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Mould in an Ontario rental is primarily a maintenance and moisture-control issue. The legal question is not simply who first noticed the mould, but what caused the condition and whether the landlord and tenant complied with their respective obligations under the Residential Tenancies Act, 2006 (RTA).
General information only: this is not legal or medical advice. Serious health symptoms should be discussed with a qualified health professional.
The legal starting point
Section 20(1) of the RTA requires a landlord to provide and maintain the residential complex and rental units in a good state of repair, fit for habitation, and in compliance with applicable health, safety, housing and maintenance standards. That obligation applies even if a tenant knew about a state of non-repair before moving in.
Section 33 makes the tenant responsible for the ordinary cleanliness of the rental unit, unless the tenancy agreement requires the landlord to clean it. Section 34 makes a tenant responsible for repairing undue damage caused wilfully or negligently by the tenant, another occupant or a person the tenant permits in the complex.
Those provisions mean that a landlord cannot automatically characterize mould as a tenant-cleanliness problem, and a tenant cannot assume that every moisture condition is necessarily a landlord breach. The cause matters.
When mould generally points to a landlord maintenance issue
A landlord should investigate when mould is associated with conditions such as:
- roof or plumbing leaks;
- water penetration through foundations, walls or windows;
- defective or non-functioning ventilation equipment supplied as part of the property;
- repeated flooding or unresolved water damage;
- building-envelope defects; or
- another condition that leaves the unit or complex in disrepair or contrary to applicable maintenance standards.
Painting over visible mould without correcting an active moisture source does not resolve the underlying maintenance issue.
When tenant conduct may become relevant
Tenant conduct can matter where evidence shows that the tenant wilfully or negligently caused undue damage or failed to maintain ordinary cleanliness. Examples are fact-specific. A landlord should not treat normal residential activities such as showering or cooking as proof of negligence merely because humidity exists.
Where functioning exhaust fans, windows or other ventilation are available, tenants should use them reasonably and report persistent condensation, leaks or ventilation failures promptly.
What a tenant should do
- Report the condition in writing. Identify the location, when it was first noticed and whether there is an active leak or recurring moisture.
- Document the condition. Keep dated photographs, videos and copies of messages.
- Allow lawful access for inspection and repairs. Landlord entry must still comply with the RTA. See Ontario landlord entry rules.
- Keep a record of follow-ups. Note inspection dates, contractors, recommendations and whether the problem returns.
- Escalate through the proper process if necessary. A tenant may be able to use a municipal property-standards process and/or file an LTB Form T6 concerning maintenance.
The LTB’s T6 instructions state that a tenant can apply where a landlord has not repaired or maintained the unit or complex or has not complied with health, safety, housing or maintenance standards. If the problem has already been fixed, the T6 generally must be filed within one year after it was fixed.
What a landlord should do
- Respond promptly to the written report.
- Inspect for both visible mould and the moisture source.
- Repair leaks, water intrusion or defective building systems for which the landlord is responsible.
- Use an appropriate qualified contractor where the scope requires specialized assessment or remediation.
- Document findings, access attempts, repairs and completion.
- Reinspect if the condition recurs.
For broader obligations, see Landlord Repairs and Maintenance Responsibilities in Ontario.
Can a tenant withhold rent because of mould?
A tenant should not simply stop paying rent because there is a maintenance dispute. The RTA provides specific remedies through the LTB. A maintenance problem does not by itself cancel the obligation to pay lawful rent. A tenant seeking a rent abatement, repair order or other remedy should use the applicable process.
What can the LTB order on a maintenance application?
Depending on the evidence and the remedy requested, the RTA permits the Board to make orders that can include requiring specified repairs or work, authorizing certain repairs, granting a rent abatement, awarding certain reasonable costs, or terminating the tenancy. The appropriate remedy depends on the proven breach and circumstances.
Evidence checklist
- Dated photographs and video
- Written notice to the landlord
- Maintenance requests and follow-up messages
- Inspection reports
- Contractor invoices or findings
- Records of lawful access notices and appointments
- Municipal inspection or property-standards records, if any
- Medical documentation only where relevant to a specific claim and appropriately obtained
Use the Ontario Landlord Communication Log and Ontario Landlord Inspection Log to keep records organized.
Frequently asked questions
Is mould always the landlord’s responsibility?
No. The landlord’s statutory repair and maintenance duties are broad, but responsibility for a particular condition depends on the cause and evidence. Tenant wilful or negligent conduct can also be relevant under section 34 of the RTA.
Can a lease make the tenant responsible for all mould?
A lease cannot contract out of the landlord’s statutory obligations under the RTA. A clause does not erase section 20 maintenance duties.
What if the landlord does not respond?
Keep written records, follow up, review municipal property-standards options and consider the LTB’s T6 maintenance process.
Official sources
- Residential Tenancies Act, 2006 — Ontario e-Laws
- LTB Form T6 Instructions — Tenant Application about Maintenance
- O. Reg. 517/06 — Maintenance Standards
Related: Ontario Tenant Resources · Ontario Landlord Resources · What to Expect at the LTB