Ok for fiberglass insulation to touch roof deck on sides of vent channel?
I have a vented roof in central NC zone 3 (user to be zone 4 until recently)with vaulted ceilings in two locations and have specified R49 for the cavity. The insulation crew installed the foam baffles between the 16” centered rafters which creates a vent channel approximately 10” wide with ~three inches on either side where the baffle is stapled to the roof deck. If the insulation batts are pushed all the way into the cavity they will touch the roof decking on either side of the vent channel.
Is that how the assembly is supposed to be configured with the insulation touching the baffle and the roof deck or should the insulation be kept off the roof deck using the baffles as a fail safe incase of an errant install?
thx!
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Bumping this same question except I’m in climate zone 7. Should the baffles act as a stopper for the whole batt and rafter bay width or should the batts be tucked to the sides touching the roof deck? I say no they should not touch the roof deck.
Thanks!
Jwolfe,
The narrow pre-made baffles are for vented attics where they are only installed at the eaves to create a passage for ventilation air to move from the soffits. In those circumstances the edges of the sheathing do take on moisture by adsorbtion, but are able to disperse it.
For cathedral roofs with continuous ventilation from eaves to peak, full width baffles should be used. The safest roofs use permeable material for baffles.
https://www.greenbuildingadvisor.com/article/site-built-ventilation-baffles-for-roofs
Ideally you want the baffle to extend all the way from rafter to rafter, creating a vent channel the full width of the rafter bay. Prefabricated vent baffles don't always do that though, but you're still OK in most cases (cathedral ceilings are most critical though as Malcolm implied).
If you're only using the baffles out at the eaves to protect against wind washing and to maintain the vent channel where the insulation is compressed a bit due to space being tight, you're probably fine. If you're working with a cathedral ceiling, then you really want full-width baffles, which you'll probably need to fabricate on site. I like to use 1/4" waferboard (thin OSB, basically) and 1x2 furring strips to do this, but you can also use 1/2" polyiso or just about any other suitable rigid material that you have on hand.
Bill