Roof truss with a room
JMConstruct
| Posted in Energy Efficiency and Durability on
I am working with a customer who is wanting to build a very efficient home. We are considering double wall for exterior walls and installing 7 1/2″ of rock wool or 2×6 studs with Zip R sheathing and filling the cavity with blown in blanket system (BIBS). Any suggestion on the best product for the money?
Our biggest struggle is with the roof design! Engineered roof trusses will be a 10/12 pitch with a 12′ wide room built in. What would be the best design on insulating. Typically the trusses have a 2×4 or 2×6 top cord. How would I seal envelope on this detail and what insulation and air barrier would be best to use?
Thanks
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Replies
Justin,
Clearly, the trickiest areas to insulate are the sloped ceilings in the attic room -- since those areas have 2x4 rafters (the top chords of the trusses). You'll need to fur down the rafters (chords) to accommodate the insulation (or the insulation plus a vent channel, if you decide to make this a vented assembly).
Justin,
I think the bigger problem then insulation is trying to air seal on the interior side around trusses.
If you want this "properly" sealed, you are looking at spray foam ($$$).
Cheaper option would be to get trusses with either 2x6 or 2x8 top chord. Put fluffy insulation on the inside and enough rigid on the outside for condensation control. This would allow you to have continuity around the exterior sheathing /roofing, use it as your primary air barrier which is much easier to detail.
I built a room over a garage on a new home, a room within the trusses. It will be more than a 2x4 top chord and probably greater than 2x6. What is your heating zone and the span of the trusses? I used a warm side air barrier and built a double wall inside the truss room opening for high R insulation. Martin has it right, you will fir down the sloped portion of the truss for a dedicated air space and insulation to code. If the room is over the garage, T & G 3/4" floor decking glued at all edges and the groove will serve as a warm side air barrier.