I'm drawing up a lead flat roof. (Its a square extension built off 2 existing walls with a parapet wall to the remaining 2 walls - see roof plan below)
Reading up on lead detailing seems to require that a lead flat roof (min. 1:80) requires ventilation of 50mm below the deck. The makeup for the roof I'm proposing is as follows:
Code 5 lead on
Geotextile membrane on
12mm WBP Plywood above
50m ventilation gap (formed with 50x50 battens) above
insulation sat on
VCL sat on
19mm WBP Plywood sat on
Joists with
Plasterboard beneath
I was planning on venting it from back to front (along the pitch) now assuming the above sounds ok I've found a detail (see below) for venting at the top of the roof where it abuts the existing house external wall, at the lower end I have a small parapet which obviously also needs to be vented too. Q1 Do I use the same detail or is there alternative?
Vent detail
Realistically I appreciate that any decent lead worker will be able to detail this ok but I'd like to understand how the detail works.
Q2Alternatively could I just vent the roof from side to side and use this vent detail at each side instead? and Q3 Do I have to vent round the rooflight as well?
Q4 Why does it need ventilation anyway, why is it different to a conventional warm roof?
Reading up on lead detailing seems to require that a lead flat roof (min. 1:80) requires ventilation of 50mm below the deck. The makeup for the roof I'm proposing is as follows:
Code 5 lead on
Geotextile membrane on
12mm WBP Plywood above
50m ventilation gap (formed with 50x50 battens) above
insulation sat on
VCL sat on
19mm WBP Plywood sat on
Joists with
Plasterboard beneath
I was planning on venting it from back to front (along the pitch) now assuming the above sounds ok I've found a detail (see below) for venting at the top of the roof where it abuts the existing house external wall, at the lower end I have a small parapet which obviously also needs to be vented too. Q1 Do I use the same detail or is there alternative?
Vent detail
Realistically I appreciate that any decent lead worker will be able to detail this ok but I'd like to understand how the detail works.
Q2Alternatively could I just vent the roof from side to side and use this vent detail at each side instead? and Q3 Do I have to vent round the rooflight as well?
Q4 Why does it need ventilation anyway, why is it different to a conventional warm roof?