Who Pays for Mold in an Ontario Rental? Landlord Rules

In Ontario, the landlord is responsible for fixing mold in a rental unit when it comes from the building itself: a roof or plumbing leak, a damp foundation, failed windows or ventilation that does not work. The Residential Tenancies Act puts the duty to keep a unit in a good state of repair and fit to live in on the landlord, and that duty applies even if the tenant knew about the problem when they moved in. Tenants carry their share when the mold is caused by how the unit is used or by damage they caused, and both sides have specific steps to follow before it becomes a Landlord and Tenant Board file.

This guide walks through the rules that apply, how responsibility is usually split, and what a proper fix looks like so the same wall is not back on the agenda next fall.

The law that sets the landlord's duty

The starting point is section 20 of the Residential Tenancies Act, 2006 (RTA). It requires the landlord to provide and maintain the residential complex, including the rental units, in a good state of repair and fit for habitation, and to comply with health, safety, housing and maintenance standards. The same section says the duty applies even if the tenant was aware of the state of non-repair before signing the lease. A clause in a lease that tries to shift all mold responsibility to the tenant does not override the Act.

Those "maintenance standards" come from two places:

• Municipal property standards bylaws. Most Ontario cities have one, and city inspectors enforce it. In Toronto that is Municipal Code Chapter 629, Property Standards, and apartment buildings with three or more storeys and ten or more units also fall under the RentSafeTO program.
• Ontario Regulation 517/06, Maintenance Standards. This provincial regulation under the RTA applies in places that have no municipal property standards bylaw, and complaints there go to the province rather than the city.

Health Canada's residential indoor air guidance on mould does not set a "safe" amount. Its position is that any mould growing in a home should be removed and the moisture causing it corrected. That is the practical standard inspectors and adjudicators tend to work from: visible, recurring mold is a sign of a repair problem, not a cosmetic one.

What the tenant is responsible for

The RTA also gives tenants duties. Section 33 makes the tenant responsible for ordinary cleanliness of the unit, and section 34 makes them responsible for repairing undue damage caused wilfully or negligently by them, other occupants or their guests.

In mold terms, that usually means:

• Wiping surface mold off shower caulking, tile grout and window frames as part of normal cleaning.
• Running the bathroom fan and range hood, and not blocking vents with furniture.
• Reporting leaks, wet ceilings and musty smells promptly instead of letting them go for months.
• Not drying laundry indoors in a closed room for weeks or covering windows so condensation cannot evaporate.

If a landlord believes the tenant caused the mold, the burden is on the landlord to show it. A bathroom with no working exhaust fan or a window that leaks around the frame points back to the building, not the occupant.

How responsibility usually splits in practice

Most cases fall into one of a few patterns:

For a condo unit that is rented out, there is one more layer. Under the Condominium Act, 1998 the corporation generally repairs the common elements and the owner repairs the unit, though the declaration can change that split. A leak from a common pipe or the building envelope may be the corporation's to fix, but toward the tenant, the unit owner is still the landlord under the RTA.

Steps for tenants when mold appears

1. Report it in writing. Email or a letter to the landlord, with photos, where the mold is, roughly how large the area is and when you first noticed it. Keep a copy.
2. Give a reasonable time to respond. A small patch from a slow drip is different from a flooded basement, but a landlord who does nothing for weeks after written notice is in a weak position.
3. Ask the city to inspect. If the landlord does not act, call your municipality's property standards office (311 in Toronto and Ottawa). An inspector can issue an order to comply.
4. Apply to the Landlord and Tenant Board. The tenant application about maintenance (Form T6) can ask the Board to order repairs, order a rent abatement, or let the tenant arrange the work and deduct the cost.

One thing not to do: stop paying rent on your own. Withholding rent without a Board order gives the landlord grounds to file for non-payment, and the mold dispute does not cancel that.

Steps for landlords

1. Respond quickly and document it. Date the tenant's report, your reply and every visit.
2. Give proper notice to enter. Section 27 of the RTA requires at least 24 hours' written notice, stating the reason, with entry between 8 a.m. and 8 p.m., unless it is an emergency such as an active leak.
3. Find the moisture source first. Spraying the wall and painting it over is the most common reason mold comes back and the dispute restarts. Moisture readings and a look at the roof, plumbing, grading and ventilation should come before any cleanup.
4. Remove the mold properly. Larger areas, mold inside walls or insulation, and anything in the attic or basement should be handled with containment so spores do not spread into the rest of the unit or the hallway.
5. Check for asbestos in older buildings. In buildings from before the mid 1980s, drywall joint compound, plaster and some flooring may contain asbestos. Get a sample tested before anyone cuts into those materials.
6. Keep the written scope and the results. If the matter ends up at the Board, a written scope of work, photos and any post-cleanup testing show what was done.

Mold inspection and removal requests are handled across the province, including Toronto, Ottawa and Hamilton.

Frequently asked questions

Can a tenant break the lease because of mold in Ontario?

A tenant cannot simply walk away from a lease because of mold. The usual route is a T6 application to the Landlord and Tenant Board, which can order repairs, a rent reduction or, in serious cases, other remedies. If the unit is genuinely unfit to live in, the tenant should get advice from a legal clinic before leaving.

How long does a landlord have to fix mold in Ontario?

The RTA does not set a fixed number of days. The expectation is a reasonable time based on how serious the problem is, so an active leak needs attention right away while a small patch can be scheduled. Municipal orders to comply do set a deadline, and failing to meet it can lead to fines.

Does landlord insurance cover mold removal?

It depends on the policy and the cause. Many policies cover mold that results from a sudden and accidental event such as a burst pipe, and exclude mold from long-term seepage, condensation or lack of maintenance. Check the wording with the broker before assuming either way.

Is a landlord responsible for mold caused by condensation?

Usually yes, when the condensation comes from the building, such as a bathroom without an exhaust fan, single-pane windows or poor insulation. If the unit has working ventilation and the tenant routinely blocks it or keeps the humidity very high, responsibility can shift. The question an adjudicator asks is whether the unit, used normally, stays dry.

Get a written scope for a rental unit

Whether you own the building or rent the unit, a clear written scope helps everyone: where the moisture comes from, which materials come out, how the work area is contained and what gets rebuilt. Send us the details through the quote form with the city, the building type and whether tenants live there, and a specialist who works in your area will review it.