Underpurlins run in straight single lengths where possible at right angles to rafters, evenly spaced, joined over supports by halving or lapped splices, cantilevering no more than a quarter of their allowable span, with a backspan at least three times the cantilever, and fixed to hips and valleys by the listed options; rafters are single length or joined over supports, birdsmouthed no deeper than a third of their depth, and in cathedral roofs designed for roof and ceiling loads; ridgeboards locate rafters (opposing rafters offset no more than their thickness), strutted at hip or valley junctions over 5 m or where underpurlins bear on them; hips and valleys are strutted or supported by underpurlins; scotch valley pitching plates are at least 35 mm thick and nailed at each crossing.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.