Old house extended at the rear has a pitch of 16 degrees and measures 10 X 10 mts. Has Marley tiles, thick plastic sheeting under rotting battens and no felt. Water getting under the tiles and going into the rendering. Sign of dips in the roof but signs of water all over. Advice from 3 builders is to replace the felt but different tile solutions: use the same tiles with more overlap and replace broken ones; same tiles with exact Marley installation directions and replace broken ones; consider other materials because of the pitch e.g. plastic tiles or stone covered steel. Very confused.
Do a search on line and identify your roof tiles and see what minimum pitch is recommended. Both Redland and Marley sell tiles for pitches down to 15 deg.
Stick with tiles they will last longer than anything else.
I have realised I can measure the roof angle more accurately by going inside the loft. yes I am a little slow. Then I can consult Marley but it looks to be nearer 25* for the current rough surface tiles and 17.5 for the smooth.
What do you think about increasing the overlap beyond the recommended distance to compensate for the lower angle?
You still need to identify the tiles and look at the Marley spec. If your pitch is lower than given in the spec then Marley have done this for a good reason and increasing the lap probably won't help.