Dormer roof and party wall question

solmend

My neighbour is having a loft extension built. I agreed that as our dormers are so close that his roof be joined to mine to avoid any water infiltration between the two. I didn't think that in order to do this the builder would have to install roofing material that crosses over the party wall line and is partly on my side of the line. I feel that I need the same guarantee of workmanship that my neighbour will get from the builder as if there is a leak due to their work on my roof in years to come I will have no comeback. The builder isn't responding to my calls or emails.
Does anyone know what my rights are in this situation? I'd rather not fall out with my neighbour but I need to act fairly quickly (in the next month) as I think the builder is hoping to carry on with the work and ignore me until their job is finished and they can clear off without having to deal with me.
Any advice would be much appreciated. Thanks.

jonnydeppiwish!

If your houses are adjoined, any loft extension/conversion will need a party wall agreement.

Give that your happy for them to get on with the work, this could be a case of the neighbour writing you a PWA letter (templates available online) saying that if they are any issues, they will pay for the repair work. Cost is nil to both parties.

Second option:
neighbour instructs a PW surveyor, at their cost, to inspect and draw up PWA, which you agree to. Cost ~ £1000. 

solmend

Thanks for this. This would be fine for my current neighbour but if they move on then surely their letter would be meaningless. Don't I need something from the builder? Is there a way to get a guarantee from them?