I am about to put a roof on my extension its 4.5mtrs long (with the 25mm over hang each end) and 6mtrs wide. I am using 200mm x 75mm timbers straight onto the block work with DPC between.
from the top down:
18mm OSB3 sheet
50mm air gap
my questions are do I need noggins and if so where and how thick? do I do them 120mm and at the bottom to keep the 50mm air gap? Should I put timber around the top of the block work or rest the timbers straight on them?