Hi All,
Last weekend I saw a new timber framed pavilion at a public park and am somewhat concerned about one aspect of it's design. My concern is with the tie beam to post joinery, or lack thereof. The tie beam is not below the plate, but is located at the plate, and there is no tying joint.
The structure is about 18 or 20 feet square and has a common rafter roof. A ridge beam supports the rafters at the peak and plate beams support the lower end of the rafters on each side.
There are three 8x8 inch posts supporting each of the two plate beams, using traditional pegged mortise/tenon joinery and a pair of braces. The plate beams are smaller in cross section, perhaps 6x6, and are flush with the outside of the posts.
There is a notch cut out of the inside of the tops of the posts, about 2" horizontal and about 10" vertical. There are 3 tie beams which perch on the 2" notches in the tops of the posts. At the center of each tie beam is a post which supports the ridge beam. Pegged braces connect each end of the tie beams to the posts.
The frame is Oak, the timbers appear to be properly sized, craftsmanship looks good. I know that with the supported ridge beam and common rafter design there is no roof thrust at the plates which would require a tension joint at the ends of the tie beams.
However, there will still be horizontal forces in the frame due to roof wind loading for example. The tie beam to post braces will work to oppose this force. The brace that is in compression will attempt to lift the end of the tie beam which is sitting in a 2" notch and free to move vertically. Perhaps the vertical roof load on the tie beam from the ridge post will prevent this and all is OK?
