You might smell a musty odor when you walk into your house or maybe just when you go into your basement.

You might sneeze, you might not.

Maybe your allergic to mildew or mold spores, and maybe your not - but chances are you really don't know. While some medical experts say that about 30 percent of the general population may be allergic to mold/ or mildew, they note that most in that group - people that are only mildly allergic - probably ignore the symptoms.

Whether or not you are allergic - mildly or otherwise - it's easy to keep minor mold and mildew under control. So for your own comfort, perhaps, and for the convenience of potentially allergic guests, here's what you should know.

Spore and Dampness: Think of mildew and mold spores as microscopic seedlings floating in the air. They are everywhere in trace concentrations; the problems start when the concentrations increase. When airborne spores make contact with damp or moist surfaces, they multiply rapidly. While you can't eliminate the spores, you can do a lot, with proper ventilation and humidity control, to eliminate the breeding grounds and lower their concentrations.

Humidity refers to moisture in the air, the higher the air temperature, the more moisture the air can hold. The amount of moisture the air is holding relative to what is able to hold is called relative humidity. If air - at any given temperature - is holding all the moisture it can, the relative humidity is said to be 100 percent.

Walls: When an air mass at 100 percent relative humidity encounters a colder surface - a glass filled with ice tea, for example - some of the air will cool. Since the cooled air can hold less moisture than it could when it was warm, some of the moisture from the air will condense, probably on the outside of the glass.

The same effect takes place when warm air comes into contact with cooler walls - something happens in various seasons at various times of the day on the inside and outside of all buildings. Inside it often occurs when heated air comes into contact with cool interior walls- especially in un-insulated basements (finished or unfinished). Outside this can happen when the air meets the shady part of the house in the evening, when the air itself is cooling and beginning to lose some of its moisture; encountering a cooler surface accelerates the condensation. In both cases, airborne spores are deposited on the damp surface and rapidly multiply.

Crawl spaces: Homes with crawl spaces rather than full basements often suffer from very damp conditions-frequently unobserved for years. The problem here is a basic one, usually caused by water seepage due to poor landscape drainage and leaking pipes, resulting in a closed area with high humidity and lots of mildew and mold. To make matters worse, the humid air tends to rise, carrying spores into the spaces above.

Heating and cooling systems: Forced-air heating systems work by recycling household aria over hot metal. Simultaneously, thy can raise the spore concentration throughout the house in several ways. " Forced-air systems often are fitted with humidifiers designed to add moisture for increased comfort during the winter. Many humidifiers operate by passing a sponge or metal discs through troughs of water that are almost always spore generators. "

• Forced-air systems also may be fitted with air conditioning coils above the furnace. The coils "perspire" and drip moisture into a drain. If the system is poorly filtered, dust can collect on the wet coils and provide a perfect environment for spore growth.
• Some forced-air systems in houses built on slabs have ducts laid under the slabs. These ducts are good spore breeding grounds because humid summer air can enter and condense on the cooled interiors. In addition, poor drainage around a house often will allow some water to seep into the ducts. Return ducts through damp crawl spaces act like vacuum cleaners sucking up spores.

Closets: Closets on outside walls often have mildew or mold growing in them because there isn't enough air movement to ventilate the space properly.

Attics: Moisture tends to rise in houses, and -if the attic is insufficiently ventilated- it can condense on the cold underside of the roof.

REMEDIAL ACTIONS

• Basement walls should be insulated with a plastic vapor barrier stretched against the foundation.
• Dehumidifiers should be run in the summer with windows closed.
• Clothes dryers should be vented to the outside of the house.
• Steamy bathrooms can be fitted with exhaust fans.
• Milder on walls can be sponged with a solution made from 1 quart of chlorine bleach, 1 gallon of water, 1/3 cup liquid phosphate. This solution may bleach out some colors, so try it first on a small, inconspicuous spot. (Because chlorine and ammonia give off a poisonous gas when they are combined, be sure the household detergent does not contain ammonia. Never mix chlorine and ammonia.)
• We have found a good source for encapsulating mildew and mold. Information can be found at this website: www.anabec.com
• Crawl spaces should be kept dry. Make certain the grading against the foundation works to keep water away. Stretch a 6-mil polyethylene (plastic) vapor barrier over any dirt. Vents through the foundation walls should be left open. Fungicides can be applied to mildewed or molding flooring.
• Furnaces should be kept very clean (include the inside coil in your air conditioning maintenance contract); ducts that run through crawl spaces should be sealed and insulated; and trough-type should be avoided.
• Closets should not be stuffed with clothing. Allow space for air circulation and consider installing a vent in the door.
• Never close attic vents for the winter and make sure they are not blocked by siding. If bath or kitchen exhaust vents open into the attic, extend those ducts directly to outside vents. Problem attics can be fitted with additional vents.

Caveat Emptor: when buying a house, persons with known allergies to mold and mildew should avoid those with basements or crawl spaces; if that is not possible, they should be certain that these spaces are bone dry. Also, avoid houses with slab duct systems and houses that are heavily shaded and surrounded by trees.

Caution: this primer has been over-simplified for quick understanding. Mildew and mold problems can be difficult to control and may require professional help by a heating and air conditioning specialist.

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