Questions on building an attic storage deck
I’m embarking on my next project, which is to build an insulated storage deck in my vented attic. First some context:
This is an addition to the house, which comprises a sunken fireplace room over a crawl space and a 2 car garage over a slab. Then there is a stick framed attic over both of these spaces. The walls are 2×4 studs in these rooms, and the ceiling is made of 2×6’s.
The sunken fireplace room is about 14′ x 19.5″. The garage is about 21’3″ x 23’5″. The reason the fireplace is 19’5″ wide and the garage is 23’5″ wide is that there is a covered porch in front of the fireplace room that’s about 4′ deep. And so the attic which covers both the fireplace room and the garage is 23’5 wide all the way across.
I’d like to use the entire attic for storage, however the project I am embarking on right now only involves the portion over the sunken fireplace room.
Presently there is R-19 fiberglass in the ceiling joists above the fireplace room. I’ve been advised to pour cellulose over this, but I think I’m actually going to remove it, because I’ve found dead rodents in other parts of the house in the fiberglass, and I want better access to cracks and things for air sealing.
My plan is to first install baffles in all the rafters from the soffit vents to slightly above the height of my storage deck. I am reading about site-built baffles, and am considering doing this. Otherwise I would just buy a pre-made product such as can be bought in the home improvement stores.
Next I would remove all the fiberglass from above the fireplace room, and frame a perpendicular deck over the existing joists, which I would also screw into the wall on the side that is adjacent to the original house for support (sort of like building a standard deck), and I would ensure the opposite end is fully on top of the 2×4 wall that is between the fireplace room and the garage. Since the fireplace room is 14′ deep, I would use 16′ 2×10’s and simply not cut them off, just let them extend over the edge of the wall into the attic area over the garage. And I would probably frame a small step in front of it as well to make getting up there easier.
Note that there is a a beam going across the middle of the fireplace room made of 3 2×12’s that will actually be in line with my new deck. The 2×6’s which will be perpendicular to the new deck, are hanging from this beam, and extend out to the exterior walls on either side, with each 2×6 being about 9’6″ long in their span.
Next I was going to use some cans of great stuff to air seal any cracks where air could enter the fireplace room below, or where cellulose could escape the deck. Then I was going to rent a machine and blow the cellulose into this deck, which is now 5.5″ + 9.5″ = 15″ high. Then I would lay 5/8″ OSB over top. And finally I would install 4″ rigid foam board against the wall of the adjacent original house, since those walls only have R-13 insulation.
My questions, besides just asking for any comments, observations or suggestions on my overall plan, are these:
Am I missing anything as far as preventing air and moisture from over time, affecting the cellulose?
Should I expect the cellulose to compress over time, and is there anything I should do to combat this?
I would ideally like to extend my storage deck over the 4′ covered deck – which rather than drywall underneath the 2×6’s has simply a vented/slotted aluminum. I obviously wouldn’t put any cellulose over this, so I would make sure that one of my 2×10’s lays over the exterior wall to act as a damn between the fireplace room and the covered porch area. Anything wrong with this plan?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part