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littleboutlot
heat loss/moisture prob

I hope I don't have a huge problem. I added a third floor to part of my house. With the black mold issue I checked multiple sources (including building inspector)and was told housewrap, no vapor barrier, and unfaced insulation. I have had the dry hung but not mudded or taped and not fixtures are in place. I was getting back to it and noticed frost on the OSB behind the insulation in the closet. It's Michigan and we just had single digit and teens for a week. Is this just heat loss and condensation (like a cheap window)? Thanks

Re: heat loss/moisture prob

If your heat is on up there and you still have frost then the frost will be condensation in the summer. so check your insulation.If you have a break in the building envelope some where that the air that has moisture entrained in it will find a surface and pop out of the air.You may have a draft from where the new and old building connect-(chimney effect) check there also.
Here is an infrared example of what your describing. Maybe you should have a Infrared scan to take the guess work out of it.
Find someone in Mi. whats another couple $100 to verfify the thousands you spent on the addition..

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goldhiller
Re: heat loss/moisture prob

If I'm understanding correctly.........you have only unfaced FG batts in the closet (no drywall yet) and the OSB you're referring to is the exterior house sheathing material.

If so........ then the cause is most likely that warm moist air from the interior of the house is entering the closet space, migrating very readily thru the unfaced FG, condensing on the colder OSB and then freezing there because of the cold outdoor temps. FG makes a better air filter than it does an air barrier.

How to handle it now depends. It kinda depends upon how much water is actually condensed there and how many BTUs ($$$) you're willing to spend to get rid of it. IOW, it really should be dried out at some point in some manner, but how and when remains in question.

You could theoretically remove the FG batts, open the door and run fans to circulate heated house air against the exterior closet walls to warm them up and dry out the moisture. This will also give you chance to dry out those FG batts by laying them out on the floor of the room as they too are likely wet to some degree. Once everything is dried out you'd quickly replace the batts and mount the drywall. The drywall will serve as both an air barrier to prevent warm air from again easily leaking thru the FG and the OSB......and as a decent vapor barrier.

Or you could wait until warmer exterior temps and do the deed then. You *might* spend less BTUs drying things out that way, but if more moisture has condensed by then......they'll be more moisture to remove and so it may be a zero sum game........unless you simply wait for spring/summer and things will more or less dry out on their own. Then mount your drywall.

It all depends.

Some of this moisture *might* also have come from the construction lumber you used (the studs, etc) as they likely arrived at a higher moisture content than the EMC of the enviroment inside the house. New houses/additions can take a while to dry out and if yours didn't before the freezing temps set in........some frost *could* result inside the stud bays just from that contained lumber mositure.

littleboutlot
Re: heat loss/moisture prob

Thanks for the advise got the fan on it now. About the drywall that's hung but not taped. Should those walls be ok? Or would the seams allow enough air to get in and condense? Thanks

canuk
Re: heat loss/moisture prob

The drywall not taped and mudded is allowing warm moist air to pass through.

I'm still questioning the validity of not using a vapor barrier between the drywall and insulation.

littleboutlot
Re: heat loss/moisture prob

Apparently the theory was a "tight" house left nowhere for moisture to go therefore creating mold. I don't really know what to think as "the experts" already changed their minds once. The only justification I can summon is that black mold recently (10 yrs) became such a widespread problem. People for years before that did not have the mold, however they may not have had the most efficient home either.

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