There's a musty smell coming from behind the basement walls - should we open them up?

A musty smell behind basement walls typically indicates moisture issues or mold growth, and while opening walls may be necessary for proper diagnosis, you should first investigate safer methods to identify the source before creating dust and potential mold exposure.

The musty odor you're detecting is usually caused by excess moisture that's allowing mold, mildew, or bacteria to grow within your wall cavities. In Ottawa's climate, this is particularly common due to our freeze-thaw cycles, high groundwater levels in many areas, and the fact that many basements were built before modern waterproofing standards. The moisture could be coming from several sources: foundation leaks, condensation from poor vapor barriers, plumbing leaks within the walls, or inadequate ventilation.

Before opening any walls, start with non-invasive investigation methods. Use a moisture meter to check different areas of the wall surface - you can rent these from Home Depot or Canadian Tire for about $30-50. Check around windows, near the foundation, and areas where plumbing runs. Look for visible signs like water stains, efflorescence (white chalky deposits), or soft spots in drywall. Run a dehumidifier for a few days and see if the smell improves - if it does, you've confirmed it's moisture-related.

When you do need to open walls, take proper precautions. Wear an N95 mask minimum (P100 is better), eye protection, and gloves. Seal off the area with plastic sheeting to prevent spores from spreading upstairs. Start with small exploratory holes rather than removing entire sections. If you discover significant mold growth (more than 10 square feet), Ontario health guidelines recommend professional remediation.

In Ottawa, this type of investigation often reveals issues that require permits for proper repair. Foundation repairs, major plumbing work, or electrical modifications all need permits through the City of Ottawa Building Code Services. Don't just patch and cover - addressing the root moisture source is critical, or the problem will return worse than before.

Professional assessment is recommended when you smell mustiness but can't locate the source, when you have a history of basement flooding, or if anyone in your home has respiratory issues. A proper moisture investigation can save you thousands compared to opening walls randomly and potentially creating a bigger remediation project.

For a thorough assessment of your basement moisture issues and proper remediation planning, contact Ottawa Basements for a free consultation - we can help identify the source and scope of work needed before you start tearing into walls.