Timber frame roof members can include common rafters, principal rafters, purlins, hips, valleys, and jack rafters. This is an extensive category, and we will be adding joint details to this category frequently.
Table of contents
Rafters and Purlins
Rough Sawn – Rafters – 4x Rafter, Simple Birdsmouth
This is the simplest way to connect a common rafter to a top plate in a timber frame structure. There are other more complicated joints but when there can be a large number of these connections that typically require a structural screw anyway, we like this simple connection. The important measurement is the H.A.P. (Height Above Plate). This measurement will be given on your frame plans. Even if your rafters change in height, if you use a common H.A.P., the tops of your rafters will plane out.
Principal Rafter – Principal Purlin Joint
One of our favorite roof systems is the Principal Rafter – Principal Purlin – Common Rafter roof. It saves material by reducing the depth of your common rafters by breaking the common rafter span in half. Housing the principal purlin is necessary to keep it from wanting to slide down hill and it also provides a good reference and self-locating position during raising. Always provide a gap between the top of the principal rafter and the bottom of the principal purlin. This keeps the bearing surfaces of the housing engaged even if the timber dries. Otherwise, the drying and shrinking of the timber could cause it to lift off its bearing surface in the housing and a split to occur.
Housed Purlin or Joist
More purlin details where the purlin, and/ or joist for that matter, are flush with the top of the carrying beams. Coping details for reducing the depth of housed members are illustrated.
King Post – Bottom Chord
In a king post truss, the king post is a tension roof member resolving the thrust. When a load is applied to the bottom chord, use a through tenon. Such loads could come from floor joists for a loft for storage or other area. In these situations, the through tenon works well to handle those forces. In most cases, it just looks cool and having 3 pegs staggered creates a solid connection.
If the ornamental cut on the through tenon is catching your eye, check out our Embellishment area of the Library.
Timber frame joint details on (34) individual letter size sheets. All drawings are printable and delivered instantly through a download link. Joint and Peg entries – 2023.
8×10 Queen Post Truss Chords
This timber frame detail shows the compression connection between the level 8×10 straining beam, the plumb 8×8 queen post, and the sloped 8×10 top chord of a proper queen post truss.
The straining beam is in compression so a 4” long tenon will do along with proper housing to keep the beam secured in its spot on the queen post.
The sloped member does not have a mortise and tenon, but a sloped bearing facet instead. This sloped bearing facet “heel” does not take out too much material and transfers the high compression forces better than a tenon and pegs.