Identify the cause and notify the landlord
When mould appears: 1) identify whether the cause is structural (landlord’s responsibility) or behavioural (tenant’s responsibility), 2) notify the landlord in writing immediately, 3) document with dated photos. Structural mould (infiltration, poor insulation): the landlord must fix it. Behavioural mould (poor ventilation, indoor drying): the tenant must address it.
Mould is a common issue in Belgian rental properties, particularly in older buildings with insufficient insulation or ventilation. The key question is always: who caused it?
- Structural causes (landlord): water infiltration, rising damp, thermal bridges, insufficient insulation, defective ventilation system
- Behavioural causes (tenant): not opening windows, drying laundry indoors, blocking ventilation grilles, excessive humidity from cooking without extraction
Identifying the cause
| Indicator | Likely cause | Responsible |
|---|---|---|
| Mould on exterior walls only | Thermal bridge / poor insulation | Landlord |
| Mould around windows | Condensation / poor sealing | Landlord |
| Mould in corners at ceiling | Thermal bridge | Landlord |
| Mould behind furniture against exterior walls | Combination (structural + ventilation) | Shared |
| Mould in bathroom only | Poor ventilation by tenant | Tenant |
| Mould after water leak | Water infiltration | Landlord |
If the cause is disputed, a professional assessment (humidity expert or building surveyor) can determine the origin. The cost is typically shared, or the responsible party pays. The expert’s report is strong evidence before the justice of the peace.
Legal remedies
If the landlord is responsible and fails to act:
- Notify by registered letter with photos and a request for intervention
- Contact regional housing inspection (DIRL Brussels, municipal service Wallonia, Wonen Vlaanderen)
- File a claim with the justice of the peace
- The judge can order works under penalty, rent reduction, or lease termination
If the tenant is responsible, the landlord can:
- Require the tenant to improve ventilation habits
- Deduct cleaning and restoration costs from the deposit at the end of the lease
- In severe cases, claim damages for property degradation
Regional specifics
Brussels-Capital Region
The Ordinance of 27 July 2017 sets strict habitability standards. Persistent mould affecting health can trigger an intervention by the DIRL housing inspectors.
Wallonia
The Decree of 15 March 2018 includes mould-related health issues in its habitability standards. Municipal inspectors can intervene.
Flanders
The Flemish Housing Rental Decree of 9 November 2018 includes mould as a quality defect. Wonen Vlaanderen can inspect and declare properties unfit if mould is caused by structural issues.
Civil Code, articles 1719-1720 (landlord’s obligation to deliver in good condition). Regional Housing Codes (habitability standards).