Yes, this absolutely requires a professional remediation company. A proper job involves more than just wiping the surface; it requires containment to prevent spores from spreading, removal of contaminated porous materials like the affected plasterboard and wardrobe backing, and addressing the root cause—the condensation on the cold wall. Expect the process to include a full inspection, air sealing the area, HEPA vacuuming, antimicrobial treatment, and most critically, identifying and fixing the thermal bridging or insulation flaw causing the condensation.

For cost, you cannot get an accurate figure without an on-site assessment. The scope depends entirely on how far the mold has spread inside the wall. A small, contained job treating just the wardrobe area will be significantly less than if the entire wall needs to be opened. Reputable companies provide detailed, scope-specific quotes after diagnostics. Always ensure the company is DHA-approved and can provide a post-remediation verification report from a third-party lab to confirm the space is truly clean and the allergen count is back to a safe level.