I've just had a lean to roof built on my rear extension (not yet tiled) and the builder has built it at a pitch of 15.5 degrees... I told him I wanted marley modern tiles that have a minimum pitch recommendation of 17.5 degrees. Is this just a guideline or is it imperative that the pitch is no less than 17.5 because he' was telling me it will be ok. Problem is he's done a runner with the money I paid him so I've been left with a potential problem that I'm going to have to rectify myself. So before I rip the roof down I was hoping for some advice if anyone had any. Thanks.