Gabel,
Thanks for the feedback. I'm trying to sort out where the forces would be coming from that might cause the tops of the posts to bow out. My assumption is that the roof trusses will be acting to prevent any spreading.
The reason I went with a hammer beam style was to gain some headroom in the loft (plus a little bit of interesting aesthetic in the space). The central bays are only 10' wide with just 6' 6" clearance under the hammer beams on the second floor. If I were to go with tie beams just below the plates I wouldn't be able to walk upright through the space. (part of the second story space will be used for a bunkhouse, so headroom was important)
Kevin,
Without a continuous tie at plate level (or really close to it) you don't have a roof truss. If you are counting on the collar beams tying the rafter pairs together and preventing spreading, then I'm not sure that's going to work. The tension would be pretty high on the joint between rafter/collar and also that would place a pretty big point load on the rafter. Also, the ridge doesn't seem to be doing anything since it isn't held up by either posts or trusses.
What's the height from the top of the loft floor to the top of the top plate?
