43422043 Roof Ventilation | Roof | Ventilation (Architecture)

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  . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . ROOFVENTILATION CI/SfB (47) Xn6Uniclass L529February 2007  ROOFVENTILATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ROOFVENTILATION CONTENTSThe need for condensation control 3  Ventilation requirements 4-6 Tile and slate ventilators Premier In-line™ Range7-9G Range7, 10-12 Ridge systems and ventilators Fulmetal Rediroll Ventilated Dry Ridge/Hip13Premier In-Line™ Ventilated Dry Ridge14-15G Range16-17 Eaves ventilators FV Fascia Ventilators18-19SV Soffit Ventilators20-21RV Rafter Ventilators22-23 Special roof ventilators Premier Ventilated Valley24-25Cross Rafter Ventilator26MR50 Monovent: Lean-to roof27Premier Leadvent Ventilator28Flat Roof Ventilation Terminals29 Roofing products DV Slate Dry Verge System30 Other information Tile and slate ventilators: standard profiles31General: references, specification etc. 32 Glidevale solutions Pages 3-6 of this brochure summarise thenew regulatory ventilation provisions for arange of pitched roof constructions.Pages 7-30 describe the range of Glidevaleproducts which can help to meet thoseprovisions.Glidevale have a comprehensive range of products designed to: ● Meet all requirements of regulations andcodes of practice throughout the UK. ● Cater for all types of tile and slate roof covering. ●  Accommodate almost any roof design andform of construction. ●  We can provide full technical advice on allaspects of roof space ventilation usingGlidevale products. New ventilation requirements The last six years have seen some heateddebate regarding the need for roof space ventilation in both warm (insulation at rafterline) and cold (insulation at joist level)pitched roofs, especially when vapourpermeable/breathable (type LR) underlaysare used.For roof design and specification purposes,this debate has now been largely resolved bytwo developments:- BS 5250: 2002 ‘Control of condensation inbuildings’ has been updated by AmendmentNo 1: 2005. This is as a result of a Partners inInnovation (PiI) research project ‘Thermaland moisture performance of pitched roofs’,funded by Dti and industry, which concludedin April 2005.- BS 5250 is now specifically cited as ameans of compliance in England and Walesby Building Regulations Approved DocumentC2 ‘Resistance to moisture’ 2004, which hasreplaced Approved Document F2.BS 5250 has always been a means of compliance in the regulations for Scotland,Northern Ireland and the Republic of Ireland. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   What causes condensation?  Warm air can hold more water vapour thancold air. Condensation begins when airtemperature drops to the dew point, or when warm moist air comes into contact with acold surface. Water vapour can pass throughmost building materials including brick,concrete, plaster and plasterboard (unlined), wood and insulation. Warm air from withinthe building, carrying water vapour, can passthrough ceilings into roof spaces. Since theroof space is likely to be colder, condensation will occur as soon as the air meets a coldsurface; this is termed the ‘wetting-outphase’. Building regulations  All Building Regulations for the UK and theRepublic of Ireland make requirements forthe prevention of harmful effects caused bycondensation in roofs.The relevant documents are:  England and Wales:  Approved Document C22004 ‘Resistance to moisture’. (ApprovedDocument F2 which previously covered roof  ventilation has been withdrawn.)  Scotland: Technical Handbook DomesticBuildings Section 3.15.2 ‘Control of condensation in roofs’.  Northern Ireland: Technical Booklet C ‘Sitepreparation and resistance to moisture’.Regulation C4 Section 2.8 ‘Pitched roofs’.  Republic of Ireland: Technical GuidanceDocument F ‘Ventilation’ 2005. Section 2‘Condensation in roofs’. ROOF VENTILATION . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . THE NEED FOR CONDENSATION CONTROL Condensation in roof spaces  A number of factors in modernconstructions have led to increased risks of condensation within roof spaces:– Fortuitous natural ventilation withinbuildings has been reduced by the use of high-performance draught-proof doorsand windows and the blockage orelimination of open-flued chimneys.– Modern lifestyles generate higheramounts of water vapour.– Average air temperatures within buildingshave increased, thereby allowing more water vapour to be carried in the air.– Increased amounts of insulation at ceilinglevel have led to colder roof voids.– The widespread use of roofing underlayshas greatly reduced the amount of natural ventilation of the roof space.– The use of vapour permeable (type LR)underlays, often with sealed laps and withno loft ventilation at all.Research has shown that about 20% of theair that enters a building, and in particulardwellings, leaves via the roof with anadditional moisture load, and that typically80% of any water vapour transport into theroof is by air motions (convection) throughthe ceiling via gaps and cracks.Condensation in the roof, taking place out of sight of the occupier, can cause seriousdamage, including severe structural weakening by wet or dry rot, loss of effectiveness of insulation, and damage todecoration through staining and mouldgrowth.  ROOF VENTILATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ROOF VENTILATION REQUIREMENTS Meeting the requirements  All the regulations supporting documentsthroughout the UK and Ireland now citeBS 5250: 2002 ‘Code of practice for controlof condensation in buildings’ incorporating Amendment 1: 2005 as the main means of compliance.Section 8.4 refers to roofs and is subdividedinto cold roofs with large voids abovehorizontal insulation and warm roofs withsmall or no voids above sloping insulation.The harmful effects of condensation can becontrolled by the ventilation provisionsshown here.  Notes to drawings: Figures are given in 000s of mm 2 per metre,eg 5 = 5000mm 2  /m.Impermeable underlays (type HR) Vapour permeable underlays (type LR) Vapour control layer Impermeable underlays (type HR)  All roof types  All roof pitches: Ventilation beneath the underlay and abovethe insulation of 25 000mm 2  /m at eaves or lowlevel and 5000mm 2  /m at ridge or high level. A ‘well-sealed ceiling’ must be provided asdefined by BS 5250 clause 8:4.1.2, and aseparate vapour control layer on the warmside of the insulation. The space between theunderlay and insulation should be at least50mm deep with a minimum of 25mm at thecentre of underlay drape.  5  2525  2525  25  5  Room in the roof construction Obstructions such as dormers, valleys, roof  windows, compartment walls, fire barriersand changes in pitch create separate voidsbelow the roof slope. Provide ventilationopenings to each void at high and low levelas shown in the examples. Ventilation at compartment walls or fire barriers 2525  25  5  5  No ventilation required subject to conditions  Vapour permeable underlays (type LR)  All roof types with a vapour control layer   All roof pitches:No ventilation is required provided thatthere is - A vapour permeable underlay, either fullysupported on insulation or drapedunsupported, a well-sealed ceiling, and aseparate continuous and effectively sealed vapour control layer on the warm side of theinsulation.If there is any doubt about the ability toprovide and maintain the vapour controllayer, provide ventilation as if the underlay were impermeable (as above).  WARM ROOFS With small or no voids above sloping insulation  well-sealed ceiling well-sealed ceiling 50mm gap well-sealed ceiling well-sealed ceiling 50mm gap 50mm gap 5 
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