Fighting Mold – The Homeowners Guide (CMHC)

What are molds?

Molds are microscopic fungi, a group of organisms which also includes mushrooms and yeasts. Fungi are highly adapted to grow and reproduce rapidly, producing spores and mycelia in the process.

You encounter mold every day. Foods spoil because of mold. Leaves decay and pieces of wood lying on the ground rot due to mold. That fuzzy black growth on wet window sills is mold. Paper or fabrics stored in a damp place get a musty smell that is due to the action of molds.

Molds can be useful to people. The drug Penicillin is obtained from a specific type of mold. Some foods and beverages are made by the actions of molds. The good kinds of molds are selected and grown in a controlled fashion.

Molds are undesirable when they grow where we don’t want them, such as in homes. Over 270 species of mold have been identified in Canadian homes. Molds that grow inside may be different from the ones found outdoors.

What makes molds grow?

Molds will grow if we provide them with moisture and nutrients. If we keep things dry, molds do not grow.

High moisture levels can be the result of water coming in from the outside, through the floor, walls or roof; or from plumbing leaks; or moisture produced by the people living in the home, through daily activities like bathing, washing clothes or cooking. Water enters the building when there is a weakness or failure in the structure. Moisture accumulates within the home when there is not enough ventilation to expel that moisture.

Different kinds of molds grow on different materials. Certain kinds of molds like an extremely wet environment. Other kinds of molds may be growing even if no water can be seen. Dampness inside the material can be enough to allow them to grow.

Why are molds a concern?

Damage to materials is one concern. Materials get stained or discolored, and over time they are ruined. Moldy paper and cardboard disintegrate over time. Fabrics are damaged. Continued mold growth can be indicative of moisture conditions favorable for growth of fungi that cause wood rot and structural damage.

When molds are growing inside the home, there may be health concerns. Molds release chemicals and spores.

Health experts indicate that, depending on the type of mold present in a home, the amount and degree of exposure, and the health condition of the occupant, the health effects of mold can range from being insignificant to causing allergic reactions and illness.

Pregnant women, infants, the elderly and those with health problems, such as respiratory disease or a weakened immune system, are more at risk when exposed to mold. Consult your family physician if you believe there is someone who may be at risk.

Is there a mold problem?

Molds are always found in the air outside and in all buildings. They come into the home in many ways —through open windows or doors, on clothing, pets, food or furniture. The problem starts when mold grows inside the home.

Some mold growing, for example on the window sill but not elsewhere, is not a cause of concern. You can clean the mold yourself. The presence of mold is a sign that there is too much moisture in your home–a situation which must be corrected.

Inspect your home to find the extent of the mold.

How much mold is growing?

One way is to estimate the area of the mold. Mold is considered to cover a “small area” if the patch is no larger than a square meter. There should be no more than three patches, each patch smaller than a square meter. Clean up small areas yourself using a detergent solution, household rubber gloves and a dust mask for protection. Refer to page 3 for the procedure.

Small moldy areas in homes may become larger over time, if ignored, so it’s important to clean up and remove even small patches of mold.

The mold area is considered “moderate” if there are more than three patches, each patch smaller than a square meter, or there is one or more isolated patches larger than a square meter but smaller than 3 square metres (size of a 4 x 8 foot sheet of plywood). Assessment by a professional is recommended. You can clean up moderate amounts of mold but you must follow the proper procedures and use the proper protective equipment (see page 3).

A mold area is considered “extensive” if a single patch of mold is larger in area than a sheet of plywood. Being exposed to this much mold is not a good idea. Do not attempt to clean up large areas of mold yourself. You need professional help to determine why the mold is there in the first place and how to clean it up.

When should you seek professional help?

You may need professional help when:

  • There is a lot of mold
  • The home is very damp and moist
  • Mold comes back after repeated cleaning
  • A family member suffers from asthma or respiratory problems or other health problems that appear to be aggravated inside the home

How do you get professional help?

Contact your local CMHC office for a list of individuals who have completed the CMHC Residential Indoor Air Quality Investigator program. A trained IAQ investigator, who operates a private business and sells his/her services, examines the indoor air quality of your home and documents your concerns. He/she identifies the problems, finds their sources and suggests solutions in a written report. Recommendations are provided to you in an action plan that consists of various options to improve the indoor air quality in your home.

“Small area” clean-up

You can clean up “small areas” of mold (fewer than three patches, each smaller than a square meter) yourself. There’s the minimum protective wear needed:

  • safety glasses or goggles;
  • a disposable dust mask (3M 8210 or equivalent); and
  • household rubber gloves.

Infants and other family members with asthma, allergies or other health problems should not be in the work area or adjacent room during the cleaning.

Steps to follow in cleaning up “small” mold areas

Washable surfaces

Scrub with an unscented detergent solution; then sponge with a clean, wet rag and dry quickly. Using an unscented detergent will make it easier for you to detect residual moldy odours.

Moldy drywall

Clean the surface with a damp rag using baking soda or a bit of detergent. Do not allow the drywall to get too wet.

Mold that comes back after cleaning is usually an indication that a source of moisture has not been removed. Seek professional help from a trained IAQ investigator.

Basic steps to prevent and reduce mold growth

Mold needs moisture to grow. Controlling the moisture and keeping your home dry prevents the growth of mold. • Check your home for signs of moisture and molds.

  • Find out if water is coming in from the outside and if substantial moisture is produced inside the home.
  • Fix any water leaks promptly.
  • Think of the different ways moisture is produced inside your home (for example, cooking, bathing, plant jungle). Remove the moisture as it is produced by using exhaust fans. In the absence of fans, open windows for a short time, but note that the wind can push the moisture to other parts of the home.
  • Measure how much moisture is in the air. To find the relative humidity in your home, you’ll need a hygrometer. You can buy one at a hardware store or electronics store. A hygrometer costs from $5 to $20. Relative humidity in the home should be under 45 per cent in the winter (or lower to avoid condensation on windows). If necessary, use a dehumidifier to lower the relative humidity.
  • Reduce the amount of stored materials, especially items that are no longer used. Molds grow on fabrics, paper, wood and practically anything that collects dust and holds moisture.

Source: Canada Mortgage and Housing Corporation