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.

 

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

 

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...

 

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

 

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.

 

The framers do there part too.

Something wrong with his trusses.

 

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.

 

Concrobium?

 

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:

 

@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

 

@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.

 

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

 

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.