Rafters

Roofs of a clear span up to 20 ft. may be constructed with common rafters only, provided that if the span does not exceed 14 ft. one collar of the same dimension as the rafters be provided to every alternate pair of rafters. If the span exceeds 14 ft. then a collar shall be provided to each pair of rafters. Collars shall be placed at a minimum height above wall plate of 1/3 the rise of roof.