20 x 30 1.5 -- Need both Rafter Ties and Collar Ties?

[gobrikings]

I just bought the 20 x 30 1 1/2 story plans and am prepping to start construction next summer on my cabin in North Dakota.  This forum is great and have already picked up a ton of pointers--truly appreciate all of the great posts, and hope to repay the favor.

In our plans, we're going to use 12" joists 16" o.c. for the loft above the bedroom/bathroom as shown in the plans, but want to leave the space above the great room open.  The catheral ceiling option in the booklet shows a design using a ridge board and rafter ties 4' o.c.   For ease of construction/insulation (it's ccccccccold in ND!), I think we want to stay with the truss rafter option instead.  In that scenario, are the 4' o.c. rafter ties necessary, or do the collar ties on the rafters provide sufficient strength?  My belief is that the collar ties should be fine, but would appreciate second opinion.

Thanks much,
Grobrikings

[John Raabe]

If you are having the trusses built be a local company, they can probably design a truss package that will serve for both the loft and cathedral sections of the house (it may be the same truss). The site built truss I have diagrammed for areas that don't have access to manufactured trusses could be stiffened by adding a rafter tie at every other truss (4' o/c) in the cathedral section. That would provide the tie that the loft floor section gets from the balloon framed wall and floor joist system.

You could also beef up the insulation value of the sloped cathedral roof (or trusses) by adding a layer (1" or 2") of foam board insulation to the interior side of the rafter.

[pinpointsharpie]

I have a similar situation with the 1.5 story.  we're planning a great room with two 6' gabled dormers (across from each other), 6 feet from the gable end of the house.  we will be using advanced ove framing 24oc.  we'd like the truss design with the collar ties 24oc but would like to extend the rafter tie spacing @ the top plate to 6 feet so they line up with the dormer. is this possible.

Thank you,

Pete

[John Raabe]

I would definitely run this question past the truss company engineers. Take a sketch or diagram of what you want to do. There is not usually a charge for this "feasibility" exercise. It may be possible to be stick framed but I don't think you could get what you want from prescriptive code book design - meaning it would also have to be engineered.