Evening all just wanted to know what you guys normally measure down from a sill. The extension in question is going out 3 meters so need to get every degree possible. And maybe a quick tip on measuring up a rafter. I know how to birdmouth etc. Thank you
Are you trying to say, " how much below the upstairs window sill can set my extension roof", if so you can go to within one course of brickwork to allow an upstand on the lead flashing, this should be more than enough pitch on a 3 Metre out extension, mines 4.5 Metres out and one course below, it still has a 20° pitch.
From upstairs cill i would allow 75-100mm for lead upstand 20mm-50mm for slate tile etc and 25mm for roof battern and felt then your rafter hight