FIRE PROTECTIONThe design and construction of flat roofs needs to take into consideration resistance against fire outbreak on both the inside and the outside of the building.Building Regulations set requirements that have to be met in order to provide a level of safety in fire for persons in and around buildings and also give guidance on how to achieve the required standard of safety. Guidance can also be sought from the Loss Prevention Council 'Design Guide for the Fire Protection of Buildings'.Resistance against fire on the outside of the roof is largely provided by the roofing system specified. Current UK Building Regulation Part B refers to a minimum designation of AC for a roof covering when tested in accordance with BS476 Part 3 (ENV 1187 test 4), if any part of the roof is within 6 metres of a relevant boundary.The British Standard test classifies a roof covering in terms of its ability to resist penetration from an external fire and its ability to control flame spread over the surface. An explanation of the designation given above is as follows: Second leter Spread of flame classificationsA Specimens with no spread of flameB Specimens with not more than 533 mm spread of flameC Specimens with more than 533 mm spread of flameD Specimens which continue to burn for 5 minutes after the withdrawal of the test flame or spread more than 381 mm in the preliminary test First leter Penetration classificationsA Specimens not penetrated within 1 hourB Specimens penetrated in not less than half hourC Specimens penetrated in less than half hourD Specimens penetrated in the preliminary flame testAll Bauder bituminous systems (except BauderTHERM Stripes) and synthetic Single Ply Systems have been tested to BS476 Part 3 and have achieved fire ratings that either meet or exceed Building Regulation requirements, please contact us for further information.? Testing a Bauder bitumen membrane in accordance with BS476 Part 3 2004 in a UCAS accredited laboratoryDECK CONSTRUCTION TYPESMaterials used for the roof deck should be selected from those listed in BS 6229:2003. It is important to refer to this document for design guidance, but, for convenience, the various materials are outlined below:Reinforced ConcreteSuitable for all Bauder waterproofing systems, this includes both in-situ and pre-cast forms, which can be covered with a cementitious screed if required. The surface should be wood float finished and the slab allowed to cure thoroughly and dry out to provide a suitable surface to which the membranes can be applied.Profiled MetalMetal decking constructed to support built-up waterproofing systems should be of a suitable profile, i.e. featuring crowns that are wider than the respective troughs. The trough span should not exceed 150 mm, otherwise the vapour barrier may sag at the laps and adequate support will not be provided for the insulation. Suitably profiled decking is available in either aluminium or galvanised steel, however consideration should be given to the fact that many systems are applied using intense heat, in which case aluminium is best avoided as it is more likely to distort at high temperatures. Similarly, plastic or painted soffit types of decking may become damaged by the heat used when installing torch-applied membranes. This type of decking is not suitable for cold roof design unless it is subsequently overlaid with plywood or OSB.Timber BoardingTimber boarding suitable for roof decks should be a minimum 19 mm nominal thickness, planed and closely clamped together, tongued and grooved or closely butted. When using this type of deck in conjunction with bonded vapour barriers, it will be necessary to first install a random nailed isolating layer prior to the installation of the main roofing system to cover the joints between adjacent boards. This decking is not suitable for hot melt or cold liquid applied systems.PlywoodPlywood used for roof decks is generally 18 mm thick, but it is possible to specify a minimum 15 mm if the supporting structure is more closely spaced. The plywood is normally square-edged. Longitudinal joints should occur on the centre line of supporting joists. Cross joints should be staggered and will require additional support, e.g. by noggins. A joint gap of 1 mm per metre of panel should be allowed at all edges. The plywood should comply with BS EN1995 to be suitable for structural use. Materials suitable for flat roofing would be marked BS EN 636-2 or BS EN 636-3 and must be suitable for exterior use. Plywood is suitable for all Bauder waterproofing systems.Oriented Strand Board (OSB)OSB used for flat roof decking should be type OSB/3 or OSB/4, conforming to BS EN 300:1997. Thickness and fixing recommendations are similar to those for plywood. Suitable for use with all Bauder systems.Woodwool SlabsWhen using this type of decking, slabs must conform to BS EN 13168 and be at least 50 mm thick. They should have a pre-screeded top surface and have channel reinforced sides. Please note that this type of decking is now classed as 'fragile' in the UK and therefore not recommended by Bauder for new build construction.Wod Particle Board (Chipboard)This type of deck is referred to in BS 6229:2003, however it is no longer recommended for use in flat roof applications due to its long term structural instability, especially if contaminated by moisture.bauder.ie202

203WIND LOAD DESIGN bauder.co.ukWhen wind strikes a building it is deflected to generate a positive pressure on the windward face. As it accelerates around the side of the building and over the roof it creates a reduced or negative pressure in its trail.The greatest pressures are experienced at the windward corners and edges of the roof, where the negative pressure exerted on the roof can be several times that experienced in the central areas.Bauder Technical Department can provide Wind Load Calculations on request in accordance with the UK National Annex to Eurocode 1 - Actions on structures Part 1 - 4: General actions - Wind actions (BS EN 1991 - 1 - 4: 2005).The Critical Layer When there is no wind, the air pressure on the upper surface of a roof system is the same as that on the underside. Wind changes this equilibrium by reducing the atmospheric pressure on the surface of the roof system. The atmospheric pressure acting on the underside of the roof will remain the same or may be increased if windows or doors are open on the windward side of the building. The result is a net upward push acting on the underside of the roof.This upward thrust will be exerted on the lowest air impermeable layer in the roof construction, which will be required to stop air flowing further into the system. In most roof constructions there is one layer that provides the dominant barrier against the upward thrusting flow of air and this is referred to as the critical layer.In roof constructions where the deck is continuous (e.g. screeded concrete) it will be deemed to be the critical layer, but for air permeable decks (i.e. those with joints) the critical layer will occur somewhere in the roof system itself.In the case of bituminous membrane systems where the deck is permeable, the critical layer will be the vapour barrier (in a warm roof construction) or the underlayer (in a cold or inverted roof). When these membranes are properly installed, the bond achieved will be far stronger than the loading imposed by wind uplift.In the case of refurbishment overlays, the critical layer will be the existing roof system and its suitability to perform adequately will need to be given careful consideration.Single Ply membranes can be restrained against wind up lift by either being mechanically fastened or adhered, both methods of attachment provide effective resistance to wind uplift forces. Both hot melt and cold liquid applied systems are fully bonded to the deck and wind uplift is not considered to be a problem.Inverted RofsWith an inverted roof specification, the insulation is laid loose and its security will be provided by a loading coat, typically gravel ballast or paving slabs.Edge DetailingDamage caused to flat roofs during severe gales usually starts at exposed windward corners and edges. It is therefore important to make sure that fascias, cappings, trims, and drips are adequately fixed. As a rough guide trims should be screw fixed at 250 mm centres with extra fixings added under conditions of extreme exposure.Specification SupportNBS SPECIFICATIONSwww.bauder.co.uk/technical-centreTECHNICAL HELPLINET: +44 (0)1473 257671E: technical@bauder.co.ukFLAT ROOFDESIGN GUIDE100kN/m2High negative pressureModerate negative pressure100kN/m2Wind directionHighnegativepressure