Basement Excavations and Section 6 Notices Explained

A section 6 party wall notice is the notice a building owner must serve before excavating near a neighbouring building, and it catches almost every basement project in England and Wales. Section 6 of the Party Wall etc. Act 1996 applies where you dig within 3 metres of a neighbour's building to a depth below the bottom of their foundations, or within 6 metres where the excavation would cut a line drawn at 45 degrees down from the base of those foundations. A basement under a terraced or semi-detached house will almost always meet the first test. This guide explains who must be notified, what the notice must contain, how the one-month period and 14-day response work, and what a basement award adds to the standard party wall notice process.

When does section 6 apply to a basement excavation?

The Act sets two distance tests, and the building owner only needs to meet one of them for a notice to be required. The 3-metre test applies where any part of the excavation is within 3 metres, measured horizontally, of an adjoining owner's building or structure and will go deeper than the bottom of its foundations. Because most older houses sit on shallow footings, a new basement floor will go deeper than every foundation on the street.

The 6-metre test applies where any part of the excavation is within 6 metres of a neighbouring building and would meet a plane drawn downwards at 45 degrees from the bottom of the neighbour's foundations, starting at the external face of their wall. In practice this bites on deeper basements and piled foundations, and it can bring in a detached house that does not touch yours.

"Adjoining owner" under section 20 covers a freeholder and any leaseholder with a term of more than a year, each of whom needs their own notice. And a "building or structure" includes garden walls, outbuildings and garages, so a boundary wall close to the excavation can trigger the notice even where the house is set further back.

What a section 6 notice must contain

Section 6(5) requires the notice to be served at least one month before the excavation begins, and section 6(6) requires it to be accompanied by plans and sections showing the site and depth of the excavation and, where a building is to be erected, its position. A section 6 notice without drawings is defective and the clock does not start.

The notice must also state whether the building owner proposes to underpin or otherwise strengthen the foundations of the adjoining building. Under section 6(3) the building owner may do so at their own expense, and must do so if the adjoining owner requires it, so far as is necessary to safeguard those foundations. For a basement this is rarely a formality: underpinning the neighbour's wall is often part of the structural design.

Most basements also involve underpinning, cutting into or building against the party wall itself, which falls under section 2 with a two-month notice period, and a new wall on the line of junction brings in section 1. Your surveyor will usually serve the section 1, 2 and 6 notices together and run them to the longest period so that one award covers the whole project.

Consent, dissent and the 14-day clock

Under section 6(7), if the adjoining owner does not serve written consent within 14 days, a dispute is deemed to have arisen and section 10 applies. Each owner appoints a surveyor, or both agree a single agreed surveyor, and the surveyors settle matters by a party wall award. Silence is dissent: a neighbour who does not reply has not blocked the work, they have started the award process. Our guide to whether a neighbour can refuse a party wall agreement explains why the Act gives no veto.

A section 6 notice lapses if the work does not begin within twelve months of service, so serving notices before planning and the structural design are settled can mean serving them twice.

What a basement party wall award usually covers

An award for a loft or rear extension is often short. A basement award is not, because the risk to the neighbour is greater and the work lasts longer. It typically deals with:

• A schedule of condition of the neighbouring property, inside and out, prepared before excavation starts and covering the flank wall, both elevations, garden walls and any finishes likely to show movement. Without it, every later crack becomes an argument. Our guide to how a schedule of condition is made explains what a thorough one looks like; the panel's surveyors prepare them through the schedule of condition service.
• The structural design and method statement, including the underpinning sequence and temporary works. The adjoining owner's surveyor can require an independent engineer to check the design, and the building owner normally pays that fee as part of the section 10 costs.
• Movement monitoring of the neighbour's building, with trigger levels at which work stops and the engineer is consulted.
• Working hours, dust and noise controls, and the building owner's right of access under section 8.
• Security for expenses. Section 12 lets an adjoining owner ask for security before work begins, so that money is available to make their property safe if the excavation is abandoned part-way through. It is requested far more often on basements than on any other work.
• Compensation under section 7(2) for any loss or damage caused by the work, with the schedule of condition as the benchmark.

Where a neighbour already has a basement, the award also deals with concrete spilled across the line of junction and with enclosure payments; the earlier post on encroaching on basement extensions covers that side.

How long it takes and what it costs

As a general picture of the market, a straightforward loft or extension can go from notice to award in six to twelve weeks. Basements usually take three months or more: there are several adjoining owners, the design has to be finalised and checked, and the schedule of condition is more extensive. Our guide to the party wall award timeline sets out each stage, and the loft equivalent of this guide, loft conversions and the Party Wall Act, shows how much simpler work above ground is.

On fees, the building owner pays the reasonable costs of both surveyors. Agreed-surveyor awards for simple work start at around £1,000; two-surveyor awards start from around £1,500 per adjoining owner, with hourly rates typically £100 to £250. A basement with several adjoining owners, a checking engineer and a full schedule of condition will cost considerably more than a single-neighbour loft, so budget the fees at the design stage; the guide to who pays for the party wall surveyor covers the section 10 rules.

Planning permission and Building Regulations approval run alongside the Act and are not replaced by it, and the award does not transfer liability: section 6(10) makes clear that nothing in the section relieves the building owner of responsibility for damage caused by the work.

Arranging a party wall surveyor for a basement

Survey Merchant provides RICS party wall surveyors through its party wall services, drawn from a national panel of 2,400+ chartered surveyors who serve section 1, 2 and 6 notices, act as agreed surveyor or for either owner, prepare schedules of condition and draft basement awards with the monitoring and security clauses the work needs. Where the design calls for it, the panel can pair the surveyor with a structural engineer to check the underpinning sequence. Coverage includes London, Manchester and other major cities, and fixed fees are quoted up front. Tell the team how many neighbours adjoin the site and how deep the excavation goes and the right surveyor will be matched to the job, or contact Survey Merchant to talk it through.