Here at Davis Timber Frame Company, we offer a variety of different options when it comes to choosing a timber frame truss style for your new home project. The two most common timber frame systems used today to build timber frames are either common rafter frames, or common purlin frames. Not all frame types fit into these categories, however the most common frames we produce here at Davis Frame do.
Common Purlin Frames
Common purlin frames consist of a series of purlins all bearing on the principal rafters of a bent. Common purlin frames are usually erected one bent at a time at uniform intervals. Perpendicular pieces are inserted as each bent is tilted into place. This process is followed by the installation of purlins to complete the frame roofing.
When decking is applied to the roof of a common purlin frame, the boards must run perpendicular to the purlins.
Common purlin frames include hammer beam truss frames, king post truss frames, queen post truss frames, and scissor beam truss frames (not shown below).
Hammer Beam Truss Frames
Hammer beam truss frames are very similar to queen post truss frames, but two seperate ties, called hammer beams, break the queen posts. Hammer beams exert great lateral pressure onto the eave posts, which must be taken into account in the design of the frame.
Queen Post Bent Frames
Queen post bent frames make use of vertical timbers called queen posts which span from floor to a part-way along the length of the principal rafters. Similar to a principal purlin frame, the interior posts of the queen post bent frame will form aisles along the eave walls. At the top of each queen post, a tie beam is used to connect the post to the opposite queen post.
Queen Post Truss Frames
Queen post truss frames are similar to queen post bent frames, but with the addition of a tie that breaks the queen posts and transfers the loads to the eave posts. Like the king post truss frame, this allows for a clear span and there are no internal posts that will affect the floor plan.
King Post Bent Frames
King post bent frames make use of vertical timbers called king posts which span from floor to ridge. Diagonal braces from the king post to the rafters create the truss that helps support the roof load. The king posts must be taken into consideration when designing the floor plans.
King Post Truss Frames
A king post truss frame is similar to the king post bent, but with the addition of a tie that breaks the king post. The use of the tie transfers the loads to the eave posts and allows for a clear span by eliminating the king posts that would otherwise affect the floor plan.
Common Rafter Frames
A common rafter frame is one in which the roof rafters span from the eave walls to a ridge beam, principal purlin or the opposing rafter. Common rafter frames are usually erected in sections of walls: principal purlin walls or ridge walls: and the eave walls. Perpendicular pieces are inserted as each wall is tilted into place. This process is followed by the installation of rafters, typically four feet apart, to complete the roof framing. When decking is applied to the roof of a common rafter frame, the boards must run perpendicular to the rafters.
Common rafter frames include collar tie frames, principal purlin frames and ridge beam frames which are described below. Larger early American frame structures like barns, for example, tend to be Common Rafter Frames.
Principal Purlin Frames
Principal purlin frames use rafters that span from the eave plates, past a pair of main purlins, and then continue on to meet with and bear on the opposing rafter. Principal purlin frames can be considered a type of aisled frame because the internal posts that support the principal purlin form aisles that are parallel to the eave walls and a central bay or nave.
Collar Tie Frames
Collar tie frames have no internal posts and therefore create open spaces but can only be used for limited widths. Rafters span from the eave plate and bear upon the opposing rafter end at the ridge. The collar tie spans between rafter pairs in the lower third of the lengths of the rafters.
Ridge Beam Frames
Ridge beam frames use rafters that span from the eave plates to a central ridge beam or beams (depending on the length of the building). Ridge beam frames have posts located centrally to support the ridge beams and that must be considered in the floor plan layout.
*Timber Frame types descriptions above can be found in our book, Timber Frames: Designing Your Custom Home. Order a copy today!