"A roof construction in which [pieces of timber] are laid between the principal rafters; they support the boards that run between the ridge and eaves of the roof." (Harris, 729) Purlins help support the roofing material. In Craftsman architecture, the purlins frequently project from the wall into the eaves.
Purlins are metal tracks used to support metal roofs or siding. Purlins can also mean the members placed at right angles to rafters to break up the roof board span. RACKING A misshaping of a frame caused when horizontal loads applied to vertical boards displace the frame from its rectangular position.
Horizontal timbers that connect rafter trusses. Queen Post: A pair of vertical posts of a roof truss standing on the bent plate or girt and supporting the rafters or collar tie. Rack: The action of straining or winching a frame to bring it into square or plumb.