Party wall notices for London extensions, lofts and basements

Which London projects bring the Act into play

The Act deals with three situations, each with its own section and its own notice.

• Section 1: building a new wall on or at the line of junction with a neighbour's land, where there is no wall there already or only a boundary wall.
• Section 2: work to an existing party structure, such as the party wall between two terraced or semi-detached houses, a party fence wall in the garden, or the floor between two flats.
• Section 6: excavating near a neighbour's building to a depth that could affect its foundations.

In practice that captures a large share of London home improvement work. A rear or side return extension on a Victorian terrace may put a new flank wall on the boundary and dig foundations beside next door's. A loft conversion usually cuts into the party wall to seat steel beams and may raise it to form a new gable. A basement conversion almost always involves underpinning a party wall and digging well below the neighbours' footings.

Minor work does not need notice. Guidance on GOV.UK gives examples such as plastering, adding or replacing electrical wiring or sockets, and drilling to put up shelves or cabinets. The line is crossed when work affects the structure itself, its strength or its support.

The Act runs alongside planning and Building Regulations, not instead of them.

Section 1: building a new wall on the boundary

Section 1 applies where you want to build a new wall at the line of junction between your land and your neighbour's. The typical London case is a side return or wraparound extension where the boundary is only a fence or a low garden wall.

You must serve a line of junction notice at least one month before you intend to start that wall. The notice describes the wall you plan to build, and it offers two routes.

1. Astride the boundary. A party wall built half on each side needs your neighbour's written consent. If they do not consent within 14 days of the notice being served, you cannot build astride the line.
2. Wholly on your own land. You can build right up to the line at your own expense without consent. The Act also lets you place projecting footings under your neighbour's land where that is needed for the foundations, subject to paying compensation for any damage caused.

Most homeowners choose to build wholly on their own side, keeping the wall and its maintenance in their own ownership. Footings are the detail that matters. A strip footing is wider than the wall above it, and on London clay the trench-fill for a single storey extension often sits deeper than the neighbour's Victorian footings. That depth means the same wall may also need a section 6 notice.

The notice needs to be served on every adjoining owner. That can include the freeholder and long leaseholders of the neighbouring property, not only the person living there.

Section 2: cutting into or raising a party wall

Section 2 lists the rights a building owner has over an existing party structure. The ones that come up most often in London houses are:

• Cutting into the wall to take the bearing of a beam, which is how steels for a loft conversion or a rear knock-through are usually seated
• Raising the wall, for example to build up a party wall for a hip-to-gable loft or a mansard
• Underpinning or thickening the wall
• Cutting off projecting footings or chimney breasts on your side
• Cutting into the wall to insert a damp proof course or flashing
• Demolishing and rebuilding a party structure that is defective

Any of these needs a party structure notice, served at least two months before the work starts. It must give the building owner's name and address, the nature and particulars of the proposed work and the date it will begin. Where the work involves special foundations, plans and sections should go with it.

A party structure notice lapses if the work has not begun within twelve months of service, and it must be carried through with due diligence. Serve too early and it can expire before the builder arrives. Serve too late and the two month period holds up the start.

Your neighbour can agree in writing to the work starting sooner. They can also serve a counter notice within one month asking for extra work for their own benefit, such as chimney copings, piers or deeper foundations to allow for building of their own later.

Section 6: excavating within 3 or 6 metres

Section 6 is the part of the Act that catches most extensions and every basement. It applies to excavation near a neighbour's building or structure, even when your wall is nowhere near theirs.

• The 3 metre rule. Notice is needed if you excavate within 3 metres of the neighbour's building or structure and any part of the excavation will go deeper than the bottom of their foundations.
• The 6 metre rule. Notice is needed if you excavate within 6 metres and the excavation will cut a line drawn downwards at 45 degrees from the bottom of the neighbour's foundations, towards your site.

The notice must be served at least one month before the excavation starts. It must say whether you propose to underpin or otherwise strengthen or safeguard the neighbour's foundations, and it must come with plans and sections showing the site and depth of the excavation and the position of any building you propose.

London conditions make section 6 very common. Many Victorian terraces stand on shallow brick footings, and clay subsoil pushes new foundations for an extension down to a depth set by the soil and nearby trees. The new trench can easily sit below next door's footings, often within touching distance.

A basement conversion will typically need section 6 notices to the neighbours on both sides, and sometimes to properties behind, together with section 2 notices for underpinning the party walls. The engineer's temporary works design and construction sequence are what the surveyors will want to see before an award can be agreed.

Consent, dissent and the 14 day clock

Once a notice is served, the neighbour has three broad options.

1. Consent in writing. The work can go ahead in line with the notice and the Act, without surveyors being appointed.
2. Dissent. The neighbour disagrees, and a dispute arises that is settled under the Act's surveyor procedure.
3. Silence. For a party structure notice or a section 6 notice, if the neighbour does not give written consent within 14 days of service, they are treated as having dissented and a dispute is deemed to have arisen.

Dissent is not a veto. The Act gives the building owner the right to carry out notifiable work. What a dispute decides is how the work is done: working hours, protection, access, the method for cutting in steels or underpinning, and what happens if damage occurs.

Consent is worth handling carefully too. Even where a neighbour is happy to agree, a photographic schedule of condition of their side of the wall, recorded before work starts and agreed by both households, is sensible. Without one, any crack that appears later becomes an argument about whether it was there before.

Talking to neighbours before the notice lands helps. A letter out of the blue full of section numbers reads as a threat. A conversation about the plans and the programme makes consent far more likely.

Agreed surveyor, two surveyors and the award

When a dispute arises, section 10 sets out how it is resolved. There are two routes.

• An agreed surveyor. Both owners appoint one surveyor who acts impartially for both. This is usually quicker and simpler.
• Two surveyors. Each owner appoints their own surveyor, and the two surveyors select a third surveyor who can be called on if they cannot agree.

If an owner fails to appoint a surveyor within ten days of being asked in writing, the other owner can make the appointment on their behalf. That stops a dispute being stalled by silence.

The surveyors produce a party wall award. It is a legal document that settles the matters in dispute, and it typically includes:

• A schedule of condition of the neighbour's property
• The drawings and method statements the work must follow
• Working hours and any restrictions on noisy work
• Access arrangements and protection of the neighbour's property
• Who pays the surveyors' costs, which in most cases is the building owner

The Act also gives workmen and surveyors a right to enter the neighbour's land where needed for the work, normally on 14 days' notice. Either owner can appeal an award to the county court within 14 days of it being served. Appeals are uncommon, and an award that has not been appealed is binding on both owners.

Starting notifiable work without serving notice is a serious risk: the neighbour can seek a court injunction that stops the job, often with the steels half in.

Building party wall time into the programme

Party wall matters are one of the most common reasons a London build starts late. The fix is to treat notices as part of the design stage rather than something the builder deals with on the first morning.

A sensible order runs like this:

1. Get the design and structural engineer's drawings to the point where the work to the party wall and the foundation depths are known.
2. Speak to the neighbours and explain what is planned.
3. Serve the notices: one month for section 1 and section 6, two months for work to a party structure under section 2.
4. Allow for the surveyor process if there is dissent: appointments, a schedule of condition visit and agreement of the award.
5. Book the start date only once consent is in hand or the award is signed.

Notices can be served before planning permission is granted, so there is no need to wait. Just keep an eye on the twelve month lapse for party structure notices if planning drags on.

Plan for the practical side too. Awards often limit noisy work such as breaking out to set hours, and basements may need monitoring points on the neighbours' walls. Both belong in the builder's programme from day one.