Vented roof with trusses that extend over porch
Hi all. As much as I’ve read/learned here, I had an unexpected question come up in my in-progress build.
Climate zone 4 (middle TN), new build of two-story house with plans for a vented roof/attic. Air barrier at the sheathing and ceiling drywall, roof is (energy heel) trusses, which leads to my question:
For a vented roof, I understand the general plan is to have an insulation dam at the soffit vent, with a ventilation channel that runs up at least to the top of the insulation, to avoid wind-washing (will be fiberglass batts in this part of the roof). How is this generally handled, though, when the roof/trusses extend over a 10′ deep porch, such that the soffit vents are at the edge of the porch, but the insulation starts at the top plate of the conditioned space? See attached fine artwork/drawing 🙂
In this scenario, is a ventilation channel needed/helpful? Would it need to run the full length of the roof over the porch to ensure any air moving air comes in above the top of the insulation to avoid wind-washing? Or will any movement have dissipated enough in the open space above the porch?
I couldn’t fully seal it due to the trusses, but would putting OSB insulation dams between the trusses on the porch side of the batts (directly above wall sheathing) to the height of the insulation be good to prevent large air movements through the insulation?
Also, who usually handles this kind of detail? The framers (who are putting the decking on and installing the soffits)? Roofer? Or insulation contractor.
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