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Old 02-27-2013, 05:59 PM   #1
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Mold inside exterior walls, WTh!!!


This is quite a shocker to me and my wife. We have been working on our house for a while and finally got to doing some interior finish. Opted out of drywall and went with 3/4" TG wide pine flooring. We found mold growing on the inside of exterior sheating, as we pulled fiberglass insulation to run some CAT5 before installing wood finish. We now checked several areas and mold is in almost every stud bay.

Profile of the wall looks like this (all new materials, foundation up):
- no siding yet
- windows not taped yet
- 1" polyiso foam, foil side to the house, not taped yet (I am debating this as the cause of a problem here)
- housewrap
- 1/2" OSB
- 2x6 studs
- R-19 unfaced batts between studs
- at some areas we had 4mil plastic, to avoid contact with fiberglass (but mold is also in spaces without plastic)

Mold is growing from the sill plate up, about 4ft high. It's also present under insulation between floor trusses (above the space we are talking about) and in the walkout basement wall, where we actually used 1" pink foam (taped at the seams) - which has damaged my theory that it happens because we haven't taped polyiso.

I am literally speechless and devastated... what do I do next?
Pull insulation, spray with borax/peroxide mix? Spray with PermaGuard?
Tape seams outside, tape windows?

Help!

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Old 02-27-2013, 06:08 PM   #2
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Mold inside exterior walls, WTh!!!


I'm confused.
Why is there no siding and no window tape but your finishing the inside?
Why are you using a vaper barrier on the outside walls?
Really need to add some pictures and add your location to your profile.

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Old 02-27-2013, 06:08 PM   #3
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Mold inside exterior walls, WTh!!!


Any pics was the insulation in with plastic covering the whole walls. First u gotta figure out how moisture got in to permanently fix not just temp to happen again where r u located near water?? Is Jose on blocks with no barrier between wood and cement
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Old 02-27-2013, 06:24 PM   #4
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Mold inside exterior walls, WTh!!!


We didn't do the siding because we simply can't afford it at this time. No tape, because of my fear that it will deteriorate by the time we go with the siding (which might be another year) - and I bet that was main reason we are getting this problem.

Why vapor barrier outside? Because polyiso (foil faced foam boards) effectively is a vapor barrier when seams are taped. And structure should have just 1 vapor barrier, or you are welcoming a mess that I have right now (area between barriers not able to dry).

What is really bugging me is that we have 1 wall where we went with pink foamular (that wall will get stone veneer later on), it's all taped and we are getting mold inside anyways.

Is it all about dewpoint screwing us right now?
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Old 02-27-2013, 06:27 PM   #5
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Mold inside exterior walls, WTh!!!


Quote:
Originally Posted by kaschmid3 View Post
Any pics was the insulation in with plastic covering the whole walls. First u gotta figure out how moisture got in to permanently fix not just temp to happen again where r u located near water?? Is Jose on blocks with no barrier between wood and cement
Mold happened in most stud bays, didn't matter if plastic was on or not (there is one entire room without plastic and still moldy).

Not near water, no moisture problems in the basement or leaks.

Treated sill plate on foam gasket, then floor trusses, OSB sheated.

There are spots with mold way high in the header panels between floor trusses (above 1st floor) and no mold in wall below. Weird.
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Old 02-27-2013, 08:33 PM   #6
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Mold inside exterior walls, WTh!!!


How high is exterior grade level in comparison to inside of house( higher lower same). Any decks attached to house that maybe weren't flashed for water or spots in we're roofs or soffits run into siding that weren't flashed right
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Old 02-27-2013, 08:35 PM   #7
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Mold inside exterior walls, WTh!!!


Without seeing could be anything from wet plywood installed and covered before dried or leaking somewhere
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Old 02-27-2013, 09:08 PM   #8
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Mold inside exterior walls, WTh!!!


Sheeting was dry, no leaks.

Top of foundation wall is 8in above where floor trusses sit on, 18" tall, then 3/4" OSB subfloor, framing and so on.

There was no mold on OSB when we installed R-19 fiberglass back in October. House was heated starting November. It had to happen during last 4 months.

One big mistake... no tape on polyiso. But how it the world would it cause so much mold?
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Old 02-28-2013, 10:45 PM   #9
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Mold inside exterior walls, WTh!!!


The indoor moisture is forced outward during a heating season due to temperature/pressure differences. The T&G was not air sealed behind it... water vapor molecules are much smaller than air molecules. If you drywall (air barrier) behind the T&G http://www.buildingscience.com/docum...wall-approach/, you would get 100 times less moisture than by diffusion alone during a heating season;

Read the two comments at the bottom of page #7; https://docs.google.com/viewer?a=v&q...GIwFLQF3YvmyFw

OSB remains wet because it is hygroscopic, unlike plywood sheathing; "Compounding this weakness is the fact that OSB is often made from aspen and poplar, neither of which are rot-resistant woods. Because OSB holds water, prolonged exposure to roof leaks or excessive humidity and condensation in unvented attics can cause OSB roof panels to degrade faster than plywood panels. So OSB, in its current state of development, is more sensitive to moist conditions, while plywood is more forgiving." From; http://www.jlconline.com/coastal-con...tal-roofs.aspx

You really need "Stucco wrap" from Dupont, as I tell others when using foamboard directly next to OSB because it creates the needed gap, even more-so in your foil-faced:http://www.buildingscience.com/docum...d%20in%20walls

Notice the low permanence of PIC (foil-faced polyiso) on page 8, and read under "Durability" there, also read pp. 13-20; http://www.buildingscience.com/docum...ting-sheathing

If in Zone 6; http://publicecodes.cyberregs.com/ic..._11_par002.htm

You would need R-11.25 to stop any (exfiltrating) cavity condensation, it's no wonder you are having problems as it does not meet code (minimum standards); http://www.buildingscience.com/docum...r-requirements. The board is faced, can only dry to the inside- right next to OSB, board is too thin to stop condensation. With or without poly, problem is the facing you have, pp. 12; http://legacy.forestprod.org/durability04cautley.pdf


Look at walls in 3d, 1 and 2; and 4d and 4e, you need a vapor retarder with thinner foam and a 2x6 cavity (more insulation interior to the foamboard); http://www.buildingscience.com/docum...nd-wall-design

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Last edited by Gary in WA; 03-01-2013 at 04:52 PM. Reason: corrected the last link.
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Old 02-28-2013, 10:55 PM   #10
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Mold inside exterior walls, WTh!!!


Gary, thanks for extensive post.

Just so I understand - to balance the insulation equilibrum in the wall assembly, with 2x6 framing and R-19 fiberglass, I should be shooting for about R-15 on the outside, right? Adding another layer of polyiso would be really close to that, as it's about R-9 new and ages to about R-6.5.

With both of polyiso layers taped, besides difficulty with proper transitioning to window and door openings, would you say I could get by without inside vapor barrier? Just to make clear, there is no drywall planned anywhere in the house. If 2nd vapor barrier (inside is necessary), it would be 4mil poly.

But then we are talking about wall sandwich wrapped with 2 vapor barriers = impossible to dry in or out.

Again, at this point I certainly don't consider using drywall (plastic instead?), as well as removal of polyiso (windows and doors are "outies", on the top of polyiso) which also prohibits removal of typar that's between polyiso and OSB.

Here are possibilities I am debating:
0. Mold has to be cleaned and OSB sprayed with some kind of mold retardant (question would be, should that retardant form a vapor barrier itself, or be permeable)
1. Polyiso seams taped (which should have been done on day one; this creates something that acts almost as vapor barrier; 0.3 perm rating, where 0.1 is VB)
2. Another layer of polyiso added (1" should be doable and economic because of added insulation; this creates 100% VB and shifts temperature profile of the wall; transition to window and door openings might be problematic)
3. Layer of house wrap added on top of polyiso (vapor barrier without extra thickness, easy to transition to window and door openings)
4. Some kind of wicking/breathable wrap (so the back of future siding can dry up)
5. Perimeter of each stud bay sprayed with foam (to prevent major air intrusion)
6. Entire surface of each stud bay sprayed with foam (vapor barrier, added insulation)
7. Entire surface of each stud bay painted (something that will create vapor barrier, possibly more mold protection)
8. 4 mil plastic added on the inside of wall assembly (vapor barrier, but then it creates a sandwich that will never dry; more potential problems)
99. 3/4" TG pine installed as wall finish.
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Old 02-28-2013, 11:29 PM   #11
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Mold inside exterior walls, WTh!!!


You can tape the seams though they may open later anyway; http://www.buildingscience.com/docum...a-foam-shrinks

H.W. on outside the foam for "outie" windows; http://www.greenbuildingadvisor.com/...s-housewrap-go

Concur; http://www2.dupont.com/Tyvek_Weather...h_Bulletin.pdf

I'll give you time to read some of the links I posted (that answer many of your new points) and answer more tomorrow...

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Old 02-28-2013, 11:55 PM   #12
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Mold inside exterior walls, WTh!!!


Yeah, read about ISO shrinkage before. With 2 layers though, and both taped, this problem should be minimized. Also, using adhesive to bond the 2nd layer vs nails could possibly help with dimensional stability.

I have seen that Tyvek pdf before too. But with 2 layers of ISO, how would exterior wrap help and if so, what kind should be used? I would consider something on exterior for wicking/siding drying purposes only.

From your links, I am seeing a strong suggestion against interior VB, whether 1 layer of ISO is used or 2. One thing or study I am missing is my case... being ISO not taped, no interior VB - is everyone in my shoes getting mold in their walls?

In the winter, without interior VB, is shifted wall temp gradient (with double ISO) enough to prohibit condensation and mold problem on the inside of OSB?
In other words, is what happening now caused ONLY by too small of a thickness of ISO?

In the summer, I should be OK with windows closed and inside air conditioned, but what about when windows are open and AC is not running?

BTW, I should have some well measured humidity levels on Sunday. I will also do more in-depth inspection of areas with and without 4 mil poly, for comparison purposes.
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Old 03-01-2013, 04:02 AM   #13
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Mold inside exterior walls, WTh!!!


The explanation for the mold is really pretty simple. The structure has experienced an ice dam and has nothing to do with vapor barriers.
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Old 03-01-2013, 03:07 PM   #14
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Mold inside exterior walls, WTh!!!


"water vapor molecules are much smaller than air molecules." That statement is just untrue. Water vapor molecules attach themselves to air molecules. That is their mode of transportation.

The problem you've created in my opinion is very simple. You have a foil barrier on the cold side of the wall. Foil is impervious to moisture travel, so that any warm moist air is being driven at higher pressure through the unfaced fiberglass until it reaches the foil. There the moisture condenses and increases the moisture level in the cavity to the point where mold can thrive. A high efficiency vapor barrier on the warm side of the wall would prevent the moisture from getting ito the insulation layer.
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Old 03-01-2013, 04:50 PM   #15
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Sorry, I should have explained that better as I was tired last night; "Water vapor is lighter than air and the water vapor molecule is smaller than air’s other molecules—nitrogen and oxygen. Therefore, water vapor can rise faster and squeeze through smaller microscopic spaces than air. When water vapor moves through a solid material, this is called vapor diffusion." From; http://blog.srmi.biz/energy-saving-t...ture-humidity/ All the cracks in the T&G are letting moisture through to the OSB where it stops because of the low perm rating (0.03) of the foil (which does nothing against radiation without an air-space).
Copied from my post 9; "Look at walls in 3d, 1 and 2; and 4d and 4e, you need a vapor retarder with thinner foam and a 2x6 cavity (more insulation interior to the foamboard);" and I left you the previous link rather than the correct one--- Zone 5 or 6; http://www.buildingscience.com/docum...nd-wall-design

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