The traditional timber sliding sash and casement window has probably been the most popular choice of architects and builders over the centuries. Operated by concealed pulleys, weights and ropes or chains, this design overcomes the difficulty of ventilation and of cleaning windows safely from inside the room. The modern equivalent is either manufactured of timber to the original design, or in timber, aluminium or PVCu and be double glazed, and utilise metal spring balances for sliding up and down and tilting into the room for cleaning.