It starts with a foggy bedroom window. A few weeks later, there’s water pooling on the sill. By January, someone notices black spots forming around the frame.
For Canadian landlords, especially those managing older properties in coastal BC or other damp regions, this is a familiar winter headache. And when mould appears, the conversation can quickly turn into a disagreement over who’s responsible.
The good news? Most condensation problems are easier to manage when landlords and tenants know what to look for, act early, and keep a record of what’s happening.
Key Takeaways
- Condensation isn’t automatically a tenant’s fault. Poor ventilation, building defects, and everyday moisture can all contribute.
- Tenants can help prevent moisture buildup by using working exhaust fans, managing indoor humidity, and wiping condensation from windows.
- Landlords are responsible for maintaining the property, including addressing leaks, defective ventilation, and other building-related moisture problems.
- Document problems as they happen. Dated photos, written reports, inspections, and repair records help establish what caused the damage.
- Mould doesn’t automatically justify a security deposit deduction. Responsibility depends on the cause, evidence, and applicable provincial rules.
Why Do Rental Windows Get So Wet in Winter?
Cold weather creates the perfect conditions for condensation.
When warm, moisture-filled indoor air touches a cold surface, such as a window or exterior wall, some of that moisture turns into water droplets. It’s the same reason a cold drink gets wet on the outside during summer.
In a rental home, everyday activities add moisture to the air. Cooking, showering, drying laundry indoors, and even breathing all contribute.
The problem becomes more noticeable in winter because windows and exterior walls are colder, while tenants are less likely to open windows for fresh air.
A little condensation doesn’t necessarily mean something is wrong with the building. But persistent moisture can damage paint, window frames, drywall, and other materials. Given enough time, mould may develop.
According to Health Canada’s guide to addressing moisture and mould indoors, controlling moisture and fixing its source are essential to preventing mould growth.
One important distinction: black spots aren’t proof that a tenant caused mould, and colour alone cannot identify the type of mould or its health risk. The cause needs to be investigated before anyone assigns responsibility.
Landlord vs. Tenant: Who’s Responsible for Condensation and Mould?
This is where things can get uncomfortable.
A landlord might notice water damage around a window and assume the tenant hasn’t been ventilating the room. The tenant might point to an old window or a bathroom fan that barely works.
Either explanation could be right. Sometimes, both contribute.
The starting point is to identify where the moisture is coming from and whether the property has the equipment and conditions needed to manage it.
| Situation | Who should address it? |
| Condensation from cooking or showering | Tenant manages everyday moisture using available ventilation; landlord maintains required, working ventilation |
| Bathroom exhaust fan stops working | Landlord arranges repair, unless tenant-caused damage is established |
| Water enters through a leaking roof or window | Landlord addresses the building defect |
| Tenant repeatedly leaves water pooling despite appropriate ventilation and warnings | Tenant may be responsible for resulting damage if their actions caused it |
| Mould develops behind a wall due to a plumbing leak | Landlord investigates and addresses the leak and affected materials |
| Mould cause is unclear | Investigate and document before assigning responsibility |
In British Columbia, the Residential Tenancy Branch’s Policy Guideline 1 helps explain the division between landlord maintenance duties and tenant cleaning responsibilities.
Landlords must maintain rental properties in a condition that meets applicable health, safety, and housing standards. Tenants are responsible for reasonable cleanliness and for damage they or their guests cause beyond reasonable wear and tear.
The same practical distinction matters across Canada, although the specific tenancy rules and dispute procedures vary by province.
For another perspective, BC’s Tenant Resource & Advisory Centre explains repairs and maintenance from the tenant’s side.
A useful rule for landlords: Before blaming poor housekeeping, check whether the tenant has a functioning fan, adequate ventilation, and a building that’s keeping outside water where it belongs.
What Can Tenants Do to Prevent Winter Condensation?
Most tenants don’t want mould growing around their windows any more than landlords do.
A few manageable habits can make a difference:
- Use kitchen and bathroom exhaust fans. Run them while cooking or showering, and continue afterward to remove excess moisture.
- Wipe wet windows and sills. Don’t leave water sitting against wood, drywall, or painted surfaces.
- Keep indoor humidity under control. Health Canada recommends maintaining relative humidity around 30–50%, with the lower end sometimes needed during cold weather to prevent condensation.
- Allow air to circulate. Avoid pushing large furniture tightly against cold exterior walls.
- Ventilate when practical. Briefly opening windows can help when outdoor conditions allow, but it shouldn’t replace functioning mechanical ventilation.
- Report recurring moisture or mould promptly. A written message with photos gives the landlord a chance to investigate.
A small digital hygrometer can help tenants and landlords understand whether indoor humidity is contributing to the problem.
However, these habits only go so far. A tenant can’t solve a roof leak by opening a window, and wiping condensation won’t repair a broken exhaust fan.
That brings us to the landlord’s side of the equation.
What Should Landlords Do When Mould Appears?
The worst response to a mould complaint is to leave it sitting in your inbox until spring.
Even a small patch deserves attention because visible mould may be a sign of a larger moisture problem.
Start with the source. Check window seals, exterior walls, plumbing, and ventilation. Ask when the tenant first noticed the problem and whether it gets worse after rain, showers, or particularly cold nights.
If the bathroom fan isn’t working, arrange a repair. If water is entering through the roof or window, investigate the leak. Cleaning the visible mould without fixing the moisture source means it may return.
Health Canada provides guidance based on the size of the affected area:
- Small areas: Three or fewer patches covering less than 1 m² in total may be cleaned using appropriate precautions.
- Medium areas: More extensive patches with a combined area below 3 m² warrant expert assessment, although some can be cleaned safely with appropriate precautions.
- Large areas: A single patch larger than 3 m² requires professional assessment and cleanup.
The type of material matters too. Mould on drywall or other porous surfaces can require a different approach from mould on a washable, non-porous surface.
For detailed cleaning and remediation advice, see our earlier article, A Property Manager’s Guide to Getting Rid of Mould in Rental Properties.
Ontario landlords can also refer to the City of Toronto’s mould guidance for additional public-health information.
Whatever the size, don’t delay investigating recurring mould or ask tenants to handle extensive cleanup themselves.
What Should Landlords Document to Avoid Disputes?
Imagine a tenant moves out in March, leaving behind stained drywall and damaged window trim.
The landlord believes the tenant ignored condensation all winter. The tenant says the windows were defective and that they reported the problem months earlier.
Without records, it’s difficult to establish what happened.
A few dated photos from December, a written maintenance request, and a repair invoice can make the situation much clearer.
Here’s a straightforward documentation process worth following:
Winter moisture documentation checklist
Photograph affected windows, walls, ceilings, and surrounding areas, with dates and room locations.
Record when the moisture or mould was first noticed or reported.
Keep tenant messages, maintenance requests, and inspection notes.
Document fan operation, visible leaks, humidity readings, and other relevant findings.
Save contractor assessments, repair invoices, and before-and-after photos.
Compare the condition with move-in and move-out inspection reports.
Photos should show both the close-up damage and the wider area. A picture of a black spot is useful, but one showing its position beside a leaking window tells a more complete story.
It’s also worth recording what happened next. Was a contractor called? Was a fan replaced? Did the moisture return after repairs?
Pendo’s mobile inspection tools can help keep property-condition records organized. Our guide to using Pendo’s mobile inspection app explains practical ways to incorporate inspections into your rental workflow.
Can a Landlord Deduct Mould Damage From a Security Deposit?
Possibly, but discovering mould at move-out doesn’t automatically make the tenant responsible for the cost.
A landlord needs evidence connecting the damage to the tenant’s actions or failure to meet their responsibilities, rather than ordinary wear and tear or a building maintenance issue.
Consider two examples.
Scenario A: A tenant reports recurring water around a window. The landlord discovers a failed window seal but doesn’t repair it. Mould later damages the surrounding drywall.
In this situation, the evidence points toward an unresolved building problem, making a tenant damage claim difficult to justify.
Scenario B: A tenant has functioning ventilation and has been advised about recurring condensation. Documented inspections show water repeatedly left pooling on the sill, followed by avoidable damage to the trim.
Here, the landlord may have a stronger claim, provided the evidence establishes that the tenant’s actions caused the damage.
The important word is may. Neither situation automatically determines the outcome.
In BC, landlords cannot simply keep a security deposit because they believe damage occurred. They must follow the province’s deposit return and dispute resolution requirements, including obtaining the tenant’s written agreement or an appropriate Residential Tenancy Branch order where required.
Our guide to move-in condition inspection reports and damage claims in Canada explains why consistent inspection records matter when a tenancy ends.
And while insurance may cover certain types of sudden water damage, gradual moisture problems and mould can be treated differently depending on the policy. See our guide to understanding rental property insurance and check the terms of your coverage before assuming a repair is insured.
A Few Common Questions About Winter Mould
Is condensation on rental windows normal in winter?
Some condensation can occur when warm, humid indoor air meets cold glass. Persistent pooling, soaked window frames, or recurring mould should be investigated rather than dismissed as normal.
Can a landlord tell a tenant to clean mould themselves?
Tenants have reasonable cleaning responsibilities, but the cause, size, and location of mould matter. Extensive growth, hidden mould, or moisture caused by building defects may require landlord-arranged professional work.
What if a tenant doesn’t report mould right away?
A delay in reporting may matter when assessing whether damage could have been prevented. It doesn’t automatically transfer responsibility for a building defect to the tenant.
Does painting over mould solve the problem?
No. Painting over affected surfaces without addressing the moisture source and properly removing mould can allow the problem to continue beneath the paint.
Catch the Moisture Before It Becomes a Bigger Problem
A wet window in November might seem like a minor inconvenience. By February, that same window could be surrounded by peeling paint, swollen trim, or mould.
For landlords, the best approach is to make moisture prevention part of winter property maintenance, respond to reports promptly, and keep a clear record of what was found and fixed.
For tenants, small habits and early reporting can prevent an unpleasant problem from becoming a bigger one.
And for both sides, good documentation makes it easier to resolve disagreements based on what actually happened rather than competing memories months later.
Pendo helps landlords and small property managers organize property inspections and related records, so important details don’t get lost between tenancies.
Start a free 30-day trial today.
This article is for informational purposes only and does not constitute legal advice. Always consult your local Residential Tenancy Branch or a qualified legal professional for advice specific to your situation.
