Roofers' Guide to Underslating Membranes - IKO

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8Typical What cold is roof a cold design roof? detailsWhat is a cold roof?There are two main types of cold roof:A traditionally ventilated void space, where all•types of underslating membranes can be used.An unventilated void space where only certain•certified breather membranes can be used.A Cold Ventilated Void Roof configuration is thetraditional form of pitched roof build-up. Theinsulation layer is placed horizontally, directly abovethe ceiling of the upper story of the habitable sectionof the building, usually positioned between the joistsin the loft space. The Rubershield-Pro breathermembrane or any type of proprietary underslatingmaterial is placed at rafter level, either drapedbetween the rafters, or supported on a sarking board(usually Scotland). In a traditional cold roof system,any void space below the underslating membrane hasto be ventilated. In this roof type, a breathermembrane or non-breathing underslating membranewould be equally suitable.When an underslating membrane is installed in a coldroof configuration draped between open rafters,the use of counterbattens is not required.In a Cold - Un-ventilated Void Roof configurationthe insulation layer is also placed horizontally, directlyabove the ceiling of the upper story of the habitablesection of the building, with the vapour control layerplaced below the insulation at ceiling level. However,in this situation, only a breather membrane certifiedfor this configuration can be used. Rubershield-Probreather membrane is approved for this purpose andshould be placed at rafter level, with overlaps,penetrations and perimeters sealed with RubershieldJointing Tape, draped between the rafters. However,there is no ventilation of any roof void space belowthe membrane; the only escape route for moisturevapour is through the breather membrane.
Typical What roof is a construction cold roof?9Use with sarking boards•As Scottish practice where using tiling battens, Rubershield-Pro must be laid beneath counterbattens of aminimum 25mm depth. In some instances tiles or slates can be installed by nailing through the membranedirectly into the sarking board. However, the tile manufacturer’s instructions must be strictly adhered to.•General guidance for coldventilated roofsWhere a roof underlay or breather membrane is to be•laid over open rafters, a drape of between 10 to 15mmbetween the rafters is desirable to guide any rainwaterpenetrating the main roof finish away from the rafters tothe drainage point.Provide for ventilation of the void space in accordance•with BS 5534 (BS 5250: 2002), with the inclusion of aproprietary eaves and ridge (high level) vents, fixed inaccordance with manufacturer’s instructions.Rubershield-Pro and all Ruberoid underslating membranes fully comply with requirements in BS 5534:2003, for use with sarking board installations in ventilated cold roof configurations.General guidance for coldunventilated roofs•Where a roof underlay or breather membrane is tobe laid over open rafters, a drape of between 10 to15mm between the rafters is desirable to guide anyrainwater penetrating the main roof finish awayfrom the rafters to the drainage point. (Themembrane must not be pulled tight against theunderside of the tiling battens.)Using Rubershield-Pro in this type of cold roof•requires no ventilation of any void space below themembrane. Also, when using clay or concrete tilesor natural slates, air movement is usually sufficient inthe void space above the membrane to negate therequirement for additional eaves and ridgeventilation. However, when using man-made slates(or some close fitting interlocking tile systems)additional ventilation above the membrane inaccordance with BS 5534: 2003 (BS 5250: 2002)is recommended to avoid potential damage tobattens and fixings caused by condensation. It isrecommended that guidance be sought from the tileor slate manufacturers concerned.To minimise the risk of condensation in cold•unventilated roofs, all penetrations into the roofspace must be properly sealed to maintain theintegrity of the vapour control layer or external seal,and loft hatches should be made convection tight. Allwater tanks in the loft space must be covered andpipework lagged. The occupied building below mustbe ventilated in accordance with Building Regulations,and rooms that experience high humidity levels musthave provision for separate air extraction.Use with sarking boards•As Scottish practice, where using proper timbersarking planks (usually 150mm wide) laid with a2mm gap between the boards, there is no need toprovide additional ventilation below the membrane.However, where using sarking boards comprisingsheets of plywood or OSB, this type of coldunventilated roof configuration is notrecommended, and a traditional ventilated voidapproach should be adopted.
Page 1: IncludingRubershield-ProBreatherMem
Page 5 and 6: Typical warm roof construction5With
Page 7: Typical warm roof design details7Ab
Page 11 and 12: Typical cold roof design details11V
Page 13 and 14: Rubershield-Pro13Typical uses of Ru
Page 15 and 16: Rubershield-Pro15Environmental cons

Roofers' Guide to Underslating Membranes - IKO

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