Cold Flat Roof Ventilation Building Regulations

Ventilation is required for these roofs.

Cold flat roof ventilation building regulations.

Because the structural elements of a cold roof are not protected by from the heat of the sun by a layer of insulation they are liable to suffer the damaging effects of thermal movement. A qualified roofing contractor will be able to advise on this but here are some of the main guidelines. Cold deck flat roof the thickness of insulation required will vary depending on the material you decide to use and the manufacturer s specification. No ventilation is required for these types of roofs.

Cold roof voids are generally always required to be ventilated. Condensation encourages rot and mould growth. The air gap dimensions shown on the drawings are the minimum widths required for clear continuous ventilation air paths at the eaves. 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.

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. 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. However where vapour permeable or low resistance lr underlays are specified the levels required may be reduced. Ventilation is required above the insulation in a cold roof to prevent the build up of moisture vapour in the roof void.

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. Building regulations state that a ventilation gap of at least 50mm must be in place between the insulation and the underside of the flat roof deck. Roof voids must be ventilated in order to stop warm air condensing on cold surfaces. For both a warm and cold flat roof a vapour control layer must be installed.

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. Ventilation at the eaves. Otherwise ventilation is required and this is known as a cold roof system.