Insulating a timber-frame building with cellulose — moisture issues?
Hi all, thanks for all the great information here…I really appreciate it.
We’re in the process of building a timber frame workshop & office. Only one of the “bays” will be insulated and heated…a 12’x24′ space, with a 9′ ceiling. There will be insulation directly above the ceiling, and then storage space above that. Below the frame is a root cellar, separated by 8″ joists. Basically we are making an insulated, conditioned cube within a section of the frame.
Right now I am thinking of doing the following:
— From inside: drywall; 2×4 strapping; Intello membrane; 2×6 studs w/ dense cellulose; pine board sheathing; 2″ Roxul board; batten & board siding (ie. battens as first layer, screwed to sheathing through Roxul)
— 2×6 studs would be flush with the outside of the timbers
— The outside boards & Roxul would extend down to the bottom of the 8×8 sill.
— From inside: 4×6 decorative joists; T&G ceiling boards; air barrier, 2×10 joists w/ dp cellulose; 1x pine boards
— Air barrier membrane would continue over ceiling, with 10″ joists on top also dense-packed with cellulose
— From inside: Finished pine flooring; 3×8 joists w/ dp cellulose; vapor retarder membrane; strapping; root cellar
My biggest concern is whether I am going to run into moisture issues at the 8×8 hemlock sill. Sill sits on both copper termite barrier & thick layer of EPDM rubber, so no issue of capillary moisture. To the inside and on top would be dense cellulose, & to the outside would be pine boards & Roxul board. Any reason I should be worried about this?
Also, I am hesitant to add an interior air barrier to the floor because of the vapor retarder on the bottom of the joists (there to prevent high humidity from root cellar from migrating upward). I assume that the vapor retarder will function as an adequate air barrier, as it is tied into the bottom of the sill….but maybe not?
ps. Climate Zone 5b
Likely heating with electric baseboard, or similar.
Use will be an office with no cooking, no plumbing, occupied by 1-2 humans 4-6 hrs/day.
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