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ntrainer

11:36AM | 07/22/06
Member Since: 12/15/02
33 lifetime posts
Bvbasement
So... we completely renovated our basement and the project seemed finished, but today we noticed mold growing on the back of a clock and warped pictures (mounted inside frames) on the same wall.

The wall is an exterior wall that is completely below grade. Because it is below grade, our contractor assured us that it did not need to be insulated, although the rest of the walls in the basement ARE insulated (since they are above grade, as the house lies on a slope).

Is the lack of insulation causing this problem, or could there be another culprit? What's the solution? HELP! Thankfully, we're within the warranty our renovation company provided, but I really don't want to perform costly repairs if (a) they're not needed, or (b) they're the wrong repairs.

Billhart

12:54PM | 07/22/06
Member Since: 04/25/05
1918 lifetime posts
Moisture may or may not be coming through the foundation.

You did not give any details of your climate or the construction.

But in may parts of the country summers are very humid.

And basement, by there nature are relatively cool. That cause the RH to increase and and can lead to mold and mildew.

One of the ways to control it is to reduce head loses through the foundation. Also a vapor RETARDER (NOT BARRIER) will help.

Sheets of foam attached directly to the foundation can provide both features.

Start with this;

http://www.buildingscience.com/resources/moisture/relative_humidity_0402.pdf

And the ones here on basement insulation.

http://www.buildingscience.com/resources/foundations/default.htm

And you can get some same details here.

http://www.buildingscience.com/designsthatwork/default.htm

You have to look at what region you are in and them look at house with basements.

Depending on all of the details you might also need a dehumdifier.


ntrainer

03:38PM | 07/22/06
Member Since: 12/15/02
33 lifetime posts
I think it's unlikely the problem is with moisture coming through the foundation, though your post reminds me that I definitely left out a few details:

We live in Northern Virginia, near Washington, D.C., so you're right that the climate is humid. In fact, it's VERY humid. Having said that, however, the house shows no evidence of moisture coming through on any other walls, including the other exterior walls. In addition, there is little evidence of trouble with the floors, which have now been covered in hard wood and probably would show buckling or other problems with moisture (I know, I know, most hard woods is not recommended for basements, but we've put in additional sub-flooring to ensure against problems, and the house shows no evidence of flood or moisture damage in the past). The room we're discussing was previously covered in wall-to-wall carpet, and certainly there was no moisture problem with the carpet, so I'm guessing the sub-flooring and hard wood added in the renovation wouldn't have caused a problem.

Other details: The house was built in 1959. The wall in question is drywall placed on studs which were built over the concrete wall. The exterior of the home is brick.

Billhart

08:50PM | 07/22/06
Member Since: 04/25/05
1918 lifetime posts
Your experience just might prove my point.

I am guessing that you installed Delta-FL, Dricore, Subflor, or something similar.

That are a plastic wafle with an plywood or osb subfloor over it to which the hardwood floor is installed.

If that is the caes then the moist air can might get under the plastic and condense. However, it is being isolated from the concerete to the wood.

In the wall, unless it is sealed PERFLECTLY air will get behind the DW. The DW helps insulate foundation so that it would be even cooler behind the DW. But then the condensation can wet the DW on the back.

It then tries to evaporate, but place that it is covered up it doesn't.


ntrainer

02:48AM | 07/23/06
Member Since: 12/15/02
33 lifetime posts
Am I just being optimistic to think that the problem COULD have been caused by a single day without air conditioning? Our A/C condenser motor conked out one day this summer (ball bearings were shot) and it took us a day to make the repair...

Billhart

05:46AM | 07/23/06
Member Since: 04/25/05
1918 lifetime posts
The AC being off just one day would not cause this.

You might want to get a hygrometer (relative humidity moisture meter) and keep it up stairs for a week and observing it.

Then a week down in the basement.

An RH of over 70 and mold will grow.

"How to Identify the Cause of a Mold and Mildew Problem

Mold and mildew are commonly found on the exterior wall surfaces of corner rooms in heating climate locations. An exposed corner room is likely to be significantly colder than adjoining rooms, so that it has a higher relative humidity (RH) than other rooms at the same water vapor pressure. If mold and mildew growth are found in a corner room, then relative humidity next to the room surfaces is above 70%. However, is the RH above 70% at the surfaces because the room is too cold or because there is too much moisture present (high water vapor pressure)?

The amount of moisture in the room can be estimated by measuring both temperature and RH at the same location and at the same time. Suppose there are two cases. In the first case, assume that the RH is 30% and the temperature is 70oF in the middle of the room. The low RH at that temperature indicates that the water vapor pressure (or absolute humidity) is low. The high surface RH is probably due to room surfaces that are "too cold." Temperature is the dominating factor, and control strategies should involve increasing the temperature at cold room surfaces.

In the second case, assume that the RH is 50% and the temperature is 70oF in the middle of the room. The higher RH at that temperature indicates that the water vapor pressure is high and there is a relatively large amount of moisture in the air. The high surface RH is probably due to air that is "too moist." Humidity is the dominating factor, and control strategies should involve decreasing the moisture content of the indoor air."

http://www.epa.gov/mold/moldresources.html


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