On a terraced or semi-detached site, a good share of the work that matters structurally happens at a wall you share with somebody else. The Party Wall etc. Act sets out how that is handled, and in practice it sets out who controls part of your programme. We see it on most of the schemes we price as quantity surveyors in London.
Owners usually budget the surveyor's fee and stop there. The fee is rarely the expensive part.
What triggers the process
Work to a shared wall, excavation within defined distances of a neighbouring structure and work to a boundary can all bring the Act into play. Whether your particular scheme engages it is a question for a party wall surveyor on the facts, not something to assume from a drawing.
The practical point for a budget is that it is triggered by the work, not by the planning route. A scheme that needs no planning permission can still need notices and an award.
Notices, dissent and the award
Notices go to the adjoining owners with a statutory period for them to respond. They may consent, in which case the process is short, or dissent, in which case surveyors are appointed and an award is produced. More than one neighbour means more than one sequence running at once.
The award sets out what may be done, how, when and with what protection, together with a record of the neighbour's property before work starts. The relevant work does not begin until it is in place.
The cost is mostly not the fee
Four things usually cost more than the surveyor's invoice. Condition surveys of the adjoining properties. Protective or temporary works the award requires. Monitoring during the works where movement is a concern. And the period during which nothing is being built because the award has not landed.
On a funded scheme the last of those is the expensive one, because finance keeps running while the programme does not. That interaction is covered in cost to complete.
Where it lands in the programme
The statutory periods are fixed and the appointment of a second surveyor takes as long as it takes. A programme that shows the award arriving exactly when the contractor wants to start excavating is a programme with no margin in the one place you do not control.
The sensible approach is to start the process as soon as the design is firm enough to describe the work, rather than when the contractor is mobilising.
Who appoints whom, and who pays
The building owner carrying out the work appoints a surveyor. The adjoining owner may agree to use the same one, which is quicker, or appoint their own, which is slower and costs more. Where two surveyors are appointed they select a third to resolve anything they cannot agree.
In the usual case the building owner carries the reasonable fees of the process, including the adjoining owner's surveyor. That is the part owners are most often surprised by, because it means the cost is not fully within your control.
None of this is a reason to avoid the process. An award is the document that lets you build next to somebody else's property with the position agreed in advance, and the alternative is an injunction risk you cannot price at all.
Condition surveys protect you, not only the neighbour
A condition survey records the state of the adjoining property before work begins, with photographs. Owners sometimes read it as a formality that exposes them to claims. It does the opposite.
Without a record, any crack discovered afterwards is arguably yours. With one, the question becomes whether the crack was there before, and that question has an answer. The survey is the cheapest insurance on the job.
What it means for the contract
If the building contract assumes access to the party wall from a date, and the award arrives later, the contractor has a claim. If the award requires a method the contractor did not price, that is a variation. Both are avoidable by sequencing the award before the contract rather than alongside it.
Where the contract has to be signed first, the right answer is to describe the party wall position honestly in the tender documents, so it is priced rather than claimed. That is part of tendering and procurement.
What to do before you commit
Establish early whether the Act is engaged, how many adjoining owners are involved and what the likely scope of the award will be. Put the surveyor fees, the condition surveys, any monitoring and a realistic period into the appraisal, not into the contingency.
Figures quoted in conversation about party wall costs are examples rather than prices. The number of neighbours and the nature of the work decide yours.
It also pays to think about the relationship rather than only the procedure. The adjoining owner is going to live next to your building site for months, and an owner who feels informed is less likely to dispute, delay or complain to the council.
That is not a soft point. Every week of delay on a funded scheme costs interest, and the cheapest way to avoid several of those weeks is usually a conversation before the first notice lands rather than a letter after it.
Finally, keep the party wall process and the building contract in the same head. The award constrains the method, the hours and sometimes the sequence, and all three of those are things the contractor priced. If the award arrives after the contract is signed and changes any of them, you have bought a variation.
Where the award is already in place when tenders go out, attach it. A contractor who has read the award prices the job in front of them, which is the only basis on which a tender comparison means anything.
Scheme with a shared wall?
Tell us the address and what the structural work involves. We will set out where the party wall process is likely to sit in your cost plan and your programme.