Can I use wider, shorter joists for flat roof to gain height
I am constructing a garden office at present with monopitch flat roof. As I had to build close to boundary I have to keep overall height at 2.5m max.
I am using C24 timber and the span between walls is 2.45 meters.
In order to gain a few cm here and there I wondered if it is OK for me to use a wider but 'shorter' roof joist e.g. 60mm x 97mm rather than a narrower but 'taller' one like a 47mm x 120mm?
Span table doesn't suggest there is a structural problem with this approach - and I am making a warm roof so space for insulation internally is not a consideration.
Advice from 2 local tradespeople
I would check with the Carpenter or Roofer to verify that it is off sufficient thickness to support weight, but from what you said you should be ok
60x97 should be fine as long as you put noggin’s in through the centre to add strength. Alternatively you double each rafter up
