Sawtooth Roof

A sawtooth roof is made up of a row of parallel ridges with two different pitches. The steeper (often vertical) side of each ridge is glazed, while the shallower side is solid and roofed. In profile the roof looks like the teeth of a saw. The design lets large, deep buildings be lit evenly by daylight from above.

Orientation

The glazed faces normally face away from the equator, that is, north in the northern hemisphere and south in the southern hemisphere. This admits steady, diffuse sky light while keeping direct sunlight, glare and solar heat off workers and machinery. In British usage the glazed faces are called north lights, and the roof is sometimes called a north-light roof.

History

The British engineer William Fairbairn may have designed early sawtooth roofs as early as 1827. The first documented example is the weaving shed at Titus Salt's Saltaire Mills near Bradford, founded in 1851. The form spread widely during the Industrial Revolution for textile mills and factories that needed good natural light over large, open floors. Its use declined as electric lighting became cheap and reliable.

Revival

Since the late 20th century the sawtooth has returned in schools, offices, galleries, warehouses and houses because daylighting reduces the need for artificial lighting. The solid slopes can also carry solar panels angled toward the sun, combining daylight and generation.

Construction and maintenance

• Each valley between teeth is a gutter, often a box gutter, which must be sized and maintained to avoid overflow into the building.
• Snow and debris can collect in the valleys.
• Glazing must be detailed against leaks and condensation, and older single-glazed north lights perform poorly thermally.
• Steel or timber trusses, or portal frames, typically support the roof.