How Far Into The Gutter Should Roof Tiles Project?

The bottom tile or slate of the roof covering should project at least half way into the gutter - the ideal distance is between half way and two thirds of the way over.

The reason for this is that whenever rain runs down any type of roof, when it gets to the lower edge it clings to the tile or slate by capilliary action - this means that the water actually runs around the bottom edge and slightlly back up the rear of the tile before gravity allows it to drop into the gutter. If the bottom course of tiles or slates only just projects into the gutter there is a real danger that rainwater will fall behind the gutter, leading to damp roof timbers or brickwork.