Reoccurring moisture problem

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  #1  
Old 12-21-13, 03:56 PM
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Reoccurring moisture problem

We are living in our home as we build it and have encountered insulation moisture issues which we simply can't understand. We discovered frost behind the insulation. We removed and dried everything and resealed the vb. A recent check has found the frost problem has returned.
The initial discovery made sense. In august we begun insulating the second floor. After all the insulation was installed and wiring verified, the 6mm vapor barrier was installed, and not necessarily as tight as it should have been. Logically, moisture would have accumulated before the vb was put up and through the small gaps that were not taped. We added a pellet stove upstairs and a dehumidifier, removed all the insulation and let it dry for a few days before reinstalling and immediately and thoroughly applying the vb. Today we cut a few slits and checked again only to find more frost. Yay.
Not all batts are frosty. Some are dry as a bone while the next is very wet. One closet was drywalled, but even it was wet. The closet next to it (not drywalled) was dry. There was one wall which was perfectly dry that did not need to be pulled out is now also frosty.
The outside of the house is unfinished. We have only this week installed the well pump and now have running water inside. Our heat source is a Mt Vernon pellet stove downstairs and a summers heat stove upstairs. Both are vented correctly.
After chatting with a few neighbors we discovered that they have found frost on insulation during stove/dryer installs on their finished houses. So now I'm left to wonder if everyone in cold climates have this issue and simply don't know it.
Other than removing everything in summer and spray foaming, is there anything I can do to prevent moisture? Or are Alaskan winters just too difficult to weatherproof?
I apologize for the information overload. There are so many variables that make this so frustrating
 
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Old 12-21-13, 04:15 PM
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Heating a space that's not finished is just asking for problems. Warm air is getting behind your 6 mil VB, either because of inadequate air sealing (no matter how well you "think" you've sealed it) or from penetrations (electrical, plumbing, outlets) that are transferring warm humid conditioned air into the cold air space. Any outlet on an exterior wall would be a primary location where this warm air would get behind the vapor barrier. Every seam and edge of the poly as well. Anytime wind blows, it will create negative pressure on the opposite wall which sucks your conditioned air right out the wall at any gap it can find. Having no drywall up to help air seal probably puts the entire thing on how well the VB is sealed. In cold temps this frost and ice will just keep accumulating. When it melts you will have a real problem on your hands.
 
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Old 12-21-13, 04:27 PM
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There are currently no outlets unsealed. The poly is still intact over boxed. Expecting issues, behind electrical boxes are foamed. No pluming exists on outside walls.
So until the house can be finished in its entirety it should not be heated? Naturally I can't drywall over wet insulation so any solution will need to wait for summer
 
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Old 12-21-13, 04:40 PM
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Its possible that if the frost inside the walls is minor, and you could seal the perimeter of the poly and all of the seams so that no more air could leak in any longer... transpiration would take care of some moisture and the rest would eventually dry to the outside.

If you have major icing inside the walls, waiting for warmer weather is your only option.

Any holes that have been drilled through the top or bottom plates for electrical wires to run through are also "penetrations", pathways for warm air to get into the walls. All these sort of penetrations should also be sealed with spray foam. Partition walls, where the poly begins and ends would also be tricky to seal unless the partition wall was actually built over the poly.

Oddly enough, even though cold air is dry air, you can actually have a higher level of humidity inside the wall (where it's warm) than the humidity outside the wall. This is because warm air can hold more moisture than cold air. That moisture is being rung out of the air anytime the temperature on the outer parts of the wall reaches the dewpoint, which is probably constantly happening at some point within the wall.
 
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Old 12-21-13, 04:56 PM
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I overlapped all rooms over nailers and into the next room for maximum coverage. Taped of course. All wiring holes were foamed. Outlet boxes will not be cut until drywall is up. The ceiling is dry walled to support the blow in insulation which isn't giving me any grief at all. The frost this time is significantly less. Would drywall help?
I am reading online that cold climates often have frost problems that are unseen. I've read it's a normal problem and there is nothing you can do about it. Or maybe Google is just telling me what I want to hear now.
 
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Old 12-21-13, 05:34 PM
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Yes drywall will help, since it is also an additional air barrier, plus it has minimal r-value (resistance to heat flow) which will help slightly. Every staple in the poly is a potential air leak until the drywall is installed and air sealed. If the bottom edges of the poly are not sealed to the framing or subfloor, I would suggest that be done.

If you google: frost in exterior walls you will find lots of posts where you will find that this is pretty common. Mostly people notice it in the winter when the drywall isn't on. (Go figure). It probably still occurs to some extent AFTER drywall is on, but not to such an extreme degree.

Some reading to put you to sleep tonight: INTERNAL AIR BARRIER http://www.efficiencyvermont.com/ste...ide_062507.pdf

Also: AIRTIGHT DRYWALL http://www.southface.org/factsheets/24ada_drywal.pdf
 
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Old 12-21-13, 05:51 PM
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XSleeper is on the right track, your moisture is coming from the warm air inside your home and from people and normal moisture sources. One of your problems is the need for an air barrier along with a vapor (moisture) barrier. A key difference is that an air barrier needs to be rigid, like drywall. If it flexes in and out it simply pumps air right past. Making a wall air tight is near impossible without extreme detail as it is being constructed.

To go forward from where you are is not a problem and many homes out there do quite well with no moisture problems. Unfortunately, the construction process during cold weather needs to be completed in days, not weeks or months. When left over the winter I have seen ice an inch thick behind the insulation.

If you hang any drywall and tape/mud it, you will need to run dehumidifiers to try to control the moisture. I would limit the mud to one coat for the winter. As long as you do not have plastic on the outside of the house, sheathing, house wrap, and siding, then small amounts of moisture trapped inside the walls should dry to the outside as X stated. But you should complete the task as fast as possible to limit that moisture.

Bud
 
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Old 12-21-13, 06:29 PM
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Exclamation Ok, this is the other half.

I don't want to come off like a know it all, but a lot of what we're hearing, we know, lol. Here's the thing, we've gone through painstaking steps to mitigate the moisture. She literally removed the insulation during a warm spell, room by room. Dried everything out, with a fan and dehumidifier. Reinstalled insulation, 6 mil vb, with all seams taped, staples taped etc. In several places, the plastic is double or triple overlapped and taped again! We even foamed edges! The outlet boxes are still covered with plastic, no through wall penetration of plumbing and all holes for electrical are foamed. Now we have moisture where we didn't and don't where we did. It's random! The humidity is below 40, and there hasn't been significant moisture, less or breath until very recently. I have discovered talking to others in finished, drywalled and sided homes that after installing something through an exterior wall, they discovered frost as well! Are we relegated to just accept this because of where we live? I see buildings being built in winter by contractors using non vented heaters and due to building size time to finish is months. Are these problems widespread and unknown? Help!
 
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Old 12-22-13, 04:20 AM
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40% RH at 70� has a dew point of 45�. That means that any of the inside air that comes in contact with a surface at or below 45� will deposit some moisture.
Temperature, Dewpoint, and Relative Humidity Calculator

As you install insulation you block the heat from the exterior sheathing and it gets colder. I recognize you are being thorough with your sealing efforts, but a long history has shown we can (almost) never get it perfect. During cold months, inside air is constantly being pushed out through the walls and ceiling somewhere, so in that sense your very cold climate has always had this problem. Consider. ALL homes exchange 1/3 of their inside air every hour and wherever it exits it is cold. Does it form ice? It has to! Does that cause a problem? In some cases, yes. Are most people aware of this? No. Can it be prevented? The majority can be prevented but it will require some additional reading as to how to seal a home and provide fresh air.

As a note, check today's outside temperature and RH. Enter those numbers into the above calculator and calculate the dew point. Clear and then use that dew point with your inside temp and calculate a new RH. It will be extremely low. That tells us the moisture is not coming from the outside.

When you say the problem seems random, that tells me there are air leaks you have missed. But be careful, you cannot seal a house completely. People and combustion appliances need fresh air.

I don't recall you saying what is on the outside of the home. As X stated, the house has to dry to the outside beyond the VB.

Get those dehumidifiers running to lower that 40% as much as possible. As you noted, some walls are dine. Dry the wet ones and quickly follow with insulation and drywall, being sure the new area cannot communicate (leak air) with the house or adjacent walls.

Bud
 
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