Theory as to why inside of wall condensed?


Old 03-23-07, 04:43 PM
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Theory as to why inside of wall condensed?

Two story 4 plex from 1950's.

Upstairs apt.

12 x 50 foot apt., approx.

220 electric baseboard heat in building.

Wall crack in the plaster above 8' electric baseboard heater on outside living room wall that faces west. And plaster bulging to point it has to be removed/redone. But no discoloration.

Wall makeup: Inside 1/2 inch real plaster, 1/2 celotex-like fiber board or 'cornboard' the plaster was applied to, 3 1/2 inch thick wall cavity with studs every 16 inches, blown in insulation completely filled cavity (the type that looks like whitish fuzzballs from a sweater), celotex up against the outside of the stud, tar paper, I believe a wood siding, asbestos shingles that are painted.

Okay, upon removal (by the landlord/handy guy) the insulation was not that first. But upon getting to the outside celotex...the insualtion was more damp and the celotex like fiber board was soaked,... bulged from it being filled with water. No real signs of stud rot damage or rot damage at the bottom plate which was surprising.

Currently waiting for the wall cavities, 4 or 5 cavities, to dry out...the. landlord ran fan at it.He came back days later after it was dry, still in the winter, and installed fully plastic encapsulated fiberglass insulation (used for sound barrier (why he used this is beyond me). It seemed to fit relatively well, friction fit, inbetween the studs.

Enter *me* in the mix. Landlord now wants *me* to do the job. Lady is fussy about sheetrock joint compound/sanding mess and I can do the work often with no sanding. So I met her there the other morning, only for me to pull away the insulation he put in, to find it just dripping inside up against the tar paper...running down the tar paper. No roof leak. New roof. No ice daming. Actually any snow we had, had already melted before he insulated, and yet all that water showed back up in the cavity again! I was able to look up past a 1/2 inch void to the outside of the double to plate with a bright light and saw the roof boards near the eaves and they are not wet nor any black mildew on them.

It had only got down to about the mid 20's that night also. Not 20 below, like how we had it a couple times!

The apt. is NOT a sauna. I detected no moisture (from showers, cooking etc.) AND, she said she hasn't even used the electric baseboard heat since the problem surfaced! So that rules out the extreme temperature difference between the heater and the outside tar paper that is just inside from the asbestos shingles and original wood siding.

Theories on how these wall cavities are reaching the dewpoint? And why isn't the wall all rotted inside as one would maybe suspect?! It's like this problem just happened? Although...just ONE stud showed early signs of deterioration to the outside 1/2 inch, vertically, with it being kind of black and a little punky ( a LITTLE...not much). So,...did the plaster crack let in moisture? Or, did the moisture problem cause the plaster crack?

And I don't know if I should bother to put a plastic vapor barrier up over the repair area, even though the rest of the house has none? Maybe this wo dmake it worse in case moisture seeped aroudn the edges, and then trap it in the wall?

I think everyone here understands the concept that when hot moisture laden air meets a cold surface, the moisture converts to water on the cold surface.
But in a situation like this, it is a little harder to get a mental image as to why this is doing this, to the degree it did.

I dug into the cavity next to these and the insulation was bone dry until I hit the soaked celotex! again. Same thing. But that cavity is still over the heater at the outer edge and the landlord should have stripped out that cavity to. I am thinking about buying a moisture meter and probing the apt.'s outside walls in the apt. that are not above a heater, to compare with the cavity I just mentioned about.
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Old 03-23-07, 08:40 PM
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I'm guessing that the crack led to the problem, especially if the wetness has only been noticed in the area where the crack was! (gotta love my deductive reasoning! LOL) However there could be other places where the same thing is happening, if the plaster is cracked behind the baseboard (where you can't see it- they are bad for that) or at the location where the plaster meets (or rather DOESN'T meet) the floor. If you have 2 extremes- 70F air meeting 20F air, you don't have to have very high humidity for there to be condensation. Plus the baseboard heater warms the wall more than you think, and when it's only 3 1/2" to cold air, and no interior vapor barrier, guess what happens?

If I was more organized I could find this link I saw once that showed dramatically how a small hole in a wall could cause a LARGE water problem, due to the amount of air passing through the wall, and how much water could condense from that volume of air. Until the air infiltration is stopped, it's basically like having a leaky pipe in your wall. When the conditions are right, it's like turning on a faucet. Which would explain why the wall isn't completely rotton- it probably doesn't happen too often and has a chance to dry out.

I think the insulation in the plastic bag is a bad idea since the studs also need to be covered by the vapor barrier. IMO, I think the reason it's still wet behind it is 1) no vapor barrier over the studs, not sealed at floor and ceiling and 2). no drywall.

This post reminds me of another, back in the fall. Someone was getting ready to drywall, or was in the process of it, and they had water literally running down the walls and were scared to put up sheetrock. I think in that case, it was also due to the outside temp and the back of the sheathing (cold) was acting like a dehumidifier when their warm conditioned air met up with it. Can't recall how that turned out- I'll have to look for it.
Old 03-23-07, 09:37 PM
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Ill say this is a wild one for sure
the insulation was not that first. But upon getting to the outside celotex...the insualtion was more damp and the celotex like fiber board was soaked,... bulged from it being filled with water.

This is what's not right to me The warm moist air is in the home and with no V/B the insulation will get damp from the inside first and work to the out side. Not come from the outside first. like if you put up batts with paper. The paper side goes to the room side or if you use the friction fit insulation then a 4 mil poly over it for a V/B. Then the drywall
That would be like a glass window it sweats on the inside of the home not the outside. Also one other I have ran into
over the years that a ceiling that has no V/B on it and insulation is blowen right on it , fiberglass or cellulose . After about 3 months. If you put you hand down in it you will feel that it does get moist down right by the ceiling. I know you say not the outside . But that is where Id start to look for where this water came from.

My .02 cents ED
Old 03-24-07, 03:58 AM
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When insulation bekame good, and plastics was reasonable available it became almoast a rule in norway to block moist-transfere thru walls.
The plastic film is put on the inside of the wall, jyst coverd by wood panels, plaster, or what ever you prefere.
At our winterclimate this is necessary, and the humidity is transfered from warm to cold zone.
I'l guess this may be different in other climates.

Old 03-24-07, 02:45 PM
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Thanks for your input, guys.

The outside looks sound with no damage to the ovrelapping asbestos shingles. And as seen from inside the wall cavity, is no less than 3/4 inch wood sheathing, or it could be original siding. Then inward from that is the tar paper, then the celotex-like fiberboard, then the insulated cavity filled with blown in insulation, then celotex again, then the plaster (not drywall).

And the lady was not running her baseboard heater in the living room for the last several weeks she said. Unless the moisture condensed when she DID and was trapped in there the whole time.

You guys more willing to bet that the heater being on, with the heat going up the wall, hot, is what created the problem in the first place? That is what *I* would have thought. But how do you explain the landlord drying it out with a fan left on the open cavities for days and he insulated when it was bone dry, and then it recondensed behind the encapsulated insulation?

Or do you maybe suppose these are two unrelated problems? That perhaps in the first case, it condensed because the baseboard heater was on (hot up the wall) and then the plaster crack exasperated the problem?...and that in the second case where the wall dried out, that the moist air got around the plastic-bagged friction-fit insulation where it then condensed? Does that sound plausible?


I quickly opened the cavity to the east of the cavities already exposed, to a fist sized hole, and when I put my fingers into the insultion, from the inside, heading toward the outside, I went, "Hmph...the insualtion is dry HERE"..until I dug all the way in and it was only when got to about 1/4 inch... of the celotex that is on the backside of the studs (as well as the front side of the studs) that I could feel moisture... and when I moved all the insulation away, the celotex on the outside was soaking wet.

I know what you are saying, Ed, about how windows normally condense. But that is easier to follow, as such cold outer air is migrating through nooks and crannies in the windows/sashes and the cold on the inner glass (being a hard surface) is in direct contact with the heated apt. and condenses there.

But with the wall, that is filled solid with blown in insulation, you are not going to have outside cold able to worm it's way through nooks and crannies, quickly..maintaining the cold temperature, like what can happen with windows...or even in the case of some aluminum windows and door thresholds, ice develops at the inside because the aluminum stays cold enough on the inside to condense.

But with the blown in insulation, one would expect that every 1/16 inch you travel through the insulation... the inner and outer temperature would equalize in the center to a temperature 1/2 way in between...gradually and perhaps not condense. Yet it is...and condensing on the inside facing of the OUTER celotex.
Old 03-24-07, 06:02 PM
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The moisture will condense when warm air penetrates and reaches the dew point. Since you are in a heating climate (cold winters) and are saying the moisture is forming on the sheathing, that makes sense, because the sheathing will be cold, while the insulation insulates. You would not see moisture condense on the warm side of the wall, you would see it condense on the COLD side of the wall. That's why the vapor barrier goes on the warm side of the wall- to keep warm moist air from the home out of the wall cavity in the first place.

In my opinion the problem has less to do with the baseboard heat, and more to do with no vapor barrier + air infiltration. Warm air condenses on cold surfaces, its pretty much as simple as that. So until the wall has a vapor barrier that is air sealed, and until the wall is re-drywalled, you will continue to see condensation when the temperature of the sheathing reaches the dewpoint.

In the first case, air infiltration through the crack (plus water vapor can move through any wall that has no vapor barrier, travelling along with heat, which always moves toward cold) caused the condensation.

In the second case, it sounds like you have open stud cavities, no continuous vapor barrier over the studs, no drywall, and plastic wrapped insulation that basically is creating small pockets of vapor barrier on the back side of the sheathing (cold side-wrong side) and no air movement on the back of that insulation to dry out the wall. I also don't like the plastic encapsulated fiberglass. You're going to see frost and moisture behind the insulation until you correct those things. And it has nothing to do with the lady running or not running the baseboard heat. It is as simple as it being warmer inside than it is outside, with the interior humidity condensing when it reaches the dewpoint. Its the same reason a glass of ice water sweats... because the conditions are right for it.

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