Does anyone have experience with cellulose insulation in cathedral ceilings? I am looking into insulation an addition and have several questions: Will dense packing a cathedral ceiling create moisture problems due to eliminating roof venting? A fiberglass insulation guy told me there is the potential of overheating the roofing and sheathing because the cellulose will reflect too much heat back upwards with no venting to remove it. Is this true or just hype?? Seems like there’s no such thing as too much insulation.
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The insulation is gonna ruin the roof by reflecting too much heat? Isn't that the plan, heat out & cool in? Or heat in & cold out? I guess his theory is fiberglass is such a poor insulator that the heat just flows right through into your house?
This has been discussed about 50 times at least, a search for cellulose or cathedral ceilings will get you more info than you want about the pros and cons of unvented dense pack cellulose in cathedral ceilings.
My opinion is do it, Gabe sez no. Joe H
Why is your attic not vented. I have a cathedral ceiling just in the living area and its vented. I dont see any reason why someone cant use blow-in cellulose in this area as in all the rest of the attic. JMHO, Roger
A great way to vent cathedrals is to make the chutes from foil faced 3/4-in. polyisocyanurate foam. Tack some 1 in. wood strips to the rafters tight to the roof sheating, and nail the foam to them, between the rafters. You can air seal with minimal expanding foam. This creates your vent space, while maintaining your R-value and keeping the inspector and the roofing manufacturer happy. Then, you can dense pack the remaining space with cellulose.
You'll also sidestep the vent/no vent discussion quite handily. <G>
Andy Engel, The Accidental Moderator
Andy, there's not much moderating needed without the vent/no vent immoderates. Joe H
Joe, I was hoping to take the weekend off....Andy Engel, The Accidental Moderator
Thanks for the reply, I guess Mr. Fiberglass thinks I'll cook the roofing because there is no airflow to remove the heat between the dense-pack insulation and the roof. If the insulation fills the cavity though, seems like there's no room for the heat to build up in the first place. Not to mention that metal roofing has ridges every 9" that would act as venting above the sheathing and possibly reduce heat build-up. Have you ever heard of concerns of mold growth in cellulose insulation because of moisture content?