It was this http://gbr.sika-trocal.sika.com/ He lined them valleys with it and it doesn't leak now. Shame- I could so with some nick me own lead valley and claim on the insurance type scam dosh at the mo.
Foggy, you can get away with 22.5 for some tiles and may be 30 will take it too high up the existing wall. A few more hips and valleys wouldn't go a miss Pitch roof for the win tho' Costs? Not cheap
All joking aside I used to run a roofing firm, you need some Saxon boards covered in Lamox and don’t forget to put Derby runners on the edges