Preventing Mold in Commercial Premises: Causes & Measures

Mold growth is one of the most unpleasant and costly issues that can occur in commercial property. In addition to health risks for employees and customers, business interruptions, renovation costs, and legal disputes between tenants and landlords may arise. Knowing the causes and implementing structural measures early on can significantly reduce the risk of mold formation in office, warehouse, or retail space.

What Causes Mold in Commercial Premises?

The most common cause of mold in commercial spaces is excessive humidity combined with insufficient ventilation. In many commercial properties, such as warehouses, production facilities, or catering premises, operational processes, machinery, or foot traffic generate significantly more moisture than in standard residential spaces. If poor thermal insulation is also present, thermal bridges form on colder exterior walls, causing condensation. Structural defects such as leaking facades, damaged flat roofs, defective window seals, or rising damp from the ground are also classic triggers. Furthermore, operational conditions often worsen the problem—for instance, when large quantities of goods are stored closely against external walls, blocking air circulation.

Another frequently underestimated factor is a change of use for a space. For example, if a former office is converted into a production facility with higher humidity without adjusting the building services accordingly, the risk of mold increases noticeably. Especially when searching for suitable commercial space, it is worth carefully inspecting the building fabric and its previous usage.

How Can You Detect Moisture Problems Early?

Moisture damage usually announces itself long before mold becomes visibly apparent. Typical warning signs include a musty odor, peeling paint or wallpaper, dark discoloration on walls and ceilings, and foggy window panes in the morning. Unusually high energy consumption can also indicate poor insulation, which in turn fosters moisture problems. Anyone who recognizes and reports these signs early can often prevent major damage and expensive repairs.

Which Structural Measures Protect Against Moisture?

Structural measures against moisture ideally start as early as the planning or renovation stage of a property. Professional thermal insulation of external walls reduces thermal bridges and prevents warm, humid indoor air from condensing on cold surfaces. Equally important is functioning horizontal and vertical waterproofing in the plinth area to prevent moisture from rising out of the ground. On flat roofs and facades, seals and connections should be inspected regularly and renewed if necessary, as leaks often cause visible damage only after years.

Another key component is controlled ventilation. In many commercial buildings, installing a mechanical ventilation system with heat recovery is recommended, ensuring regular air exchange regardless of user behavior. Particularly in rooms with increased moisture production, such as kitchens, workshops, or storage areas with cooling units, ventilation technology tailored to the specific use is essential. The following structural points should receive special attention during new construction or renovations:

• Professional exterior insulation without thermal bridges
• Sealed and regularly inspected roof and facade connections
• Functioning horizontal and vertical damp-proof barriers against rising damp
• Mechanical ventilation with a sufficient air exchange rate
• Vapor-permeable building materials capable of regulating humidity

How Can Tenants and Landlords Prevent Mold?

Mold prevention in commercial property is not just a matter of the building structure, but also of daily user behavior. As a tenant, you should ensure regular burst ventilation instead of keeping windows continuously tilted, position furniture and shelving units at a distance from external walls, and keep room temperatures as constant as possible. Using hygrometers is especially worthwhile in storage areas to monitor relative humidity; values above 60 percent over extended periods are considered critical.

As a landlord, pursuant to Art. 256 CO, you are obliged to hand over and maintain the leased property in a condition suitable for the intended use. This means that structural defects facilitating moisture are fundamentally your responsibility. Forward-looking property maintenance planning with periodic inspections of the roof, facade, and building systems helps detect damage early and avoid costly consequential damage.

Who Is Liable for Mold in the Rented Property?

If mold appears during the lease term, it must be treated as a defect within the meaning of Art. 258 et seq. CO. The tenant is obligated to report the defect immediately, as failure to do so may make them jointly liable for any resulting damage. If the cause lies in the building fabric, such as defective insulation or a leaking facade, the landlord generally bears the cost of remediation. If, on the other hand, mold can be traced back to obvious misconduct by the tenant—such as a persistent lack of ventilation despite appropriate instructions—the allocation of costs may differ. Since proving causation in such cases is often complex, involving a specialist or the competent conciliation authority in the respective canton is recommended for major disputes.

Conclusion: Keeping Your Commercial Space Mold-Free

In most cases, mold in commercial spaces can be avoided if structural quality, appropriate building services, and prudent user behavior work hand in hand. A careful inspection of the building fabric before the lease begins, regular checks during occupancy, and clear communication between tenant and landlord form the foundation for a healthy, value-retaining property in the long term.

This article serves general informational purposes and does not replace individual legal or professional advice. In the case of specific mold issues or legal questions, consulting a specialized expert or legal counsel is recommended.