Who Is Responsible for Mould in an Alberta Rental? A Grande Prairie Landlord's Guide

The first hard cold snap in Grande Prairie usually brings a familiar call from tenants: water running down the inside of the windows, black spots on the sill, or a musty smell in a basement bedroom. For a rental owner, the next question comes quickly. Who is responsible for mould in a rental property, the landlord or the tenant, and who pays to fix it?

In Alberta the starting point is clear, but the final answer depends on what caused the moisture. This guide explains who is responsible for mould in an Alberta rental, where tenant responsibility begins, what two real Alberta disputes show about evidence, the winter humidity targets that matter in a northern climate, and how to respond when a tenant reports mould. It is general information, not legal advice, and every rule below comes from a public source listed at the end of the article.

The short answer: the owner is responsible for fixing mould

Section 16(c) of Alberta's Residential Tenancies Act (RTA) makes it a covenant of every residential tenancy agreement that the premises will meet at least the minimum housing standards made under the Public Health Act. Section 4 of the Housing Regulation then requires the owner to maintain the housing premises in compliance with the Minimum Housing and Health Standards.

The standards never use the word "mould", but they cover the conditions that create it. The owner must keep the premises structurally sound, in good repair, and in a waterproof, windproof and weatherproof condition. Basements, cellars and crawl spaces must be free from water infiltration and accumulation (section 1(b)). Building materials that show rot or other deterioration must be repaired or replaced (section 1(c)). Bathroom walls and floors must be non-absorbent to moisture with watertight joints (section 5(a)), plumbing fixtures must be free from leaks (section 6(c)), and windows in habitable rooms must protect against cold weather with double glazing, a storm sash or a similar barrier (section 2(b)(ii)).

The Centre for Public Legal Education Alberta (CPLEA) puts it plainly in its tipsheet on mould and rental properties: property owners and landlords are responsible for fixing mould problems, because mould can be a deficiency that affects whether a property is fit to live in and whether the tenant can enjoy it. Because the duty comes from a public health standard, a lease clause that makes the tenant responsible for all mould does not remove the owner's legal obligation.

What tenants are responsible for

Tenants still carry real obligations. Under RTA section 21, every tenancy agreement includes tenant covenants to keep the premises in a reasonably clean condition and not to do or permit significant damage. CPLEA adds a practical duty that matters a great deal with mould: tenants should tell the landlord about mould problems right away, in writing. A tenant who stays silent may be found to have contributed to the problem and to their own losses.

Day-to-day habits also play a part. Health Canada lists everyday indoor activities such as showering, cooking and drying laundry, especially when exhaust fans are not used, along with overcrowding and inadequate ventilation, as common sources of indoor moisture. A tenant who blocks vents, never runs the bathroom fan or runs a humidifier around the clock can contribute to the problem even in a well-built home.

Why the cause decides who pays

Fixing mould and paying for mould are not always the same question. Health Canada's guide to addressing moisture and mould indoors sorts the causes into two broad groups. Some are building problems: water infiltration through cracks in the foundation, walls, roof or unsealed windows, plumbing leaks, and snowmelt that does not drain away from the house. Others are usage problems: moisture from daily activities, humidifiers and poor ventilation habits. Condensation on cold surfaces sits in between, because it is driven both by indoor humidity and by how cold the window or wall is.

That is why the owner should move first on any report, and then work out the cause. If the source is a roof leak, a failed window seal or a dripping trap, the repair is the owner's cost. If the evidence shows the tenant created or worsened the problem, the owner may be able to recover costs as damages. As CPLEA notes, disputes about who contributed to mould involve findings of fact for the Residential Tenancy Dispute Resolution Service (RTDRS) or the courts to decide.

A real Alberta case: Brown v. Libertas Property Management

In Brown v. Libertas Property Management Inc., 2011 ABPC 148, summarized by CPLEA's LawNow magazine, a tenant claimed the return of a $1,495 deposit, $3,040 in rent abatement and $3,000 in general damages. One issue was a toilet leak that led to mould and mildew in the floor tile, which the tenant said worsened their asthma. The judge found the tenant knew about the mould and should have told the landlord and taken some steps of their own, and that failing to do so contributed to the damages. The leak, broken tiles and mould still affected the home, so rent abatement was appropriate. Damages and abatement were assessed at $1,000, and the landlord was ordered to pay $2,495 in total, including the deposit.

The lesson for owners runs both ways. A tenant's silence can reduce what the landlord owes, but it does not erase the landlord's duty to repair a leak and the mould it caused.

A second Alberta example: the humidity dispute in Cochrane

CBC News reported in November 2023 on a Cochrane family who rented a two-storey home from July 2022. When the weather turned cold that December they noticed condensation on the windows, and in January 2023 mould appeared on the baseboards of a bedroom closet. The landlord brought in roofing contractors, and one written report cited some attic airflow issues and wet insulation but stressed monitoring indoor humidity. The landlord said the tenant's humidifier was set too high. At the RTDRS hearing the dispute officer sided with the landlord, writing that it was "nonsensical" that humidity would keep rising with the humidifier off when there was no evidence of structural deficiencies.

The tenant told CBC she could not prove the cause because no mould expert assessed the home. For owners, the takeaway is not that humidity arguments always win. It is that the side with a documented inspection, written findings and a clear timeline is in a far stronger position, and that ventilation problems flagged by a contractor should be fixed rather than ignored.

Winter humidity targets for a Grande Prairie rental

Northern winters make condensation the most common mould trigger in otherwise sound homes. Health Canada recommends keeping indoor relative humidity between 30 and 50 per cent and running a dehumidifier in damp areas such as basements, or whenever moisture is condensing on cold surfaces like window panes. Canada Mortgage and Housing Corporation (CMHC) goes further for cold weather: to prevent window condensation during the heating season it recommends 30 to 50 per cent, and about 30 per cent when it is below minus 10 degrees Celsius outdoors.

The City of Grande Prairie's Home Energy Check Kit guidance suggests indoor humidity of roughly 20 to 40 per cent, with lower humidity during very cold weather, and rooms within two to three degrees Celsius of one another. The City lends six of these kits for up to two weeks from the AccessGP counter at City Hall (10205 98 Street) and the City Service Centre (9505 112 Street), with a deposit. An inexpensive hygrometer left in the unit gives both owner and tenant the same reading to work from.

Cold rooms and heat: where the owner's heating duty meets mould

CMHC lists cold surfaces as a major cause of condensation, including inadequate heat to parts of the home, heat blocked off in unused rooms, wide swings in indoor temperature, furniture pushed against exterior walls and poorly insulated walls and ceilings. Natural Resources Canada adds that air flow across window glass keeps it warmer, which is why heat registers sit under windows, and that deep sills, closed drapes and nearby furniture can let cold air pool against the glass.

Where the owner controls the heat, the Minimum Housing and Health Standards require habitable rooms to be kept at a minimum of 22 degrees Celsius, subject to the cold-weather exception. Our guide to Alberta rental heat and utility rules covers who pays for heat and what the standards require through the winter.

An owner's pre-winter moisture checklist

Before the deep cold arrives, confirm that bathroom fans and the kitchen range hood work and vent outside rather than into the attic. Turn on the heat recovery ventilator if the home has one and clean or replace its filters along with the furnace filter. Check window seals, weatherstripping and caulking, and replace any unit where condensation forms between the panes, because that means the seal has failed. Make sure eavestroughs and downspouts carry water away and that the grade slopes away from the foundation so spring melt does not end up in the basement. Look under sinks and around the toilet and tub for slow leaks. Our rental property winterizing guide and our article on plumbing maintenance and repair cover these jobs in more detail.

It also helps to give new tenants a short written note at move-in about running fans during showers and cooking, keeping furniture a few inches off exterior walls, not blocking heat registers and reporting condensation or musty smells early. That record shows the tenant was informed if a usage dispute ever arises.

How to respond when a tenant reports mould

Speed matters. Health Canada warns that mould will begin to grow within 48 hours in an area with excessive moisture, and that the underlying moisture problem must be solved or the mould will come back. Acknowledge the report in writing, then inspect promptly. Entry for inspection or repairs requires proper written notice under section 23 of the RTA, normally at least 24 hours, unless the tenant consents or there is an emergency.

Health Canada's guide also sizes the job. Three or fewer patches totalling less than one square metre is a small area that can be cleaned with proper precautions. More than three patches, or patches between one and three square metres, is a medium area where an expert assessment is recommended. A single patch larger than three square metres, mould that returns after cleaning, or water damage involving sewage requires a qualified professional. Health Canada advises against using bleach to clean up mould; washable surfaces are scrubbed with an unscented detergent and water, and porous materials such as soaked drywall or carpet are usually removed.

Documentation that protects owners

Both Alberta examples above turned on evidence. Keep the tenant's written report, your reply and every notice of entry. Photograph the affected area with a date and a ruler or tape for scale, and record humidity readings at each visit. Ask any contractor for a written report on the source, not just a verbal opinion. Compare the findings against the move-in inspection report; our guide on how to conduct a tenant walkthrough inspection explains how to make that record hold up later. If the parties agree on a plan, CPLEA recommends putting it in writing, including whether the tenant moves out during repairs, who pays and whether any rent reduction applies.

What happens if mould is ignored

Tenants who report a problem that is not fixed can contact Alberta Health Services Environmental Public Health. A public health inspector may inspect the rental and speak with the landlord, and the inspector will not tell the landlord who complained. Under section 28 of the RTA, a tenant can end the tenancy with 14 days' notice if a public health order about the premises is not complied with.

Under section 37 of the RTA, a tenant can also apply to the court or the RTDRS for damages, an abatement of rent, compensation for the cost of performing the landlord's obligations, or termination of the tenancy. Our overview of the RTDRS process for Alberta landlords explains how those hearings work. Owners should also read their property policy's wording on mould and gradual leakage with their broker, since coverage for long-term seepage can differ from sudden water damage. Our guide to landlord insurance in Alberta covers the questions to ask.

A quick checklist when a tenant reports mould

Thank the tenant and confirm the report in writing the same day. Serve proper notice and inspect within a day or two. Photograph the area, measure its size and take a humidity reading. Look for the source first: leaks, failed seals, blocked or broken fans, cold rooms or high indoor humidity. Clean small areas properly and bring in a qualified professional for larger or recurring growth. Fix the cause, give the tenant written guidance where habits are part of the problem, and only pursue costs where the evidence shows the tenant caused or worsened it.

Let Sutton handle the moisture calls this winter

Mould reports tend to arrive in the coldest weeks of the year, when a quick, documented response protects both the property and the tenancy. Sutton Property Management manages rental properties across Grande Prairie, from marketing and tenant screening to rent collection and day-to-day tenant communication. Learn more about our Grande Prairie property management services, or contact our office to talk about your rental before the deep cold sets in.

Sources: Residential Tenancies Act, SA 2004, c R-17.1, ss. 16, 21, 23, 28 and 37; Housing Regulation, Alta Reg 173/1999, s. 4; Government of Alberta, Minimum Housing and Health Standards (rev. June 30, 2012), ss. 1, 2, 4, 5, 6 and 8; Centre for Public Legal Education Alberta, "Mould and Rental Properties" tipsheet (2021); LawNow, "Mould and Rental Properties" (July 2021), discussing Brown v. Libertas Property Management Inc., 2011 ABPC 148; CBC News, "Renter sought compensation for mould but tenancy dispute board stuck her with the bill" (November 13, 2023); Health Canada, "Guide to addressing moisture and mould indoors" and "Healthy home guide"; Canada Mortgage and Housing Corporation, "Measuring Humidity in Your Home" and "Moisture and Air"; Natural Resources Canada, "Condensation"; City of Grande Prairie, "Home Energy Check Kit"; MyHealth Alberta, "Renting in Alberta" (June 2025); Alberta Courts, "Residential Tenancies Process". This article is general information, not legal advice. Confirm your obligations for a specific property with Alberta Health Services, a qualified remediation professional, or a lawyer.