Case Summary


County Court
 Not Binding
Current Legislation:
Party Wall etc. Act 1996, s. 20
Historic Legislation:
 London Building Acts (Amendment) Act 1939

The School wanted to undertake works to a party wall as well as adjacent excavation works to their property at 21 – 23 Graham Terrace, London. They served notice on Wassef, who occupied No 25 on a Rent Act protected tenancy.

An award was issued authorising the works. After the works a third surveyor published an award dealing with remedial works for damage to No. 25.

Wassef’s surveyor also issue a further ex parte award. The the school appealed that award on, among other grounds, that having reconsidered the position, Wassef was not in fact an “adjoining owner” within the meaning of the 1939 Act.

Wassef accepted that he was not an owner within the meaning of the 1939 Act, but relied on the doctrine of “estoppel by convention”; put simply, where parties have proceeded under a shared mistake, and had relied on that mistake, they are bound by it and cannot “undo” their previous actions.


The Court found that Wassef was not an “owner” within the meaning of the Act, but by reason of the shared mistake in all parties thinking that he was, and their reliance that on it, it would be unconscionable to now hold that the whole process was invalid. Estoppel by convention therefore applied, and the School was prevented from arguing that the awards were invalid on this point.

However, the Court held the ex-parte award to be invalid for other reasons.


It should be borne in mind that the estoppel by convention will applyonly to previous acts; once the parties become aware of their mistake the estoppel no longer applies.