Reciprocal frame

A reciprocal frame is a class of self-supporting structure made of three or more beams and which requires no center support to create roofs, bridges or similar structures.

More commonly, these roofs are constructed with roundwood poles where each rafter is laid upon the previous one.

In both of these approaches, the roof is assembled by installing a temporary central support that holds the first rafter at the correct height.

The structure is most effective at lower pitches where there is minimal spreading force exerted at the ringbeam, most being transferred directly downward.

The reciprocal frame, also known as a Mandala roof,[1] has been used since the twelfth century in Chinese and Japanese architecture although little or no trace of these ancient methods remain.