What is a party wall agreement and do I need one?

A party wall agreement is a legal document required under the Party Wall etc. Act 1996 when you carry out certain types of building work near a shared boundary with your neighbour. The three main triggers are: building on or along the boundary line, cutting into a party wall (for example to insert a steel beam), or excavating within three to six metres of a neighbouring building below its foundation level. You must serve a written notice on your neighbour at least two months before work starts. If they consent in writing, you can proceed without a surveyor.

If your neighbour does not consent or does not respond within fourteen days, both parties need to appoint a party wall surveyor. You can agree on a single surveyor to act for both sides, which is cheaper, or each appoint your own. The surveyor prepares a party wall award that records the condition of the neighbour's property before work starts and sets out what work is permitted and how it should be done. The cost for a single surveyor is typically £800 to £1,500, but if each side appoints their own, you pay for both — usually £1,500 to £3,000 total.

I always advise clients to speak to their neighbours early, ideally before formal notice is served. A friendly conversation explaining what you plan to build and when goes a long way. Most neighbours consent in writing once they understand the project, which saves the surveyor costs entirely. If you skip the party wall process altogether and your neighbour later claims damage, you have no legal protection. The schedule of condition recorded in the award is your evidence that any cracks or issues existed before your work began. It is not worth cutting corners on this.