# Mold between insulation and sheathing during remodel



## Ckelley617 (Jul 12, 2015)

Hello all. I am working on a remodel of my great room. Most of the room has been taken down to the studs. All of the old Fiberglass Insulation was replaced with Rockwool. It was been sitting insulated but with no drywall for a couple of Months and I just found Mold growing between the insulation and the sheathing! I am beside myself. The sheathing is also brand new. Can anyone explain why this is happening?? Is it because I don't have the drywall up creating an air/moisture barrier? Should I leave all of the stud cavities empty until I am ready to put up drywall?

Thanks in advance for any advice!


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## Windows on Wash (Aug 30, 2011)

Because the drywall is your air barrier. If the insulation was left exposed, plenty of moisture laden air was able to contact that cold sheathing. 

Treat the mold, re-insulate, and either close up the wall or cover it with a proper air barrier.


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## Bud9051 (Nov 11, 2015)

Yup, something you or I will never do again, although I learned my lesson 40 years ago. When inside air can reach that cold sheathing it cools and deposits its moisture. That moisture then breeds the mold which is already everywhere.

Leaving the insulation out may help as long as the surface doesn't get too cold.

Do you run a humidifier in the rest of the house?

Heavy plastic may do the job but depending upon where you are you may want to remove it before the drywall.

Bud


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## APA (Jul 13, 2018)

Ckelley617 said:


> Hello all. I am working on a remodel of my great room. Most of the room has been taken down to the studs. All of the old Fiberglass Insulation was replaced with Rockwool. It was been sitting insulated but with no drywall for a couple of Months and I just found Mold growing between the insulation and the sheathing! I am beside myself. The sheathing is also brand new. Can anyone explain why this is happening?? Is it because I don't have the drywall up creating an air/moisture barrier? Should I leave all of the stud cavities empty until I am ready to put up drywall?
> 
> Thanks in advance for any advice!



Just think about the houses that sit open during construction. Anyway, if I knew all I know now back when I built my house, I would have just rented or built a log home. I have also read lots on here about rockwool being a great air barrier...


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## Bud9051 (Nov 11, 2015)

APA said:


> Just think about the houses that sit open during construction. Anyway, if I knew all I know now back when I built my house, I would have just rented or built a log home. I have also read lots on here about rockwool being a great air barrier...


IDK, I would say Rock wool (batts) are better at slowing air movement than fiberglass insulation, but it is far from being an air barrier. 

Bud


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## SeniorSitizen (Sep 10, 2012)

APA said:


> I have also read lots on here about rockwool being a great air barrier...


That was my thoughts while reading all the above posts. I guess possibly not so great.


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## Nealtw (Jun 22, 2017)

SeniorSitizen said:


> That was my thoughts while reading all the above posts. I guess possibly not so great.


 Often stated by people who don't like a vapour barrier. 

If every little cavity had been filled with insulation and a well sealed barrier had been installed, everything would have been fine. 

We see that in unfinished basements all the time when a builder is just meeting min. code. :wink2:
How many times have we seen it being suggested rock wool is all you need in rim joist cavities.


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## APA (Jul 13, 2018)

Nealtw said:


> Often stated by people who don't like a vapour barrier.
> 
> If every little cavity had been filled with insulation a well sealed barrier had be installed, everything would have been fine.
> 
> We see that in unfinished basements all the time when a builder is just meeting min. code. :wink2:



Mold has been around forever. It wasn't until that lady's house in Texas was on TV for mold and scared everyone to death that it became big business. I'm not saying not to clan it up, but that it CAN without losing yourself over it. Does rockwool not have paper facing? My upstairs set open for over a year with no issues, but every little cavity was filled and there was paper on the face of the fiberglass...


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## Nealtw (Jun 22, 2017)

APA said:


> Mold has been around forever. It wasn't until that lady's house in Texas was on TV for mold and scared everyone to death that it became big business. I'm not saying not to clan it up, but that it CAN without losing yourself over it. Does rockwool not have paper facing? My upstairs set open for over a year with no issues, but every little cavity was filled and there was paper on the face of the fiberglass...



I have never seen rock wool with paper, so I don't know. Paper faced fiberglass is few and far between here because code calls for a barrier. 



You need a few things to grow mold that you may not of had. 

1 Cold that can work thru to the room side.
2. Warm moist air that comes into contact with a cold surface. 



It is always easier to see what went wrong than why with luck things work out.


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## SeniorSitizen (Sep 10, 2012)

We see rockwool claims to fame vids frequently showing no air barrier and assume it isn't needed but if the dry wall isn't installed soon , like possibly that day depending on atmospheric conditions , we can have a mold problem. I don't know of the different trades ever working together that way.


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## Nealtw (Jun 22, 2017)

SeniorSitizen said:


> We see rockwool claims to fame vids frequently showing no air barrier and assume it isn't needed but if the dry wall isn't installed soon , like possibly that day depending on atmospheric conditions , we can have a mold problem. I don't know of the different trades ever working together that way.


 Here any holes that will be in the wall like outlets are wrapped by the trades people installing them. The insulators do the vapour barrier right away and the inspectors are really tough on the quality of the barrier job. All holes in the top and bottom plates are sealed thru out the house, I think by the trade using them.


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## SeniorSitizen (Sep 10, 2012)

Nealtw said:


> Here any holes that will be in the wall like outlets are wrapped by the trades people installing them. The insulators do the vapour barrier right away and the inspectors are really tough on the quality of the barrier job. All holes in the top and bottom plates are sealed thru out the house, I think by the trade using them.


What's typically used for the vapor barrier when wool is installed? I'd like to see a vid of that process.


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## Nealtw (Jun 22, 2017)

The framers do there part too. 

Something wrong with his trusses.


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## Nealtw (Jun 22, 2017)

SeniorSitizen said:


> What's typically used for the vapor barrier when wool is installed? I'd like to see a vid of that process.


It is treated just like fiberglass I think. I think most of the insulators use fiberglass because that is were they get the big discount. Their wholesaler delivers the product so I suspect if you want rock wool the price would go up because it might be retail.


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## Ckelley617 (Jul 12, 2015)

Update:

I removed all of the exposed insulation and bleach washed the affected area and then did a second bleach soak and air dry. Thankfully I caught the issue early and the mold was only spotty. I plan to leave the stud bays empty and until I am ready to hang drywall and just insulate as I go. 

I can't help but think of all the new construction homes that sit insulated for weeks or months while waiting for drywall guys to do their part. YIKES....


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## Nealtw (Jun 22, 2017)

Ckelley617 said:


> Update:
> 
> I removed all of the exposed insulation and bleach washed the affected area and then did a second bleach soak and air dry. Thankfully I caught the issue early and the mold was only spotty. I plan to leave the stud bays empty and until I am ready to hang drywall and just insulate as I go.
> 
> I can't help but think of all the new construction homes that sit insulated for weeks or months while waiting for drywall guys to do their part. YIKES....


 Maybe home owner builds. Production builders are in a hurry after they get the framing inspection passed.
Bleach is good for hard surfaces not so much for porous surfaces, if mold shows up again, there is a better product to use but the name has slipped my mind right now.


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## Timborooni (Apr 16, 2011)

Concrobium?


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## SeniorSitizen (Sep 10, 2012)

Nealtw said:


> I have never seen rock wool with paper, so I don't know. Paper faced fiberglass is few and far between here because code calls for a barrier.


You've lost me.
Are you saying the paper on fiberglass is not a barrier but rock wool is a barrier without paper is the barrier in itself?


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## Nealtw (Jun 22, 2017)

SeniorSitizen said:


> You've lost me.
> Are you saying the paper on fiberglass is not a barrier but rock wool is a barrier without paper is the barrier in itself?



If they make rock wool with paper I have not seen it. All our house have to have 6 mil poly vapour barrier so paper is not needed. I think some of the box stores sell paper faced FG but the lumber yards don't.
It is pretty safe to say we don't have air leaks.


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## SeniorSitizen (Sep 10, 2012)

I'll try to find a vid of that 6 mil install. I'm seeing that as a fiasco more times than not.:vs_mad:


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## Bud9051 (Nov 11, 2015)

@Ckelley617:
"I can't help but think of all the new construction homes that sit insulated for weeks or months while waiting for drywall guys to do their part. YIKES.... "
One difference might be the type of heat. Yours is a remodel and probably sharing the heat from the house which would have a lot more moisture. A garage will often have the condensation behind the insulation without a finished air barrier due to snow and moisture from vehicles.

Leaving the stud bays open will help but you will still need to keep the inside surface above the dew point where condensation will occur. Closets that have no heat will often form mold in the back corners.
@Nealtw "It is pretty safe to say we don't have air leaks." The drywall is your air barrier but I know you don't want to hear that. This link may help, the author originated in Canada.
https://www.buildingscience.com/documents/insights/bsi-073-macbeth-does-vapor-barriers

Bud


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## Nealtw (Jun 22, 2017)

@Bud9051


How many times have you asked me to read material, I have and I do, what i find in some of those write ups leads to me too think you only read the lines you like. 

We have basements we live in and walls that don't leak. I understand that you don't believe that and I am sure that you have seen failures. 



The argument isn't whether drywall is a barrier or not. The argument is what you do about the holes in that barrier. We have agreed about sealing the ceiling from the attic, this is never a problem here with a house less than about 20 years, because that is inspected before the drywall goes up. We were having problems around the windows but in 2006 we went to rainscreening, before that they wanted air holes in the sheeting and lot's of people were like Building Science and blamed the barrier. 

So if you could be so kind to explain how you seal all the holes in drywall around all the stuff that might go thru the drywall or even thru the wall, while you are telling me the sky is not blue. 



This what a sealed ceiling looks like here.


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## APA (Jul 13, 2018)

Nealtw said:


> Maybe home owner builds. *Production builders are in a hurry after they get the framing inspection passed.*
> Bleach is good for hard surfaces not so much for porous surfaces, if mold shows up again, there is a better product to use but the name has slipped my mind right now.



I would say you could find mold inside 90% of homes' walls. It would be impossible to say otherwise. Knowing what I know now, I would have used plywood and felt to wrap my house because of the drying potential.


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## APA (Jul 13, 2018)

Ckelley617 said:


> Update:
> 
> I removed all of the exposed insulation and bleach washed the affected area and then did a second bleach soak and air dry. Thankfully I caught the issue early and the mold was only spotty. I plan to leave the stud bays empty and until I am ready to hang drywall and just insulate as I go.
> 
> I can't help but think of all the new construction homes that sit insulated for weeks or months while waiting for drywall guys to do their part. YIKES....



You are most likely fine. It is hard to resist that urge to rip it all out and start fresh. You wont get the return on your investment if you do that.


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## Bud9051 (Nov 11, 2015)

Nealtw said:


> @Bud9051
> 
> 
> How many times have you asked me to read material, I have and I do, what i find in some of those write ups leads to me too think you only read the lines you like.
> ...


Sorry Neal, but when I post links like Building Science it is because they have tone of experience and lots of education. You hang your hat on anecdotal information based upon where you live. These experts provide high quality advice that will perform at a higher level of quality. 

Not going to argue with you, send your objections to building science corp and let them battle you.

Post what you want, I'll respond to the op. not you.

Bud


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## Nealtw (Jun 22, 2017)

APA said:


> I would say you could find mold inside 90% of homes' walls. It would be impossible to say otherwise. Knowing what I know now, I would have used plywood and felt to wrap my house because of the drying potential.


Mold is everywhere, that is why you don't want to feed it with moisture from the house and keep the cold out. Sealing the wall dosen't matter if you leave gaps in the insulation,then cold will get to the back of the drywall and you will have moisture and mold inside the room on the drywall.


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## Nealtw (Jun 22, 2017)

Bud9051 said:


> Sorry Neal, but when I post links like Building Science it is because they have tone of experience and lots of education. You hang your hat on anecdotal information based upon where you live. These experts provide high quality advice that will perform at a higher level of quality.
> 
> Not going to argue with you, send your objections to building science corp and let them battle you.
> 
> ...


 Then stop telling me to read things, and quit calling me when your experience is failure when the barrier was not done completely. 

If drywall is all you need why do we need to air seal an attic side of the ceiling


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## user_12345a (Nov 23, 2014)

The only type of loose fill style insulation that works well without a vapor barrier or thermal break on outside is dense pack cellulose retrofitted into existing above grade exterior walls.

("thermal break" stops surfaces from getting cold enough to have condensation in the first place)

The dense pack stops enough air movement for moisture to not be a problem - whatever moisture gets into the wall can get it, there has to be drying potential on both sides.

Stopping the air from moving through the wall and hitting cold surface is a must when using batts in a cold climate, above grade.

Air/vapour barriers are not perfect - they work okay above grade because of the drying potential to the outside. House-wrap has drying potential.



> Then stop telling me to read things, and quit calling me when your experience is failure when the barrier was not done completely.
> 
> If drywall is all you need why do we need to air seal an attic side of the ceiling


 Drywall doesn't do a very good job of air sealing especially when you have electrical penetrations and it doesn't extend all the way to the floor

Still helps a great deal and can be enough to stop mold.

But the key is to stop the air movement, "vapour barrier" properties of materials are not important, it's the "air barrier" properties that really matter.


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