Why is there mold growing behind my new kitchen cabinets on an exterior wall?

Mold behind new kitchen cabinets on an exterior wall is almost always caused by moisture infiltration from outside or condensation due to inadequate vapor barriers and insulation. This is unfortunately common in Vancouver's wet climate, especially in older homes or when proper moisture management wasn't addressed during the renovation.

The most likely culprits are water penetration through the building envelope or condensation forming when warm, humid indoor air meets the cold exterior wall. In Metro Vancouver, exterior walls face significant moisture challenges from our 1200mm+ annual rainfall, and kitchens generate substantial humidity from cooking and dishwashing. When cabinets are installed directly against an exterior wall without proper moisture management, you create the perfect conditions for mold growth.

Common causes include inadequate or damaged vapor barriers behind the drywall, missing or insufficient insulation creating thermal bridging, exterior water infiltration through compromised siding or windows, or poor ventilation allowing humidity to accumulate. Many Vancouver homes built before 1980 lack proper vapor barriers entirely, and even newer homes can have installation gaps. If your renovation didn't address the wall assembly properly, moisture can migrate through the wall and condense on the cooler exterior side.

Vancouver's climate makes this particularly problematic because our mild, wet winters create ideal conditions for condensation. The temperature differential between heated indoor spaces and cool exterior walls, combined with high humidity from rain and cooking, creates a perfect storm for mold growth. This is why the BC Building Code emphasizes proper rain screen assemblies and vapor control layers.

You need professional assessment immediately because mold remediation requires proper containment and safety protocols under WorkSafeBC guidelines. A qualified contractor should inspect the wall assembly, identify the moisture source, and determine if the insulation and vapor barrier need replacement. Don't attempt DIY mold removal on areas larger than 1 square meter.

Next steps: Stop using the affected area and improve ventilation immediately. Contact a licensed contractor experienced with building envelope issues to assess the wall assembly and moisture source. You may need both mold remediation and building envelope repairs. Check if your renovation contractor provided any warranty coverage for this issue. Document everything with photos for potential insurance claims, though coverage for gradual moisture damage is often limited.

The fix typically involves removing affected materials, addressing the moisture source, properly insulating and vapor-sealing the wall, and ensuring adequate ventilation before reinstalling cabinets.