The Series 20 vertical sliding unit is designed for the treatment of traditional double-hung sash windows. It features spiral spring balances with adjustable tension to fully support the weight of the sash and allow opening to any position. The sashes are attached to the balances and are not removable but contra-slide to facilitate cleaning. A minimum 75mm cavity between the inner and outer windows is recommended. Where the external window incorporates window catches or specialist locks on the meeting stile the cavity may need to be increased to permit access or an alternative treatment considered. Twin brush seals ensure high sealing efficiency. Fixings are concealed within the frame to provide a clean appearance on the room side. Frames may be linked with a purpose designed mullion/transom section.

• A fitch catch lock, available in silver, white or bronze, can be fitted to the interlock stile.
• A heavy duty box interlock section allows wider sashes to be produced subject to weight limitations.
• The window heads can be curved to a fixed radius. It should be noted however that this will shorten the balances and so reduce the travel of the sliding sashes.