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Author Topic: moisture problem in heated attached garage  (Read 11465 times)

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Offline sbishop

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moisture problem in heated attached garage
« on: December 10, 2006, 06:54:33 PM »
Hi, any of you have a heated garaged attached to your house? i've got a moisture problem. my windows are sweating so bad that the window sill is soaked. I've crack open a couple of windows and it seems a bit better but it warmed up a bit today!

my air exchange is doesn't have a line into the garage because it was against code!

THANKS

Sbishop

Offline Don_Papenburg

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Re: moisture problem in heated attached garage
« Reply #1 on: December 10, 2006, 07:10:11 PM »
Run a dehumidafier , make sure the doors have a good seal  all the way around. try storm windows also and make sure the windows have good seals .
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Offline SwampDonkey

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Re: moisture problem in heated attached garage
« Reply #2 on: December 10, 2006, 07:17:46 PM »
sounds like a lot of cold coming in around the windows. Are they single pain?
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Offline Ironwood

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Re: moisture problem in heated attached garage
« Reply #3 on: December 10, 2006, 07:29:38 PM »
How about moisture coming from under the concrete slab? Is the slab insulated from the ground? Just a few thoughts.

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Offline beenthere

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Re: moisture problem in heated attached garage
« Reply #4 on: December 10, 2006, 08:06:07 PM »
Good points raised about where moisture is coming from, plus if you happen to have a ventless heater in the garage, there is where most of it is coming from, I believe.  ::)
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Offline Don P

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Re: moisture problem in heated attached garage
« Reply #5 on: December 10, 2006, 11:22:35 PM »
The better you seal the worse the problem will be, its not an outdoor air leak or you'd be getting drier not wetter in the winter.
Air at 60 degrees can hold about 6 grains of moisture at 100% humidity, at 50%rh it would have 3 grains of moisture.
 At 120 degrees air can hold about 35 grains of moisture at 100%. The 50% air at 60 degrees would only be about 12%rh at 120. Sorry my example comes from a kiln discussion but the principles are the same.
Bringing in cold outside air even at 100% rh and warming it up is going to cause the indoor rh to crash, no sweaty windows in a drafty house.

The problem is indoors I think, there's a leak, something is unvented, a vent is dumping into the garage, or the slab is wet? Are you bringing snow covered cars inside? You can check for moisture in a slab by taping plastic over a section and looking for moisture under the plastic the next day.
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Offline Gary_C

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Re: moisture problem in heated attached garage
« Reply #6 on: December 11, 2006, 12:44:17 AM »
I would guess that you have single pane windows or poor quality insulated windows. When the surface of the glass is below the dew point temperature, you will get moisture condensing on the windows. One quick solution would be to add those plastic window coverings either inside or outside. Storm windows would be a more permanent solution. A dehumidifier may help, unless the temperature is too low or you are bringing in too much water or snow on vehicles that will simply overwhelm the dehumidifier.

Concrete does not wick moisture unless there are cracks or holes thru the slab. The moisture you find under things sitting on the concrete is from condensation just like the windows. When you place anything on the surface, it can insulate the surface from the heat and allow the temperature to drop below the dew point so condensation will form.
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Offline SwampDonkey

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Re: moisture problem in heated attached garage
« Reply #7 on: December 11, 2006, 05:16:49 AM »
The better you seal the worse the problem will be, its not an outdoor air leak or you'd be getting drier not wetter in the winter.

Ever attend church in a drafty old community church in winter? Can't see nut'n through them old single pain windows for frost and damp. IF you ever get it hot enough the dew runs down them windows onto the ledge, making a nice mess. ::) The same thing happens with old drafty single pain windows in old farm houses. Ya need storm windows or plastic like Gary suggests.  ;)
Move'n on.

Offline dewwood

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Re: moisture problem in heated attached garage
« Reply #8 on: December 11, 2006, 06:19:06 AM »
You would not by chance be drying some green lumber in your garage would you?  That would cause a great deal of excess moisture.
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Offline sbishop

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Re: moisture problem in heated attached garage
« Reply #9 on: December 11, 2006, 07:44:53 AM »
Hi Guys, thanks for all the feedback!

i'll try and add some missing info!

1. the slab is well insulated. there is 2" insulation under it with a vapor barrier. did I mention I have in floor heating?
2. the windows are brand new  (house is 2years old). they are double pane, with gas inside them.
3. Yes I do bring in the vehicle with snow on them. I try and sweap out all the water the next morning!
4. there is no vents inside this garage.(no air circulation)
5. THIS MIGHT HELP, I don't have my windows fully insulated yet. I haven't done the buildout yet so the windows only have insulation around the window itself not the whole thickness of the wall. (2X6 wall)

I think it's an inside problem (probrably the snow on the vehicles) cause i'm just doing the crackfilling now and notice on rust on the end of the screws. I would like to tackle this issue now and then an deal with it later!
I haven't had the vehicle in the garage for 4 days now and no moisture problem on the windows but it's not that cold out and I have the windows cracked open just a hair!

THANKS

Sbishop

Offline TexasTimbers

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Re: moisture problem in heated attached garage
« Reply #10 on: December 11, 2006, 07:54:28 AM »
You have been given some good, but also some contradicting advice. I don't believe I saw where you stated how you are heating this space. I believe I would want to know that first. It sounds like you are bringing the heat up rapidly when you turn it on. just a guess.

Whoever said that the better you seal your garage the higher the humidity will be if nothing else is done is correct. This is just plain physics and arguing it is pointless. Cold, dry air that leaks into homes from the outdoors lowers the relative humidity indoors.

The temperature of your glass surfaces is at or below the dew point for the amount of humidity in your inside air. Snow on the vehicles being rapidly evaporated by high heat could definately do it, but there could be other reason also.
Have you noticed the problem sans the snow-covered autos?
The oil is all in Texas, but the dipsticks are in D.C.

Offline Minnesota_boy

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Re: moisture problem in heated attached garage
« Reply #11 on: December 11, 2006, 07:59:54 AM »
From what I've read here, I'd say that you simply have too much moisture in that garage.  Since it seems to be coming in from outside as snow or rain on cars, you need to put it back outside.  Check into an air-to-air heat exchanger so you can put the moist air back outside without dumping all the heat with it.
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Offline TexasTimbers

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Re: moisture problem in heated attached garage
« Reply #12 on: December 11, 2006, 08:06:52 AM »
Concrete does not wick moisture

This is true in the sense that it doesn't "wick' moisture, but moisture can permeate up through a  concrete slab that has no vapor barrier. This is semantics possibly and a moot point now that we know there is a insulation barrier in place.
many contractors here do not install a vapor barrier on porch slabs to save a few pennies. the homeowners are never told that their slabs are going to sweat when the coditions are right.
the whole point of installing a vapor barrier, at least here in the South, is to prevent this moisture from coming up through the slab and rest assured it will.
The oil is all in Texas, but the dipsticks are in D.C.

Offline sbishop

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Re: moisture problem in heated attached garage
« Reply #13 on: December 11, 2006, 08:38:13 AM »
regarding the heat. I usually keep it around 5c (just enough to melt the snow and not have anything freeze inside the garage!

Offline DR_Buck

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Re: moisture problem in heated attached garage
« Reply #14 on: December 11, 2006, 08:46:50 AM »
I still don't see where you said how you are heating?.   If you are using propane froma ventless heater you will need a dehumidifier.   A by-product of propane is water.
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Offline Gary_C

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Re: moisture problem in heated attached garage
« Reply #15 on: December 11, 2006, 09:44:28 AM »
kevjay

Sorry to disagree but concrete is not porous and cannot "wick" nor "permeate" moisture or water. If it was porous, it could not be the best material for reservoirs and dams. Sure, there are many types of concrete, but none of them are classified as porous.

There are two reasons for vapor bariers under slabs on the ground. On insulated slabs, it can protect the insulation from becoming waterlogged when the watertable is high. On other non insulated slabs it can prevent the soil from wicking away the water in the concrete before the concrete is cured when the slab is poured. 

As far as the garage problem, the best solution is to remove the water before the warm slab evaporates it into the air. Floor drains would be the best solution. Without those or being able to sweep up the water immediately, you need to be able to remove moisture from the air by dehumidifiers or an air to air heat exchanger. And do it quickly before you have a mold and mildew problem.
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Offline TexasTimbers

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Re: moisture problem in heated attached garage
« Reply #16 on: December 11, 2006, 09:58:51 AM »
Well I don't have degree in engineering so I can't attempt to elaborate your points. I just know that if you do not install a vapor barrier down here under a porch slab, it will sweat under certain conditions.
probably it is condensation but I have always heard from old timers that it permeates through the concrete.
not the first time I have passed on bad info that I have always thought was right.  ::)

I stand corrected.  ???
The oil is all in Texas, but the dipsticks are in D.C.

Offline TexasTimbers

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Re: moisture problem in heated attached garage
« Reply #17 on: December 11, 2006, 10:51:13 AM »
Gary,

I hope this doesn't come across as me just needing to be right, because that is not the case. It just has been bothering me that my experience with this could be so wrong and that others in this area who have been working with concrete all their lives could also be so wrong, so I did some research.

It appears that moisture movement through a slab is a well established phenomenon, and a very frequent problem. I found many engineering type of articles on the subject and I have provided a link to one very well researched case study that happened right here in the DFW area. Maybe it just doesn't happen in Minnesota but it does here. LINK

If you don't want to read the whole thing, the nexus of the study could be summed up with this sentence . . .

"The article describes the driving force for moisture movement through a slab as the differential in vapor pressure between the above- and below-slab environments. Figure 1 shows the vapor pressure of moisture in air at different temperatures and relative humidities. . . ."

I know that in a perfect world the concrete paste will be impermeable, but we do not live in that perfect world (I wonder if concrete in heaven will have to have additives in certain conditions?)  ??? Oh never mind the streets are made of gold.  :)


Another article which emphasizes the importance of harnessing moisture movent through a slab can be found   HERE, but again if you don't want to read the whole thing here is an excerpt which is not taken out of context of the entire article I don't believe . . . .

" . . .It is the flow of moisture or moisture vapor, better described as moisture vapor transmission, that causes most adhesion problems. There are reported cases of bond failures on above grade slabs, but almost all are related to moisture vapor transmission rather than moisture content. The real area of greatest concern is concrete slabs-on-grade and how to dry out and/or minimize the vapor transmission . . . "

I intitally conceded your assertion because I am not schooled enough to be able to constructively counter it on my own, but like I said it just didn't sit right in my little brain that water vapor could not travel through concrete since I have heard so many times to the contrary.
 I guess if none of this makes any sense to you we will just have to agree to disagree, but I enjoy the discussion as I am getting an education about it!  :P

The oil is all in Texas, but the dipsticks are in D.C.

Offline Furby

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Re: moisture problem in heated attached garage
« Reply #18 on: December 11, 2006, 11:13:40 AM »
Gary, Concrete IS porous.
Dams DO leak, they are designed that way.
If concrete wasn't porous, why would building codes REQUIRE water or damp proofing of basement walls before backfilling?
When you float the surface of a slab, you bring the cream to the surface. That cream tends to be water resistant by nature, but the concrete is still porous.

This link is from within the one Kevjay posted, read it. ;)
Link

Offline Gary_C

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Re: moisture problem in heated attached garage
« Reply #19 on: December 11, 2006, 02:43:53 PM »
OK, my mistake.   I should have known better than to try to slip the simplified explanation past you guys.  ::)

Yes, water vapor and even some water contained in a slab on grade will permeate thru the concrete. And yes it can migrate to the surface and cause problems including bond failures of adhesives. However this "migration" is a very slow process and the volumes are significantly less than the amounts of water you see when there is condensation on the slab.

The leakage of water in some dams is probably caused by the "honeycombing" created in concrete when the slump or moisture content is too low when pouring and/or partial setting of one portion of the concrete during the pour. In most cases this leakage is just minor weeping. If there was significant flow, it would eventually erode a large channel and the dam would fail.

So concrete is still considered non porous, although it is a relative term.   ;D

Sorry for the "relative" cover up, I didn't think you would notice.   :-[
Never take life seriously. Nobody gets out alive anyway.


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