Party wall agreement

[Lanclain]

We are planning an extension which will likely to impact a lean-to structure attached to our neighbours house.
They are not at all bothered that our building work could cause the collapse of this structure and are quite keen to use the new wall of our extension for their own structure at a later date.
Our builder will do all he can to avoid damaging the wall of the lean-to but obviously he can't guarantee not to cause damage.
We wanted to avoid using a surveyor and were planing to adapt a generic party wall agreement which would need to say that we would not be liable for any damage to the wall of the lean-to.
Is there anybody out there who can confirm this is an ok course of action considering the amenability of our neighbours or should we get a surveyor involved?

But surely you would be liable? I would advise a surveyor having recently had our fingers burnt by not having one.

"keen to use the new wall of our extension for their own structure at a later date. " They can only do that if you build the wall across the boundary as a party wall. You'd have to serve notice to do that. When they want to enclose the wall on their side they would have to pay for half the wall costs.
"Our builder will do all he can to avoid damaging the wall of the lean-to but obviously he can't guarantee not to cause damage.
We wanted to avoid using a surveyor and were planing to adapt a generic party wall agreement which would need to say that we would not be liable for any damage to the wall of the lean-to. "
There's notice and an award but no such thing as an agreement.
The legal position is if you damage something you pay for it. The idea of the party wall act is to allow you to get an independent survey of the structures on their side to have an award drawn up to suggest how the work should be done to avoid damage and what condition the structures are in to ensure you don't damage a wall that's on its last legs and end up paying for a brand new wall.
There's no way of absolving responsibility for damage, but you don't want to be on the hook unnecessarily.
If you suspect your neighbour will try to claim more than his need them a surveyor would be worth the money.

Thank you both - that's very helpful

Legally all that would be required is a waiver of some sort, a contract that states that your neighbour is happy for you to damage his property albeit accidentally!!

Sounds like trouble brewing. Get a party wall surveyor get it documented properly. I'm sure it would be a whole lot cheaper then ending up in court!