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Old 01-24-2013, 04:13 PM   #16
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Gary, thank you for the post,

So I understand correctly, the addition of rigid foam in the cavities to seal them and more rigid foam over the face of the studs would provide the "best" possible for this installation? You would minimize air movement and create a thermal break on the interior of the wall?

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Old 01-24-2013, 04:55 PM   #17
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Sounds like he wants you to cut rigid foam and fit it within each stud bay. tight to the exterior sheathing. Then spray foam all those edges. Then put batt. insulation with thickness to fill the remaining depth. Also adding 1-1/2"x1-1/2" rigid foam strips to the face of the studs.

Pretty labor intensive and alot of expensive foam waste...imo...plus it doesn't really provide you with a true moisture retarding system that is code worthy. Code requires a vapor retarder on the warm side in winter unless you have a continuous R-10 foam layer on the outside (for zone 5). With you in zone 6/7, that R-10 requirement is likely higher, if allowable at all. The method explained above does not provide a continuous layer and therefore does not satisfy that aspect of the code. You would still need to provide a vapor retarder (kraft paper facing) at the interior. BUT, with 2" XPS on the exterior side of the cavity, adding kraft paper on the inside would form a double class II retarder system, which is even worse for moisture issues than a continuous layer of rigid beneath the gypsum board.
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Old 01-24-2013, 05:05 PM   #18
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Yep, AGW nailed it, at least in the description. You will have a warmer cavity for the f.g. and air-tight from the exterior air this way. ADA the drywall for air-tight from the interior. Vapor diffusion will be very slight compared to all the gaps between boards for sheathing. Is more work, lol. Is the wall 11' or 20' exterior wall? 16"oc, 14-1/2" between into a 48" sheet= 4-1/2" rip of waste to use in the attic where the roof slope meets the exterior wall...

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Old 01-24-2013, 05:05 PM   #19
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I would tend to agree...

Basically looking at gutting, adding r-15 Fiberglass, then furring horizontally to accommodate drywall (Something like 24 OC with 2x2 and 2x3) and some vertical only to allow for outlet attachment. Then go back and fit 1.5 foam between and use caulk to seal between joints. Then I can drywall over with a theoretical R in the 22 range. I would loose some to thermal bridging in the end but placing the drywall support on horizontal would minimize that.

I would probably also take the time to seal the slat board as best I could with silicone. That in itself will take forever but such is life I suppose.

Does stucco have an air permeability? It seems like this house is very well sealed from drafts and such, I would assume it is from the continuous siding the stucco provides.
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Old 01-24-2013, 05:07 PM   #20
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Quote:
Originally Posted by Gary in WA View Post
Yep, AGW nailed it, at least in the description. You will have a warmer cavity for the f.g. and air-tight from the exterior air this way. ADA the drywall for air-tight from the interior. Vapor diffusion will be very slight compared to all the gaps between boards for sheathing. Is more work, lol. Is the wall 11' or 20' exterior wall? 16"oc, 14-1/2" between into a 48" sheet= 4-1/2" rip of waste to use in the attic where the roof slope meets the exterior wall...

Gary
One of each, the room has two exterior walls, which is why I want to insulate as best I can...
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Old 01-24-2013, 05:40 PM   #21
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"When moisture storage effects are added, things get real interesting. Take a
brick veneer cladding that experiences rain-wetting followed by exposure to
solar radiation. The sun tends to drive moisture inward. It makes sense to put
a vapor barrier behind a brick veneer to stop this inward flow. But what
happens when you install a vapor barrier behind a brick veneer in a cold
climate? Do you also want to install a vapor barrier on the inside? I think not ?
that would be a vapor barrier on both sides. Maybe we want a vapor barrier on
the outside behind the brick veneer and a
vapor retarder on the inside. Maybe
we should use an insulating sheathing that is vapor semi-permeable on the
outside with sufficient thermal resistance to elevate the temperature of the
condensing surface during the heating season, and have a vapor permeable interior finish to permit drying to the interior? It sounds complicated and it is."

"So under dry-cup testing the kraft facing has a
perm rating of 1 perm, and under wet-cup testing the kraft facing has a perm
rating of 5 perms. In the winter months, when the inside relative humidity is
high, we have vapor retarder on the inside, that permits drying to the inside." Bold is mine, from: http://www.buildingscience.com/docum...vapor-barriers

Gary
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Old 01-24-2013, 05:45 PM   #22
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Dang stucco! Always causing me problems!

Im understanding what you are saying Gary, just trying to come up with a way to get everything done without spendin 15 days insulating.
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Old 01-24-2013, 06:05 PM   #23
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Yet another link, lol. Paper facing "checks" moisture, Ginger vs. Mary Ann: " Figure A: The traditional “vapor barrier” on a fiberglass batt is actually “asphalt-coated kraft paper” that varies in vapor permeance as a function of relative humidity. It pretty much is a vapor barrier only in the absence of vapor. It really functions much like a valve that opens and closes depending on available moisture. In the winter in most older homes the interior relative humidity is in the 20 percent range whereas in the summer the interior relative humidity is in the 50 percent to 60 percent range. So in the winter a kraft-faced batt has a vapor resistance of approximately 1 perm—an interior vapor retarder on the correct side of the thermal control layer—reducing outward vapor flow. And in the summer the same kraft faced batt has a vapor resistance of approximately 10 perms—allowing the same assembly to dry inwards. It is interesting to note that latex painted gypsum board works pretty much the same way. And now we have new “smart materials” that are engineered to take advantage of the differences (2nd Generation Vapor Control Membrane)." From; http://www.buildingscience.com/docum...024-vocabulary

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Old 01-24-2013, 06:07 PM   #24
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LOL. Just do it the "easy" way as AGW said, and let us know how that works out for you. Remember... you came here...lol.

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Old 01-24-2013, 11:02 PM   #25
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Thank you gary, I do appreciate your comments! Your logic makes sense, Do you believe I would need 1.5 or 2 in the cavites to get the vapor retardant or could go with a thinner (.5 ) to seal and still have space for the fiberglass?
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Old 01-25-2013, 12:46 PM   #26
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Gary does have alot of internet links and quotes, though just because it's on the internet doesn't make it right (my info included). Here in CT, code is code, and unless you can convince the local officials that the code is wrong and get a signed approval, you'd best stick to the code. Gary doesn't like code in some instances, and this is one of them. So, if you're going to follow Gary's advice then I'd check with your local official before you spend all that time and money. It would be horrible to get it all done and either have to rip it out or pay some kind of fines (don't know your laws).

I will say that buildings have been placing the vapor barrier on the warm side in winter for MANY years now and there aren't too many cases where that has caused extreme issues. Sure there are cases of mold/etc. but that usually stems from other problems with the constructed assembly (bad gutters, leaky roof, leaky siding, etc.). In your climate (in winter) the majority of the moisture is generated within the living space. Not allowing it to enter the wall cavity is of great importance (hence the code). Your studs are still directly touching the exterior cold and are not so thermally broken as to mitigate that cold within the same dimension as the foam and will have colder surfaces behind that foam layer. Those cold surfaces, left exposed to moist air, may condense the moisture laden air coming from the interior.

I always like to side on the code as it is a set of rules that is reviewed year after year and changes are usually well thought before being enacted. The same process goes for variances to the code. You must submit documentation and reasonings based on your specific project's parameters. The officials will review and make a determination.
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Old 01-25-2013, 01:01 PM   #27
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Quote:
Originally Posted by Gary in WA View Post
"When moisture storage effects are added, things get real interesting. Take a
brick veneer cladding that experiences rain-wetting followed by exposure to
solar radiation. The sun tends to drive moisture inward. It makes sense to put
a vapor barrier behind a brick veneer to stop this inward flow. But what
happens when you install a vapor barrier behind a brick veneer in a cold
climate? Do you also want to install a vapor barrier on the inside? I think not ?
that would be a vapor barrier on both sides. Maybe we want a vapor barrier on
the outside behind the brick veneer and a vapor retarder on the inside. Maybe
we should use an insulating sheathing that is vapor semi-permeable on the
outside with sufficient thermal resistance to elevate the temperature of the
condensing surface during the heating season, and have a vapor permeable interior finish to permit drying to the interior? It sounds complicated and it is."

"So under dry-cup testing the kraft facing has a
perm rating of 1 perm, and under wet-cup testing the kraft facing has a perm
rating of 5 perms. In the winter months, when the inside relative humidity is
high, we have vapor retarder on the inside, that permits drying to the inside." Bold is mine, from: http://www.buildingscience.com/docum...vapor-barriers

Gary
I'm wondering when your posts will start with a disclaimer that this information could very well be contradictory to the legally-required building codes...Last I checked this isn't strictly a building science theory forum...
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Old 01-25-2013, 06:15 PM   #28
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Originally Posted by quackaddict View Post
Thank you gary, I do appreciate your comments! Your logic makes sense, Do you believe I would need 1.5 or 2 in the cavites to get the vapor retardant or could go with a thinner (.5 ) to seal and still have space for the fiberglass?
--- If you leave the studs at existing 3-1/2" with 2" foamboard inside against the wood boards, and add the 2" f.b. strips to the studs edge inside, fill the cavity with R-13 (3-1/2") asphalt paper-faced, your total will be R-23. Code is R-21 for your location- Zone 7; http://publicecodes.cyberregs.com/ic..._11_sec002.htm

If you want only 1/2" of f.b. glued to the boards, you need to make the wall depth enough for the required total R-value, a problem; need full 6" for R-19 = 6" + 1/2" XPS (R-2.5) = R-21.5 but keeping thicker f.b. on the studs face without sagging of the drywall (past 2" f.b.). You could add 2" f.b to the studs and 1" of wood to get the needed 6-1/2". Getting into long screw lengths for the drywall... while still keeping the studs thermal break.

For any that I confused (sorry), Post 21 and 23 show it is acceptable to use a vapor retarder (kraft paper) and foam in the same wall. As per code; Class 1 or 2 for location Zone 7; http://publicecodes.cyberregs.com/ic...001_par003.htm
And paper faced is a Class 2; http://publicecodes.cyberregs.com/ic...001_par005.htm

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Old 01-25-2013, 07:40 PM   #29
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AGW, please elaborate: " Gary doesn't like code in some instances, and this is one of them."

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Old 01-28-2013, 01:02 PM   #30
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Quote:
Originally Posted by Gary in WA View Post
Post 21 and 23 show it is acceptable to use a vapor retarder (kraft paper) and foam in the same wall.
Above is such an example. Post 21 and 23 do not mention any lawful building codes I'm aware of, yet you suggest building methods that are generally against code practices. As a comparable example: In the Massachussetts code (A zone 5 state) it states that the exterior "barrier" must be 10x more permeable than the interior "barrier". These are the things people NEED to know. Building science is great for what it is, but when it comes to giving REAL people REAL advice, the theory is only as good as it applies to the building laws that govern.

Unless of course you're a government bank builder

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