i'm building a small single storey extension with flat warm roof, walls are up, and considering a modular green roof. Basic roof joists on a 2.6m span, 125 x47 C16 at 400mm centres or less. Will this be adequate for the additional load between 65 and 100 per mtr?
Probably not. A small modular green roof apparently weighs about 64.5kg/m2, or an imposed load of roughly 0.63kN/m2; 47x120will only just span 2.6m for imposed loads of no more than 0.75 kN/m2. Add in any wind loading, snow loading, factor-of-safety, etc.and you'll be well above that. 47x170 C16 will give you a maximum clear span of 3.18m with a max imposed load of 1.5kN/m2 but you'd be best working out what your actual imposed load is. (I'm going by the charts from the NI Technical Booklets 2012)