Condensation may be cause of damp garage walls

Q. My garage walls are damp after every rain. The walls are above ground. I have a concrete deck on top of the garage with steel plates under it.

Why are the walls damp, and what can I do to prevent this? I tried painting them outside and inside, but they are still damp.

A. I assume you mean that the garage walls are damp inside; dampness outside when it rains is obviously normal. Unless the block walls are painted with a waterproof coating, it may be that the rain is penetrating the blocks all the way through, but I would think this would happen only if the rain is of long duration and hitting the walls. It also would seem that the moisture would cause the paint to peel if it is not a waterproofing paint.

Another possibility is that the rain is causing the air outside to drop significantly in temperature, while the temperature of the air inside your garage is warmer. This could result in condensation on the inside walls as they cool. The rain may also cool the concrete roof and its metal deck, adding to the problem.

It’s difficult to pinpoint the cause or causes without knowing more about where you live, the climate in your area, and whether this happens all year or only in certain seasons.

Q. I have loose insulation that rises 4 to 6 inches above the joists in my attic. I wish to install some walking surface to allow for inspection and maintenance in the attic. Near the middle of the attic, the space adjacent to the entry ladder was provided with 100 to 200 square feet of crudely installed plywood. This was nailed down over the insulation and compacted it.

I don’t want to do that to any of the uncovered remainder, about 2,100 square feet. The rest of the area is a sea of loose insulation. I just need a few narrow runs to access the gables, some vent fans and lighting units. I emailed Attic Dek to inquire about decking that might install several inches above the joists, but I have received no reply. Other attic deck sources (Atticraft, Uwe, Martin) seem to have only flat panels. We do not intend to store any heavy items up there.

Some have installed 2-by-3 to 2-by-6-inch extensions over the existing joists, then applied 5/8-inch plywood. I’m not sure if the added wood extensions will conduct more Btu past the insulation, which currently covers the tops of the joists. What if the extensions were run perpendicular to the joists? What do you suggest?

A. A catwalk, as it is called, is a very good idea in any attic not already floored for storage.

The proper way to accomplish what you have in mind is to screw 2-inch by 4- or 6-inch lumber across the existing joists. It’s not only much better for energy saving, but also more stable than installing these pieces parallel to and on top of the joists, as it is easier to fasten them to the joists.

Depending on the size and location of your access ladder, you may have to cut the plywood that you are probably planning to use in smaller pieces. Keep in mind that plywood is strong across the grain and not lengthwise. You should cut the plywood in strips across its length so you end up with pieces that are 4 feet by whatever the spacing is of the 2-bys. Three screws on each end are sufficient. Avoid nailing, as it may damage the ceilings below.

Q. My wife and I purchased a new (spec) home in January 2011. When the weather warmed up in the spring, we opened the windows to enjoy the outside breeze. Within 10 minutes, our house had a terrible odor like cat urine. (We do not have a cat.)

It smells more strongly in some rooms than others. We do not notice any smell outside or by the open windows. It doesn’t seem to matter which windows are open — first or second floor — to cause the odor. We do not have any specific odor-causing plants outside the windows. If we close the windows, the smell disappears as fast as it appeared, and the odor is not present if we keep the house closed up. We also do not notice anything if we run the air conditioner or heater.

Please help so we can open our windows and enjoy the outside air.

A. Since the odor is noticeable only when the windows are open, it has to be coming from some element outside the windows. And since you are not smelling any odor outside, we can discount any odor from farming nearby.

If the odor were coming from carpeting or any other material in the house, you would smell it when the house is closed up.

I suspect the odor comes from fiberglass screens on the windows. You haven’t said whether the odor is present only when the sun shines on some windows, but I have investigated such occurrences, and they took place only when the sun hit the screens. When everything else is analyzed, and discounted, it’s the only thing that makes sense from your description of the problem.

Why don’t you take down some of the screens and open your windows on a breezy day and see if this solves the problem? If it does, have the fiberglass screening replaced with new fiberglass in the hope that it won’t happen again, or with metal screening. Hardware stores or glass shops are the places to go.

Q. Have you heard of Krud Kutter, which is supposed to eliminate mold, mildew and spores? Is it effective? Should these areas be scrubbed or power washed?

A. I have heard of Krud Kutter, but I have not used it and do not know how well it works. If you decide to try it, please let me know if it was effective.

Scrubbing or power washing should be done only if the manufacturer of Krud Kutter recommends it and if the things you plan to clean will not be harmed by water and pressure.

Q. I own a home that was built in 1969. It is a ranch built on a crawl space. The crawl space is roughly 4-feet deep.

I have several cracks in my poured concrete foundation. Additionally, the house has an attached garage whose foundation has several cracks in it. The floor has dropped on the outside edges by up to 10 to 12 inches.

What type of an inspector should I hire to inspect the foundation and tell me if there are any issues that need to be addressed before repairing these conditions?

A. Small hairline cracks are a normal process of curing concrete, but larger cracks can be serious, and yours sounds as if they are of concern. Particularly worrisome is the sinking of the garage floor, which can be caused by a substrate that was not hard-packed, settlement from the weakness in the foundation, or possibly an underground spring that is eroding the soil below the slab.

A structural engineer is the person to call to evaluate the conditions and come up with a sound fix.

Q. My question concerns radon gas. For my own peace of mind, I bought a radon detector kit at Lowe’s. I followed the instructions to the letter. The result came back at 3.9 pCi/L. Since this was near the 4.0 threshold for action, I waited a month and repeated the test.

Nothing was changed in the home between the tests. The second test came back at “less that 0.7 pCi/L.” Should I continue to run tests, or can the radon change that much day to day?

A. You must have used charcoal kits, which give a short-term reading over 24 to 36 hours. Radon readings can fluctuate considerably depending on a number of circumstances: the time of year, where the kit was located, the comings and goings of the occupants, the location of the kits near a heat or ventilating source, etc.

This is why I recommend the use of an alpha track kit, which measures the radon level over several months. It can be started any time and left for up to one year. If you want to keep it only a few months, the testing is best done during the winter, because that is when the radon level is most important. Summer readings may be the same as radon levels outside, over which we have no control in climates that depend on open windows for ventilation. The Environmental Protection Agency recommends alpha track kits as the best way to measure radon levels over an extended period.

I have had similar reservations about the use of the radon-measuring systems that some home inspectors use to tell prospective buyers what the level of radon is in the home. They also give short-term readings that are not a true representation of the radon levels year-round, and they vary with the time of year.

Alpha track kits can be found in some hardware stores and through Amazon.

Q. I have a generally dry basement at my single-story house in Burlington. As a way to keep my escalating electric costs down, I sometimes open a couple of the basement windows, keep the cellar door to the kitchen open, open windows in the house as well, and hopefully let any dampness out of the basement with the cross-drafts. I do this only on cooler, crisp days, not hot and humid days. Otherwise, I run my dehumidifier. Is this a wise move?

A. Perfect strategy! The warmer air in the living quarters exits through the windows, drawing cool, crisp outside air through the basement windows. Open all the basement windows for better ventilation.

Basement windows and crawl-space vents should not be left open in humid weather, as this introduces unwelcome moisture into these spaces.

Q. I am considering having an interior French drain installed in our basement. Any pros or cons?

A. The French drain was invented by Henry F. French, a lawyer from Concord, Mass., who became assistant U.S. Treasury secretary in the late 1800s. He described its construction in his book “Farm Drainage.”

It requires digging a trench and filling it with rocks, sometimes covering a perforated pipe, to capture water and discharge it away from a building or other feature. Usually French drains are installed outside, filled with rocks to the top and left open, whereas curtain drains are covered with soil.

Interior sub-slab foundation drains are used to capture water that is building pressure under slabs to keep it from flooding the basement or, in combination with a slot at the base of the walls, to capture water leaking through foundation walls. In the latter case, there are other, less disruptive and less expensive ways to prevent water leaking through walls from flooding the basement. This is done with fiberglass gutters glued to the floor that lead water to a sump pump.

Before I can more fully answer your question, I need to know why you are considering having a sub-slab drain installed inside.

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.

© 2012, United Feature Syndicate Inc.