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details of joints between purlin collar and rafter
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and known as a lower king-strut. This type of roof truss was soon superseded by the queen-strut roof with through-purlins clasped at the angles between principal rafter and collar. Occasionally a tenon was provided at the cut-back of the principal rafter engaging a mortice in the underside of the purlin.
The feature of these two roof types is that the principal rafters are in the same plane as the common rafters and are, in most cases, only slightly larger in section. When the purlins are clasped at the back of the principal rafter, that section of the rafter from this point to the ridge is often reduced in depth to that of the common rafters. In addition windbraces between the principal rafters and purlins were also introduced to increase stability. Side-purlin roofs were economical in both timber and labour in that they no longer required collars to all the common rafters, and at the same time the area between the trusses was open and unimpeded.
Clasped purlin roofs with queen-struts remained the most popular of the two and, although found here and there throughout the medieval period (the earliest example of a type of clasped purlin being at the Wheat Barn, Cressing Temple, Essex, of about 1250), it was not until early in the sixteenth century that they became universally adopted in lowland England; then they continued to be used until the beginning of the nineteenth century. Towards the end of this period the queen-struts tended to be set at an angle rather than vertically. In the transitional period between the use of the crown-post and side-purlin roofs, complex hybrid roofs using both old and new methods were built, one fine example being the roof of the granary at Rookwood Hall, Abbess Roding, Essex, where crown-posts and collar-purlins were used in addition to side purlins with windbraces. Although butt-purlins were found in high-quality medieval carpentry in highland England – for instance, in Hereford & Worcester and Shropshire, it was not until the sixteenth century that they were generally adopted as an alternative to clasped purlins in much of southern and eastern England. The purlins could be either tenoned to the principal rafter on line or staggered, a method which appears to be somewhat later in date.
The crown-post and butt-purlin roofs belonged predominantly to the South-East and eastern England. In the North it was the king-post truss (39), in which a stout post, the king-post, rises from the tie-beam to support the ridge-piece, with the principal rafters rising from tie-beam to ridge being framed to the tie-beam and the side of the king-post. Between each principal rafter run the purlins, trenched partly or wholly into them to support the common rafters. In addition the principal rafters were sometimes supported by struts off the tie-beam. Variations within this general arrangement were not as numerous as in crown-post construction, the main variation being
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