The ALUPLAN vertical sliding window (Vertlite) windows are designed to offer the same look and thin profile as the old wooden box sash windows. These window units are space savers and allow no exterior protrusion. Both top and bottom portion may slide allowing varied airflow. The units are durable, highly versatile and low maintenance. High density pile is located on both sides of the sashes to ensure that there is no metal to metal contact as well as providing a weather tight seal. The sections used are comparable to the ISO44 series windows. The spring balance mechanism used is completely concealed from view and very easy to use. The vertical sliding windows may be 600 mm x 900 mm tall to a maximum 1200 mm x 1800 mm tall. Bigger windows and doors are made with the ISO100 system. Larger, heavy duty vertical sliders are possible using a counterweight system. The maximum size is 2000 mm x 3000 mm tall, as with traditional Victorian windows but weather and wind proof.