7 Warning Signs You Have Mold in Your Home (And What to Do Next)

Mold is patient. It grows in the dark, behind walls, under floors, and inside attics for months before most homeowners notice anything at all. By the time it becomes visible, or starts causing health symptoms, it's often been there for a long time. In Coquitlam's wet coastal climate, where homes see over 1,700 mm of rain per year, mold risk is higher than in almost any other region of Canada.

The good news: mold almost always leaves clues. If you know what to look for, you can catch it early, before it spreads to structural framing, before your family is breathing spores for months, and before it tanks a real estate deal. Here are the seven most reliable warning signs, ranked from most obvious to most overlooked.

The Short Answer: Trust Your Nose First

If you consistently notice a musty, earthy, or damp odour in a room or area of your home, even when it looks completely clean, treat it as a mold signal until proven otherwise. Smell is often the first and most reliable indicator of hidden mold growth. The seven signs below will help you build a clearer picture.

Sign 1: A Musty Smell That Doesn't Go Away

Mold produces metabolic byproducts called microbial volatile organic compounds (mVOCs). These compounds have a distinctive musty, earthy smell. Think old books, wet wood, or a damp basement. The smell is strongest near the mold source but can travel through HVAC systems, crawl space venting, and ceiling penetrations to other areas of the home.

What makes the smell diagnostic is its persistence. If airing out the house or running an air freshener temporarily masks it, but the smell keeps coming back, that's mold, not general stuffiness. Pay particular attention to:

• Basement and crawl space areas, especially after rain
• Bathrooms, particularly around the toilet base, vanity cabinet, and behind the shower
• Under kitchen sinks and around appliances with water lines
• Upstairs bedrooms and ceiling areas (often a sign of attic mold)
• HVAC vents (mold inside ductwork or near the air handler can spread the smell throughout the whole house)

Sign 2: Visible Discolouration on Walls, Ceilings, or Grout

Not all mold is black. Mold can appear white, grey, green, yellow, brown, or black depending on the species and the surface it's growing on. Common locations for visible mold in Coquitlam homes include:

• Bathroom grout and caulk (white or black fuzzy growth)
• Ceiling corners in bathrooms and kitchens
• Drywall near windows or exterior walls, especially basement windows
• Around window frames and sills
• The underside of bathroom vanity cabinets
• Behind and under refrigerators

A mistake a lot of homeowners make: assuming surface mold is the whole problem. If you can see mold on a wall surface, there is almost certainly more growing on the back side of the drywall. The paper backing is a perfect food source. What looks like a small patch on the surface can mean a large colony behind the wall. If you see any dark or discoloured growth that reappears after cleaning, stop cleaning it and get a professional mold assessment instead.

Sign 3: You've Had Water Damage in the Past

Mold can begin colonizing a wet surface within 24 to 48 hours. If your home has ever experienced water damage (a burst pipe, appliance leak, roof intrusion, window leak, or flooding) and wasn't professionally dried and inspected, there's a real chance mold is already growing somewhere.

This is especially true if you handled the drying yourself. A towelled-up puddle and a fan running for a few days rarely dries the inside of wall cavities or the subfloor beneath. Those are exactly the spots where mold takes hold. Water always finds its way into the lowest point.

Visual clues to look for in the aftermath of water damage: brown or yellow staining on ceilings and walls (even if the original leak was repaired), soft or spongy drywall, and warping at the base of walls or cabinets. These all suggest moisture has been trapped. A professional mold inspection with thermal imaging can identify hidden moisture pockets without opening walls and confirm whether mold has already started growing.

Sign 4: Respiratory Symptoms That Clear Up When You Leave

This is one of the most reliable signs of hidden mold, and honestly one of the most overlooked. Mold spores are airborne, and prolonged exposure in an enclosed space can cause or worsen a range of symptoms including:

• Nasal congestion and runny nose
• Chronic coughing or throat irritation
• Wheezing or shortness of breath
• Watery or itchy eyes
• Unexplained headaches
• Fatigue that doesn't improve with rest
• Skin irritation or rashes

The key question: do these symptoms improve noticeably when you spend time away from home, say at work, on vacation, or staying somewhere else? If yes, the source is likely in your home environment. Children, the elderly, and anyone with asthma or a compromised immune system are particularly vulnerable and may show symptoms at lower spore concentrations than healthy adults.

If health symptoms are present and you've ruled out other causes, don't wait for visible mold to appear. An indoor air quality assessment can measure spore levels throughout your home and identify elevated concentrations before any visible growth is apparent.

Sign 5: Peeling Paint, Bubbling Wallpaper, or Warped Trim

Paint and wallpaper peel or bubble when moisture is pushing through from behind the wall surface. In most cases, that means moisture is trapped inside the wall cavity, which is exactly the environment mold needs. Unless the peeling is happening on an exterior-facing wall that's obviously old and sun-damaged, treat unexplained paint failure as a moisture signal.

Similarly, watch for baseboard trim and door frames that are warping, swelling, or separating from the wall at the base. Ground-level warping often points to moisture wicking up from a wet subfloor. It's a common result of slow leaks under sinks or appliances that went unnoticed for a long time.

Sign 6: Your Home Was Built Before 1995

Many homes in Coquitlam and the broader Metro Vancouver area were constructed during the 1970s through early 1990s with building practices that are now known to promote moisture intrusion. The most notable example: the BC leaky condo crisis, which affected tens of thousands of units built primarily between 1982 and 1999. But single-family homes from the same era share many of the same vulnerabilities:

• Inadequate or non-existent crawl space vapour barriers
• Bathroom fans vented into attic cavities instead of through the roof
• Older window and door seals that have degraded over time
• Minimal attic ventilation by modern standards
• Plumbing materials (poly-B, galvanized steel) prone to slow leaks

If your home was built before 1995 and has never had a professional moisture assessment, scheduling one is worthwhile even if you haven't noticed any symptoms. Mold discovered proactively is dramatically cheaper and easier to fix than mold found during a home sale inspection, or after health symptoms have been going on for months.

Sign 7: You Haven't Checked Your Crawl Space or Attic in Years

Crawl spaces and attics are where the majority of undetected mold problems in Coquitlam homes are found. They share two characteristics that make them ideal for mold growth: high moisture exposure and minimal human attention. If you can't remember the last time you looked inside your crawl space or attic, or if you've never had either professionally inspected, they deserve a look.

In crawl spaces, the primary cause is high groundwater and inadequate vapour barrier coverage. In attics, it's almost always ventilation failure, specifically bathroom exhaust fans that terminate inside the attic space instead of through the roof.

Neither of these problems produces obvious symptoms in the living space until the mold colony is very large. By the time you smell it upstairs or notice soft flooring, you may be dealing with years of accumulated growth on structural framing.

What to Do If You've Spotted These Signs

The single most important rule: don't disturb visible mold before you understand the scope of the problem. Scrubbing, sanding, or spraying visible mold without proper containment releases spores into the air and can spread contamination to areas of the home that were previously unaffected. Here's the right sequence:

1. 1

   Document what you're seeing (or smelling)

   Take photos and note exactly where the signs are occurring: which rooms, which surfaces, how long it's been happening. This information helps the inspector understand the scope before they arrive.

2. 2

   Book a professional mold inspection

   A certified IICRC inspector will perform a visual survey, thermal imaging scan, and collect air and surface samples. This tells you the species involved, the extent of growth, and the moisture source. Those are the three things you need to know before any work begins.

3. 3

   Get a written scope of work with a fixed price

   A reputable remediation company gives you a written remediation plan and fixed price before starting. No estimates that balloon after demo begins.

4. 4

   If applicable, notify your insurer

   If the mold was caused by a sudden water event like a burst pipe or appliance failure, call your insurer promptly. Most policies require notification within a reasonable timeframe of discovering the damage.

Frequently Asked Questions