Designing a roof with 2 different framing styles

Hi all, I’m designing an 8/12 cathedral roof for our 2 story 48’x28’ cape (zone 4c, snow 25, wind 85, seismic D2). I’m considering framing half of it with manufactured scissor trusses (bottom chord ~6/12), and the other half with 2×10 rafters/ridge board with exposed rafter ties. A couple reasons for this: 1) we have some extra 2×10 Doug fir milled on site, but not enough for the entire roof, and 2) my wife doesn’t want exposed ties in the master bedroom area. I’ll be the GC, and framing this myself.
Does anyone have experience with this? I’m mostly wondering about framing a secure connection between the last truss and the ridge board, given our seismic zone. Would the trusses be able to resist lateral movement of the ridge board?
I’m aware that the insulation would need to be contained where the two meet, any tips on this are appreciated. Planning on loose-fill cellulose in the truss section, dense pack in the rafter section.
We’ll be working with an engineer soon, but I’m looking to get insight into the issues so we don’t go in the wrong direction.
Thanks for the advice!
Adam
Replies
Roof sheathing will provide part of the load coupling between your truss area and the rafter part.
Your engineer will be able to specify acceptable details, and the truss manufacturer will be able to help as well. Trusses mostly require additional bracing installed to complement the truss properties, (which are limited to the plane they are in for the most part).
Bracing design for the trusses can be integrated with calculations for the rafter and ridge board.
Thanks for that info, I’m meeting with the engineer next week and I’ll see what he says. I’m also realizing that the difference in R-value between the two assemblies will have to be remedied (by furring down the 2x10s I guess). This might make the effort not worthwhile since the ceiling planes might be so close as to look like a mistake was made! I’ll think about it some more..