Insulating floor of vented attic in 19th century former farmhouse
I own a mid-nineteenth century farmhouse in upstate NY. A prior owner had built out the third floor attic space. Those improvements (sheet rock and fiberglass insulation) have been removed, because of roof leak issues damaging the sheet rock and mold growth on the sheetrock. The third floor (attic) had not be used for other than storage for over a decade.
I am now making some renovations to the house and plan to return the attic back to vented, unimproved attic space. But I am struggling with how best to insulate the second floor from the vented attic.
For environmental reasons, I would like to stay away from spray foam.
The attic floor is comprised of roughly 5 inch wide boards (which I believe were milled shiplap rather than tongue and groove), with a thickness of about .75″. The joists are roughly 3″ by 4.5″.
My preference is to remove the attic floor boards, clean out any material between the joists, pack in cellulose insulation, and rebuild the floor.
The attic space above will be vented with a ridge vent and eave vents (that will be installed this spring when the space is reroofed).
1. Ought there to be a vapor barrier under the cellulose and above the 2nd floor ceiling?
2. With or without a vapor barrier, 4 inches of cellulose has a lower R-value than I would like. I want to keep the attic usable for storage. I has been suggested to me that I could get a higher R-value but adding to inches of insulating board (blue board?) to the attic floor, and cover the usable floor with .5 inch plywood. I’ve been told I would need a vapor barrier below the cellulose to avoid condensation on the insulating board. Do I need a vapor barrier in any event?
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