Neighbour started extension without a Party wall agreement

shaun_from_Africa

TELLIT01 said:

The builder is simply trying to avoid the cost and time involved in doing things properly.  My inclination would be to put an form of words together whereby he accepts full responsibility for any associated problems with your property.

Personally, I would get two separate agreements about any future damage or problems and get one signed by the builder and one by your neighbour, making sure that the documents state that each party (neighbour and builder) is willing to be held jointly and separately liable and if/when they sign it, get it witnessed and signed.
IMO, this is the sort of thing that needs proper legal advice to make sure that the contracts are correctly worded and binding.

It's okay getting the builder alone to sign but what happens if there are future problems and they have gone out of business or have no money to sort out any repairs and if your neighbour knows that they could be held to account, they may well take a bit more interest in what goes on.