How Mold Can Spread Through Shared Walls in Semi Detached Homes

Posted in Mold Removal, on June 17, 2025

Mold is a serious issue in any home, but in semi-detached properties, it poses an even greater risk due to shared walls. Moisture and mold in one unit can easily affect the neighbouring unit, especially when insulation, ventilation, or building materials are compromised. Many homeowners are surprised to discover that water damage in Toronto homes next door can lead to their own mold problems. In these cases, early detection and professional mold removal in Toronto are essential to prevent long-term damage. If your neighbour's water damage or mold is affecting your property or if you're looking to avoid water damage from affecting your neighbour, contact Canada's Restoration Services to learn more about our water damage cleanup services and IICRC-certified mold removal in Toronto. 

Here is what you should know about how mold damage can affect your neighbours in semi-detached homes in the Greater Toronto Area. 

How Mold Can Transfer Through Shared Walls

In semi-detached homes, the dividing wall (called a party wall) is meant to separate the two units. However, this wall doesn't always provide a perfect barrier against moisture or airflow. If your neighbour experiences a leak, plumbing failure, or poor ventilation, the resulting humidity or water damage in Toronto can seep into your side, especially if the shared wall isn't well-sealed or lacks a proper vapour barrier. If you notice signs of water damage on the party wall, it's important to act fast and contact the Canada's Restoration Services team, which specializes in remediation of water damage in Toronto and mold removal services. 

Here are a few common ways mold can transfer between attached homes:

Moisture Through Porous Materials

Drywall, insulation, and even wood framing can absorb moisture. If your neighbour has a leak that soaks their wall cavity, the dampness can slowly migrate through the shared structure, feeding mold growth on your side without you realizing it.

Poorly Sealed HVAC or Ventilation Systems

Sometimes, semi-detached homes share parts of a ventilation system or have exhaust fans that are not properly vented outside. This can allow humid air and mold spores from one unit to enter the other, especially if there are gaps or leaks in the ductwork.

Roof or Foundation Leaks

A roof or foundation leak near the party wall can result in water pooling along the entire dividing structure. If only one homeowner takes action, the moisture can remain in the wall and allow mold to spread into the other unit. Unfortunately, what starts as water damage in Toronto on one side can escalate into a shared mold problem.

Signs Your Neighbour's Mold Problem Is Affecting Your Home

If your neighbour has confirmed mold or visible water damage, it's essential to stay alert for symptoms that it's spreading into your space. 

Here are some signs to watch for:

• Musty odours near the shared wall: A damp, earthy smell that wasn't there before can indicate mold inside the wall cavity.
• Staining or discolouration: Yellow, brown, or dark patches on walls, especially near the party wall, could mean mold is growing beneath the surface.
• Peeling paint or bubbling drywall: These signs often appear after moisture has already started spreading.
• Health symptoms: If you or your family are experiencing respiratory issues, headaches, or allergy-like symptoms only when at home, airborne mold spores might be the cause.

If you notice any of these signs, don't wait to investigate. Book a mold inspection with Toronto's leading mold remediation company, Canada's Restoration Services. The sooner you act, the easier it will be to stop the spread and protect your home.

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