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Mouldy Homes and Buildings

Managing indoor mould

​​​What if I find mould in my home or building?

You have to find what’s causing the moisture problem and fix it, or the mould will come back. Remove any mould and material that the mould has grown on. It’s important to protect yourself and others while you’re doing this work.

You may need the help of a building expert (such as a construction engineer or a building repair or construction specialist) for foundation, roof, or exterior wall problems. You may need a plumber for leaky plumbing fixtures or sewer backups.

How do I clean and remove mould?

Porous and semi-porous material

Porous material has openings on the surface or has cavities inside. Examples include carpet, upholstered (covered in fabric) furniture, wallboard, ceiling tiles, clothing, books, and pressed wood products. You can’t clean these materials, so you need to remove them. (Restoration specialists can restore some porous materials.)

If there’s mould growing in a heating, ventilation, or air conditioning (HVAC) system, replace porous materials such as filters and insulation lining ducts. You’ll likely need to call a company that deals with HVAC systems.

With semi-porous material like wood framing, you can often clean the surface and leave the material in place. If the mould has gotten into the material, you need to remove the material.

Non-porous material

You can usually clean non-porous material such as metal, plastic, and glass. 

Clean non-porous materials using a HEPA (high efficiency particular air) vacuum, wiping with a damp cloth, or pressure washing.

Can I use biocides (chemicals) to clean and remove mould?

Using biocides (chemical products like chlorine bleach that kill living organisms) isn’t usually recommended for removing mould.

Biocides may be needed for sewer back-ups or surface floodwaters on certain HVAC parts. Check with the manufacturer of the parts for what they say you should use. Not many biocides can be used in duct systems. They must not leave any residue in the HVAC system and must be certified by Health Canada. Contact a company that works with HVAC systems for help.

How do I stay safe when cleaning and removing mould?

The most important thing is to protect yourself and others when you’re cleaning and removing mould. Follow this advice:

  • Make sure no one is in the work area other than the people doing the cleaning.
  • Try not to disturb the mouldy area so mould spores don’t spread through the area. It can help to mist (lightly spray, not soak) the area with water.
  • Put all waste with mould on it into a plastic bag and seal it. You can throw the bag away in a regular outdoor garbage bin.
  • For all cleaning work, scrub surfaces with soap and water.
  • Clean the work area and the exit well (for example, use a HEPA vacuum or wipe with a damp cloth) after the work is done.
  • Leave all work areas clean, dry, and free of any mould or garbage.

When do I need professional help for mould?

Depending on the type of building, the size of the area, or how long it takes, you may need professional help to clean and remove mould.

1. Less than 1 square foot of mould that is close together (contiguous):

  • You or regular cleaning staff can easily clean these areas by scrubbing surfaces clean with soap and water. It’s a good idea to wear personal protective equipment (PPE, such as a face mask). Wash your hands as soon as you’re done the work.

2. Between 1 and 10 square feet of mould that is close together (contiguous):

  • You or regular cleaning staff can easily clean these areas by scrubbing surfaces clean with soap and water. People doing the work should be trained on clean-up methods, personal protection, and possible health hazards. Personal protective equipment (PPE) should include a disposal N95 respirator and disposable gloves.
  • Babies younger than 12 months old and people with weakened immune systems, long-term lung problems, or allergies should stay out of the area. Seal door openings, ventilation system openings (like vents and grills), and other openings that let air move.

3. Between 11 and 99 square feet of mould that is close together (contiguous):

If you own and live in the home, it’s best to hire a professional contractor who knows how to clean and remove mould and an environmental consultant. If you decide to do it yourself or have regular cleaning staff do it, follow this advice:

  • PPE: Wear a full-face N95 respirator and disposable gloves.
  • Limited containment: Isolate the work area (keep it separate from other areas) using floor to ceiling plastic sheets with a slit entry and covering flap. This stops dust and debris from spreading. Cover any ceilings, walls, or floors that are not affected by mould.
  • Isolation: Use barriers and signs to keep the area separate and don’t let anyone in who doesn’t need to be. This also stops mould particles from spreading through the air. Seal openings or pathways that let air move, such as the HVAC system vents and grills, pipe chases, electrical outlets.
  • Pressurization control: Use negative pressure so air can move into but not out of the work area. Block supply and return air vents within the area.
  • Dust suppression: Mist (don’t soak) surfaces before you start the work to stop mould spores from travelling through the air.
  • Cleaning: When the work is finished, HEPA vacuum or clean the work area and nearby areas with a damp cloth or mop and a detergent solution. Make sure all exposed surfaces that are part of the building are wiped dry.

For rental home, public facilities (such as schools, daycares, hospitals), and commercial buildings, follow this advice:

  • You need to hire a professional contractor that knows how to clean and remove mould and an environmental consultant. The consultant is an independent professional who provides quality assurance and quality control. This means they let the building owner and Alberta Health Services know that the work has been done properly.

4. For 100 square feet or more of mould that is close together and marijuana grow operations (MGOs):

  • You need to hire a professional contractor who knows how to clean and remove mould and an expert consultant, even if you own the home and live in it. The consultant is an independent professional who provides quality assurance and quality control. This means they let the building owner and Alberta Health Services know that the work has been done properly.
  • The expert consultant is responsible for doing a full investigation, finding, and cleaning and removing all mould, both visible and hidden.
  • MGOs must be fully assessed for mould, both visible and hidden.

Go to Alberta Health Services Environmental Public Health for more information (see the Rental Housing and Grow Ops section).

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Current as of: February 18, 2021

Author: Environmental Public Health, Alberta Health Services