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Old 06-15-2010, 10:01 PM   #1
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Really confused about vapor barrier and insulation


Im turning my upstairs 3 bedroom and half bath to a 2 bedroom full bath. There is a very small attic above these rooms and knee walls along the long sides of the house. I thought installing faced insulation was the proper thing to do but now, the more I read, the less sure I am. I have it about halfway insulated with R38 faced insulation but dont want to spend the extra money or time to continue with the faced stuff if the drywall, primer and paint covers will do an equally good job. I have a 130 cfm fan installed above the shower (w/ gfci breaker, thank you for your concern) so I dont think that moisture will be a problem but what about the warm air meeting the cold air in the attic during the winter. So... do I continue with the faced throughout the two bedrooms and bathroom or do I return it for the much cheaper and easier to install unfaced stuff? Thanks everyone!

Shane

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Old 06-16-2010, 01:30 AM   #2
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Really confused about vapor barrier and insulation


Shane: First, I am a (pretty experienced, educated in these matters) DIY'er, not an expert. The questions I'd be asking are (1) Is this faced insulation a real vapor barrier? IMHO, is certainly is neither an air nor a vapor barrier AT ALL THE SEAMS (2) Do I need a vapor barrier like 6 mil visqueen, or is a more "breathing" system best for me? That translates to a more robust insulation, like blown cellulose, cellulose batts, or cotton and an air-tight drywall system w/ latex vapor retarding paint. Having built w/ fiberglass insulation 30 years ago and having no complaints, I would have been inclined to encourage you to use it. However, I will never use it again after reading for the last year+. CELLULOSE or cotton; perhaps rock wool. NO fiberglass insulation is going into anything I build again, including my 24 x34 addition. ••Your bathroom is, as you know, not the only source of water vapor, and stopping air movement is what is critical. Perhaps do a lot more reading/asking, here and places like greenbuildingadvisor.com, before you finish up. GL. john


Last edited by jklingel; 06-16-2010 at 01:35 AM.
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Old 06-16-2010, 08:18 AM   #3
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Really confused about vapor barrier and insulation


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Originally Posted by jklingel View Post
Shane: First, I am a (pretty experienced, educated in these matters) DIY'er, not an expert. The questions I'd be asking are (1) Is this faced insulation a real vapor barrier? IMHO, is certainly is neither an air nor a vapor barrier AT ALL THE SEAMS (2) Do I need a vapor barrier like 6 mil visqueen, or is a more "breathing" system best for me? That translates to a more robust insulation, like blown cellulose, cellulose batts, or cotton and an air-tight drywall system w/ latex vapor retarding paint. Having built w/ fiberglass insulation 30 years ago and having no complaints, I would have been inclined to encourage you to use it. However, I will never use it again after reading for the last year+. CELLULOSE or cotton; perhaps rock wool. NO fiberglass insulation is going into anything I build again, including my 24 x34 addition. ••Your bathroom is, as you know, not the only source of water vapor, and stopping air movement is what is critical. Perhaps do a lot more reading/asking, here and places like greenbuildingadvisor.com, before you finish up. GL. john
Thanks! Why the sudden aversion to fiberglass? The way I see it, neither the faced insulation or the paint are going to be perfect seamless vapor barriers due to recessed lights, door frames, outlets etc. I am taping the seams of the faced insulation with tyvek tape, which I read to do somewhere and it seemed like a good idea. However, Im tempted,unless someone convinces me otherwise, to just use unfaced insulation and call it a day. It will go up much faster and cheaper. I just dont want rotten wood holding up my roof in a matter of years.

Shane
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Old 06-16-2010, 08:28 AM   #4
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Really confused about vapor barrier and insulation


You need a vapor barrier, drywall & paint do not meet the requirement

Faced is considered a vapor retarder
Plastic/etc is a vapor barrier

I've never considred unfaced easier to install
Here we are required to have an insulation inspection
No vapor barrier & you fail the inspection
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Old 06-16-2010, 08:38 AM   #5
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Really confused about vapor barrier and insulation


I dont recall anything in the building departments paperwork about insulation inspection. However, the old insulation was installed with kraft paper and the wood behind it is as dry as a bone. I certainly respect your opinion Dave. You think I should remove the kraft paper and run plastic over it? What about around the recessed lights, how does one create a barrier there? Thanks guys!

Shane
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Old 06-16-2010, 08:51 AM   #6
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Really confused about vapor barrier and insulation


I use faced instead of plastic
If you are using plastic as a vapor barrier then you do not need faced
I'm not 100% on vapor barriers/retarder etc
Different parts of the country do things different due to weather/humidity etc
I lived in MD but as a kid - so not much DIY except help Dad finish the basement
I know where we lived - Pasadena - it was very humid in the summer

I've used faced because then I can staple it to the studs
So for me that is easier
Not only do we have an Insulation inspection we also have to pass an insulation/energy audit before we submit our plans to the building Dept
The windows/doors/insulation must meet energy guidelines or the Building Dept will not give you a permit

I've read a couple studies that seemed to suggest a couple layers of paint formed a decent vapor barrier. Can't remember if they compared it to faced/unfaced

Maybe someone with more experience can help
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Old 06-16-2010, 01:48 PM   #7
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Really confused about vapor barrier and insulation


Depending, perhaps, on your area, code may require a vapor retarder of only one perm, if I recall. Latex vapor retarder paint and sealed drywall system will apparently meet that requirement. Vapor BARRIERS are often not suggested unless you are in climate 7 or 8 (Freezeville). Instead, interior vapor retarding and an AIR barrier, w/ a breathable air barriered exterior, is suggested so that the wall can breathe in both directions as temps/humidity change. That is why some folks are real big on cellulose or cotton insulation. Again, read greenbuildingadvisor.com; they are very knowledgeable folks and in agreement with other reputable sources.
The reason I quit on fiberglass in its lack of real effectiveness. Conductive air currents within the walls severely reduce its R value, and it is impossible to fit the inevitable voids (bent studs, around pipes and wires, etc.) Besides, I absolutely hate installing the stuff. I have 13" of it in my walls, and it is doing OK. We experience (over 30 yrs now) a heat loss of 4 btu/sf/hr, which is very good but could be better. I will fill my double walls and lid w/ dense-packed cellulose in the upcoming addition.
BTW: Having dry walls, IMO, is not necessarily a reflection of a good vapor retarder/barrier, but may only be a reflection of how leaky the walls are.
Around electrical outlets, get the outlets with pre-formed gaskets and glue your visqueen (if required) to them w/ appropriate sealant, like Tremco Acoustical Sealant. I just found out about that stuff 2 yrs ago on a remodel, and it really does stick to visqueen. I glued up a couple of scraps to test it, and so far it is holding onto the visqueen well. There may be better sealants, too. Also, tape (special tape) and seal visqueen overlaps.
If you use visqueen, I see no need to remove the foil facing. Two vapor barriers are tight against each other, so should not be a problem. Besides, I still can not see how facing does not leak at the edges. My 2 cents. GL. john
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Old 06-16-2010, 02:04 PM   #8
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Really confused about vapor barrier and insulation


The concern with moisture is not in the summer, but in the winter. Your shower makes a lot of moisture year round.

Face or unfaced matters not-- neither one will stop mold. I'd actually prefer the unfaced in your case, as the mold won't have the Kraft paper to feed on-- and you WILL have mold, from what it sounds like. Ever notice how shower mold needs soap residue to live on? So it is with kraft paper and various materials like that.

IMO, before you will the stud cavities, you need to make sure they are airtight as much as possible. You *must* stop air movement/migration through the cavity. Insulation does NOT do that job. It slows it down, but doesn't stop it. If you really want to make sure you will NOT have mold problems, you could run a thick bead of acoustic sealant along all the seams where the studs meet the outer wall and top and bottom plates; then line each stud cavity with 6mil and adhere it to the acoustic sealing. Then stuff your batts-- THEN you install the 6mil vapor barrier. Tons of work yes. But all but eliminates any chance of mold.

Short of that, I'd recommend a good 6mil over your batts, making sure you TYVEK tape all the seams. It must be airtight-- not even a pinhole is allowed. Foil HVAC tape also theoretically works, but can make a sharp edge that will cut the barrier-- I'd advise against it.

I'm not sure how best to address plastic penetrations from drywall fasteners. If you barrier each stud cavity individually and seal to the stud, you have the wood exposed as a potential moisture conduit. But the plastic wouldn't be penetrated by nails/screws. If you run the plastic across the studs, then the drywall screws penetrate the plastic.

It might be helpful to run a small bead of acoustic sealant across all the edges of the studs and under the 6mil. Then the drywall fastener will squish the sealant around enough to "heal" a hole in the plastic.

Then again, maybe the holes in the plastic right on the studs don't really matter, is they are pinched between wood and drywall.

I'm no expert, just thinking out loud (and trying to think out of the box as well)
JH

Last edited by Hohn; 06-16-2010 at 02:09 PM.
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Old 06-16-2010, 02:11 PM   #9
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Really confused about vapor barrier and insulation


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The concern with moisture is not in the summer, but in the winter.
JH
Unless you live in a hot, humid zone. That is one place where visqueen is not recommended, as it traps vapor in the walls. I'm glad I live in a fairly dry, albeit cold, place!
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Old 06-16-2010, 03:57 PM   #10
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Really confused about vapor barrier and insulation


If you live in a hot, humid zone, I highly recommend the new refrigerated sheathing panels. They cool the house AND pull moisture out of the walls
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Old 06-16-2010, 04:20 PM   #11
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Really confused about vapor barrier and insulation


I wonder if they make HEATED exterior sheathing. Man, that would make life sooo much simpler up here.
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Old 06-16-2010, 09:54 PM   #12
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Really confused about vapor barrier and insulation


I hope the pic comes through. It is a table of permeability of some common building materials. No idea where I got it. GL. j
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