Q: Gil, I think we have a mildew problem. It causes problems for my daughter when she comes to visit ... We think we may have to remove all the panelling and carpeting, apply something to kill the mildew on the walls and floors and refinish the affected basement rooms. -Helen Bates

A: It might not be necessary or advantageous to tear up the whole basement at this point. At any rate, if you don't remove the conditions which are supporting the growth of mildew, you'll likely have a recurrance. It's somewhat difficult to speculate, not having seen your home, but here are some things to consider...

Mould and mildew can occur in a house at almost any time of the year, if the moisture content of the building materials is about 20 percent or greater. High relative humidity, or saturation at or below grade, can create this condition.

A good plan of attack begins with decreasing dampness and increasing ventilation. Maintain a negative grade slope away from the house; and ensure that evestroughing, down-spouts and drains are free of debris, and properly directing water at least two meters away from your foundation wall. Even if your house is relatively new and has properly installed, working footing drains, excessive surface water can saturate the foundation wall, and evaporate to the interior faster than it can be drained away. Check to see if water pools anywhere beside the house during a downpour or period of melting.

Severe mould on inside wall and ceiling.Moisture problems can originate inside or outside the house, or both. In cooler weather, condensation will occur on any surface that is below the dew point of the air in contact with it (temperature at which condensation will occur at the existing humidity level). This moisture usually appears first on the inside surfaces of windows, and may also appear around door jambs and where outside walls meet the floor or ceiling. Closets can also become damp due to reduced air circulation. In warm, humid interior conditions, foundation walls may "sweat" profusely at any time of the year.

Dehumidifiers can remove large amounts of moisture from the home, and in summer, an air-conditioner is also a powerful dehumidifier;. Air conditioners however, consume considerable amounts of energy and may not be useful in spring and fall, when cooling is not required.

Ventilation is an effective and inexpensive means available to you for reducing humidity, and can be obtained by opening windows or operating an exhaust fan as soon as significant window condensation appears.

HANDY HINT

Throroughly dry a damp spot on an exposed foundation wall or floor with a hair dryer. Tape a 12 inch square of heavy plastic over the spot, and check it in one or two days. Seepage will cause the underside of the plastic to be wet, but condensation will form on the top side!

Q: We have a dehumidifier, but it is in the sump pump crawl space and probably doesn't do much good. If we turn it up very high, it just runs all the time. Maybe this is because it is pretty old, I'm not sure. It seemed to work fine in our last house.

A: The required size of dehumidifier will vary with conditions, and the size of the house - but in any house with a severe humidity problem such as yours, a new 60 pint (minimum size) dehumidifier with a drain hose directed to the sump or laundry drain should start to produce results. If you prefer to keep the crawl space closed, you'll likely need two machines.

THE BOTTOM LINE: First things first - look for external sources of moisture, then internal; and then study ventilation followed by dehumidification, and if necessary, insulation and/or vapor barriers where required.

A FEW QUESTIONS FOR HELEN:

1. How is your lot grading? (any slope toward house?) Settlement around the perimeter of the foundation?

2. Downspouts and drains in place?

3. What type of heating/ventilating systems do you have? Same in basement?

4. Is your kitchen range hood directed to the outdoors?

5. Bathroom exhaust fans installed and used regularly? Vented through the wall or roof (not into the attic, hopefully).

6. Clothes dryer vent directed to the outdoors?

7. Is ventilation provided for the basement?

8. Are any windows sweating?

9. How old is your house?

10. Construction: solid brick/brick veneer/siding etc.

11. Are roof/ridge/gable vents visible?

Also, check the lowest course of bricks for the presence of "weep holes" about every fourth mortar joint. (If your home is wood-framed with a brick facing, the mortar should be left out, to allow any condensation between the exterior sheathing and the brickwork to escape to the outdoors.)