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A1 The particular membranes in question typically comprise spunbonded polypropylene or spunbonded polypropylene/polyethylene laminated either side of a micro-porous polypropylene or polyethylene film.
Monolithic spunbonded membranes are also used. They have a structure that is sufficiently fine to prevent liquid water penetration in service conditions, but not too fine to prevent the transfer of water vapour (molecules of water in air), see figure 1.
All materials, including vapour control layers, have a finite permeability to water vapour transfer. However, in the context of this Article, a breathable membrane is a material which, in service conditions, is sufficiently permeable to water vapour transfer to adequately limit the risk of condensation in roofs.
Current published definitions include the following:
BS 5250: 2002 section 3.2 “Breather membrane” – vapour permeable membrane with a vapour resistance less than 0.6 MNs/g. The Standard goes on to describe the use of ‘Breather membranes’ in walls.
BS 5250: 2002 section 3.26 “Vapour permeable underlay” – Pitched roof underlay which meets the recommendations of BS 5534-1 and NFRC TB6 and is additionally water vapour permeable with a vapour resistance of less than 0.25 MNs/g
These two figures can also be expressed as water vapour transmission rates of at least 341 or 820 g/m2/day respectively, when tested under standard conditions of 25o C and humidity of 0% rh and 75% rh on each side of the membrane. Links: 缝纫线, 绣花线,Sewing basket, latch hook, rug hook, cross stitch, sewing thread 防水透气膜 防水材料 保温材料 墙体材料 律师 breathable membrane, roofing membrane, roofing foil, membrane, valve , button材料 Links: Opennews conglomerate Sunwukong S2 S3 S4 Dir1 Dir2 Dir3 Dir4 Jayde Sr Awarenessnetworks GlassBuy IeTrade P1 P2 P3 Lead LiveSpace E1 E2 E3 Mechdir Blonder Meebq Maverick Bruce Zegna Nings Cilo 385857762 SoulCast SpotsDir DreamHome EcTrade MySpace Exportnation Pro PerfectCondoz Myekoo Efreedir Fukesi CleverDir blogtext Ca-Yahoo Uk-Yahoo
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