Can an Unvented Cathedral Ceiling be Insulated with Dense-Pack Rock Wool?
John Roy has contacted a well respected insulation contractor in his area who says there’s no need to install ventilation chutes in the rafter bays before packing them with insulation because rock wool won’t absorb water. The plan has the blessing of the local building inspector, who will sign off if soffit vents are installed.
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In this post at GreenBuildingAdvisor’s Q&A forum, Roy wants to know whether he’s getting the right advice.
As it turns out, he probably isn’t. Not only will the amount of insulation he can pack into the rafter bays be insufficient to meet code recommendations, it also raises old concerns over moisture accumulation.
Roy’s best approach may be to make his own ventilation chutes and seal them carefully to prevent air leaks. In conjunction with an additional layer of rigid foam insulation, his roof could clear the super-insulated bar.
One approach to venting the roof:Installing sheets of rigid foam insulation slightly below the tops of the rafters and sealing the edges with foam is one way of providing an air channel for ventilation.