Hi Guys, So just needed some help with my firrings basically ive got a 6m long flat roof that leads to 1 gutter in the parapet and i need to work out the firrings ratio im doing a warm roof and wanted to know the ideal ratio/slope needed for the 6 meter fall any help would be apreciated. roof is having a lantern fitted Thanks Give me a call if you can so i can explain it all a little better if needed.
Road drainage has a camber of 1 in 40, minimum slope for sewerage pipes 1 in 80, rainwater off roof 1 in 120. i.e. 50mm in 6m
If your ceiling 'follows the fall' if the warm roof above it you wouldn't even notice the drop of 50mm over 6m.
Standard fall for a flat roof is 1 in 80 but we usually adopt 1 in 60 to avoid the risk of hollows if the roof deflection is on the high side. This equates to 1 degree. You need 100mm fall. Use firrings and keep ceiling flat you will see it and it will wind you up. (Daughters rear extension done like this so voice of experience)