Why Vancouver Garages Grow Mould
Mould needs three things: moisture, moderate temperature, and organic material to eat. A Vancouver garage supplies all three almost year-round, which is why this is the single most common problem we're called out for in the city.
- Moisture: roughly 1,200 mm of rain a year over more than 160 wet days, high winter humidity, and — in most garages older than the 1970s — a slab poured without a vapour barrier that wicks ground moisture upward continuously.
- Temperature: Vancouver winters rarely freeze hard. An unheated garage sits in the 2–12°C band for months — cool enough that nothing dries, warm enough that growth never stops.
- Food: cardboard, paper, wood framing, drywall paper facing, fabric, leather, camping gear. In a dry climate these are inert storage. Here they're substrate.
That's worth internalising because it changes how you think about the fix. Mould in a Vancouver garage is not a cleanliness failure — it's the default outcome of the climate acting on an unheated, unventilated room full of organic material. Killing the visible growth without changing the moisture picture just schedules the rematch.
Identifying It: Mould vs. Efflorescence vs. Dirt
Vancouver homeowners misdiagnose this in both directions — panicking over harmless mineral deposits, and ignoring real mould because "it's just that white concrete stuff." Two minutes with a spray bottle settles it.
| Test | Mould | Efflorescence | Dirt / exhaust film |
|---|---|---|---|
| Spray with water | Stays put, may smear | Dissolves and disappears | Runs or smears grey |
| Colour | Black, green, white, grey, pink, orange | White or grey-white only | Uniform grey-brown |
| Texture | Fuzzy, spotty, filamentous | Crystalline, powdery, gritty | Flat film |
| Where it appears | Any surface, loves organic material | Concrete and masonry only | Everywhere, evenly |
| Smell | Musty, earthy | None | None |
| Pattern | Patches, worst in damp corners | Follows water paths through the slab or wall | Worst near the door |
One nuance: efflorescence and mould are answers to the same question. Efflorescence proves water is moving through your concrete. It's harmless in itself, but the moisture it advertises is exactly what mould needs — so treat it as an early warning, not a cosmetic annoyance. There's a fuller breakdown on our garage floor cleaning page.
The Six Places It Hides
Visible mould is usually the minority of what's actually there. If any of these describe your garage, check them first — in order of how often we find growth:
- Behind anything stacked flat against an exterior wall. No airflow, condensation trapped, never inspected. The single most common hiding spot.
- Inside cardboard boxes on the floor. The box wicks slab moisture; the contents mould from the inside out.
- The lower 60 cm of drywall. Wicking from the slab keeps the paper facing — mould's favourite food — damp from behind.
- The north-facing wall. Never gets sun, never dries. On sloped North Shore lots, the uphill wall doubles this effect.
- Under floor-stored fabric and carpet. Gym mats, area rugs, moving blankets — each one a moisture trap with a food supply.
- The garage-side face of the house door and its frame. Warm house air meets cold garage air and condenses right there.
The Health Question, Honestly
Health Canada's position is clear enough to repeat plainly: indoor mould exposure is associated with eye, nose and throat irritation, coughing and phlegm, wheezing and shortness of breath, and worsened asthma symptoms — with children, older adults and people with existing respiratory conditions most affected. There is no established "safe" species or amount of indoor mould; the advice is simply to fix moisture problems and remove growth.
The garage-specific point: an attached or under-house garage shares air with your home. Air moves through the connecting door every time it opens, and through service penetrations and shared framing when it doesn't. A mouldy detached lane garage is mostly a property problem. A mouldy under-house garage beneath a bedroom — the standard Vancouver Special configuration — is an indoor air quality problem, and worth treating with more urgency.
What You Can Safely Clean Yourself
A sensible DIY boundary, consistent with what Canadian public health guidance suggests for small areas:
- Small patches — under about a square metre — on hard surfaces. Sealed concrete, metal, glass, plastic. Wash with warm water and dish detergent, dry thoroughly, done. Wear gloves, eye protection and a mask, and open the garage door while you work.
- Mouldy items that are cheap to replace: don't clean them, bag and bin them. A $4 mouldy cardboard box is not a restoration project.
- Washable fabrics: hot wash, full dry, then store them somewhere that isn't a damp garage floor.
What Not to Do
- Don't bleach porous surfaces. The most common and most understandable mistake. On bare concrete, wood or drywall, bleach kills surface growth and whitens the stain while the root structure survives deeper in the material — the patch returns in weeks looking "cleaned" the whole time. Detergent and water does as well on surfaces bleach can help, and nothing rescues the surfaces it can't.
- Don't dry-brush or dry-scrape. That aerosolises spores into air you're breathing. Damp methods only.
- Don't paint over it. Stain-blocking paint over live mould is a cosmetic delay, and it makes the eventual proper fix harder to see and bigger.
- Don't keep mouldy drywall or insulation. These can't be reliably cleaned. Affected sections need cutting out — which is also the point where the job stops being DIY.
- Don't clean and close the door. A cleaned, still-damp garage sealed shut regrows fastest of all. Drying and airflow are part of the job, not an afterthought.
When to Call Someone — and Whom
Call a professional when any of these is true:
- The affected area is bigger than about a square metre
- Drywall, insulation or framing is involved
- You've cleaned it and it came back — the moisture source is still active
- There's a musty smell you can't find the source of
- The garage shares air with living space and anyone in the house has asthma or respiratory issues
And know which professional. A garage cleaning company — us, on our Vancouver garage cleaning service — treats surface growth with substrate-appropriate products, removes contaminated materials, force-dries the space, and identifies where the moisture is entering. A certified mould remediation contractor handles contamination inside wall assemblies, HVAC systems and living spaces, with containment and air scrubbing. If we open up your garage and find the problem goes into the wall cavity, we tell you and refer you — pretending otherwise would be doing you a disservice at your expense.
Preventing It From Coming Back
Every one of these attacks the moisture leg of the triangle, which is the only leg you control:
- Nothing porous on the slab. No cardboard, fabric or bare wood on the floor — sealed bins on raised shelving. This alone eliminates the most common growth sites.
- Air gap behind everything. Pull shelving and stored items a few centimetres off exterior walls so air can move.
- Fix the water paths. Door seal, downspout discharge, grading at the apron, the uphill wall on sloped lots. Our cleans come with a written list of the entry points we find.
- Ventilate. Even passive vents help; a cheap humidity-triggered exhaust fan helps more. Target is keeping relative humidity under about 60%.
- Dry wet gear before it goes in. A dripping wetsuit or soaked tent in a closed garage is a humidifier with extra steps.
- Clean before the rains, not after. An autumn clean means entering the wet season with nothing for mould to colonise. Spring cleans repair; autumn cleans prevent.
If the storage side of that list is the sticking point, that's exactly what our garage organization and storage solutions services exist for — damp-climate design is the whole premise.