Leasehold Improvements Site Condition: Mould

18.5.16 Leasehold Improvements Working with Mould.png

Unexpected finding of mould growth can be a major roadblock for construction projects, throwing off the schedule and budget due to added labour, remediation cost, and delayed completion dates.

What is Mould?

Mould is a microorganism commonly found in nature. Mould spores are present in the atmosphere. It can carry itself into a building through air transfer. However, most mould growth in buildings are not due to scattered mould spores. It is more likely due to undiscovered or unaddressed moisture problems. Mould can thrive on a range of building materials such as insulation, drywall, wood, and carpet which are highly susceptible to mould. Mould growth can begin within 48-72 hours when a porous material such as drywall remains saturated.

The presence of mould can cause health risks for individuals, including dizziness, headaches, sneezing, cough, and difficulty concentrating. Although there are currently no regulations in place in relation to mould abatement, most clients will make the decision to abate it for the health and safety of their occupants.


As mould spores are present in the indoor and outdoor environment through air transfer, there is no absolute way to eliminate it completely. The first step in managing mould growth is to control indoor moisture by reducing the indoor humidity level to an acceptable level through natural ventilation, dehumidifiers, exhaust fans, and air conditioners. Care should be taken to reduce potential for condensation on cold surfaces by installing insulation to separate cold surfaces from warm surfaces.

Any new building materials brought into the building should be allowed time to dry and adapt to the indoor environment prior to installation. Wood is an material that can hold quite a bit of moisture that can eventually be released back into the indoor environment. If installed right away, the moisture could be absorbed by other porous materials such as drywall and invite mould growth.

Presence of Mould on Drywall Surface


Several identification methods are available. Visual Inspection is the most reliable method. Common signs of mould appears as dark spots, stains, and patches. Mould are often hidden behind drywall or other niches as these locations are often unchecked and become perfect conditions for mould growth. Standing water is an indicator of nearby mould. A trained technician will often cut a small area to reveal conditions beyond the wall surfaces to conduct further visual inspection.

Surface and bulk sampling methods are often used in combination with a monitoring device to determine the extent of mouth growth and identify mould compositions within a laboratory. Monitoring devices measure the moisture level of drywall, wood and other surfaces. Air sampling is another testing method to determine concentration of mould spores in specific areas.

Indoor Mould Remediation3
Example of a Surface Sample


If mould is identified, one should take a step further and investigate the sources of moisture that is leading to mould growth. There may be a leaky pipe that is hidden behind a drywall or condensation issues due to a lack of insulation. Always make sure the building assembly is water tight and sealed especially at openings such as windows and doors. When in doubt, bring in a specialist to perform additional testings.

The underlying problem should be addressed immediately to prevent future mould growth. The next step would be to remove and clean up the mould finding.

Mould Abatement

There are currently no standard or regulations established for airborne mould contaminants. The scope of mould abatement depends on the extent of the water damage and mould contamination. In general, porous materials such as drywall, ceiling tiles, paper, cardboard, wall paper is recommended to be safely discarded and replaced as they are difficult to be properly cleaned. Non-porous materials such as metal, hard plastic, glass and semi-porous materials such as concrete can be cleaned up.

The Environmental Abatement Council of Ontario (EACO) Mould Guideline had been prepared to assist parties who have duties under the Occupational Health and Safety Act and its Regulations to safely perform work activities involving mould abatement and remediation. Under the EACO guideline, mould abatement is classified into three levels.

Please see below for a general overview only. Please refer back to the EACO guideline for specific procedure and requirements.

Level 1 abatement is for small isolated areas less than 10 square feet of building material or clean up of mould growth in non-occupied areas. Level 1 method of procedure is the least extensive. Workers are required to protect themselves by wearing full body suits to avoid direct contact with mould. Area is to be thoroughly cleaned and vacuumed.

Level 2 abatement is suitable for medium areas between 10 to 100 square feet. A qualified health and safety professional is to be engaged prior to remediation work to provide quality assurance and approval. In additions to level 1 abatement requirements, the abatement area must be enclosed with Polyethylene sheeting.  Negative pressure must be maintained until all abatement is completed. HEPA vacuum or HEPA filtered exhaust fan are used to maintain a minimum stated negative pressure.

Level 3 abatement is the most extensive all of the three. It is directed at large mould growth areas of more than 100 square feet. In addition to requirements outlined in level 1 and level 2 abatement procedures, level 3 involves multiple quality assurance measures including a combination of site inspections prior to abatement, during abatement, after abatement and clearance sampling (such as air sampling) prior to taking down the abatement work area.

Other mould remediation guidelines are available. Additional resources are listed below:

IHSA (Infrastructure Health & Safety Association)

EPA (Environmental Protection Agency)

NCCEH (National Collaborative Centre for Environmental Health)


Related Posts:

Introduction to Commercial Interior Fit-Out and Leasehold Improvements

Leasehold Improvements: Start-Up Documentation (Ontario)

Leasehold Improvements: Cutting, Coring, and Drilling (Base Building Structural Work)

Leasehold Improvements: How to Minimize the Impact of Construction on Commercial Tenants

Leasehold Improvements Site Condition: Asbestos

Leasehold Improvements Site Condition: Mould

Leasehold Improvements: How to Handle Unforeseen Site Conditions

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