Odour Inspection: Find the Source of a Musty Smell

An odour inspection is a diagnostic air quality assessment that identifies the source of a persistent smell in a building. We test the air, look for the moisture conditions that let mold grow, and report what we find with lab-verified results.

The key word is diagnostic. Plenty of companies will deodorise a space, fog it, or run an ozone treatment. That addresses the smell you can perceive. It does nothing about the thing producing it, which is why the smell tends to come back a few weeks later once the masking agent wears off.

Our inspectors approach it the other way around. If there’s a musty odour, something is generating it, and that something almost always involves moisture. Find the moisture, and you’ve found the real problem. The smell is just how the building told you about it.

A typical inspection covers the affected area and a control comparison, uses calibrated sampling equipment, and produces a written report you can act on. If you want the full step-by-step, we’ve documented what to expect during an air quality inspection start to finish.

Mold smells musty, earthy, or damp. Most people describe it as the smell of an old book, a wet basement, or a forgotten gym bag. Some notice a slightly sweet or sharp edge to it.

Here’s the part most homeowners never get told: you’re not smelling mold itself. You’re smelling microbial volatile organic compounds, or MVOCs. These are gases mold releases while it’s actively growing and metabolising. Your nose picks them up at remarkably low concentrations, often long before there’s anything visible to see.

That’s genuinely useful information. It means a musty smell is frequently an early signal rather than a late one. The mold might be small, hidden, or just getting started.

Because the growth is somewhere you can’t look. In our experience, hidden mold is more common than visible mold in odour complaints, and it usually sits in one of a handful of places.

Wall cavities are the usual suspect, especially on exterior walls or anywhere a plumbing line runs. A slow supply-line weep behind drywall can feed growth for months without ever showing a stain on the painted side. Subfloors are another, particularly under vinyl or laminate where a spill or appliance leak got trapped between layers.

Then there’s the HVAC system, which deserves special mention because it’s the one that fools people. If growth is established on a coil, in a drain pan, or inside ductwork, the system distributes those MVOCs through the whole house every time it runs. The homeowner smells it in three different rooms and concludes the problem is everywhere. It isn’t. It’s in one place, being broadcast.

Crawl spaces, the cavity under a bathtub, the back of a vanity, behind a finished basement stud wall. We’ve found growth in all of them. None were visible without opening something up, and that’s precisely why sampling the air is more reliable than trusting your eyes.

We combine air sampling with a moisture-focused walkthrough. Air samples tell us what’s airborne and at what concentration. The walkthrough tells us where the conditions for growth exist.

Air sampling uses a spore trap, a cassette that draws a measured volume of air across an adhesive slide. That slide goes to an accredited laboratory, where an analyst counts and identifies what’s on it. Results come back as spores per cubic metre, and for culturable samples as CFU per cubic metre (colony forming units).

Alongside sampling, our inspectors check relative humidity, look for temperature differentials that cause condensation, and use moisture meters on suspect surfaces. The sampling methods and lab standards behind all of this follow IICRC S520 and IAQA guidance, and our inspectors hold both certifications. Once the lab results come back, understanding what your air quality test results mean is its own subject, and we’ve written that up separately.

Mildew is a type of mold, so the distinction people draw between them is mostly about appearance rather than biology. Mildew usually grows flat, looks powdery, and shows up white or grey on damp surfaces like grout and window sills. What most people call “mold” is the fuzzier, darker, more established growth.

Both smell musty. Both need moisture. Mildew is generally easier to deal with because it sits on the surface where you can see and reach it, while the growth behind a wall is the one that needs sampling to confirm.

Not every musty smell turns out to be mold, though, and we’d rather say that plainly than let you assume otherwise. We’ve been called out to homes where the odour traced back to a floor drain that had dried out, a damp crawl space with no growth yet, old carpet underlay holding moisture, or a stagnant sump. Those are real findings and they’re worth knowing, because the fix is completely different and usually cheaper.

If our sampling comes back clean, that’s what the report says. A negative result is still a useful result. It rules out the expensive possibility and points you somewhere else.

Book one when a smell persists after cleaning and airing out the space, or when it keeps returning. A one-off odour that clears with ventilation usually isn’t worth testing. A recurring one is.

• The smell showed up after water damage, a leak, or spring flooding.
• Someone in the house has respiratory symptoms, congestion, or worsening allergies that ease when they leave the building.
• You’re buying the property and noticed it during a viewing.
• It’s concentrated in one room, which usually means the source is close by.

Seasonal timing matters more here than people expect. Across Ontario and Quebec, we see odour complaints cluster in a few predictable windows. Spring thaw drives groundwater up against foundations and basements start smelling in March and April. Summer humidity plus air conditioning creates condensation on cold surfaces. And when heating starts in the fall, warm dry air moving through the building pulls MVOCs out of cavities that had been quiet all summer.

If the smell is specifically musty and you already suspect the cause, mold testing may be the more direct route. Odour inspection is the better starting point when you genuinely don’t know what you’re dealing with.

You get a written report with your lab results, what they mean, where we found the source, and what we recommend doing about it. Same-day reporting is available.

The report includes the sampling locations and methods used, the laboratory analysis with indoor and outdoor comparisons, an interpretation in plain language rather than raw data you’d have to decode yourself, and specific recommendations. If there’s a moisture source driving the problem, it’s identified in the report, because fixing the growth without fixing the water just resets the clock.

We write these so they’re usable by someone who isn’t an air quality professional. If you’re a homeowner deciding what to do next, a landlord documenting a tenant complaint, or a buyer negotiating on a property, the report should be able to stand on its own. Buyers and sellers in particular find this matters, which is why we cover air quality testing for real estate transactions as its own topic.

Should the results point to mold that needs removing, we’ll tell you what the report supports. We don’t do remediation ourselves. If you want to understand what that work involves before you get quotes, there’s useful background on professional mould removal worth reading first.

Air quality testing in Canada generally runs between CAD 300 and CAD 1,500. Where a specific inspection lands depends on the size of the property, how many samples are needed, and how much investigation the situation calls for.

A single-room complaint in a condo needs fewer samples than a whole-house investigation in a century home with a fieldstone basement. Lab analysis is charged per sample, so sample count is the main driver of the number. Properties with multiple affected areas, or where the source isn’t obvious after the first walkthrough, sit at the higher end.

We’ll give you a price before we book, not after we’ve finished. If you want the full breakdown of what moves the number, we’ve written up what air quality testing costs in Canada with the variables laid out.

We cover Ontario and Quebec, with inspectors working out of the Ottawa and Montreal regions.

Our regular service areas include Ottawa, Montreal, Gatineau, Kingston, Carleton Place, Brockville, Belleville, and Cornwall, along with the surrounding communities. If you’re outside those, call and ask. We travel further than the list suggests, and the answer depends on scheduling more than distance.

You can find your closest coverage area on our service area pages, each with local booking details.

If something in your home or building smells wrong and you can’t find why, that’s worth a call. Our inspectors are IICRC and IAQA certified, we’ve completed over 15,000 inspections since 2005, and we’ll tell you what we actually find.

📞 Call 1-866-528-2897

Monday to Friday, 8:00 AM to 3:00 PM. Or book an inspection online and we’ll get back to you with available times.