A qualified roofing contractor will be able to advise on this but here are some of the main guidelines.
Cold flat roof ventilation building regulations.
Ventilation is required for these roofs.
Cold deck flat roof the thickness of insulation required will vary depending on the material you decide to use and the manufacturer s specification.
However where vapour permeable or low resistance lr underlays are specified the levels required may be reduced.
Warm deck this is where the insulation is placed on top of the rafters joists and the roof covering is then placed over the insulation.
For both a warm and cold flat roof a vapour control layer must be installed.
No ventilation is required for these types of roofs.
The air gap dimensions shown on the drawings are the minimum widths required for clear continuous ventilation air paths at the eaves.
Ventilation is not required to a warm roof system which is where the insulation is placed above the joists or rafters.
Cold deck this is where the insulation is placed between the joists rafters or in between the ceiling joists in the case of a pitch roof.
Ventilation at the eaves.
Roof voids must be ventilated in order to stop warm air condensing on cold surfaces.
Cold roof voids are generally always required to be ventilated.
Condensation encourages rot and mould growth.
Ventilation is required above the insulation in a cold roof to prevent the build up of moisture vapour in the roof void.
Duo pitch roofs greater than 200 pitch or greater than 10m span should have additional ventilation at the ridge to assist airflow through the roof void equivalent to at least a 3 mm wide continuous gap.
A ventilation gap usually 50mm should be.
Not all roofs need to be ventilated.
There must be a slope of 1 80 part h of the building regulations regarding drainage state that water should drain to one or two edges waterproofing should extend up the adjacent walls at least.
When ventilating a roof the air should be able to enter at one end and travel through to the other end where it can exit.