Is my landlord responsible for mould in Ontario?

Almost always, yes. Landlords must keep the unit in a good state of repair and fit for habitation. Mould from a leak, failed seals, or poor ventilation is the landlord's responsibility to remediate at their cost, even if it's unclear exactly when it started.

What do I do if my landlord won't remove mould?

Report it in writing with photos and keep a copy. If the landlord doesn't act, call 311 for municipal property standards, consider a public-health complaint, and file a T6 application at the LTB for an order to remediate plus a rent abatement.

Can I break my lease because of mould in Ontario?

Mould alone isn't an automatic right to leave, but if the unit becomes uninhabitable and the landlord won't act, that can support a T6, a rent abatement, and in serious cases an argument to end the tenancy. Get advice from a tenant clinic first.

Can I get money back for living with mould?

Yes. Through a T6 application the LTB can order a rent abatement — a partial refund — for the period you lived with an unremediated hazard, on top of ordering the landlord to fix it.

Home BlogMould in a Rental in Ontario

OntarioSeptember 11, 20266 min read

Mould in a Rental in Ontario: Whose Problem Is It?

A patch of black mould on the bathroom ceiling or behind a leaky window is more than ugly — it's a health hazard, and in Ontario it's almost always your landlord's job to fix. Here's how to make that happen.

By the LeasePlain Editorial Team · Checked against Ontario's Residential Tenancies Act per our editorial standards·Last reviewed September 2026

The Landlord Has to Deal With It

Under the Residential Tenancies Act, your landlord must keep the unit in a good state of repair and fit for habitation and comply with health and safety standards. Mould caused by a maintenance defect — a roof or plumbing leak, failed window seals, poor ventilation — is squarely the landlord's responsibility to remediate, at their cost.

When Could It Be on You?

The narrow exception is mould that results from a tenant's own negligence — for example, never using the bathroom fan, blocking vents, or failing to report an obvious leak for months. Even then, the landlord usually has to fix the underlying problem; the dispute is about who pays. Reporting promptly protects you.

Report It in Writing — Immediately

Tell your landlord in writing (text or email) as soon as you see mould, with photos and the date. Keep the copy. A written record is what turns a he-said/she-said into a winnable case, and it starts the clock on the landlord's duty to act.

Escalate If They Ignore You

You have more than one lever, and can use them together:

Municipal property standards / 311: the city can inspect and order remediation, often faster than the LTB.
Public health: significant mould can be a health-hazard complaint.
File a T6 at the LTB: ask for an order to remediate plus a rent abatement for the time you lived with it.

Don't Just Stop Paying Rent

Withholding rent on your own can put you at risk of an N4 and eviction. Instead, document everything, escalate through the city and the LTB, and let a T6 application recover an abatement. See can I withhold rent over repairs? for why the formal route is safer.