Knee wall

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A knee wall is a short wall, usually under about 3 feet (1 meter) tall, that provides support for roof rafters in timber-framed roofs. Instead of long rafters spanning from the ridge to the eaves, the knee wall supports rafters at mid-span, allowing shorter, lighter rafters. The wall is typically finished with plaster or gypsum board.

The name comes from its resemblance to a bent knee. Knee walls are common in houses where the attic ceiling is the underside of the roof and the roof slopes down on one or more sides. There is no single standard for how tall a knee wall must be or exactly how to measure it; in practice, it is placed where the floor soffit ends and may extend to where the outer wall meets the rafters.