Thanks for this reply, sorry for being slow, I didn't get notified of the reply. So you just bonded the entire roof together? I like your thinking but I don't think the building inspector will let me get away with that, so massive long screws it is.
I've done an epdm roof once before, it was a really simple roof and it went well. This time the roof has a few complications and I'm trying to decide between grp and traditional felt. I'm concerned about the longevity of grp - I'm hearing a lot of stories of premature failure, plus cracking noises due expansion/contraction. On the other hand, traditional felt is tricky for details and for the edges (I have a parapet detail). I've seen a couple of roofs done in a newish system called Kemper but this is a bit unproven and is very expensive (£85/m2 against £55-65 for grp and £50 for felt). Anyone got any thoughts on my quandary?