Cill support has always been a crucial part of window installation, but is often overlooked. The detrimental effects of not having cill support bars, are not immediate but usually manifest themselves over a period of time, and hence we see an indifference to using them. Most joinery is fixed to the building framing, through the jamb liners thereby creating a cantilevered action. This action stresses the corners, mullion joints, frame/liner connection, and eventually compromises their integrity, and in turn the integrity of the whole window system. With Double Glazing becoming more common place, the weight is practically doubled and the problem is further compounded .  The combination now of both double glazing and cavities becoming the norm, the stresses placed on joinery has been increased.

With this in mind,  all windows and doors, irrespective of their size and  construction/cladding type must have cill support. Cill support is dealt with differently depending on the type of construction i.e. Cavity Construction or Direct Fix.

CAVITY FIX :    The E2/AS1 document has dealt with cill support in a cavity situation by  simply putting it back on the window system supplier saying “ Make allowance between packer at sills for support brackets for larger windows . Such brackets require specific design , and shall be supplied by the window manufacturer”.  The major window joinery system suppliers, came together under the umbrella of the Window Association of New Zealand (WANZ) to work out a solution and the WANZ support bar was born.

There is a variety of of WANZ support bars in  4 different widths (20mm, 30 mm, 40mm, 55mm) allowing for support in common situations, depending on the cavity/cladding thickness. Ventilation as per E2, and fixing is allowed for by having the support bar pre- punched .

The fixing of these bars and their alignment has been made user friendly by the WANZ Support Bar Location bracket. For the support bar to be effective the frame must have adequate support between it and support bar or some part of the frame extrusion must rest on the support bar. Proprietary cill support blocks in the frame would be supplied by the window manufacturer and pre glued to the frame at the appropriate load points or distances (usually under mullions and in the middle of large glazing spans).  These WANZ support bars are available through your local window supplier and must be used the full length of the window/door.      



DIRECT FIX :   Cill support is not  limited to use on cavities but also extends to Direct fix applications. However, the bar itself is less elaborate and is a simple  angle is recommended as there is no requirement for ventilation in the bar, as ventilation is mandatory between the cill tray and window frame.  The overhang is limited to the thickness of the cladding. The angle is usually  75 X 25 X 3 mm thick, this may vary depending on cladding thickness.