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stangboy68 12-04-2007 02:56 PM

Molde: Underside of Attic Floor
First, a little background information. Previously, the attic had a 2x6 floor, most of which had fiberglass batts and blown in pink insulation from when the house was built in 1970. About half of the 500 square foot attic had a plywood floor. Last spring I proceeded to install 2x10's perpendicular to the 2x6 attic floor joists to allow enough room for me to add more insulation. I added about 10" on home depot blow in insulation for about an R-49 attic like is recommended. Then I covered the entire floor with 1/2" plywood for storage. Now, as winter has come (I'm near atlantic city, NJ) I went in the attic to get down my xmas stuff. Low and behold alot of the plywood was a bit warped and I had two basket ball sized spots of mold on the floor. At first I thought the roof was leaking. But then I pulled up some of the floor and noticed the underside was damp and had white fuzz mold growing :sigh: . I never had any problem until I added all this insulation. I also noticed the top of the insulation was a bit damp. The insulation is even with the top of the new floor, hence no air space between the underside of the floor and the insulation. The only other thing I can think of is that I have a small room humidifier that runs all the time. The part that perplexes me is that I have always had this humidifier running for years. Why all of a sudden should I have this problem? Is there too much insulation, too much plywood, should there be an air gap between the plywood and the insulation? I'm freakin out here!!

Handyman50 12-04-2007 04:54 PM

It sounds to me like you have a ventilation problem. My guess is that you didn't assure that your vents were covered with baffles while adding the new insulation. The baffles stay in place and will assure that you have adequate ventilation. If this is the problem, you should get into the attic and remove the insulation from them. Then, place baffles over the vents. An attic fan would also help draw the hot air out.

stangboy68 12-04-2007 05:44 PM

The house doesn't have any soffit vents, just a gable vent on the front and back.

Handyman50 12-04-2007 06:04 PM


Originally Posted by stangboy68 (Post 78423)
The house doesn't have any soffit vents, just a gable vent on the front and back.

If it were me, I would have soffit vents added. In fact, building codes in our area of the country (Pacific Northwest), state that we should have them every so many feet along the soffit and gable or ridge vents, also. The inspectors would be very unhappy if they weren't available. The air comes in through the soffit vents and rises to exit through the gable or ridge vents.

As I stated previously, an attic fan in one of the gable vents would also be very helpful. The fan is setup to suck hot air from the attic. I would buy a thermostatically controlled fan.

Sammy 12-04-2007 06:17 PM

Is there a vapor barrier between the living space and the new/old insulation?

If not, moisture that may have vented away from the living space was trapped by the attic flooring. Its amazing how much moisture moves up like that.

It also could be an issue with the new/old insultation not being compatible and trapping moisture.

stangboy68 12-04-2007 06:25 PM

There is no vapor barrier anywhere in the ceiling. I now wish I had one but I am not about to rip down the ceiling to put one up. I was actually looking at some of those vapor barrier paints. Some have ceramic in them and was even looking at an elastomeric.

Sammy 12-04-2007 06:30 PM

The added insulation may be the issue but the plywood is probably what is sealing things up too well over the insulation since there is no vapor barrier.

Is it possible to move the attic floored area over a non insulated space such as an attached garage?

I would spot check a few areas away from your floored attic to see if the mold is occuring there also. That would tell ya...

stangboy68 12-04-2007 06:40 PM

Yeah, I'll have to get up there and pull some boards. it's just a PITA since now there is only 4' of headroom and I have a bunch of stuff up there. I suppose worst case scenario I will have to permanently remove the plywood. I just want to know why this is happening.

Sammy 12-04-2007 06:46 PM

I would keep an eye on it as the weather gets colder..

Check some spots under the attic flooring and then in unfloored areas to compare.

I had a few small open holes to the attic last fall when I was rebuilding some interior walls and the moisture would pass thru to the attic and freeze on the roofing nails sticking thru the roof sheathing. Then melt on me when I got a drop light near em.. I thought it was a roof leak at first.

Big Bob 12-06-2007 09:53 AM

Consider adding venting in your attic floor. The insulation needs to expell that moisture as does your plywood. The blown Insul will settle in time and you will end up with an air space that you need.

Lots of ways to vent your attic.


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