Information on the origin of the term "purlin" is scant. Original roof of closely spaced trusses with collars and former collar purlin and crown posts. Heavier "under purlins" or "purlin plates" are used to support longer rafter spans. On a purlin roof the ridge posts carry the ridge purlin. The outshut roof was probably repaired in the seventeenth century with an inserted purlin. A comparable element in roof construction is a purlin. Log cabins were constructed with either a purlin roof structure or a rafter roof structure. It has a triple purlin roof which is tiled in stone. Purlin plates are very commonly found in large old barns in North America. A purlin roof consists of horizontal logs that are notched into the gable-wall logs. Purlin plates are beams which support the mid-span of rafters and are supported by posts.