The British Standards Institute (BSI) has published a new code for standards of flat roofs BS 6229:2018 – flat roofs with continuously supported flexible waterproof covering. The guidelines contained a number of changes.
The update of the previous definition for a “vapour control layer” to an “air and vapour control layer” as they perform two important functions. The change now recommends to avoid the traditional cold roof construction due to the difficult of forming an effective AVCL, cross ventilation and the increased risk of condensation.
An additional breather-layer is now shown over the insulation to provide an external air-leakage barrier and to help protect the insulation against any environmental factors which may be detrimental.
For more information please see https://buildingproducts.co.uk/new-code-sets-new-standards-flat-roofing/