Steel Products
Steel Window Performance Characteristics
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.
| WINDOW TYPE | RANGE | TEST PRESSURE CLASS | EXPOSURE CATEGORY |
||
|---|---|---|---|---|---|
| AIR | WATER | WIND | |||
| Fixed Light | W20 SMW |
600 600 |
300 300 |
2400 2400 |
2400 spl 2400 spl |
| Top Hung | W20 SMW |
300 300 |
200 200 |
2000 2000 |
2000 2000 |
| Side Hung - Open Out | W20 SMW |
300 300 |
200 200 |
2000 2000 |
2000 2000 |
| Side Hung - Open In | W20 | 200 | 100 | 1600 | 1200 |
| Bottom Hung | W20 SMW |
200 200 |
100 100 |
1600 1600 |
1200 1200 |
| Horizontal Pivot | W20 SMW |
200 300 |
100 300 |
1600 2400 |
1200 2400 |
| Vertical Pivot | 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.
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.
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.
