Essentially derived from the Roman bathhouse model, hammams normally consisted of four main chambers: a changing room, from which one then moved on to a cold room, a warm room, and a hot room. Heat and steam were generated by a hypocaust system which heated the floors. The furnace re-used natural organic materials (such as wood shavings, olive pits, or other organic waste byproducts) by burning them for fuel. The smoke generated by this furnace helped with heating the floors while excess smoke was evacuated through chimneys. Of the different rooms, only the changing room was heavily decorated with "zellij", stucco, or carved wood. The cold, warm, and hot rooms were usually vaulted or domed chambers without windows, designed to keep steam from escaping, but partially lit thanks to small holes in the ceiling which could be covered by ceramic or coloured glass.