Saw-tooth roof

A saw-tooth roof is a roof comprising a series of ridges with dual pitches either side. The steeper surfaces are glazed to admit daylight and face away from the equator to shield workers and machinery from direct sunlight. This kind of roof admits natural light into a deep plan building or factory. It was therefore most commonly built during the Machine Age from the mid-nineteenth century to the mid-twentieth, when electrification of factories was not yet common. Many factories of the era had little or no electrical wiring; their main power sources for the machinery were often steam engines driving line shafting, and the lighting was chiefly via daylighting through the windows. Work done at night, when necessary, was typically lit by oil lamps and candles, but many factories closed for the night. Their norm of an early working day (for example, 6 a.m. to 4 p.m.) was not merely a tradition but a functional decision based on this reliance on daylighting. The same was true of the farmer's workday, for the same reason.