Opinions please. I bought a mid terrace Victorian house with butterfly roof. Got planning permission for a mansard extension requiring tin hat and overhanging scaffold on both sides and build up of chimney stacks and party wall on both sides of the roof. Both neighbours wanted me to pay for party wall surveyors to act for them. No problem. Party wall award for one neighbour states amongst the conditions that no one should walk on his butterfly slated roof. I send both party wall awards to builder before contract and say let me know if any of the conditions will add costs. He adds the cost of scaffold alarm, hoarding etc but nothing costs related to avoiding walking on neighbours roof. His guys walk on neighbours roof when putting protection down and when cleaning up mess made from party wall build up. Also scaffolder drops a pole and puts a hole through neighbour's box gutter causing leak, internal damage etc. Neighbour calls the roofer who did his roof 5 years ago to come round. Roofer says the 10 year insurance backed warranty he gave neighbour is now invalid. Hole in box gutter is repaired and internal redecorations done and builder and scaffolder cover the costs. But after much back and forth the PW surveyors say I am liable for any unseen damage caused by slates popping open for next 5 years and any damage that could be proven to be caused by builders walking on slates "in perpetuity." Builder tells me that it was impossible to do the job without having some people walk on neighbours roof. "My men can't fly" He says the fault is the Party Wall Surveyors for putting something in PW award that was unachievable. I say to him why didn't you flag it was unachievable. He says not his responsibility. Who is it at fault: Me, Party Wall surveyors, Builder?