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Old 02-29-2012, 08:21 PM   #1
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cover insulation in attic?


I've got a small attic that's vented and seems to have significant air flow. It seems to me that, at least on the vertical spaces, it would make sense to cover the insulation with tyvek. From my searching on the web, I find that some people think this is a good idea and some don't like it at all. I was just wondering what people on this forum think about the idea, pro or con.

Also, would it be OK to cover the horizontal areas with plywood? That's mostly just to create a little more storage space.

Thanks.
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Old 02-29-2012, 08:27 PM   #2
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cover insulation in attic?


No you can not cover the insulation. It is made to be that way in an attic space. As for storage, an attic is the worst place to use for storing stuff.

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Old 02-29-2012, 08:28 PM   #3
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cover insulation in attic?


tyvek actually has an attic wrap so i would say yes to both
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Old 02-29-2012, 09:13 PM   #4
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cover insulation in attic?


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tyvek actually has an attic wrap so i would say yes to both
No reason that you can't cover those kneewalls with an air impermeable (need to be vapor permeable though) covering.

You need to stop the air leakage first but tyvek on the kneewalls is fine.

I also partially agree with greg that the plywood is a no-no and using and attic for storage is usually a bad idea unless special precautions are taken.
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Old 02-29-2012, 09:23 PM   #5
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cover insulation in attic?


1 out of 2 ain't bad
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Old 02-29-2012, 10:06 PM   #6
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cover insulation in attic?


I would be more concerned with fixing the wires,you need to fasten them.
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Old 02-29-2012, 10:38 PM   #7
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cover insulation in attic?


Thanks for the comments. It looks like Tyvek AtticWrap would be just the thing.

Space is tight and storage is very limited here, so I have put a few things up in that attic already (not much, since it's small, and the access is not good). So, what sort of "special precautions" would need to be taken to use an attic for storage?

As for the wires... I was actually doing some electrical work in there today, and I'll get the wires secured soon.
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Old 03-01-2012, 07:34 AM   #8
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cover insulation in attic?


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1 out of 2 ain't bad
You were 2 for 2.

You can floor out and attic but most folks don't take the time to build up the floor to get proper insulation depth under it.
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Old 03-01-2012, 07:44 PM   #9
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cover insulation in attic?


I'd take it a couple steps further while you're in there getting dirty. Foam up all of the penetrations to air seal, and then put up an additional layer of fiberglass running horizontally across that kneewall (vertical area). Then put on your tyvek wrap. The attic floor could likely use additional insulation (and air-sealing) as well.... If you're gonna do it, you may as well do it right.
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Old 03-01-2012, 08:22 PM   #10
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cover insulation in attic?


When I did my knee walls I framed them with 6x's then added fibreglass with 4 inch of form and enclosed all with fire board.
It sure helped with the overall comfort of the upstairs.
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Old 03-01-2012, 09:13 PM   #11
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cover insulation in attic?


JHB, Building Science recommends housewrap on the knee wall, fig. 4: http://www.buildingscience.com/docum...ty-insulation/ I would also air seal the space under the knee wall to stop attic air from reaching uninsulated floor cavities inbound. The diagram shows solid wood blocking with a sealant bead, though rigid foam board is easier to fine tune while placing it and canned foam around it.

If that is a bath fan housing in your picture, air seal and insulate it to stop it from acting as a heat sink, not much R-value in thin metal. Is that mold on the gable-end rafter or just discoloration?

Few other pointers, may not be needed; After you air seal the attic (good indicators with f.g.: http://www.finehomebuilding.com/PDF/Free/021105092.pdf), air seal the basement/crawl space floor to help stop the "stack effect"; http://www.wag-aic.org/1999/WAG_99_baker.pdf, then seal the rim joists if accessible; http://www.buildingscience.com/docum...l_seal_rev.pdf

Did you add a sill sealer under the knee wall bottom plate, a possible leakage area? Depends on how far you want to carry this- remove baseboard (if easy) and caulk the drywall to subfloor. OR tape the H.W. for the air/thermal boundary. May sound a little over-board, yet it is required in the IRC:http://publicecodes.citation.com/ico...002_par021.htm

Reasoning is having that barrier uninterrupted- continuous- against the attic air = outside air temperature; http://oikos.com/esb/51/sideattics.html

Gary
P.S. I would not store items in the attic, especially on solid sheathing material.
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Old 03-02-2012, 12:40 AM   #12
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cover insulation in attic?


Thanks everybody for all of the detailed info. But, I probably should have provided a little more info. Better late than never, so here goes...

You can't tell from the picture, but the rafters that you see are not actually the current roof. That is, another roof was built over the top at some point in time. There are a few big holes in the "visible" roof, and roof vents in the actual roof. So, there is significant air circulation thru this attic space, and I assume that's a good thing. But, there are also some electrical outlets in the knee wall, and that's the reason I'm particularly concerned about air flow around the vertical surface.

The main roof of the house consists of exposed wood/beams with some rigid foam insulation between the exposed wood and roof. The overall R-value of that can't be much above R-13, so it's probably not worth getting too carried away on this attic space. In fact, there was absolutely no insulation in this attic when we moved in 4 years ago (this strange addition to the house must be at least 25 years old). In fact, there was no access to the attic either.

I believe the discoloration GBR mentioned is soot. When we moved in, there was a decrepit wood-burning stove just below that area, and that entire adjacent wall was turning black. The wall has been cleaned and painted, and the wood-burning stove replaced by a modern pellet stove. Btw, that uninsulated area at the far end in the photo definitely needs to be insulated too.

In any case, I'm wondering whether replacing the batts with some rigid foam insulation might not be a better solution for the knee wall. I know it's kind of a pain to cut and squeeze that stuff into place, since I used EPS (i.e., styrofoam) for a previous insulation project. It seems to me that the pink XPS stuff might be the right thing for this application. Once that's in place, I could use a couple cans of the spray foam to fill in any gaps and get a good seal around the outlet boxes. How does that sound?
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Old 03-02-2012, 08:12 AM   #13
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cover insulation in attic?


Leave the fibreglass,scab some wood on the top and bottom so you have a surface to attach fire board to but fill the void in between with ridged foam.
Either way you need to fire proof the knee wall.
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Old 03-02-2012, 09:11 AM   #14
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cover insulation in attic?


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Leave the fibreglass,scab some wood on the top and bottom so you have a surface to attach fire board to but fill the void in between with ridged foam.
Either way you need to fire proof the knee wall.
What is "fire board"?

Also, would such a setup trap moisture in between? The reason I was considering Tyvek is that it allows water vapor to exit. As for the rigid foam, I was thinking that if it's tight against the drywall, that would prevent any moisture penetration in the first place (kinda like sprayed on rigid foam).

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Old 03-02-2012, 09:30 AM   #15
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cover insulation in attic?


Fire board is fire rated drywall such as 5/8" either way you need a fire break on the wall.

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