what size rafters should i use please

[john25043405]

hi all

I'm currently building a new extension and I'm trying to work out the size of Rafters using the trada tables and I am being completely blind or stupid or possibly both.

The measurements are as follows:

Rafter Span = 4300 to external wall
Rafter spacing = ?
rise = 1100mm
Pitch =14.35 degrees
roof slope length =4438.4mm

Covering is with concrete tiles and the area is Wiltshire so believe the load to not be more than 0.75KN/m2

I think that the size required is 220x47mm,C16 graded with rafters spaced at 400mm, but could anyone confirm this please?

All posts gratefully recieved

 

[Blagard]

Whoever is responsible for that design ought to come up with the details, including what tile is being used on the roof. That 14.35 degree pitch is too low for most roof tiles.

If possible you should seriously consider introducing purlins, to allow a reduced rafter size.

 

[noseall]

Yeah Blag, the guy has double posted , in b'regs and I suggested the same thing regards pitch and suitable tiles!