I have boxed lead guttering on a pitched roof of an out building, which has been giving problems ever since it was installed by my builder. It is a long run of 21 metres,and is leaking at various sections.I have been told by another builder that it should all be replaced with a new one using type 4 lead. Please advise what disance I should have between joins for thermal expansion. I would be most grateful if anyone can help 
