Does my extension need a party wall notice?

The Party Wall etc. Act 1996 is the single most common cause of an extension start date moving, and almost always because notice was served too late rather than because a neighbour objected.

It is separate from planning permission and separate from building regulations. You can have both and still be unable to start.

Three notices, three different periods

Most guidance collapses this into “two months”. It is not — it depends which section applies, and getting it right can save you a month.

What you are doing	Section	Notice period
Work to an existing party wall or structure — cutting in for beams, removing a chimney breast, raising or underpinning it	s.2/3	2 months
Building a new wall at or astride the boundary	s.1	1 month
Excavating near a neighbour’s foundations	s.6	1 month

A typical rear extension on a semi or terrace often engages two of these at once — excavation near next door’s foundations, and cutting into the party wall for a steel. When two apply, you are governed by the longer of them, so plan for two months.

The two excavation rules that catch nearly every extension

This is the part people do not realise applies to them, because there is no shared wall involved.

The 3 metre rule. You are excavating within 3 metres of a neighbour’s building or structure, and going deeper than their foundations.

The 6 metre rule. You are excavating within 6 metres of a neighbour’s building, and the work would cut a line drawn downwards at 45 degrees from the bottom of their foundations.

Foundation trenches for an extension are routinely a metre deep or more. On a typical suburban plot, an extension anywhere near a boundary will trip the 3 metre rule against the neighbour’s house, their garage, or their garden wall.

Note it says building or structure, not house. A substantial boundary wall counts.

What happens after you serve

Your neighbour has 14 days to respond in writing.

• They consent. You can proceed, and you can start earlier than the full notice period if they agree to that.
• They dissent. A dispute exists under the Act. Surveyors are appointed and a party wall award is drawn up setting out what may be done, how, and what condition the neighbour’s property is in beforehand.
• They do nothing. This is the one that catches people. Silence is deemed dissent. After 14 days with no response, a dispute has arisen automatically and surveyors must be appointed, exactly as if they had objected.

That last point is worth repeating, because plenty of people serve notice, hear nothing, assume it is fine and start work. It is not fine. A neighbour who never replied is in dispute with you as a matter of law.

Surveyors and awards

If a dispute arises, either a single agreed surveyor acts for both parties, or each appoints their own. You cannot act as your own surveyor, even if you are qualified.

The award records the works, the method, working hours, access arrangements and — critically — a schedule of condition photographing the neighbour’s property before work starts. That schedule is what protects both of you if a crack appears later.

Surveyors’ fees are normally paid by the person doing the work. That is a real cost to budget for, and it is the reason serving early and getting written consent is worth the effort.

Other timings in the Act

• A counter-notice must be served within one month
• Notices expire after one year if work has not started
• Appeal against an award: 14 days to the county court
• Access to a neighbour’s land for the works needs 14 days’ notice

What happens if you skip it

The Act gives you rights you would not otherwise have — to place foundations under a neighbour’s land, to cut into a shared wall, to access their property. Serve no notice and you have none of those rights. Your neighbour can seek an injunction stopping the work, and you have no schedule of condition to rebut a claim that you caused damage.

It also surfaces when you sell. Buyers’ solicitors ask.

How to get this right

Serve as early as you possibly can. The notice period runs in parallel with everything else — planning, building regs, waiting for the builder. Served at the same time as the planning application, two months costs you nothing. Served after the builder is booked, it costs you a start date.

Talk to the neighbour before the letter arrives. A formal notice landing with no warning is how a neighbour who would have consented becomes a neighbour who dissents. Five minutes over the fence explaining what you are doing, when, and for how long converts far more consents than the notice itself.

Get consent in writing. A verbal “yeah, that’s fine” is not consent under the Act.

Serve on the right people. The owner, not the occupier — so if next door is let, it goes to the landlord. If the property is jointly owned, both owners. Where there is more than one, all of them.

What to do next

If you are planning an extension and there is a neighbour within six metres of where you will be digging, assume the Act applies and serve early. It is the cheapest month you will ever buy back.

Tell us about the project and we will tell you which notices your job is likely to need, and when they should go out.