Basements and the Party Wall etc. Act alongside planning
Planning permission does not let you start digging. The Party Wall etc. Act runs separately, with its own notices, timescales and costs for a basement project.
A basement party wall notice has nothing to do with planning permission. The Party Wall etc. Act 1996 is a civil statute that governs the relationship between you and your neighbour during building work, and it operates whether or not the council has granted permission. You can hold a valid planning permission and still be unable to lawfully start digging, because the party wall procedure has not been completed.
For a basement under a terraced or semi-detached house, the Act is almost always engaged. Excavation close to a neighbouring building is one of the situations it covers, and most urban plots are close to something.
What the Act covers and what it does not
Three categories of work fall under the Act. Building a new wall at the line of junction between two properties. Work to an existing party wall or party structure, such as underpinning, cutting into it or raising it. And excavation near a neighbouring building.
What the Act does not do is give you permission to build. It does not override planning control, it does not replace Building Regulations approval, and it does not authorise you to enter your neighbour's land except in the limited circumstances the Act allows for carrying out the notifiable work.
It also does not settle whether the work is a good idea. A neighbour who thinks a basement will damage their house cannot stop it through the Act; the surveyors will regulate how it is done rather than whether it happens.
The three metre and six metre notice rules
Two excavation rules matter for basements.
The first applies where you propose to excavate within three metres of a neighbouring building or structure, and to a depth lower than the bottom of their foundations. The second applies where you propose to excavate within six metres of a neighbouring building or structure, and any part of the excavation would fall below a line drawn downwards at 45 degrees from the bottom of their foundations.
A basement under a terraced house almost always triggers the first. A basement in a detached house with a neighbour eight metres away may trigger neither, and a garden basement close to a boundary wall may trigger both.
Measure from the actual foundation depth, which means you need to know it. Where it cannot be established from records, a trial pit on your own side close to the boundary will usually answer it, and the answer belongs in the structural design as well as in the notice.
Notices under the excavation provisions must be served at least one month before the work starts. Notices for work to an existing party structure require two months. Where both apply, work to the longer period.
Timing against the planning application
Serve party wall notices after planning permission is granted, and before you need to be on site.
Serving too early wastes the notice. A notice describes the proposed work, and if the scheme changes during determination the notice no longer matches what you intend to build. Serving too late is the more common mistake, because a dissent triggers the surveyor process and an award can take weeks or months.
A reasonable sequence for a householder basement runs like this.
- Obtain planning permission, including discharge of any pre-start conditions.
- Complete the structural design far enough to describe the excavation accurately.
- Serve the notices, allowing the statutory period plus contingency.
- Deal with consent or dissent, and let the surveyors produce the award.
- Start work in accordance with the award and the planning conditions.
Talk to the neighbours before the notice arrives. A formal document landing unannounced turns a neutral neighbour into a dissenting one, and dissent costs money.
Surveyors, awards and costs
A neighbour receiving a notice can consent, or dissent. If they do not respond within fourteen days, a dispute is deemed to have arisen, which is the same practical outcome as dissent.
Where there is a dispute, each owner appoints a surveyor, or both agree on a single surveyor acting for both. The surveyors produce an award: a document setting out the work permitted, how and when it may be carried out, and the condition of the neighbouring property beforehand.
Costs usually fall on the building owner, meaning you. That covers your surveyor, the neighbour's surveyor and, where appointed, a third surveyor resolving a disagreement between them. On a basement with two adjoining owners the fees are a real budget line rather than a rounding error.
The award is enforceable and can be appealed to the county court within fourteen days of service. Appeals are uncommon and expensive.
Schedules of condition and their value
A schedule of condition records the state of the neighbouring property before work starts, usually as a written description with photographs, room by room and elevation by elevation.
It is the single most useful document in the whole process. Without it, every crack that appears during your excavation is your crack. With it, the argument is about what changed rather than about what was already there.
Push for a thorough one. A schedule covering only the party wall, when the neighbour's rear extension is on shallow foundations two metres from your excavation, leaves the disputed area unrecorded.
The same logic underlies the pre-works condition survey referenced in a Basement Impact Assessment, and where both are required they should be carried out together rather than twice.
Where a planning condition and an award conflict
Conflicts are usually about hours, access and sequence. A planning condition may restrict working hours to protect amenity, while an award may require a particular excavation sequence that is slower than the programme assumed. Neither document defers to the other.
Resolve it before starting. The planning condition can sometimes be varied. The award can be amended by agreement between the surveyors. What cannot happen is quietly working outside the permitted hours because the award requires it, since that is a planning breach the council can act on.
The construction sequence itself is usually controlled through the planning side as well, as set out in a construction management plan for a basement excavation. Vibration limits are another area where two regimes can set different expectations, discussed in piling vibration and neighbouring structures.
Practical sequencing for a householder
Budget for the party wall process at the same time as the planning fees, not later. Expect surveyor costs for both sides, a period of at least a month between notice and start, and longer if a dispute arises.
Get the structural information early. A structural survey of your own property, and knowledge of the neighbour's foundation depth, feed both the basement design and the notice.
And keep the tone civil throughout. The Act works best where the neighbours are talking, and it is an expensive and slow machine where they are not.
Enter your postcode on PlanScope to see which planning reports a basement project is likely to need.
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.
Frequently asked questions
When does a basement trigger a party wall notice?
Where you excavate within three metres of a neighbouring building or structure and go deeper than the bottom of their foundations, or within six metres where any part of the excavation falls below a 45 degree line drawn down from the bottom of their foundations. A basement under a terraced house almost always triggers the first.
How long before work must a notice be served?
At least one month for excavation notices and two months for work to an existing party structure. Where both apply, work to the longer period. Add contingency, because a dissent starts the surveyor process and producing an award can take several weeks beyond the statutory notice period.
What happens if my neighbour does not reply?
If they do not respond within fourteen days, a dispute is deemed to have arisen. That has the same practical effect as a dissent: surveyors are appointed and an award is produced. Silence does not mean consent, so build the surveyor process into the programme whenever a notice is served.
Who pays for the party wall surveyors?
Usually the building owner carrying out the work. That covers your own surveyor, the adjoining owner's surveyor and any third surveyor appointed to resolve a disagreement between them. On a basement with two adjoining owners the fees are a meaningful budget line rather than an incidental cost.
Does a party wall award override a planning condition?
No, and neither defers to the other. Where an award requires a sequence that conflicts with conditioned working hours, resolve it before starting: the condition can sometimes be varied and the award can be amended by agreement between the surveyors. Working outside permitted hours remains a planning breach.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.