W20 is the traditional heavy-duty framing system, which is 32mm wide, having 5mm thick flanges. It originally developed for commercial and industrial appli-cations, and was introduced in the early 1960s to consolidate the various commercial steel window ranges available at that time most notably the Small, Medium and Heavy Universal ranges. It accommodates single and insulating glass units up to 20mm thick. All glazing, wheth-er in fixed lights or casements, is in the same plane due to the unique design of stepped steel profiles. It can be divided into small panes with tee glazing bars, having a sightline face width of 29mm. Opening windows are weather-stripped using integral gaskets or weather-strip. Hinged casements, hung at the top, bottom or side, and swing windows can pivot horizontally or vertically and can all be constructed from the same selection of profiles.t can accommodate single and insulating glass units of up to 20mm thick in the same profiles, by selected the appropriate bead. It can be divided into small panes with tee glazing bars, having a sightline face width of 20 or 25mm. Hinged casements, hung at the top, bottom or side, and swing windows, can all be constructed from the same selection of profiles.
An evolutionary development from W20, W40/MW40 offers continuity of style with the same casement sightlines as W20, but the 40mm wide profiles permit the use of double or triple glazing up to 27mm thick. The insulating glass units are drained and ventilated in accordance with modern best practice and gasket glazed to ensure consistent neatness and reliability of seal. In addition, to improve thermal performance, weather tightness is significantly enhanced and fittings can be less obtrusive with variable geometry hinges, friction pivots and multi-point locking cremone bolts concealed within the profiles. The W40/MW40 range of profiles is the most heavy-duty of the available mild steel window ranges and achieves the Secured by Design standard.