Flat Roof Air Gap

For both a warm and cold flat roof a vapour control layer must be installed.

Flat roof air gap.

Many properties use this option as there are no additional costs for scaffolding or organising how to gain safe access to the roof exterior. Continuous 5mm gap at ridge depending on the type of roof you are considering here s some technical details you may find useful. A cold deck flat roof. Flat roof u value 0 18 w m2k 2 warm deck flat roof the type of insulation for this is usually of a rigid type and the thickness will vary depending on the manufacturer s specifications.

To prevent condensation forming when the insulation is placed at ceiling level a minimum of 50mm gap is provided for ventilation above insulation. Closed cell spray polyurethane foam ccspf at bottom of roof sheathing. An unvented roof assembly is possible only if you keep the roof sheathing warm enough to prevent conditioned air from condensing against it. A boarded roof with plywood sheet providing structural strength over the rafters.

The map at right which is based on table r806 4 of the irc lists the minimum r values required to prevent condensation in unvented assemblies in various climate zones. Roof sheathing to be air sealed. This may involve the use of 50mm x. If less analysis is required.

On a warm flat roof the layer is installed underneath the insulation to stop moisture interacting with it through. This is placed over the. In a concrete deck for example this gap could be created by fixing 50x50mm timber battens at 600mm centres and attaching the insulation to. The insulation material is placed between the supporting joists leaving a gap of 50 60mm between the roof and insulation.

Let s start with the only situations with between rafter insulation where you do actually need a 50mm ventilated air gap over the insulation a loft conversion where there is a bitumen felt in place. 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. R value of ccspf to be 40 of total assembly. 2011 code of practice for control of condensation in buildings stipulates that there should be a ventilation gap between the insulation and the bottom of the flat roof deck of at least 50mm.

Foil lined plaster board on the ceiling will help because it forms a partial vapour barrier. Acceptable if above is not feasible. Ventilation air follows exactly the opposite path. You have various options.

Purlins at a 45 degree angle still provide sufficient support for installation of the metal roof panels. Rising along the underside of the angled purlin until it reaches a gap then rising up to the next purlin and so on to exit at the ridge or gable.