Am building an extension with a Lean to roof pitch angle of 16 degrees, Architect has specified roof tile to match existing. The existing tile is a flat concrete interlocking tile and assume the architect sped'ed it from an asthetics viewpoint. However when I look at the specs for different tiles they all have a minimum pitch angle the lowest pitch angle for the flat concrete tiles is 22.5 degrees. When I did some research there is a Marley tile called Marley Wessex which has a minimum pitch of 15 degrees which I can possibly get (think they have one Irish supplier). What I really want to know is ? do I have the option of going with the flat tile that matches the existing roof tile if I put in a serious overlap or should I get the Marley Wessx hopefully in a similar shade ? Can anyone tell me what features in a tile define its minimum pitch is it something to do with the smoothness of the surface finish or is it related to additives within its concrete ? All advice much appreciated.