Mold in a Rental: Landlord and Tenant Rights in Ontario

When mold shows up in a rental, the argument that follows is almost always the same: the tenant says the unit is unhealthy, the landlord says it is the tenant's ventilation, and nobody has a neutral fact to settle it. In London, where a huge share of the rental stock houses Western and Fanshawe students in older homes, this is a weekly story. An independent mold test is the document both sides, and the Landlord and Tenant Board, will actually accept. This is general information, not legal advice. In London that document comes from independent mold testing in London, Ontario, and if the landlord then has to fix it, mould removal in London, Ontario shows how the job should be scoped so neither side overpays.

The responsibility question, in plain terms

Under Ontario's Residential Tenancies Act, a landlord is generally responsible for keeping a rental in a good state of repair and fit for habitation, which includes addressing moisture problems and the mold they cause. A tenant is generally responsible for ordinary cleanliness and for not causing damage. In practice most mold disputes turn on cause: is the mold from a building fault, a leak, a failed foundation, poor ventilation the landlord must fix, or from how the unit is being used, showers with no fan use, windows never opened, damp laundry indoors? Specific rights and obligations depend on your situation and your agreement, so confirm the details for your case.

That cause question is exactly why an independent test matters. Neither the landlord nor the tenant can credibly grade it, they are the two sides of the argument. A result from a service that has no stake and does no removal is the neutral input the whole dispute has been missing.

Why this is a London student-rental story

London's rental market is shaped by Western University and Fanshawe College, and much of the near-campus stock is older housing, subdivided, heavily occupied, and not always well maintained. Basements are finished into bedrooms, ventilation is an afterthought, and multiple tenants generate a lot of indoor moisture. The result is a recurring cycle of musty basements, bathroom mold and disputes at lease-end over deposits and habitability. A test cuts through it with a number instead of a shouting match.

How independent testing settles it

• It establishes whether mold is actually present, where, and at what level, by accredited-lab sampling with an outdoor baseline, not by either party's opinion.
• It gives both sides the same document. A landlord can act on a real result; a tenant can escalate a real result. A clean result protects a landlord from a bad-faith claim just as a positive one supports a tenant.
• It stands up where it counts. For a Landlord and Tenant Board matter or an insurer, a self-run kit or a phone photo does not carry weight; an independent accredited-lab report does.

Documenting it properly, whichever side you are on

A neutral test is strongest when it sits on top of a clear record, and the record is where most rental mold disputes are actually won or lost. If you are a tenant, put the concern in writing to your landlord (email or text, dated), keep photos with timestamps, note when it appeared and any water event that preceded it, and hold onto any medical note if a doctor has connected symptoms to the home. If you are a landlord, respond in writing, keep records of what you inspected and repaired, and have an independent test done before and after any work so you can show the problem was addressed rather than papered over. In both cases, an accredited-lab result attached to a dated paper trail is what turns "he said, she said" into something the Landlord and Tenant Board can actually rule on.

The escalation ladder, step by step

Most tenants stall at step one because nobody tells them what step two is. In London there are three rungs, and each one produces a document that strengthens the next.

Step 1: put it in writing to the landlord. Email or text, dated, describing what you see and where, with photos. This matters less for politeness than for evidence: every later step asks when the landlord was notified and what they did. A verbal complaint leaves no trace and effectively resets the clock.

Step 2: complain to the City of London. The City investigates rental-property concerns on behalf of tenants through a Request for Service under the Property Standards By-law CP-24, the Vital Services By-law and the Municipal Act. You can report a concern with your rental unit online, or reach Licensing and Municipal Law Enforcement at 519-661-4660 or enforcement@london.ca. Municipal Compliance staff investigate every complaint, and where a violation is found they can issue an order requiring the owner to correct it.

Step 3: apply to the Landlord and Tenant Board. The tenant application for maintenance issues is Form T6, "Tenant Application about Maintenance", filed with the Landlord and Tenant Board. This is the rung that can produce money and enforceable repair orders rather than just an inspection.

The London rental licence angle most tenants never hear about

London runs a Residential Rental Units Licensing programme under By-law CP-19, and it applies to essentially the entire near-campus housing type: all rental units in the city except apartment buildings, townhouses and stacked townhouses. The converted single-family house rented room by room to Western or Fanshawe students is squarely inside it.

Three consequences worth knowing:

• A licence is required, valid one year, and must be posted near the front entrance. If there is no licence posted in a licensed-class unit, that is itself a question worth asking the City about.
• New licence applications require a property standards inspection. Renewals do not, which is why a long-licensed property can drift well below standard between inspections without anything automatically flagging it.
• The penalties are not nominal. Contravening CP-19 carries a maximum fine on first conviction of $25,000 for a person and $50,000 for a corporation.

For a tenant in a musty converted basement bedroom, the licensing route is often faster and cheaper than the Board, and it runs in parallel: nothing stops a tenant from filing a City complaint and a T6 at the same time.

What the Board can actually order

This is the part that changes behaviour, and most tenants underestimate it. On a maintenance application the Landlord and Tenant Board is not limited to telling a landlord to fix something. Depending on the findings it can order a rent abatement, order the landlord to complete specified repairs by a deadline, authorise the tenant to arrange repairs and recover the cost, order payment of a tenant's out-of-pocket expenses, prohibit a rent increase until the work is done, or in serious cases terminate the tenancy.

Rent abatement is the remedy that does the most work in mould cases, because it is retroactive: it can reach back over the months a tenant paid full rent for a unit that was not in the condition it was supposed to be in. Establishing when the problem started and when the landlord was told is therefore worth as much as establishing that mould exists, which is why step one of the ladder matters so much.

Where the landlord's side sits

The ladder cuts both ways, and a landlord who reads it as a threat is reading it wrong. A landlord facing a mould allegation has the same evidentiary problem the tenant has: no neutral fact. An independent test that comes back clean is the cheapest possible answer to a bad-faith habitability claim or a lease-end deposit dispute, and it arrives before a City order or a Board hearing rather than after.

Where a test comes back positive, the finding usually identifies a moisture source, and fixing the source is both the cheaper repair and the defence at any subsequent hearing. A landlord who can show a dated complaint, a prompt independent test, an identified cause, a repair and a clearance test afterwards has a complete record. That record is what a Board member is looking for.

Common questions