Weather Performance Long experience has demonstrated the suitability of steel windows for most sites and exposure conditions in the UK, where an exposure rating of 1200 Pascals satisfies most locations. Extensive laboratory prototype and production audit testing to the methods prescribed in BS.5368 give the typical results tabulated below, classified in accordance with BS.6375:Part 1. The extra weatherseals introduced in W40 to provide an external rainscreen, internal airseals and a pressure equalised cavity have significantly improved resistance to air and water penetration in severe exposure conditions, particularly for windows that open inwards. Window type Range Test pressure class Exposure category Air Water Wind Fixed Light W40 600 300 2400 2400 spl W20 600 300 2400 2400 spl SMW 600 300 2400 2400 spl Top Hung W40 300 300 2400 2400 W20 300 200 2000 2000 SMW 300 200 2000 2000 Side hung open out W40 300 300 2400 2400 W20 300 200 2000 2000 SMW 300 200 2000 2000 Side hung open in W40 300 300 2400 2400 W20 200 100 1600 1200 Bottom Hung W40 300 300 2400 2400 W20 200 100 1600 1200 SMW 200 100 1600 1200 Horizontal pivot W40 300 200 2400 2000 W20 200 100 1600 1200 SMW 300 300 2400 2400 Vertical pivot W40 300 150 2400 1200 W20 200 50 1600 1200X Test pressure class and exposure category in Pascals of typical types and sizes when tested to BS.5368 and classified as BS.6375: Part 1. Thermal Performance Concern is often expressed about the low thermal resistance of a steel frame and the occasional risk of condensation through cold bridging, but steel windows glazed with insulating glass units have a thermal performance quite adequate to demonstrate compliance with the energy conservation requirements of the Building Regulations. Steel windows with an insulating glass unit air space of 6mm. have typical U-values of 3.7W/m²K with ordinary clear float, reducing to 3.3 with low-E glass. When that air space is increased to 16mm. the expected equivalent U-values are 3.3 and 2.8W/m²K. Given an extreme temperature differential from -5ºC outside to a +20ºC inside and no ventilation air movement, condensation will form on internal frame surfaces when relative humidity is above 33%. Although inconvenient, such condensation will not harm the window. It is perhaps preferable that condensation should manifest itself first on visible window surfaces rather than in concealed cupboard and wardrobe spaces: it should encourage people to seek more ventilation as the recommended means of control. Security The inherent strength of steel ensures maximum rigidity once the window frames have been installed and glazed. The most secure steel window is a regular, standard window divided into small panes of glass, with vertical and horizontal bars tenon-riveted into the frame and with strong intersecting joints. Even if the glass is broken, entry cannot be made through this window. A high measure of security can be achieved with large pane steel opening windows by a variety of locking methods, while a supplementary ventilator, mounted in the top glazing rebate will give permanent or controlled ventilation with locked window security. Fire Safety Wherever the specifier wishes to combine fire safety with maximum daylight and vision, steel framed fire resistant glazing is the preferred choice. A hot rolled steel framing system has been developed to offer one hour fire resistance. Its strong, slim, coloured steel framework complements other adjacent hot rolled steel windows and doors which do not have to be fire rated. It can be used internally, or externally when its weather and corrosion resistance qualities are important. A fixed screen prototype 3.0m. x 2.5m. in 6 panes, glazed with Pilkington Pyroshield Polished Wired Glass, has been tested to BS.476:Part 22: 1987 and maintained its integrity for 77 minutes. A further test, discontinued after 75 minutes, has confirmed the performance of an enhanced version, incorporating a door and Pilkington Pyrostop fire insulating laminated glass, which was assessed by Warrington Fire Research Centre as satisfying the integrity requirement for one hour and insulation for 14 minutes. Assessments are also available for other types of fire resistant glass, such as 14mm. Pyrobel, 6mm. Pyran, 6mm. Pyrocet or 5mm. Firelite. Alternative fire resistant glazing systems using cold formed hollow steel profiles, all backed by authenticated test evidence, are offered by individual manufacturing members of the Association. Operation and Control Fittings available offer a comprehensive selection of casement handles and stays, folding openers, hinges, pivots, catches and bolts all designed to provide the optimum in performance and flexibility. Stringent quality control procedures, combined with modern manufacturing techniques, ensures that all products are of a consistently high standard. Surface Finishes An integral part of BS.6510 Specification for Steel Windows, which is adhered to by all SWA members, is that all windows are hot dip galvanized to BS.729. During this process the steel windows are thoroughly cleaned and then dipped in a bath of molten zinc. The zinc reacts with the iron in the steel to form alloy layers which are then covered with pure zinc as the window is withdrawn. This combination of soft zinc and relatively hard alloy layers underneath produces a very durable protective coating that will not flake or peel. If it is accidentally damaged, the galvanized coating will corrode in preference to the steel and so prevent rusting. Galvanized steel windows do not require painting for protection, but their appearance is enhanced by the addition of a factory-applied polyester powder coating, introduced as a finish for galvanized steel windows in the late 1970’s, it is the most economical and effective coloured coating. A comprehensive range of colours is readily available, with the matt finish proving the most popular because of its surface enhancing properties. Installation Fixing Steel windows are suitable for fixing direct to brickwork, concrete, stone or into subframes. The size of openings should be 6mm. overall greater than the window dimension in length and height. Windows and integral sills must be installed in accordance with good building practice allowing for damp proof course and finishes. No load shall be applied to the head of any window. On all perimeter seals refer to manufacturers recommendations. Where direct fixing is not achievable, lugs are available from the manufacturer Glazing Steel windows can be single glazed or fitted with insulating glass units. Glazing practice should always comply with BS.8000:Part 7:Glazing. Reference should also be made to the Glass & Glazing Federation’s detailed recommendations on glazing techniques, particularly the instructions about the use of setting, location and distance blocks and clips. (Note: Manufacturers may offer their own preferred glazing methods). Specific glazing compounds are available for use with factory finished steel windows. Aftercare and Maintenance The modern steel window is an extremely durable, high performance product. This performance can be enhanced if good maintenance practices are observed. Frames should be cleaned at regular intervals, using a mild, non-alkaline detergent in warm water, applied with a soft cloth or sponge. Glazing and perimeter sealants should be inspected on an annual basis and appropriate maintenance action taken. Galvanized steel windows, which are not factory finished with a polyester powder coating, are manufactured with clearances set to allow for up to three or four coats of paint on the meeting surfaces. When the repainting programme has exceeded this, strip the paint off all meeting surfaces prior to repainting. All hinges, pivots, handles, stays and other mechanical parts should be checked for operation, kept free of excessive paint build up and lightly lubricated The above information is reproduced courtesy of the Steel Window Association