can someone tell me what centres should be for a single storey roof, joists are 6x2 c24 timber 4.5 mtrs long on a 9x5 steel supporting them on a 15 degree sloping roof, thanks
Google span tables. I think you will need bigger section I recently did flat roof 3m ish 6x2 on 400s the 15deg might help you
Do you mean the 9x5 is supporting the joists in the centre, if not, mentioning steel and its size is superfluous to the question?
600 would do as it complies with Building Reg Span Tables but agree 400 would provide a stronger roof