A vapour-permeable drainage membrane for use beneath standing seam metal sheet roofs over timber boarding. Allows condensation beneath stainless steel, copper and zinc roofs to drain away. Membrane should be installed over 150mm wide timber boarding with 2mm gaps between. Integral lap tape provided. DuPont Tyvek Metal can be termed a metal roof drainage membrane for application into standing seam metal roof systems. The product consists of a Tyvek vapour permeable membrane (Tyvek Supro) bonded to an open mesh of polypropylene strands approximately 8mm deep. The function of the product is to provide protection to a roof structure and thermal insulation against condensation that may occur beneath rigid standing seam cladding of zinc, stainless steel, aluminium and copper. In addition to its drainage function, the product will provide suitable separation between layers by allowing movement between the metal sheet and timber boarding. DuPont Tyvek Metal will also offer a reduction in sound transmission typically generated by structure borne sounds such as rain clatter. Properties Length: 25m. Width: 1.5m. Roll size: 37.5m2. Roll weight: 11.5kg. Mass per unit area: 350gsm. UV exposure: 4 months. Certification: CE marking. Composition: Composite of high density polyethylene, nonwoven and open mesh spacer. Installation The product is installed directly beneath the standing seam sheet, with the open mesh providing adequate support, whilst maintaining a clear airspace to allow any condensate to drain away. The vapour permeability of the membrane will allow water vapour from the construction beneath to diffuse through and into the mesh zone. To accommodate this breathable function the supporting substrate beneath DuPont Tyvek Metal must also be vapour open. A proven arrangement of 150mm timber boards with a 2mm gap is recommended for this purpose. Controlling condensation DuPont Tyvek Metal does not eliminate the risk of condensation occurring in metal roof systems, but will minimise the risks of condensation build-up. A holistic approach to the design of the roof system should therefore be employed, with an emphasis on vapour control and airtightness in the internal lining. A suitable Air & Vapour Control Layer for this type of construction is DuPont Airguard Reflective.