Mold in a rental turns into a dispute faster than almost any other maintenance issue, and usually for the same reason: nobody writes anything down until it is already a fight. This is a plain-English guide to where the obligation actually sits in Ontario, what a tenant can reasonably ask for, and what a landlord should do in the first week to keep a repair from becoming a Landlord and Tenant Board application.
We remediate mold for homeowners, landlords and property managers across the GTA. What follows is not legal advice — it is what we see on site, set against what the Board itself has published.
The obligation sits with the landlord, and a lease cannot move it
Section 20 of the Residential Tenancies Act requires a landlord to keep the rental in a good state of repair, fit for habitation, and compliant with health, safety, housing and maintenance standards. The Board’s own LTB Interpretation Guideline 5 is explicit that this duty is broad and cannot be transferred to the tenant through a clause in the lease. It also covers common areas — lobbies, hallways, laundry rooms, parking — not just the inside of the unit.
The guideline applies three tests: is it in a good state of repair, is it fit for habitation, and does it comply with the applicable standards. A problem is a breach if it fails any one of them, not all three.
There is no “mold standard” in Ontario, and that surprises people
Neither the province nor the City of Toronto publishes a numerical mold limit for rental housing. The City of Toronto property standards bylaw talks about adequate ventilation and general upkeep; it does not name a spore count. In practice this means arguments are settled on evidence of the condition and its cause — dampness, staining, smell, a failed seal, a leak that was never fixed — rather than on a threshold number.
That has a practical consequence for both sides. A lab report on its own rarely wins anything. A documented moisture source, a written report and a record of what was requested and when is what actually carries weight. It is also why we treat mold inspection as a diagnostic step rather than a formality — the useful output is where the water is coming from, not just what is growing.
If you are the tenant
1. Put it in writing, even if you already said it out loud
Under subsection 30(2), when a tenant applies to the Board the adjudicator must consider whether the landlord was told about the problem before the application was filed. Notice is not strictly mandatory — and the guideline is clear that if the landlord already knew or reasonably should have known, a reduced remedy is not justified — but a dated written request removes the argument entirely.
Email is fine. Include the date, the room, what you can see or smell, and a photograph. Keep the sent copy.
2. Photograph before anything is cleaned or moved
- Wide shot of the room, then close-ups of the affected area
- Anything that shows the source: a stain spreading from a window, a pipe, a ceiling below a bathroom
- Personal property that has been damaged
- The date on every file — do not crop it out
If water is actively coming in, that is a separate and more urgent problem. Speed matters more than paperwork in the first 48 hours, which is the whole logic behind emergency mold removal.
3. Escalate in order
- Written request to the landlord or property manager.
- If nothing happens in a reasonable time, contact the City. In Toronto that is 311, and the City investigates. In an apartment building covered by RentSafeTO — three or more storeys and ten or more units — the landlord has 24 hours to respond to an urgent service request and seven days for a non-urgent one.
- If it is still unresolved, file a T6 application with the Landlord and Tenant Board.
Do not stop paying rent because a repair has not been done. Withholding rent is not a recognised remedy in Ontario and it exposes you to an eviction application. The Board can order an abatement; you cannot award yourself one.
4. What the Board can actually order
Guideline 5 lists the remedies available where a maintenance breach is found:
- A repair order specifying the work and a deadline
- A rent abatement — a percentage of rent reflecting how bad the loss of use was and how long it lasted
- Reimbursement where the tenant arranged necessary repairs themselves
- Compensation for damaged property and reasonable out-of-pocket costs
- A prohibition on rent increases until a serious breach is fixed
- Termination of the tenancy — but only in serious cases where the unit is genuinely uninhabitable
Termination is rare. Abatement and a repair order are the usual outcome.
If you are the landlord or property manager
The commercial case for moving quickly is simple: an abatement is calculated on how long the condition lasted. Delay is the expensive variable, and it is the one entirely within your control.
Week one, in order
- Acknowledge in writing the day you receive it. A dated reply is your first piece of evidence and it changes the tone of everything that follows.
- Attend and find the moisture source. Not the growth — the water. Cosmetic cleaning of a wall fed by a leak returns within a season, and the second complaint is worse than the first.
- Get it documented by someone independent. A written report with photographs and a scope is the document that protects you if this reaches the Board.
- Do the work under containment. In an occupied building, disturbing growth without sealing the area spreads it to units that had no problem.
- Close it out with clearance testing. A test result is proof; an invoice is not.
Where the growth sits inside a wall or under flooring, mold testing tells you the extent before anyone opens anything up. That matters in a rental, because scope disputes are usually about how far the damage runs.
The three sources we see most in GTA rentals
- Below-grade units and basement apartments. Seepage through foundation walls and summer humidity condensing on cold surfaces. This is the most common one by a distance — see basement mold removal.
- Bathroom ventilation that vents into a ceiling void or attic rather than outside. Common in converted or subdivided houses.
- Slow appliance and supply-line leaks behind laundry stacks and dishwashers, which run unnoticed for months in a unit the owner rarely enters.
If what you are looking at is dark, spreading and in a chronically damp area, read black mold removal before deciding it is cosmetic.
Multi-unit buildings have a spread problem, not just a repair problem
Shared HVAC and stacked plumbing mean one unit’s leak becomes several units’ complaint. In a building, the sequence that keeps this contained is: assess the affected unit, check the units above, below and adjacent, and contain before removal. That is the difference between one abatement claim and five, and it is the reason multi-unit and commercial remediation is scoped differently from a single-family job.
Who pays?
The landlord is responsible for repair under section 20. The realistic exception is damage caused by the tenant’s own wilful or negligent conduct — and the burden of showing that sits with the landlord, not the tenant. In practice, condensation from ordinary living, seepage, ventilation faults and leaks are the landlord’s to fix.
Insurance is a separate question from liability. Most Ontario policies distinguish sudden, accidental water damage from gradual deterioration, so the cause and the timeline usually matter more to a claim than the mold itself. A tenant’s contents insurance covers their belongings, not the building. If cost is the sticking point, what affects the cost of mold removal sets out what actually drives the number.
The short version
- Landlords: the duty is yours, a lease clause will not move it, and the cost of an abatement scales with how long you take.
- Tenants: write it down, photograph it, escalate in order, and keep paying rent.
- Both: the moisture source is the real issue. Remediation that leaves the cause in place is a repair you will do twice.
This is general information about how the rules work, not legal advice on your situation. For that, speak to a paralegal, a lawyer, or your local community legal clinic — and the Landlord and Tenant Board publishes its own guidance for both sides.
Need the remediation side handled properly?
We work with landlords, property managers and condominium corporations across Toronto and the GTA, and every project ends with clearance testing and documentation you can put in front of a tenant, an owner or an insurer. See our remediation process, or call 647-956-6121 — the inspection is free.
Looking for mold removal in Toronto more generally, or a specific city? Start across the GTA.