 6(2) covers excavation within 6m where the excavation cuts a line drawn downwards at 45 degrees from the bottom of the neighbour's foundations. A basement at 3m depth will usually catch the 6m line. Both section 6 notices require one month's notice.

A basement under a terraced or semi-detached house therefore typically needs a section 2 notice to each party wall owner and a section 6 notice to anyone else within the distances. Serve all of them.

Appointing surveyors and the award

The adjoining owner has 14 days to respond to a notice. Consent in writing ends the matter for that neighbour. Silence or an express dissent creates a dispute under the Act, and surveyors must then be appointed.

The owners can agree a single agreed surveyor, which is quicker and cheaper, or each appoint their own, in which case the two select a third surveyor to resolve any disagreement between them. The surveyors are not advocates for the owner who appointed them; their statutory duty is to resolve the dispute impartially.

The output is a party wall award, a document that records the agreed working method, the hours of work, access arrangements, the schedule of condition, the security for expenses if any, and who pays the surveyors' fees. It is binding and appealable to the county court within 14 days.

On a basement the award will usually specify the underpinning sequence, the maximum length of each bay, the curing time between bays, monitoring requirements and trigger levels for movement. Those provisions have cost and programme consequences, which is why the structural engineer should see the draft award before it is agreed.

Schedules of condition before work starts

The schedule of condition is a photographic and written record of the adjoining property before work begins, usually covering the rooms closest to the works, the party wall faces, the external elevations and any existing cracking.

Its purpose is evidential. Without one, any pre-existing crack becomes an argument, and the building owner usually loses that argument because they cannot prove the crack was there first.

Get the schedule done properly and in detail. Insist on access to the rooms that matter rather than accepting an external-only inspection, and keep the dated original. On a basement, monitoring points installed at the same time give you a movement record alongside the condition record.

Where the adjoining property is itself listed or in a conservation area, the schedule should be more detailed still, and any damage to historic fabric carries consequences beyond the civil claim.

Why permission does not authorise excavation

This point is worth stating plainly because it causes real disputes. A planning permission is a public law consent. It does not confer any private right over anyone else's land or structure, and it does not override the 1996 Act, restrictive covenants, rights of support, rights of light or the law of nuisance.

Excavating next to a neighbour's foundations without serving notice is a breach of the Act. The adjoining owner can seek an injunction, and courts have granted them where notice was not served. An injunction partway through an underpinning sequence is the most expensive outcome available in this area of construction.

The same logic applies to a crane jib oversailing the neighbour's airspace, which is covered in the piece on crane oversailing third party land, and to temporary works that bear on their land.

Costs and how they are usually allocated

The building owner, meaning the person doing the work, normally pays the reasonable costs of the surveyors and of any works necessary because of their project. That includes the adjoining owner's surveyor's fees where a dispute has arisen.

The usual costs on a basement are the notices and service, one or two surveyors' fees through to the award, the schedule of condition, monitoring during the works, and a further inspection at completion. Where the adjoining owner wants additional protective works beyond what the Act requires, they can be asked to contribute.

Security for expenses is available under section 12. An adjoining owner can request that the building owner deposit a sum before work starts, which matters where the building owner is a company with no assets. Expect it to be raised on a basement.

Budget for the party wall process as a separate line item alongside the planning costs. It is not included in an architect's fee and it is not optional.

Sequencing notices against the application

1. Establish the structural approach at concept stage, so the underpinning method and depth are known.
2. Commission a Basement Impact Assessment and a Geotechnical Assessment early, since the ground conditions drive both the planning case and the party wall method.
3. Talk to the neighbours before the application is validated, not after the notices land.
4. Submit the planning application.
5. Serve party wall notices once the design is settled, allowing two months for section 2 and one month for section 6, timed so the award is in place before the planned start.
6. Agree the award, install monitoring, complete the schedule of condition.
7. Start work, with the award's method statement as the controlling document.

Serving notices before planning permission is granted is allowed and sometimes sensible, but a design change afterwards means re-serving. Settling the planning position first usually costs less. Where structural condition is in question, a Structural Survey of the host building supports both processes. Where the works sit close to retained trees or a boundary, the piece on temporary works on tight sites covers the sequencing.

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This is general guidance rather than 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.