Old 11-27-01, 09:45 AM
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My house is about 30 years old. It has a crawl space below the living room and kitchen. The crawl space does have a cement floor with poured concrete walls. The ceiling above the kitchen and living room is vaulted, with 4" fiberglass bat insulation. The ceiling gets fairly hot in the summer, so their isn't much ventilation. I did paint the living room and kitchen with radiance low emissivity paint. The humidity in the house stays at 65%. I put new Hurd casement windows in last summer, that get moisture in the corners due to the high humidity. Crawl space humidity stays at 70%. Could the high humidity be caused by poor ventilation in the vaulted ceiling. Or, would it help to add a moisture barrier in the crawl space, though it stays dry year round?
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Old 11-27-01, 03:49 PM
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Perhaps running a dehumidifier in the crawl space will remove the excess moisture...

good luck

Old 11-27-01, 06:21 PM
Join Date: Dec 1999
Location: Northeastern NC On The Albemarle Sound
Posts: 10,952

There is an insulation question in the Fireplace forum that you can probably answer, if you will.
Old 11-27-01, 08:52 PM
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Greeting, By Auslin

You didn't mention if you were in a high humidity area. That would aggravate the problem.

You can control the moisture from the crawl space but you have two other possible areas of concern.

Do you have a ridge and soffit vent system. If not, you could be getting the moisture from the condensation in the FG batt in the ceiling. If you have direct sun lite on the south west and east walls, those fiberglass walls are probably condensating alot of moisture in the summer time. The high wall temps could be driving that moisture into the house.

You are now aware of how useless fiberglass is because you have applied a RB paint. That paint is about 30-40% efficient compared to about 10% for the fiber glass. But, you have two other problems here. Notice how problems come in twos?

1st, the increased surface area of the ceil'g compared to a flat ceiling, more radiating surface, plus the gable/s area too.
2nd, the rafters are conducting a large quantity of heat energy directley from the shingles to the drywall.
The answer. If you are willing to install a single sheet of RB over the ceil'g drywall and redrywall the ceil'g, then you will get much, much better results. I will give you specific details if you want go this route.

The crawl space. Install a single sheet of 4 mil plastic to the side of the top plate and let it hang down to, and across, the floor. Install two layers of 4 mil over the floor. Crossed over and overlaped seams, 6". Seal all vents and foam/caulk all holes to out side. Install a 48" RB to the side of the top plate and let it hang to the floor. Remove the FG batts between the joists at the rim board and replace with RB. No moisture problem and the crawl space temp will be within a few degrees of the upstairs.

You can also paint he inside of the exterior walls with RB paint.
You might also want to consider installing a RB over the insulation in the rest of the attic. This would cut your a/c bills. It will make the house more comfy too. You have the potential of reducing your heat/cool energy bills up to 40%.

Thank you for considering my opinion.
Old 11-28-01, 05:51 PM
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Thanks for the info rbisys. I live in Iowa, so the current outside temp is 35 degrees. The indoor house humidity is at 63%. As for the crawl space, what type of radiant barrier would you recommend? The crawl space does have a cement floor, so would it help to lay the moisture barrier over it also?
About the vaulted ceiling, I'm interested in helping it as much as possible, but concerned about the weight the extra drywall would add. From what I can tell, the rafters above the vaulted ceiling are only 2x4's. The ceiling above the bedrooms is flat, so I had 12" of fiberglass insulation blown in above that a year ago. With the extra insulation, there isn't any room in that portion of the attic to access. Where the vaulted ceiling meets the flat part, vent chutes were installed so the blown fiberglass insulation wouldn't plug any possible air movement from the vaulted portion. The roof does have a ridge vent. Unfortunately, the shingles are black. So, the roof gets very hot in the summer. There are also plenty soffit vents. Do you think it would be better to remove the drywall above the vaulted ceiling, allowing the insulation to be removed and vent chutes installed. Then installing a 3" higher R-value rigid foam insulation in the rafter cavity. Then possibly a 1" or 2" rigid foam board with reflective back to the underside of the rafters, and drywall over the foam board. This is provided the existing rafters wouldn't handle the weight of the extra drywall.

Old 11-30-01, 08:34 PM
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If you do indeed have 2x4 rafters then the best method is to remove the drywall and redo. Foam is only about 20% efficient, the RB 97% so your best bet is the RB. The foam can also cause condensation in this type of app. Also the heat energy would still conduct thru thru rafters. In this type of situation the best method for highest efficiency is as follows.

Remove the dry wall and FG. Be sure to use a mask as FG is a carcenogenic material, like asbestoes.
Install a single layer of RB material between the rafters about 1" from the bottom. Install a second sheet on the surface of the rafters, like a vapor barrier. Install across the rafters 7/8" steel furring strips (drywall supply house). Install drywall and finish. By installing the RB to the bottom of the rafters and using furring strips you are breaking the conductive flow of the rafters. Even if the RB gets up to 110 degs it will only radiate about 3 BTUs/hr/sf to the drywall. The system you have now allows the drywall to get up to 110 degs or more and with a 75 deg floor temp it is radiating about 37 BTUs / hr/ sf. This why the room gets so hot. In winter the process is reversed.

The RB material you want is a 20# or lighter kraft paper with foil laminated to both sides. If you cannot get it locally I can supply your requirements. Do not use bubble foil. It will not perform any better, is expensive and harder to install.

This method will out perform any other system. The RB is also a superior vapor barrier.

Reread the recommendation for crawl space to answer your vapor barrier question, first two sentences. Either you do alot of cooking, you have teen age girls, or you're getting alot of moisture from the crawl space. Do you know if your crawl space is properly drained, I MEAN REALLY WELL DRAINED. This method practically stops crawl space moisture problems. I'm guessing you have mildew odors in the rugs above the crawl space.

If you need more info on installing or material supply, contact me at [email protected]

You may still be able to slide a HD RB material over the ceiling FG. You have no idea how much difference this could make. If that is really impossible, use the RB paint on the ceiling.

I thank you for your interest.

Thank you for considering my opinion.

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