GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Questions on building an attic storage deck

Ryan O'Rourke | Posted in General Questions on

Hi folks,

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?

Thanks,
Ryan

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.

Replies

  1. GBA Editor
    Martin Holladay | | #1

    Ryan,
    Q. "Am I missing anything as far as preventing air and moisture from over time, affecting the cellulose?'

    A. I don't think so.

    Q. "Should I expect the cellulose to compress over time, and is there anything I should do to combat this?"

    A. Settling is normal. For more information, see How to Install Cellulose Insulation and Air Sealing an Attic.

    Q. "I would ideally like to extend my storage deck over the 4' covered deck - which rather than drywall underneath the 2x6'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 2x10's lays over the exterior wall to act as a dam between the fireplace room and the covered porch area. Anything wrong with this plan?"

    A. No.

  2. Ryan O'Rourke | | #2

    Thanks for the quick reply. I was actually just considering that perhaps I should add 2x12's to my existing 2x6's, instead of 2x10's to get closer to R-60, and also ensure that I stay above R-49 even after any settling. But the joist hangers seem extraordinarily more expensive. I'll look around though to see if I can find them more reasonably.

    Would it be advisable to aim the cellulose down while blowing, to minimize settling?

  3. Ryan O'Rourke | | #3

    Just realized I can use 2x10 hangers on 2x12 joists. In fact some of them are described as 2x10-12 hangers.

  4. GBA Editor
    Martin Holladay | | #4

    Ryan,
    Q. "Would it be advisable to aim the cellulose down while blowing, to minimize settling?"

    A. That's what Bill Hulstrunk advised in the article I linked to: "The installed thickness is somewhat dependent on how you hold the hose. The settling chart on the bag assumes that you hold the hose at a 45-degree angle and shoot it upward. But if you don’t have the room to do that, and you shoot it straight out or downward, you increase the installed density — and in some cases it won’t settle at all. The coverage per bag goes down, but you don’t have any settling."

  5. Ryan O'Rourke | | #5

    Yeah I read that article which is where I got the idea. I wasn't sure if I was reading it as advice to do it that way, though, so just wanted clarification. Thanks.

Log in or create an account to post an answer.

Community

Recent Questions and Replies

  • |
  • |
  • |
  • |