Mould (Mold -US) has seen its fair share of publicity in the media over the recent years. Most people will have some awareness of mould and will typically associate mould with the horror stories they have encountered on the daily news. 
The truth is moulds exist everywhere — indoors and outdoors. 

There are more than 100,000 species of mould. Mould will manifest whenever excessive moisture accumulates in a home or on the building materials within that home. Moulds will particularly grow if the moisture problem remains undiscovered or not addressed.

Mould is often used interchangeably with the word mildew. They are the generic terms that describe a variety of microorganisms, including fungi, algae, rusts, yeasts, and bacteria.

Health Concerns

Minute spores are carried by air, they are deposited everywhere, and everyone breathes them every dayThe vast majorities are not harmful Spores and microscopic fragments of mould growth are a natural component of both outdoor and indoor air however, when moulds germinate and grow, they can produce large amounts of spores. When allowed to grow, damage to building materials can occur, and when spore concentrations are very high, health can be affected.

Some people react differently than others. 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 mould.

Health experts indicate that, depending on the type of mould present in a home, the amount and degree of exposure, and the health condition of the occupant, the health effects of mould can range from being insignificant to causing allergic reactions and illness. Some moulds can have deleterious effects, typically in the form of:

  • Toxigenic: means that they can release toxins, strong poisons. (Stachybotrys chartarum, Aspergillus niger, Aspergillus versicolor)
  • Allergenic: means that they can cause or a allergies.
  • Pathogenic: means that they can cause diseases. (Aspergillus fumigatus from compost— that can be tracked in underfoot, Cryptococcus neoformans from bird droppings and bat dung).

Mould Growth 

Moulds produce tiny spores to reproduce and these waft through indoor and outdoor air continually. When mould spores land on a damp spot indoors, they may begin growing and digesting the materials they are in contact with in order to survive. In this sense moulds seek nutrients, just as any plant does in order to grow.

Mould spores need a favourable environment to germinate, or become active, grow, and spread. The most important condition mould needs to germinate is moisture. What constitutes a favourable environment is different for each species. After landing on a host material, a spore must obtain sufficient moisture to germinate and find enough food.

Where Does Mould Grow?
The simple answer is everywhere but to narrow it down to materials in the home that mould uses as nutrients. These might be:

  • Wood products including panelling, sub-floors, cabinetry, and structural components)
  • Acoustic tile
  • Gypsum board (drywall)
  • Wallpaper
  • Insulation
  • Carpets
  • Dust - deposited in minute quantities on all surfaces, even those that are inert such as window frames.
How Does Mould Grow?
Mould Propagation (Growth) Requires 4 Elements
  • Mould / Fungi Spores
  • Nutrients
  • Temperature (18 - 24C or 65— 80F)
  • Moisture
    • Bulk Moisture - Leaks and floods
    • Rh (Relative Humidity) - The ratio (%) of water in the air to the amount of water that air could hold at the current temperature.
    • Water Vapor — Airborne water introduced into the home via building materials, openings in the building envelope, ventilation systems and humans Everyday Sources: In-house moisture generation (high RH) comes from a variety of common, everyday sources. For example breathing, showering, bathing and mopping the floor.

Water Vapor: This can come from rain soaking into construction materials during construction the house is built with the moisture already it; Condensation inside the house from showering, clothes washing, cooking, breathing, drying clothes. Water vapor also moves into the building through the ventilation system, through openings in the building envelope, or directly through building materials such as paint, plaster, etc.

Water-Rich Materials: All materials contain some water, and for the most part is it bound water. When the amount of water in the air is about 60% there is usually enough free water to allow for mould growth.

A microclimate is the climate of a small, specific place within the home as contrasted with the climate of the entire area. (i.e. the amount of moisture generated and found within the microclimate differs from the rest of the home.)

A humid bathroom or a damp basement is effectively a microclimate, and it only takes one such room in a home to spread mould spores throughout the entire house. In this sense, microclimates are another key to fungal growth.

Microclimate Example 
Microclimates occur literally everywhere in the home, however the most mould prone are in:

Bathrooms: Moist areas include around tubs and showers at the base. In the grout lines. In cold corners. Inside the walls and floors — shower penetrations, worn toilet seals. Water left on showers and around tubs. Towels drying. Inside cabinets with leaky drains or supply lines.

Closets: Moisture is trapped when wet clothes are stored and the closet door is closed hence there is no air circulation. Closets are also notorious places for home owners to stow any unwanted items to keep them out of sight — these can sometimes be wet boxes, shoes, winter boots, coats or unsightly wet materials of any sort.

Laundry Rooms: Excess moisture from drying clothes in the house on a drying rack or clothesline. Using a dryer with a disconnected duct or a duct not directed outside. Warm room with cold spots around windows and corners.

Bedrooms: Water vapor moves around the house and condensates in bedrooms that are kept cooler. In colder corners. In closets. Behind stored material — mildew blooming. Behind curtains and window blinds. How often do I look behind a blind that is rarely opened and find mould and dirt.

Kitchens: Cooking and washing dishes releases water vapor, gas burning releases water vapor. It can condense in cold corners, on windows, and move to other parts of the house. Leaking drains or supply lines in the cabinet under the sink are notorious for supporting mould growth.

Living Rooms, Dining Rooms, Family Rooms: Living rooms: primarily behind curtains and blinds and sometimes in cold corners

Inside walls: Leaks from plumbing lines occur inside walls and ceilings. These have a tendency to propagate the more toxic moulds. Water vapor can condense inside the walls and ceilings where it does not evaporate easily; mould can form and has a ready source of nutrients with drywall paper.

Attics: Leaks from seepage through old roof coverings, or small holes in the roof coverings, or poorly maintained flashings, or small gaps not easily seen; as well as poor ventilation in the attics and crawlspaces or exhaust ducts terminating inside the attic.

Crawlspaces and Basements: Don’t forget about leaks in foundations in crawlspaces or through the skim coats. A crack in the foundation, soil too high, a poor drainage at a window well, poor window installation or poor siding installation can let moisture in and mould can grow.

Basements: In a basement, drywall can wick water from the concrete, or this could be from careless wet mopping.

Controlling Mould Growth As mentioned previously, the goal is not to remove mould but to inhibit its growth both in the short and long term. You can and should take steps to control the growth of mould in the home. 

Controlling Mould Growth 

Basements, Crawlspaces and Attics 
  • Reduce stored materials
  • Dehumidify
  • Avoid carpets on slab-on-grade or below grade
  • Clean the drains, sumps
  • Avoid standing water
  • Check for efflorescence, powder, discoloration, odors
  • Reduce the amount of clothes, paper and furnishings stored in moisture prone areas. Allow for air circulation; keep them away from walls and off basement floors. Discard water damaged material. Store only washable items
  • Dehumidify in warm months since air entering will have higher moisture content and some could condense in the colder basement or crawlspace. Remove or do not use humidifiers.
  • Cover sump pits
  • Clean HRV (Heat Recovery Ventilation) system
  • Do preventive maintenance checks in hidden areas, crawlspaces, under stairs, storage closets, garages, attics — look at the sheathing, particularly close to the soffits.
  • Check the drainage sump outside during a rain storm to see that water is running in and running out. Look for clear water in the sump, clean the sump so that water will not backup in the drainage system around the house and hold water against the foundation.
  • Check the attics for any leaks, discoloration, deterioration, high temperature or humidity. Clean soffit vents, do not compromise the roof vents with other equipment — and while you are there, look for any signs of vermin, birds, insects or rodents.
  • Do not vent to crawlspaces and do not use them as a source of air for the furnace system. Keep vents open for cross ventilation to promote evaporation.

Laundry Areas 
  • Ensure dryer exhausts to the outside
  • Remove lint every time you use the dryer
  • Don’t hang clothes to dry indoors
  • Dry the laundry tub after using it
  • Aerate the room if it is warm
  • Often we find dryer ducts disconnected, sometimes inside the wall; or the flapper outside is jammed closed. Ducts going through attics need to be cleaned regularly; a blockage can build up water that can leak and cause considerable damage. Insulate ducts. If the ducts vent through a soffit ensure that the soffits are solid for at least 4’ on each side so moisture does not blow back into the attic.
  • Moist air in warm rooms can condense in cold corners leading to mould growth.
  • Lint can block the duct or reduce the air-flow to the outside leading to a buildup of moisture inside.

  • Ensure bathroom fan exhausts to the outside
  • Turn fan on when showering, bathing and leave it on for up to ½ hr afterwards. Many new houses have timers on the bathroom fans — to exhaust general moisture in the house, not just the bathroom, so don’t disconnect them. Invest in a quiet fan when needed.
  • Wipe moisture from tub & shower walls after using
  • Clean then replace caulking, clean grout, seal, check around toilets for evidence of leaks at base or condensation on tank dripping onto floor
  • Remove carpets and replace with ceramic tile or vinyl
  • Check for water leaks regularly
  • Keep drains free flowing. Remove debris. Use a handful of baking soda and a cup of vinegar; let stand 20 minutes; flush
  • We often see dark stains on the caulking — wash it off and if it doesn’t come off, replace the caulking and check the wall.
  • Staining on the grout is mildew or mould; clean it, kill it, seal the grout lines every 6 months
  • Ensure that the flapper works on the fan exhaust outside, block soffit vents at least 4’ each side of the exhaust so moisture doesn’t enter the attic.

  • Ensure range exhaust hood vents to the outside
  • Use the range exhaust hood
  • Minimize open boiling
  • Clean refrigerator drip pan, vacuum dust from coils, check for leaks regularly under sink and around dishwasher
  • Take garbage out daily
  • Range hood ducts do not always exhaust to the outside. When they go through a cold area such as an attic, they need to be insulated to reduce internal condensation.
  • Cooking and particularly cooking with gas is one of the primary sources of water vapor inside the house. Use the range hood.

Bedrooms and Living Rooms 
  • Open the curtains and blinds
  • Clean the windows and frames
  • Check for water entry
  • Check behind furniture and arrange furniture spaced away from the wall
  • Keep stored materials away from the walls
  • Reduce the number of plants — soil contains mould

  • Check the condition of the roof
  • Check building envelope
  • Check flashing
  • Clean eaves troughs or gutters, extend rain water leaders
  • Watch for flat surfaces and reverse slopes
  • Monitor soil height
  • Check crawlspaces and attics
  • Check the roof twice a year — spring and fall.
  • Check the siding for any loose pieces, knot-holes, cracks, holes, staining. Clean and paint regularly
  • Make sure the flashing are not damaged
  • Keep the rain from running near the house — directed away.
  • Flat surfaces are all the wood trim pieces we see around windows, doors and other decorative trim including window sills. Flashing at the base of windows and walls that might not be sloped away, can lead water back into the wall.

Clean Up Because moisture is the key to mould control, it is essential to clean up the mould and get rid of excess water or moisture. If the excess water or moisture problem is not fixed, mould will most probably grow again, even if the area was well cleaned.

Determine the Size
It is important to assess the size (amount) of the mould outbreak in order to determine the next steps. Mould manifestations can be classified into three main categories; small, moderate and excessive.
Small: No larger than one sq m
  • Wash with unscented detergent, sponge dry. Use baking soda or detergent on drywall. Leave open to air dry, use a fan if you have one.
  • Absorbent materials such as ceiling tiles may have to be discarded.
  • If mould is under paint, then remove the drywall and any other damaged material and replace it, vacuum wood with a HEPA vacuum use detergent, sponge dry, open windows.
  • Concrete can be vacuumed cleaned with detergent or TS
  • Replace caulking, clean and seal grout
Moderate: More than 3 patches each smaller than a sq m or one or more patch larger than 1 sq m but smaller than 3 sq m — 4 plywood
  • This should be sampled and evaluated by a professional to determine next steps.
Extensive: More than 3 sq m call a professional.
  • This should be sampled, evaluated and remedied by professionals.