I am looking for a little help understanding the thermal issues associated with exposed metal wall studs in an attic space in South Florida.
Condensation is forming, running down the studs, and contributing to mold growth on the walls in the living space below (at top of stair landing area w/ vaulted ceiling).
What would be the appropriate way to address/prevent the condensation? Should an insulated panel/board be installed across the exposed metal studs?
There is no insulation between the metal studs. R-19 on the attic floor.
The developer is saying that the HO is keeping the temp inside the townhouse too cold, thereby causing the condensation in the attic. They have offered to remove the mold-impacted materials and spray a 6-inch layer of cell over the R-19 fiberglass insulation, IF the HO agrees to allow the developer to attach a regulator to his AC so it can’t be set lower than 72.5 degrees (F).
The HO refuses because he feels there is a construction issue involved. HO says he does not set the temp that low (maybe 72F), but sets it low enough to be comfortable. The inside temp was about 75F in the stair landing area when I went to take a look as a favor.
Thanks.
Edited 3/19/2005 12:57 am ET by Rafe82ABN
Replies
Not that I have much to offer but............
If it is sweating now, in the spring season, imagine what will happen when the heat and humidity arrive!
If it were my house I would not allow the attachment of a "regulator"! There is another problem that must be addressed other than a temperature setting!
Are they standard non-structural studs, or are they structural grade?
What is their function in the attic space?
How many metal studs are involved?
Is r-19 the normal for Florida heat versus A/C? .........or r-30.
Are the bathroom vents dumped into the attic? Is there excess moisture in the house envelope from spa, pool, ventless fireplace, etc. that might migrate into the attic?
Is this a new house? Or an existing house that has developed a new problem?
What is the ventilation system for the roof?
..........................Iron Helix
The townhouse is about 2 years old, and the problem has been going on for about 18 months.
The bathroom does not vent into the attic space.
I think R-19 is the minimum required by local code. Would there be any kind of modifier when using metal studs? Is there a chance the code was developed based on wood?
At risk of sounding like a smart guy, it's not the heat, it's the humidity. If the space is air conditioned, the humidity should be out of it--but on second reading, if it's the attic, it isn't a conditioned space probably. Then I'm with "Helix"--vent the attic. In heating climates, they talk of "cold roofs" so you don't have ice damming and so on; I would think in Florida, you may want a "warm roof" to prevent condensation. Either insulate the floor under the attic and have lots of air flow to keep moisture from condensing in the attic, or somehow put a vapor barrier and possibly insulation on the surface closest to the outside (the opposite of what you would do in a "heating climate", since their is higher humidity and warmer temperatures outside the house than inside.) The problem is how to do that. (In this case something like vinyl siding with Styrofoam would possibly work--it doesn't work as well up north.)
The other solution would be to dehumidify the air in the attic by "conditioning" it (refrigerating it).
I like the thought of sealing off the lower chamber and conditioning it. I think DanH mentioned this also. The builder will balk at this for fear of having to do this to everyone's unit. The HO feels that they should not be out of pocket to fix the problem.
I guess if the builder doesn't want to condition the space, then the answer is to insulate between it and the conditioned space (vapor barrier on the unconditioned side of the insulation) and ventilate the heck out of the unconditioned space!
Edited to add: Is the AC distribution box insulated? If not, it may be cooling the lower attic space, but not removing the moisture, adding to the condensation problem.
Edited 3/19/2005 7:56 pm ET by Danno
The box is insulated, but was cold to the touch. There was evidence of past condensation around it.
Humidity in the vented portion of the attic would be expected to a point. Since the lower chamber is not completely sealed from the upper, there are lots of cracks and seams for humid air to infiltrate. The humidity in my area today ranged from 36% to 97%, but I live in South Florida.
I read somewhere on the net, maybe the Building Design site linked above, that an insulated panel should be attached to metal wall studs before the sheetrock, as sheetrock has very little insulating power.
The HO has hired an attorney. If he does not get anywhere with the builder he said he was going to try sealing the lower chamber completly, and conditioning the lower space.
Thanks for your suggestions!
I finally found a conversion program to make the image files. Attached are two sketches, one looking at the space from the side, the second looking from the back.
I seen the photos. the whole thing screems shotty craftmanship. this is all from trying to have passive climate control over half of the attic. possibly a hairbrained attempt to save on insulating ducts & air-handler. or to sidestep fire barrier. we have condo builders in wi too. building the same thing over and over around the state. i suggest finding an older one or 2 or 3 and getting pix there and compare, talking to those owners too.
All the units were recently built, approx 2 years ago. The HO was going to try and talk to some of the neighbors to see if they will let us in their attic.
Thanks
Edited 3/20/2005 1:39 am ET by Rafe82ABN
im just sayin, he probably built very similar units off site 4 yrs ago, 6 yrs ago. those are the attics to see.
Man..............what an enigma!
IMHO............from what I can best make of the situation.
The insulation between the lower and upper attic is present but ineffective for this situation. Too many gaps, no continuous vapor barrier. Fiberglass infiltration rating is low and a tight continous vapor barrier is essential in holding heat and negating air infiltration.
The distribution box for the AC flex ducts sits upon the top of tne HVAC unit and the conditioned air that hits it from the HVAC coils is as low as 55 degrees and therefore this piece is a "block of cold steel" in a hot humid attic space and it has no choice but to sweat profusely. Inadequate insulation and separation from the humid zone.
The upper vaulted area holds warmer house air with higher humidity levels and therefore the moisture moves through the envelope into the lower attic which contains the the chilled distribution cube. The back wall of the vault should be spray foamed.
While the "foamer" is present.. cover the steel studs and metal joist....zero infiltration and what ever r-value is needed to kill the thermal migration. The partition between the upper and lower attic could be dow covered with 1/2" dow foam and the foamer could add another inch as a continuous barrier.
The builder and or designer/archi should own this problem and it's solution.
....................Iron Helix
Thanks guys for your help and insight. It looks like we are all unanimous that this is a design/construction issue, and not caused by the HO.
I'll try and keep updating the post as the evetns unfold between the HO and his attorney, and the builder.
Thanks again.
I check the Miami weather and Monday it is going to 81 with a dewpoint of 62, maybe higher if it rains.
Your moisture is coming form the outside.
And also looking at the temp/dewpoint chart I am not sure that thermo bridging is the problem.
http://tinyurl.com/5jyxe
It looks like the studs in the attic could get cold enough at night and with the high DP for water to condense on them.
Spraying FOAM those studs themselfs with would be a good idea.
But I see another potential problem. Or maybe this is the one that you where talking about and used the wrong term.
If the walls are steel I susepct that the ceing joist are steel also. And they are in contact with ceiling and would be much nearer the internal room temp.
And I looked at the DP for Aug 1, 2003 and I see that it was 74 so those steel joist realy need to be insulated and also have something to keep the moist air away.
I am not sure if cels is appropirate for a climate with that much moisture, but otherwise I think that is a good solution.
But it should work without limiting the inside room temp. At least not until soem one tries to make it into a meat locker.
Is there any HVAC equipment up there or duct work? If so insulating and sealing that is very, very important.
The "best" solution would be to convert the attic into condictioned space. But I doubt that you could get the contractor to do that, at least not without some cash.
http://www.buildingscience.com/topten/south.htm
http://www.buildingscience.com/housesthatwork/default.htm
Look at the houses that are built in the warm/humid climates.
Edited 3/19/2005 9:30 am ET by Bill Hartmann
The subject property is a 2-story townhouse (middle unit). The attic space is divided into two spaces. If you were able to look at a view from the 2nd floor elevation, you would see the the upper attic space with R-19 on the floor. The left half side of the upper attic space is over the vaulted stair landing area (where mold is forming). The metal wall studs are covered by sheetrock in the living space (stair landing), but are exposed above the ceiling level (attic space).
The right side of the upper attic space is over a lower attic space. The "floor" of the right side upper attic space is level with the "floor" of the left half side (side over stair landing vaulted ceiling). The "floor" is actually formed by faced R-19 suspended between 2x4's. This suspended R-19 floor ties in to the attic floor over the vaulted ceiling space.
The upper attic space is vented through soffits at the front and back ends of the roof. The roof truss structure is made of wood. No mechanical equipment or ductwork in the upper space. I think R-19 is the minimum required by the South Florida Building Code.
The lower attic space is located over the master bedroom closet, and the upstairs AC closet (located in the stair landing vaulted ceiling area). The metal wall studs are exposed in the lower attic space too. The attic floor joists are metal as well. The ceiling of the lower attic space is formed by the suspended (faced) R-19 floor from the upper attic space. There is not provision for venting in the lower attic space. Rust, corrosion, and mold are visible around the AC distribution box in the lower attic space. There is not insulation on the floor of the lower attic space.
The faced R-19 over the lower attic space makes me uncomfortable. It is in effect a vapor barrier seperating the unvented lower attic from the soffit-vented upper attic space. I am going to bring a digital thermometer next time I go to his house to gets some readings of the exposed metal studs. I will check Rh, temp and DP as well.
I will try and attach a rough sketch.
Edited 3/19/2005 3:14 pm ET by Rafe82ABN
Here is the sketch.
You need to post it as a jpg or gif.
Any idea how to convert it from a word doc to an image?
Here is the sketch as a pdf. I could not find a free utility to convert it to an image.
So, close as I can read this, you have a "roof within a roof". The inner roof is insulated, but below that is a sort of attic area that is nominally a part of the conditioned space, though unventillated by either external air or the AC. This is where the condensation is occurring.Basically you need to punch a hole in an air duct (and probably install a ceiling vent) to provide positive airflow through this inner "attic" area. Best would be to simply make it the return air plenum, and have return air from the house dump into it.You should measure the temperature and humidity in various areas when the problem is occurring. Likely you'll see a buildup of humidity there, possibly from leakage from bathroom vents, etc.(BTW, there isn't a bathroom vent dumping into this area is there??)
No bathroom vents dumping in the area. The condensation is forming in both attic spaces, but primarily in the upper, vented chamber.
The only thing separating the upper and lower spaces in the R-19 suspended between 2x4's. The R-19 is not taped, so it is not a perfect seal, but it fills the void between the 2x4's.
There is no ventilation (in or out) in the lower area. The attic is accessed thru the master closet. The access hatch leads to the lower chamber, which is the one with the AC dist box, and the flex duct.
The builder is saying that the HO keeps the temp too low in the house, which causes the metal studs behind the sheetrock in the living space to get too cold. The cold metal is in the attic space is not covered, so the bare metal is exposed to the warm, humid air coming in thru the soffit vents in the upper chamber. Condensation forms on the metal in the attic, and runs back down behind the wall into the living space area where the mold is growing.
I have never heard of a HO being forced to limit his AC temp to prevent something like this. I think it is a poor design issue, and the builder is afraid to admit it is a design/construction issue for fear of having to perform retro work on all the units.
Certainly the metal studs are an issue (lousy design), but I'd want to know why it's so humid up there, and why the studs are that cold. If the temp in the home is 72 it shouldn't be any colder than about 78 where the insulated ceiling is, unless cold air is escaping from the AHU into there.
Hard to imagine he's transmiting enough cold via thermal bridging (in the conditioned space) to the studs & up to the attic to make them cold enough to have much condensation when the humid outside air leaking in from the vented space hits them.....
Here is a photo from the lower attic scpace showing the suspended (faced) R-19, leading into the upper attic space. You can see some of the metal studs off to the left, which would be toward the vaulted ceiling area.
Edited 3/19/2005 3:26 pm ET by Rafe82ABN
This is the lower attic space, looking at the attic side of a wall in the vaulted ceiling area. These are typical of the exposed metal wall studs I mentioned.
I'm missing something here. If this is an attic (presumably un-cooled), what's making the studs cold? (And what are studs doing in the attic anyway?)