Typically, structural issues that cause water intrusion, such as leaking pipes within the walls, faulty AC drainage systems (especially the main ducting), or cracks in the building envelope that allow humid air to seep in, are the legal responsibility of the landlord. Since you mentioned the AC unit makes the room feel constantly damp and the mold is on an exterior wall, there is a high probability this is a building-related issue.

However, if the moisture is determined to be a result of tenant behavior—such as a failure to run the AC consistently, blocking ventilation grilles with furniture, or creating excessive indoor humidity—then the cost of remediation could fall to you.

Given your description, this is not a simple surface cleaning job. The fact it’s spreading from behind the wardrobe indicates a potential hidden problem. The first and most critical step is a professional inspection and moisture mapping to definitively identify the source. DIY attempts can disturb the mold, spreading spores and making the problem worse. We use thermal imaging and borescopes to pinpoint the exact cause without unnecessary damage.

My strong recommendation is to immediately notify your landlord or property management company in writing, with photos, and insist on a professional assessment. Do not attempt to remove it yourself. For a definitive diagnosis and a report that can be used to establish responsibility with your landlord, you can call our team at 800-MOLDS (800-66537) or email hello@saniservice.com. We provide detailed, certified reports that are often used in such disputes.