Attic Baffles for Airflow and Low Slope Roof
Hi,
In CZ4 and buttoning up the air sealing detail on a remodel / addition. The new addition has a hip roof with ~16″ vented soffit, gable vents on my existing structure, and a newly installed ridge vent. I installed the Durovent baffles from the orange store over the weekend to not block airflow once cellulose is blown in down near where the rafters intersect the top plate. For a number of other oddly sized rafter bays, I cut and cobbled with 2″ of foam and created a 1.5″ vent channel between top of foam and bottom of sheathing about 3′ up the roof until I have more than enough clearance to pile in as much fluffy as I want. My plan is to insulate the attic floor, not any portion of the roof assembly for an unconditioned space.
First, how critical is it to air seal between the top of the top plate and the bottom of my “vent channels” with more cut and cobble foam? It’s going to be tedious but I think I understand if air leaks there it could windwash out the cellulose and create more problems downstream? How big is the risk of the seal breaking where I cut and cobble, thereby dismissing all the effort to seal it up?
Second, it seems like there will be instances where the cellulose contacts the bottom of my roof sheathing as the depth near the edges is not the full height needed for code. Is that a risk factor for condensation or am I overthinking this?
Third, we have a low slope (2/12) cricket on each side of the house. If the rest of my attic is vented, but I spray closed cell foam there, is that a problem? In other words can portions of an attic be vented while others are not?
Thanks,
Michael
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Replies
It's best to seal the baffle but cellulose is pretty good at resisting wind washing so if you can't seal the baffle, it will be ok, just not great.
If your house is older (and dry) and solidly built, so framing members aren't moving around, cut-and-cobble will probably stay reasonably well-sealed. It's more time-consuming than installing other types of insulation and I wouldn't rely on the insulation staying well-sealed forever, so if you have a risky situation I'd do something else.
It's more important to allow air flow through the insulation baffles than to get the code-required insulation depth, so your insulation should never touch the roof sheathing.
It's impossible to predict what will happen in interstitial spaces such as those under your crickets. It would be safest to remove the roof sheathing under the crickets so they are part of the attic space and can be vented or spray-foamed.