Casement windows are the most common and cost effective of timber window.
The simplest of window styles they are outward opening and available in side hung (like a door) and top hung (like a letterbox) formats.
The size of openable parts (sashes) is restricted. For a side hung sash the maximum size is 700mm wide and 1300mm high, with a semi-perimeter of 1900mm. For a top hung sash the maximum size is 1300mm wide and high with a semi-perimeter of 2500mm. The degree to which sashes can be opened is also restricted.
Side hung and shallow top hung sashes can be fitted with easy-clean hinges, to facilitate cleaning the outside from inside. Suitably sized side hung sashes can be fitted with fire egress hinges.