Basement Mould in Toronto: What Bleach Cannot Fix and When to Stop Cleaning
Toronto basements do not start smelling in July. They start smelling in late October, within a week or two of the furnace coming on, and that timing is the most useful clue you will get about what is actually happening down there. (Canadian sources spell it mould and American ones spell it mold. Same organism, same problem.)
The reason is not that the basement suddenly got wetter. It is that the foundation wall has become the coldest surface in a house now full of warm, moist air. Warm air carries far more water vapour than cold air can hold, so when heated household air drifts downstairs and meets concrete sitting at the temperature of the soil outside, the water leaves the air and lands on the wall. Mould does not require a leak. It requires a damp surface and something to eat, and a cardboard box pressed against a cold foundation wall supplies both at once.
What to do next is where the advice falls apart, and not because anyone is being careless. Health Canada says plainly not to use bleach on mould. The City of Toronto hands you a bleach recipe on its own basement flooding page. Health Canada draws the do-it-yourself line at three square metres; the City draws a different line at four. Every one of those statements is correct about the question it is answering. This guide is about working out which question is yours.
Why Toronto Basements Grow Mould in October, Not August
A basement is the one room in a Toronto house that is cold in winter and cool in summer, because it is surrounded by soil rather than air. Soil temperature lags air temperature by weeks, which is why a foundation wall is still giving up summer warmth in October and still holding winter cold in May. For most of the heating season, that wall and the cold-water pipes running along the joists are the coldest things in the building.
Everything you do upstairs adds water vapour to the air: showers, cooking, dishwashing, laundry, houseplants, breathing. That vapour spreads through the house and condenses wherever it finds a surface cold enough. In a Toronto winter, that surface is almost always below grade. This is the same mechanism that fogs your windows in January, only it happens out of sight, on a wall behind a shelf, where nobody wipes it off.
Health Canada's guidance on reducing humidity, moisture and mould settles on one number above all others: keep indoor relative humidity between 30 and 50 per cent. It adds a specific trigger for acting — run a dehumidifier when moisture condenses on cold surfaces or when relative humidity climbs above 50 per cent. That second instruction is the one that matters in a basement, because the condensation shows up long before the whole-house humidity reading looks alarming.
The Forty-Eight Hour Rule
Health Canada's guide to addressing moisture and mould indoors puts a clock on it: mould will begin to grow in an area with excessive moisture within 48 hours. The Canada Mortgage and Housing Corporation applies the same window from the other direction in its housing guidance — after a water event, discard anything that will not dry within 48 hours, naming insulation and drywall, carpets, particleboard furniture, mattresses and box springs, stuffed toys, pillows and cushions, and furniture coverings.
Forty-eight hours is not a grace period you can spend deciding what to do. It is the entire budget. If a pipe lets go on Friday night and you look at it on Sunday, you are no longer preventing mould; you are cleaning it. This is also why a slow, chronic condensation problem is worse than a dramatic one. A burst pipe gets attention. A wall that stays damp for four months never does.
Where the Moisture Actually Comes From
There are four sources, and in a Toronto house they are not equally likely. Ranked by how often each one turns out to be the answer:
Condensation from indoor air. The most common cause and the least suspected, because there is no water to find. The wall is simply damp. You will see it as a dark band low on the foundation, a bloom in the corner behind storage, or beads on a cold-water pipe. Health Canada specifically names condensation on plumbing pipes, clutter and storage near outside walls, cardboard boxes on the floor, and carpeting as basement concerns.
Humid indoor air with nowhere to go. If the laundry is downstairs, the basement is the wettest room in the house by a wide margin. Health Canada's indoor air quality guidance is specific here: vent the clothes dryer outside, keep that vent unblocked, clean the lint tray after every use, and check the outside vent for lint. It also notes that hanging laundry indoors adds moisture to the air, and recommends drying outdoors when conditions allow.
Drainage failure. The City of Toronto lists this as stormwater or groundwater seeping in through foundation cracks, poor lot grading, weeping tile or sump pump failure, overflowing or leaking eavestroughs, and plugged downspouts. Toronto's older neighbourhoods are full of houses where the grade has settled toward the foundation over fifty years and nobody has looked.
Sewer backup. The City attributes this to blockages from items flushed or poured down drains, sewers overwhelmed by heavy rain or meltwater, and tree roots entering cracks in sewer lines. This is the one category where the cleanup rules change completely, for reasons covered below.
The Bleach Question, and Why Two Canadian Authorities Disagree
This is the point where most people give up and do whatever the bottle says, so here is the conflict stated plainly.
Health Canada says no. Its guide to addressing moisture and mould indoors states, without qualification, do not use bleach to clean up mould. The department's consumer mould page is blunter still: there is no need to use bleach. What it recommends instead is warm water and unscented dishwashing detergent, baking soda or unscented soap on walls, and unscented soap with warm water on concrete.
The City of Toronto says yes. Its basement flooding page gives a cleanup mix of one cup of bleach to five gallons of water.
Both are right, because they are solving different problems, and the distinction is worth understanding rather than memorising.
Bleach is a disinfectant. The City's advice sits inside a flood-cleanup context, where the water may have come up through a sewer and the hazard is bacterial contamination of surfaces you will touch. Disinfecting those surfaces is sensible, and bleach does it well.
Mould is not a contamination problem you disinfect. It is a biomass you physically remove. And chlorine bleach is mostly water. On a porous material, the water soaks into the substrate while the chlorine stays near the surface, oxidizing the pigment in the visible colony. The stain fades. The root structure underneath is still there, now in a wetter material than before you started. Two weeks later the patch is back and slightly larger, and the usual conclusion is that the bleach was not strong enough. It was not the wrong strength. It was the wrong tool.
The working rule for a Toronto basement: if your basement took in sewage or floodwater, follow the City's disinfection advice for the hard surfaces you will be handling. If your basement simply grew mould out of its own damp air, follow Health Canada's method — detergent, water, and physical removal. And as a matter of basic safety, never combine bleach with an ammonia-based cleaner, which is a more common accident in a poorly ventilated basement than anyone expects.
Porous or Non-Porous: The Sorting Rule That Decides Everything
Before you clean anything, sort it. Health Canada's guidance turns on one distinction, and once you apply it, most of the hard decisions make themselves.
Materials that can be cleaned must be non-porous. Health Canada names glass, metals, leather, plastics and vinyl, and gives window sills, hard surfaces and tiles as examples. These have no interior for mould to root into, so washing the surface genuinely removes the organism rather than just its colour.
Materials that cannot be cleaned are the porous ones. Health Canada's wording is that porous materials, such as fabrics, often cannot be properly cleaned and must be discarded. The list it gives is long and expensive: soft furnishings, mattresses, bedding, stuffed toys, carpets, sofas, pillows, paper and cardboard products, and clothing with active mould growth.
Which brings us to the most Toronto-specific problem in this whole article. Basement storage in this city is cardboard. Boxes of books, old tax records, holiday decorations, children's artwork, the contents of a parent's house — stacked on the floor, pushed against the exterior wall, in the coldest and dampest part of the building. A cardboard box in that position is a porous material sitting on a cold damp surface with a cellulose food supply built in. There is no cleaning procedure for it. If it has gone soft at the bottom or smells musty, that is a disposal decision, not a cleaning one.
The fix is unglamorous and permanent: sealed rigid plastic bins, lifted onto open shelving, with a genuine air gap between the shelving and the exterior wall. Health Canada's broader advice to keep beds and furniture away from outside walls and to keep baseboards and heating vents clear of furniture is the same principle applied to the floors above — air has to be able to move across a cold surface, or that surface will sweat.
Drywall is the awkward middle case, because it is porous but not disposable. Health Canada's instruction is to clean it with a damp cloth so you do not make the drywall wet, which is a meaningfully different action from washing a tile. After a flood, CMHC's guidance is firmer: remove all wet drywall at least 30 centimetres above the flood water level, because the material wicks water upward well past the visible line. If the mould is on painted drywall rather than inside it, the same finish-and-sheen logic applies as anywhere else in the house, which we covered in our guide to cleaning painted walls in Toronto.
How Big Is Too Big: Three Thresholds That Do Not Match
There is no single number, and pretending otherwise is how people end up cleaning something they should not have touched. Here are the published thresholds, from the actual sources.
Health Canada, small: three or fewer patches, each less than one square metre (about 10 square feet), totalling a square metre or less. Clean it yourself.
Health Canada, medium: more than three patches, or a patch larger than one square metre but under three square metres (about 32 square feet). The department's position is that you can generally clean small and medium sized areas of mould by yourself.
Health Canada, extensive: a single patch larger than three square metres. Here it says you should consider getting professional help.
The City of Toronto, via 311: an area of one square metre or less can be cleaned with household cleaner, while larger or extensive areas of mould contamination — four square metres or larger — should be addressed using a professional trained in mould remediation.
The gap between three and four square metres is not an error on anyone's part. Health Canada is giving health guidance to a homeowner. The City is setting an operational line for a municipal service. And in a rental unit, that municipal line is the one with teeth.
For mould in a Toronto rental larger than four square metres, the City directs tenants to Toronto Public Health, reachable at 416-338-7600. Below four square metres, Municipal Licensing and Standards handles it as marks and stains under Chapter 629, Property Standards, Section 27.C. The City also names the deficiencies it will look at: heating or ventilation systems that are broken or not working, including blocked air vents; moisture entering through floors, walls, windows, ceilings or roofs; and faulty plumbing such as leaking pipes. Its first instruction to tenants is procedural but important — advise the superintendent, the property and the owner in writing. A written record is what makes the rest of the process work.
Read all four thresholds as a ladder rather than a contradiction. Under a square metre, clean it. One to three square metres, clean it only if you can do it properly, with the right protection, and you already know where the water came from. Over three, stop and call someone. And Health Canada adds one more test that overrides every measurement: get professional help if the mould keeps coming back after cleaning. Recurrence is not a cleaning failure. It is a moisture source you have not found yet, and scrubbing it again will not reveal it.
How to Clean a Small Basement Mould Patch Properly
This is for small and medium patches only, as defined above, on surfaces you have confirmed are cleanable. Work through it in order, because the sequence is doing real work.
1. Fix the water first. Cleaning before the moisture source is addressed guarantees a repeat. If you cannot identify why that surface is wet, that is the job to do before any cleaning.
2. Protect yourself. Health Canada's stated minimum is safety glasses or goggles, a disposable well-fitting N95 respirator, and household disposable gloves. If N95 respirators are unavailable, it suggests a P100 or N100. A cloth mask is not on the list and does not substitute.
3. Isolate the room. Health Canada advises isolating the area with plastic sheeting and keeping susceptible people out. It identifies children, seniors, and people with conditions like asthma or severe allergies as more susceptible, so this is not a formality in a family home.
4. HEPA-vacuum before you start. Health Canada recommends vacuuming with a HEPA vacuum both before and after cleaning. Doing it first removes loose spores you would otherwise push around with a wet cloth.
5. Wash with detergent, not bleach. Warm water and unscented dishwashing detergent is the method. Baking soda or unscented soap works on walls; unscented soap and warm water on concrete. On drywall, use a damp cloth only, and resist the urge to soak the stain.
6. Remove rather than lighten. You are finished when the material is physically clean, not when the colour is gone. If the colour will not come out of a porous material, that material needs to go.
7. Dry it completely. CMHC calls rapid drying essential for mould prevention and recommends fans, heaters and dehumidifiers. A cleaned surface left damp is a cleaned surface you will clean again.
8. HEPA-vacuum again, then dispose of the kit. Gloves, mask, cloths and sheeting all go out. Reusing them moves the problem to the next room.
Humidity Control: The 30-to-50 Window and the Winter Trap
If you only do one thing after reading this, make it this one. Buy a hygrometer, put it in the basement, and keep the reading between 30 and 50 per cent. They cost very little, and they convert an argument about whether the basement feels damp into a number.
Run a dehumidifier in the basement year-round, with the windows closed. Health Canada's guidance says exactly that, and the windows-closed part is the instruction people get wrong most often. Opening a basement window on a warm, humid day does not dry the basement out. It imports water vapour directly onto the coldest surfaces in the house, where it condenses. The intuition that fresh air dries things is correct outdoors and backwards below grade in a Toronto summer.
That seasonal inversion is worth understanding in both directions, and we covered the warm-weather half of it in our guide to summer humidity in Toronto and preventing mould. It is the same physics running the other way — warm wet outdoor air meeting cool indoor surfaces, instead of warm wet indoor air meeting cold outdoor-facing ones.
Air movement matters as much as the dehumidifier. Health Canada's indoor air quality guidance recommends leaving interior doors open, keeping baseboards and heating vents clear of furniture, and keeping beds and furniture away from outside walls. Upstairs, it recommends using bathroom and kitchen fans and running the range hood on high with the back burner, which it says can reduce particles and gases by more than 80 per cent compared with slower speeds. Every litre of vapour you exhaust at the source is a litre that never reaches the basement wall. If you are also wondering what moving air through the ductwork does and does not accomplish in heating season, we looked at that separately in our article on duct cleaning in Toronto and winter indoor air.
Stop Testing. Start Fixing.
Mould testing is sold aggressively, and it is almost always the wrong purchase. Health Canada's Residential Indoor Air Quality Guideline on moulds, published in 2007, declines to set exposure limits at all, explaining that the large number of mould species and strains and the large inter-individual variability in human response preclude deriving them.
That has a direct consequence the guideline states outright: because there are no limits to compare against, air fungal test results cannot be used to assess risks to the health of building occupants. The consumer-facing page puts the same point in plainer language — in most cases there is no need to measure the actual concentration of mould in your indoor air, and no need to determine the species. It also notes there is no safe limit for mould, which is precisely why a number on a report would tell you nothing actionable.
The guideline's two recommendations are, in its own words, to control humidity and diligently repair any water damage in residences to prevent mould growth, and to clean thoroughly any visible or concealed mould growing in residential buildings. Both apply regardless of which species is present. Health Canada's overall position is that mould growth in residential buildings may pose a health hazard, with reported effects including eye, nose and throat irritation, coughing, phlegm build-up, wheezing, shortness of breath, worsened asthma and other allergic reactions.
So the money goes into a dehumidifier, a hygrometer and a drainage fix, not a lab report. The one exception is a dispute — with a landlord, an insurer, or a buyer — where documentation serves a purpose beyond informing your own decision.
Where the Water Gets In, and What Toronto Will Pay to Fix It
Cleaning mould is treating the symptom. If the cause is drainage or a sewer backup, Toronto will cover most of the cost of fixing it, and a surprising number of homeowners do not know the program exists.
The City's Basement Flooding Protection Subsidy Program pays up to $6,650 per property, at 80 per cent of the invoiced cost in every category. The current per-item maximums are a one-time home plumbing assessment up to $500; a backwater valve installation or replacement up to $1,600 per device, for up to two devices; a sump pump installation or replacement up to $2,250 for one device; a sump pump battery backup up to $300; and foundation drain, or weeping tile, severance and capping up to $400. Sump pump and backwater valve alarms are also listed as eligible work.
The dates matter. The expanded program took effect on 1 May 2026, and the expanded amounts apply to eligible work completed on or after 12 November 2025. For work completed before that date, a backwater valve was capped at $1,250 and a sump pump at $1,750, with no subsidy available for a plumbing assessment or a battery backup. The application deadline is two years after installation for work completed on or after 12 November 2025, and one year for earlier work.
Eligibility has real conditions attached. You must be the registered owner of a single-family, duplex, triplex or fourplex property in Toronto. Your eavestrough downspouts must already be disconnected from the sewer system, or you must hold a City exemption — and disconnecting the downspouts is not itself subsidised. Front yard paved areas, including parking pads, must meet the Zoning By-law. Your contractor and any sub-contractors must hold a valid City of Toronto business licence at the time the work is done. You must submit original electronic invoices marked paid in full, and you must have no outstanding taxes or debts owed to the City when the application is processed. Funding is first-come, first-served and subject to annual Council approval, so applying is not a guarantee.
If the basement is actively flooding, the City's own instructions are to shut off the power if water is near outlets or the electrical panel, avoid using drains if a sewer backup is suspected, and report it to 311 — which it says normally responds within four hours, with technicians working around the clock.
What a Cleaning Service Can Honestly Do About Basement Mould
It is worth being straightforward about the boundary here, because the industry often is not. Routine cleaning is prevention and early detection. It is not remediation, and anyone telling you otherwise about a large patch is selling you something.
What regular cleaning genuinely catches is the stage before the problem: the musty, earthy smell that Health Canada notes often indicates mould, before you have stopped noticing it; the condensation ring forming on a cold-water pipe; paint beginning to blister where moisture content is higher; the first grey bloom in the corner behind the storage shelf; the box that has gone soft at the bottom. Health Canada's list of places to watch is a useful cleaning checklist on its own — drywall, wood, ceiling tiles, wallpaper, carpets, wall cavities, basement subfloors and crawl spaces, plus the hidden locations behind walls, under carpets, under basement floorboards and in the HVAC system.
What it cannot do is a patch over three square metres, anything growing behind a finished wall, or anything after sewage has come up through a floor drain. Those need a remediation trade with containment equipment and training. A thorough deep clean of a basement is a genuinely useful thing — it clears the porous clutter off the floor, gets a HEPA vacuum into the corners, and puts eyes on every exterior wall — but it is honest work with honest limits.
Custom Maids Toronto has been working in this city's houses for more than 48 years, and the main thing that teaches you is which basements come back every single winter and which ones were fixed once and never mentioned again. The difference is almost never the cleaning. It is whether anyone traced the water. For the wider context on what professional cleaning does and does not cover, our complete guide to professional cleaning services in Toronto lays out the categories.
One detail of how we work matters more in a basement than almost anywhere else in a house: our clients supply the cleaning products, not us. Health Canada's method for mould calls specifically for unscented detergent, and a basement is a poorly ventilated room where whatever gets sprayed stays in the air you are breathing while you work. Because you choose the products, you control exactly what enters your home — which is the right arrangement for anyone with asthma, allergies, scent sensitivity, small children or pets.
A Toronto Basement Calendar
Mould prevention below grade is seasonal, and the work is different in each part of the year.
October, as the furnace comes on. Put a hygrometer in the basement. Check the cold-water pipes and the foundation wall behind any storage. Pull everything porous off the floor and away from the exterior walls now, before the wall starts sweating. This is the highest-value hour you will spend down there all year.
November through March. Dehumidifier running, windows closed. Watch the inside of the basement windows and the pipes for condensation, because those show the problem weeks before a wall does. Keep interior doors open so air can move.
During the January and February thaw cycles. This is when drainage failures reveal themselves. Snowmelt on frozen ground runs sideways instead of soaking in. Check that downspouts are discharging well away from the foundation, and not onto a sheet of ice that funnels the water straight back to the wall.
Spring, before the heavy rain. Book the plumbing assessment while contractors still have availability, and start the subsidy application if a backwater valve or sump pump is the answer. Grading and eavestrough work is spring work.
Summer. The dehumidifier stays on and the windows stay shut. This is the season when the instinct to air the basement out does the most damage.
Sources and Research
Federal health guidance in this article comes from three Health Canada sources, all consulted directly. The consumer guidance on humidity, moisture and mould supplied the 30 to 50 per cent relative humidity range, the small, medium and extensive patch thresholds, the recommendation against bleach, the water-and-dish-detergent method, the HEPA vacuuming and personal protective equipment requirements, and the statement that there is no need to measure mould concentrations in indoor air (Health Canada, Mould). The 48-hour growth window, the porous and non-porous material lists, the instruction not to use bleach, the damp-cloth method for drywall and the basement-specific moisture sources come from the departmental guide to addressing moisture and mould indoors (Guide to addressing moisture and mould indoors, PDF).
The position that exposure limits cannot be derived, that air fungal test results cannot be used to assess occupant health risk, and the formal recommendations to control humidity and clean visible or concealed growth are taken from the Residential Indoor Air Quality Guideline: Moulds (2007). Ventilation, dryer venting, range hood performance and the advice on furniture placement relative to exterior walls come from Health Canada's guidance on improving indoor air quality in your home.
Drying timelines, the 48-hour discard rule for materials that will not dry, the 30-centimetre drywall removal line above a flood level, and the foundation grading and sealing recommendations are from the Canada Mortgage and Housing Corporation's Mould in Housing guidance.
All Toronto-specific figures are the City's own. Subsidy amounts, eligibility conditions and the November 2025 and May 2026 dates come from the Basement Flooding Protection Subsidy Program page. The causes of basement flooding, the 311 response commitment and the bleach-and-water flood cleanup mix come from the City's basement flooding pages. The four-square-metre routing between Toronto Public Health and Municipal Licensing and Standards, the Chapter 629 Section 27.C reference, the list of property standards deficiencies and the instruction to notify the owner in writing come from the City's 311 guidance on property standards and mould and on mould cleanup thresholds and contacts. No figure in this article is an estimate, and nothing here is drawn from a commercial remediation source.
A Word from Custom Maids Toronto
(Sponsor of the Article)
For more than 48 years, Custom Maids Toronto has cleaned homes across this city through every kind of winter it can produce. We know which rooms the damp finds first, and we know that a basement is usually telling you something about water long before it is telling you anything about cleaning.
Our clients supply the cleaning products, which means you decide precisely what gets used in the least-ventilated room in your house. For anyone managing asthma, allergies, scent sensitivity, young children or pets, that is not a small detail — it is the whole point.
If your basement needs the kind of thorough, methodical attention that gets a HEPA vacuum into the corners and eyes on every exterior wall, get in touch with Custom Maids Toronto and we will talk through what your home actually needs.
Frequently Asked Questions
Does bleach kill basement mould?
Not in any way that solves your problem. Health Canada says plainly not to use bleach to clean up mould and that there is no need for it, recommending warm water and unscented dish detergent instead. Bleach is mostly water, so on a porous material it soaks the substrate while removing the pigment from the surface colony. The stain disappears and the mould does not. The City of Toronto does recommend a bleach-and-water solution, but in the context of disinfecting after a flood, where the hazard is sewage contamination rather than mould.
My basement smells musty but I cannot see any mould. Is that still a problem?
Yes, and it is worth taking seriously. Health Canada notes that a musty or earthy smell often indicates mould, and that mould frequently grows where no water is visible — behind walls, under carpets, under basement floorboards, in wall cavities and in the HVAC system. Dampness inside a material is enough for growth. Start with a hygrometer rather than a demolition plan: if the relative humidity down there is above 50 per cent, you have found your first problem regardless of what is or is not visible.
How much basement mould can I safely clean myself?
Health Canada's guidance is that you can generally clean small and medium areas yourself: up to three patches each under one square metre, or patches between one and three square metres. Above three square metres it recommends professional help. The City of Toronto draws its professional line at four square metres and advises household cleaner for a square metre or less. The overriding test is recurrence — if mould comes back after you clean it, Health Canada says get professional help, because an unfound moisture source is the real problem.
Should I pay to have my air tested for mould?
In almost all cases, no. Health Canada's Residential Indoor Air Quality Guideline states that exposure limits cannot be derived for mould, and that air fungal test results therefore cannot be used to assess risks to occupant health. Its consumer guidance says there is usually no need to measure concentrations or identify species. The money is better spent on a dehumidifier, a hygrometer and finding the water. Testing has a role in a dispute with a landlord, an insurer or a buyer, where the point is documentation rather than decision-making.
Can a mouldy mattress, sofa or box of papers stored in the basement be saved?
Generally not. Health Canada's position is that porous materials such as fabrics often cannot be properly cleaned and must be discarded, and it names mattresses, bedding, carpets, sofas, pillows, stuffed toys, paper and cardboard products, and clothing with active mould growth. Only non-porous materials — glass, metals, leather, plastics, vinyl, tile and hard surfaces — can genuinely be cleaned. It is an expensive answer, but surface-cleaning a mouldy mattress leaves the colony intact inside the foam.
Why does my basement seem to get worse when I open the windows?
Because on a warm, humid day you are importing water vapour and delivering it onto the coldest surfaces in your house. Warm air holds far more moisture than cold air, so outdoor summer air entering a cool basement condenses immediately on the foundation walls and pipes. Health Canada's advice is to run a dehumidifier in the basement year-round with the windows closed. Ventilation does help, but it needs to be mechanical, and it needs to exhaust moisture outward rather than draw humid air in.
My landlord will not deal with mould in my unit. What can I do in Toronto?
Start by notifying the superintendent, the property and the owner in writing, which the City specifically advises — a written record is what makes everything after it work. For mould larger than four square metres in a rental unit, contact Toronto Public Health at 416-338-7600. For smaller areas, Municipal Licensing and Standards addresses it as marks and stains under Chapter 629, Property Standards, Section 27.C. The City will also look at the underlying deficiencies: broken or blocked heating and ventilation, moisture entering through floors, walls, windows, ceilings or roofs, and faulty plumbing.
I have asthma. Is it safe for me to clean basement mould myself?
Health Canada identifies people with conditions like asthma or severe allergies, along with children and seniors, as more susceptible to mould, and its guidance is to keep susceptible people out of the room during cleanup rather than to equip them for it. Reported effects include worsened asthma, wheezing and shortness of breath. If the cleaning does fall to you, the stated minimum protection is safety glasses or goggles, a well-fitting disposable N95 respirator and disposable gloves, with the area isolated by plastic sheeting. This is general information rather than medical advice, and anyone managing a respiratory condition should take direction from their own healthcare provider on whether to do this work at all.
Will a dehumidifier on its own fix a mould problem?
It will fix a condensation problem, which is the most common cause of basement mould in Toronto and the one people least suspect. It will not fix a leak, a drainage failure or a sewer backup — those need the water stopped at the source, and the City subsidises most of the cost of the plumbing side of that work. A dehumidifier also does nothing about mould that already exists. Health Canada's two instructions run together rather than separately: control the humidity and repair the water damage, and clean the growth thoroughly.
