Home repair: Fan may dry wet spots under basement furniture

Q. Two years ago, we finished a room in our cellar and painted the floor with epoxy paint. We run a dehumidifier, but our area has a very high water table, and our sump pump runs almost year-round. The painted areas under furniture get damp and wet, which we assume is warm, humid air hitting cold cement floors that we have now sealed. The rest of the cellar floor that is not painted is fine. We do not open windows down there.

Can we carpet the floor and, if so, with what type of carpet? We are assuming the carpet will keep the warm air off the cold floor but do not want to set up a mold and mildew problem. Since the room is not used except in the summer, we are not 100 percent sure the floor is not damp in cold weather also.

A. Your assumption is correct: The condensation is caused by stagnant air under the furniture. If there is enough clearance below the furniture, running a fan may help alleviate this. It is unlikely the condensation occurs during the heating season, if the room is heated.

I am afraid that any type of carpeting would not eliminate the problem, but you might put a small piece under the furniture and see what happens.

Q. Thank you for your previous helpful information and advice (regarding mold at the peak of a ceiling). I have decided to have the contractor who applied the present shingles inspect the roof for visible damage and possible leak source. We also will get an energy audit.

The roof was replaced in January 2008 because water was streaming into the house from a leak in a valley. Three contractors agreed that the entire roof should be replaced instead of attempting a limited repair. I do not recall their reasoning, if I ever knew what it was. I suspect the shingles were not properly applied the first time, because the house was built under a lot of budgetary pressure.

I do not have good understanding about the possible role of the structural panels. The roof panels, I believe, are wood outside and Sheetrock inside with plastic foam between, joined by splines. I do not see how they could shrink without a visibly obvious manifestation.

However, they may not have been properly joined at the peak of the roof when the house was built as a post-and-beam structure.

A. My answer to your earlier question alluded to the fact that the mold problem at the peak of the ceiling you first wrote about may be due to shrinkage of the foam structural panels of your roof. I doubt that a roofer will be able to determine if the structural panels have shrunk.

The energy audit should, but it will need to be done in cold weather for any shrinkage to show.

There must have been something else wrong with your earlier roof for three roofers to recommend a total replacement to take care of a leak in a valley. The shingles may have been in bad shape, which would not surprise me since you mentioned earlier they were a brand with a history of early failure.

Foam structural roof panels are built just as you describe, and it is the foam that shrinks, not the OSB sheathing or the drywall, which makes it more difficult to fix the problem, if there is one. The splines align the panels properly, but they are not an insulation material of any consequence. A mismatch or inadequate insulation at the ridge may also be part of the problem.

Q. Someone on TV the other day talked about using roof tape on all the deck seams as an extra precaution against leaks. This would be underneath all the normal underlayment. Would you recommend this? My contractor says it is not necessary.

A. TV presenters have to have something different to say to keep their programs interesting and going. Most of these programs are really entertainment and are of limited use for viewers.

Your contractor is correct. If he or she installs an ice and water protective membrane at all eaves, valleys and roof penetrations, and reinforced felt elsewhere on the roof deck, there is no reason to go to that extra expense. There is no harm in taping the deck joints, but it’s like wearing a belt and suspenders, and still holding your pants.

Q. I’ve attached pictures of water damage done to the wall of our garage from cracks in the exposed cement porch, which is the roof of the garage. What would you recommend to repair both the cement on the porch and the block? As you can see from the pictures, we tried cement to repair the face of the block. Do you think we need to replace the block, and if so, do you know of any sources? This is the only section with damage.

A. It looks like you have caulked cracks on the concrete porch floor with silicone, which is unlikely to last when exposed to moisture for any length of time. Check to see if the caulk is peeling at the edges. If and when the caulk fails, peel it off, clean the cracks thoroughly and seal them using polyurethane caulking. You should also consider cleaning the concrete and sealing it with a masonry sealer.

The damage to the block foundation of the garage looks as if it was caused by seepage from the concrete porch floor that wet the inner core of the blocks and caused spalling in freezing weather.

Not enough of the blocks have been seriously damaged to present a structural risk to your garage, as long as you seal the porch floor and repair the cracks to stop the leakage. A competent mason can easily repair these blocks and attempt to re-create the textured look.

Q. My 15-year-old home in southwest Pennsylvania seems to have high humidity levels year-round. When it was built, we used the most energy-efficient methods we could afford: 10-inch block foundation with vapor barrier and 2-inch foam on the exterior; 2-by-6 walls with R-19 fiberglass and 1-inch (R-5) foam all wrapped with Tyvek; Andersen windows; and a brick veneer. The basement floor has a vapor barrier, and the walls have been Drylok-ed.

We are using a 90 percent-plus-efficient gas forced-air furnace with central air. The dryer vents outside, as do all the bathroom exhaust fans. Currently the humidity level is about 65 percent. We have tried a stand-alone 50-pint dehumidifier in the basement, and it runs almost constantly.

I always hear of adding a humidifier to the furnace for the heating season. I’m considering adding a dehumidifier instead to get the humidity down.

A. If you had the windows open during a good part of the summer, it would not be unusual to have the level of relative humidity (RH) you experience. But if you used the air conditioning throughout the summer, the relative humidity should have come down by now.

Because you experience a high RH level year-round, and because you have a tight house with an efficient furnace, you should look at the possible sources of such a high reading. Do family members take very long showers? Do you keep the bathroom fans on long enough after showering? How many of you live in the house, and how big is it? Do you have a lot of water-loving plants? Do you use a woodstove and store firewood in the basement?

How many pets do you have? Do you dry laundry on racks or always use the dryer?

Have you checked the grade around the house to make sure that it slopes away from the foundation? Do the driveway, patio, walks, etc., lead water toward the house? Are downspouts discharging water onto splash blocks and onto a grade that slopes away from the house?

You mention having applied Drylok to the inside of the basement walls. Unless you know that your foundation is properly backfilled so that no water can put pressure on the walls, it is possible that the block cores are filled with water, which would cause the excessive moisture.

It sounds like you may need an air-to-air heat exchanger.

Correction: In a recent column, I wrote, “Housewraps such as Tyvek are not really vapor barriers, but vapor retarders. A vapor retarder needs to be installed inside between the drywall and the wall insulation in climates that depend more on heating than cooling, whereas it should be installed under the siding in climates where cooling is prevalent.”Actually, housewraps such as Tyvek are not vapor barriers or vapor retarders. They are vapor permeable, and they are installed under the siding in any climate. I apologize for the error, which occurred in my rush to meet a deadline and which I noticed only after publication.Ÿ Henri de Marne was a remodeling contractor in Washington, D.C., for many years, and is now a consultant. Write to him in care of the Daily Herald, P.O. Box 280, Arlington Heights, IL 60006, or via email at henridemarne@gmavt.net. $PHOTOCREDIT_ON$© 2011, United Feature Syndicate Inc.$PHOTOCREDIT_OFF$