What are mold and mildew?

Molds are fungi that grow in different shapes, sizes and colors. They also tend to be fuzzy in appearance. Mold is natural and is important for the normal function of the environment, as it breaks down dead and decaying material. However, when mold grows indoors it can cause health and structural problems. 

Mildew is a fungi that can cause damage to plants and crops. Mildew grows in a flat pattern and may look powdery. 

Download a brief fact sheet here.


Mold can cause:

  • Watery eyes, runny nose, sneezing, nasal congestion
  • coughing, wheezing, difficulty breathing
  • headache and fatigue


Mold requires oxygen, moisture and a food source (wood, paper and certain glues found in building materials). While you cannot prevent mold spores from coming inside your home, you can prevent mold from growing. If you see mold, that indicates you have a moisture problem. See below for ways to identify the source of the moisture.

We do not recommend testing for mold. If you have mold, you should remove it, using the steps listed below. For large areas of mold, you may need to call in specialists to safely remove the mold.

Mold and Mildew Prevention

Find and control the moisture source
  • Check behind furniture placed against exterior walls, under carpet, inside wall spaces, basements, and attics
  • Leaky gutters and pipes lead to moisture problems
  • Don't put furniture against the wall to the outside- that can cause condensation.
  • Humidity gauges are available at your home electric store. The range you are looking for is between 30-50% relative humidity inside.
  • Read more here
Increase ventilation
  • Fans and exhaust system
  • Dehumidifiers are useful for basements but only work when the temperature is above 65°F.
  • Don't block air supplies and air vents with furniture or other items
  • Cloth dryers should be vented to the outside, not into the attic or crawl space

How to clean the mold and mildew

  1. If you are sensitive to cleaning chemicals, be sure to wear personal protection such as gloves, goggles, and a respirator. Do not use bleach. Use a detergent or vinegar-water solution to clean.
  2. Remove visible mold. If the mold is dry, use a spray bottle filled with water to mist it. This prevent mold spores from releasing into the air when you clean the mold
    1. Small areas on slick surface:
      1. Mist with soapy water, scrub, clean and dry thoroughly.
      2. If mold is dry, be careful not to disturb and spread spores.
    2. Plush, fleecy or porous items may need to be thrown away (carpet, drywall, wood, stuffed animals, fabric, and cloth furniture)
  3. Dry water-damaged areas and items with 24-48 hours to prevent mold growth 
  4. Remove moldy or dusty wallpaper and regularly wipe walls and hard floors with a damp cloth. Absorbent or porous materials, such as ceiling tiles and carpet, may have to be thrown away if they become moldy.
  5. Regularly ventilate your house. Read more about home ventilation here. 

Common Questions

The following information is only relevant for Oregon residents. Out of state residents should contact their own Building Codes Division. All information in from the Oregon Building Codes Division.

How do I remove moisture buildup in my kitchen? 

Kitchen exhaust can be in the form of a hood or down draft appliance and are required to be vented to the exterior to remove moisture and other byproducts from the cooking process. Link to ORSC CH 15

What are the requirements for ventilation in bathrooms? 

Bathroom requirements vary depending on the configuration. Half baths are required to have either natural (window) or mechanical (exhaust fan) ventilation. Bathrooms with bathing facilities are required to have an exhaust fan with a timer that can be intermittent or continuous exhaust Link to ORSC CH 15 Link Link to ORSC CH 3

My current exhaust does not meet requirements, and/or I do not have an exhaust system in my bathroom/kitchen. How do I replace it?

The installation of new or replacement exhaust fan or exhaust duct requires a permit for mechanical work. Electrical work may also require an electrical permit. Read more about the permit here.

Additional Resources

* All information given compiled from above sources 

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