How to prevent mould by controlling moisture

Implementing a comprehensive moisture management strategy is key to reducing health risks
Monday, May 5, 2014
By Steve Hudson

With spring’s snowmelt and rain showers comes moisture, which increases the potential for mould growth. Property management and owners would be wise to prevent mould, because in large amounts, or over a period of time, it can cause any number of health issues among building occupants, including coughing, wheezing and nasal congestion, as well as eye, skin and throat irritations. If a mould allergy is severe, exposure can be fatal.

In Ontario, the Ministry of Labour considers mould growth in buildings such as condominiums to be a workplace hazard. The Ontario Occupational Health and Safety Act requires that the joint health and safety committee or the safety representative for employees be informed of any investigation relating to health and safety, including testing for mould growth.

Water damage

When water damage occurs, time is of the essence. Mould can arise when susceptible building materials are wet for long enough to allow the spores to germinate, grow and multiply. The longer the response takes, the greater the chances of mould growth.

Where a building has been contaminated with water containing a high level of pathogens (such as sewage or flooding from rivers and streams), and visible mould is present, a consultant trained in mould remediation should be retained. The contaminated area must be enclosed, sealed and put under negative pressure. The consultant will then complete the necessary testing to identify the extent of mould growth and provide a report that includes a protocol for remediation. The restoration contractor follows this protocol and performs the remediation.

When a water episode is reported soon enough, restoration can prevent or limit mould growth and allow most finishes and contents to be saved. Signs of uncorrected water damage, musty odours or reports of potentially mould-related health effects should prompt an investigation for possible mould growth.


Owners or property managers of buildings where mould contamination is suspected should retain a professional to determine whether the building is indeed contaminated. The assessment should answer the following questions:

  • What is the extent of the mould contamination (type of mould and quantity)?
  • What types of materials are affected?
  • What is the source of the moisture?

The initial assessment may include a visual building inspection, taking and analyzing samples, and interviews with occupants and building maintenance staff. The person taking samples must be suitably protected (respirator, gloves and eye protection).

Mould can grow on almost any substance where common building materials are present. For instance, mould growth may be caused when flooring materials such as concrete do not dry completely. Flooding, leaky roofs, building maintenance problems or indoor plumbing problems can also lead to mould growth. Other common sites for growth include ceiling tiles, drywall, carpets, wood and any paper products.

Moulds thrive in dark, moist environments and it may be hidden from view. A moisture meter can be a useful tool for measuring the moisture content of materials such as wood, brick, concrete, insulation and carpet. Water-damaged areas must be thoroughly inspected. This may involve looking into wall cavities, behind drywall, under carpets and above ceiling tiles.


Once the consultant finishes testing and reporting, remediation should begin as soon as possible. Susceptible occupants, namely infants, the elderly or those with compromised immune systems, must be relocated from the work area during abatement. All occupants must be informed of the work to be performed and the method to be used.

The clean-up process for remediation involves locating and repairing water damage; isolating contaminated areas (sealing all doors and windows between the contaminated area and other rooms); covering doorways; suppressing all possible dust by misting contaminated areas as materials are removed and bagged; removing all wet and mould-damaged porous materials; cleaning and scrubbing all non-porous materials and wood surfaces that are mouldy; and allowing all the cleaned surfaces to dry completely before repair begins.

Once these steps are complete, surfaces must be HEPA-vacuumed and cleaned with a damp cloth and detergent solution. A visibility test is then performed. All areas should be visibly free of contamination and debris. No dust and no dirt means no mould.

The last step is to determine whether clean-up efforts have been successful. The primary failure in addressing occupant complaints is usually that the property manager didn’t respond fast enough and strictly follow the protocol specified in the consultant’s report. The independent consultant originally retained to conduct the initial assessment must perform clearance testing.


The most important aspect in preventing mould is moisture control, which is aided by the following steps:

  • Where practical, diverting water away from buildings.
  • Installing and maintaining eaves troughs.
  • Fixing any plumbing or building leaks immediately and cleaning up wet areas within 48 hours.
  • Preventing moisture caused by condensation by dehumidifying during warmer months and keeping humidity below 60 per cent.
  • Venting moisture sources such as bathrooms and dryers to the outside.
  • Keeping heating, ventilation, and air-conditioning (HVAC) drip pans clean and in good repair.
  • Ensuring that mould-susceptible materials are stored in a dry place and protected from moisture during construction projects.
  • Choosing water-resistant materials where moisture may be a problem when designing or renovating existing facilities.

When it comes to mould, implementing a comprehensive moisture management strategy is key to decreasing potential health risks and liability.

Steve Hudson, B.A., is the president of Hudson Restoration Inc., a group of property loss and environmental professionals based in Burlington, Ont. The company services the insurance industry and the private sector across the GTA and is an official service provider of Biosweep Toronto.

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