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Old 02-07-2009, 10:07 AM   #1
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Attic Storage - What did I do wrong?


Greetings!

Over this past summer, I blew about 8 inches of cellulose in over about 6 inches of blown fiberglass. There is no moisture barrier, which each contractor that gave me a quote told me was ok. (This house is in a DOE rated zone 5 area in the northeast)

I wanted attic storage, so I put 2x8s perpendicular to the trusses and put plywood on top of that. The storage is great, but now there's moisture and mold collecting on the bottom of the plywood (and in the top of the blown in cellulose). I didn't initially leave an air gap between the insulation and the plywood.

If it matters, I have soffets and a ridge vent for ventilation.

What should I do to fix the problem? Would 2x4s on edge and braced, perpendicular to my 2x8s give enough air circulation to fix the problem? Should I really have a moisture barrier and if so, is it worth shoveling this stuff around to put one in?

Thanks for your help!

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Old 02-07-2009, 11:48 AM   #2
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Attic Storage - What did I do wrong?


you could always just drill a whole bunch of holes in the plywood? probably not sufficient though.

if it were me, i'd lose the plywood and make a deck style floor with your idea of 2x on edge, but 2x4 perp to them and screwed/nailed together to make a breathable floor. leave a half inch or so gap between boards of course.

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Old 02-07-2009, 02:50 PM   #3
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Attic Storage - What did I do wrong?


You have a truss system and you put the weight of 2x8's and plywood on top of it? Was this something you had okayed by a structural engineer or was this a thing you did on your own?
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Old 02-07-2009, 04:16 PM   #4
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Attic Storage - What did I do wrong?


@DangerMouse - I thought about the holes and also about cutting "breather" strips out of the plywood, but figured raising the plywood would provide less mess and greater circulation.

@Ron6519 - No engineer on this; I used 2x8s just for their height, not their load handling ability. The previous homeowner compressed all the insulation with some thin particle board they put down. I tore out the particle board and used the 2x8s to raise up the new plywood I put in. I'm not using it to support weight you would normally expect a 2x8 to carry. Sure it added some extra weight on the trusses, but I'm only storing a Christmas tree and some empty plastic totes up there; nothing super heavy.

Thank you both for your comments. Any other thoughts are really appreciated.

Last edited by deputy575; 02-07-2009 at 04:40 PM.
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Old 02-07-2009, 07:25 PM   #5
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Attic Storage - What did I do wrong?


How about cutting 2" holes, with a holesaw, 6" on center, all over the plywood!
Your plywood is acting like a vapor barrier, that's the reason for the moisture!
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Old 02-08-2009, 02:41 PM   #6
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Attic Storage - What did I do wrong?


Deputy 575, my concern was for the added weight on the truss system, not the load bearing capacity of the 2x8's. It is unlikely the truss system was engineered for all the added weight.
You don't mention how much area was covered.
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Old 02-09-2009, 07:37 AM   #7
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Attic Storage - What did I do wrong?


Wildie has it right. The glue in the plywood is acting as a vapor retarder on the wrong side of the system. Forget the holes. Raise the deck so you have at least 1-1/2" of clearance between the bottom of the deck and the top of the insulation. I've seen plastic garbage bags and totes with condensation on the bottoms in cold attics. Setting them over the drilled holes will just block the ventilation that the holes were supposed to provide.
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Old 02-11-2009, 07:56 PM   #8
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Attic Storage - What did I do wrong?


Thanks, everybody, for your comments. Since the plywood had mold on it, I ended up wrapping it in plastic and throwing it out. I left my 2x8s up there and, for the few things stored up there, I propped them on perpendicular 2x4s. I made sure to pull the insulation back a bit from the 2x4s for air circulation. If I really need the storage space, I'll put in more 2x4s perpendicular and put the decking on top of that.

Too bad it didn't work out, it was so nice to walk in the attic and have flooring to walk on.

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