Mineral wool application
Philly_Marc
| Posted in General Questions on
I am insulating the ceiling of a rowhouse in Philadelphia.
I am interested in using R-30 mineral wool.
The insulation would be placed between the rafters, directly against the bottom of the old roof boards. The boards are solid and have a new (2016) protective roof above them.
Sheet rock would be attached to the rafters, creating the ceiling.
There will be no open space between the bottom of the roof, the insulation, and the sheet rock.
Is this a feasible idea?
Would it require vapor barrier?
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Replies
Philly_Marc,
Unfortunately no. Roofs with permeable insulation require a vented air space under the sheathing. Otherwise warm, moist air from the house makes its way through the batts and condenses on the colder sheathing above, which can cause it to rot.
Here is a link to five options that work: https://www.greenbuildingadvisor.com/article/five-cathedral-ceilings-that-work