Putting batt insulation between 2×4 top chord truss for unvented low slope roof
Hello,
It’s been awhile since I’ve asked a question here but I need some of this community’s expertise yet again.
I am connecting an a two story addition to an existing home. The project qualifies for a historic rehabilitation tax credit so I have to follow the guidance of the historic rehab people at the State and Federal level. They don’t want me to have a “flat” shed roof, but rather a low slope gable roof. And this roof has to fit under the eaves of the existing home. It’s a tricky problem for me, but I think I’ve figured it out.
My build is in Climate Zone 4A.
I will have low slope trusses made, but the height from the bottom chord to peak of the truss can’t be higher than 18″. I will make this an unvented roof/attic assembly. I only have enough room to put 3″ of foam board above the roof deck. 2″ of polyiso foam board (R-13) and 1″ of EPS (R-5) for a total of R-18.
Under the roof decking in my “attic” I can fulfill the rest of the R-20 to meet R-38 minimum by putting in R-21 batt insulation. However, how do I attach batt insulation to 2×4 top chord trusses? Should I just dense pack my entire attic since there’s barely any room in there anyways? Maybe I should specify the truss maker have a 2×6 top chord in order to use tiger teeth, but that would raise the price of trusses by a few hundred bucks. Not a big deal if this is the easiest method.
Thanks for any advice one can give.
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Replies
Not what you are thinking, but with the right amount of adhesive, cellulose can be wet sprayed overhead. With less air movement, performance should exceed batts.
Yeah that's an idea. I have done wet spray cellulose on walls before. I don't know how it will hold up over 5" in a nearly horizontal application.