Help with this timber frame

[Garry Barnett]

  I need help with this timber frame that we are trying to build ? The pictures don't show the post and beam at the end of the lowered section of the frame. Also the struts, braces, and rafter/purlins will be added when I figure out if this will work for us.

   1. This is going to be a hybrid timber frame, with the rest built with 2x conventional framing.

   2. We are in the big lake area of Alaska, Wind Speed 100+, Snow Load 50-70, Seismic real bad.

   3.  With the truss tie beams at about 9'6 high, do you folks think it will feel too crowded with the tie beams that low?

   4.  With a 10/12 pitch will the trusses seem to large ( 10' king post ) for the area? would it be possible to go to a 8/12?

   5.  The 21x12x 8'3 area is the kitchen with no loft above and regular energy heel trusses.

   6.   We will use witterbounds roofing method
        " I put two layers of three inch polyphysomething on top of my t&g to insulate my roof.  I think the order was t&g, felt, 6 
         inches of insulation, 2x4s over rafters with 12 inch screws through into rafters, sheathing, felt and metal roof."

   7.  What will work best for this roof, rafters or purlins?  
 
   8.  What size material would you use to build this frame, and have it look right. I'm using Douglas fir. (8X8 post 8x12 tie beams)

   9.  Would you build the frame with kiln dried or green?

  10.  Any suggestions on improvements from you all, will be much appreciated.  Thanks.
  
 

 

 

[doc henderson]

I am not a timber framer, but looking at it, I think it is ok.  could consider a more decorative scissor style truss ect. for the center 2 trusses.  I do not think the outer two will matter

[Don P]

Hi Garry, welcome to the forum.
With those conditions an engineer would be a good idea.

You can lower the pitch, as the pitch lowers the horizontal thrust, the toggle action of the rafters against the tie increases, dramatically.

The end bents are only restraining that thrust with pegs, very dubious. The internal trusses, I really cant tell how your joinery is intended but it looks like a lot is coming together there. The devil is in those details.
Look up kingpost trusses in the timberframe truss series by the NPS and TF Guild, also various tying joints in Sobon's Historic American Timber Joinery.

Rafters would put half the roof load on the plates, purlins would put the entire roof load on the trusses.

Don't size just to look right, determine the minimum sizes to resist the loads, then upsize if you wish.

I prefer to work with dry material, it moves less. For instance if your kingpost shrinks in width up top, the rafter tops move closer together and the king drives the tie beam downward, it sags.