‍

Calgary’s summer storms are quick, fierce, and often unpredictable. They roll in fast, bring heavy rain, and disappear just as quickly leaving behind soggy lawns, damp corners, and sometimes, a musty-smelling basement.

If you’ve walked downstairs after a storm and noticed a persistent damp or earthy odour, you’re not alone. Musty smells in the basement are one of the first warning signs that moisture is seeping into your home and your plumbing or drainage system may be to blame.

Today we will help you understand what causes that smell, what it might mean for your home, and how Calgary homeowners can prevent water damage and mould before it becomes a serious problem.

What causes a musty basement smell after a storm?

A musty smell is almost always caused by excess moisture and poor air circulation, both of which are common after a heavy summer rain. That scent is typically mould or mildew forming, either on exposed surfaces or hidden behind walls and floors.

‍

In Calgary, this is often triggered by:

• Water seepage through foundation cracks
  
  
• A malfunctioning or overwhelmed sump pump
  
  
• Clogged or broken downspouts and exterior drainage
  
  
• Leaking basement windows or window wells
  
  
• Poor ventilation in older homes

‍

Over time, if the source of moisture isn’t found and fixed, this smell turns into mould growth, which not only damages property but can trigger respiratory issues, especially for children or people with allergies.

How do I know if the smell is from plumbing or stormwater?

It can be hard to tell if the musty smell is from stormwater intrusion or a plumbing-related issue, but here’s how to narrow it down:

• Did the smell appear right after a storm? It’s likely weather-related,especially if your yard pooled water or if gutters overflowed.
  
  
• Do you hear running water or dripping sounds? This could point to leaking pipes, a sump pump issue, or a cracked drain.
  
  
• Is the smell worse near floor drains or laundry areas? Your sewer system may be backing up or slow-draining after the storm.
  
  
• Do basement walls feel damp or cold to the touch? Water may be entering through porous concrete or unsealed cracks.
  

If you’re unsure, a licensed plumber in Calgary can use moisture meters and drain cameras to identify the source within minutes.

What should I do immediately when I smell damp or mustiness?

1. Ventilate the basement

Open windows, run fans, and use a dehumidifier to reduce humidity levels. A dehumidifier is especially important in the summer when Calgary’s humidity can rise suddenly after rain.

2. Check your sump pump

Make sure it’s plugged in, operational, and not clogged. Pour water into the pit to see if it activates. If it doesn’t, call for service immediately.

3. Inspect for visible water or leaks

Look behind furniture, in corners, and around appliances for damp spots. Lift rugs and check baseboards.

4. Use a mould-killing cleaner

Clean visible spots with vinegar or a non-toxic mould remover. Avoid bleach unless used cautiously and only on hard surfaces.

5. Call a plumber if you suspect water entry

Even if you can’t see it, water can pool behind walls or under flooring. Early intervention is far less costly than full remediation.

Could my sump pump be the problem?

Absolutely. Your sump pump is your home’s last defence against a flooded basement during summer storms. In Calgary, where sudden downpours are common, your sump pump must be able to:

• Handle sudden water volume increases
  
  
• Pump out stormwater quickly
  
  
• Operate even during power outages (ideally with a backup battery system)

If the musty smell started shortly after a storm and your sump pump didn’t engage or struggled to keep up it may be time for service or replacement.

What if my basement only smells sometimes?

Intermittent musty smells are a red flag. It may mean that moisture is entering and evaporating, leaving behind mould spores that become active only when humidity rises again. This pattern often suggests:

• Small, seasonal leaks
  
• Poor drainage near the foundation
  
• Plumbing vents or drains backing up under pressure
  
• A failing backwater valve (especially in older Calgary homes)

This is a sign your basement isn’t fully sealed or protected from external moisture and you’ll want a professional to investigate before structural damage occurs.

How can I prevent the musty smell from returning?

To stop this problem at the root, focus on waterproofing drainage, and ventilation. Here’s what Calgary homeowners should prioritize:

1. Clean out gutters and downspouts before every summer storm season
   
   
2. Extend downspouts at least 6 feet from the house
   
   
3. Ensure the yard slopes away from your foundation
   
   
4. Install or maintain a sump pump with backup power
   
   
5. Seal cracks in the foundation with waterproof epoxy
   
   
6. Upgrade to a proper backwater valve
   
   
7. Keep a dehumidifier running in humid months (aim for under 50% humidity)
   
   
8. Book a professional plumbing inspection every year‍

These steps are not only preventative, they can help preserve your home’s value and reduce health risks from mould exposure.

How can ERM Plumbing and Heating help you?

At ERM Plumbing and Heating, we offer maintenance services that keep your home in top shape all year long. Our expert technicians are trained to identify potential issues before they turn into costly problems.

We offer a range of maintenance packages, including annual checkups that cover everything from air filter replacement to thorough inspections of your heating system. 

‍