Executive Summary
Inter-flat condensation represents one of the most challenging mould issues in Singapore's HDB flats, often leading to prolonged disputes between neighbours. This white paper presents a structured resolution framework based on analysis of 240 reported cases, providing clear guidance for root cause identification, responsibility allocation, and sustainable remediation.
The Problem
Inter-flat condensation occurs when temperature differentials between adjacent units cause moisture to accumulate on shared surfaces. Common scenarios include:
- Air-conditioned unit adjacent to non-air-conditioned unit (72% of cases)
- Different AC temperature settings between neighbours (18% of cases)
- Structural thermal bridging in older buildings (10% of cases)
Case Distribution (240 Cases, 2025)
| Root Cause | Percentage | Avg. Resolution Time |
|---|---|---|
| AC temperature differential | 72% | 4.2 weeks |
| Structural issues | 10% | 12+ weeks |
| Water leakage (misdiagnosed) | 8% | 6.5 weeks |
| Ventilation inadequacy | 6% | 3.1 weeks |
| Other | 4% | Variable |
Resolution Framework
Phase 1: Diagnostic Assessment
- Thermal imaging of shared walls
- Humidity and temperature logging (72-hour minimum)
- Moisture mapping of affected surfaces
- Interview both parties regarding AC usage patterns
Phase 2: Root Cause Determination
Using thermal data and moisture mapping to identify:
- Condensation patterns (typically follows wall temperature gradients)
- Water ingress patterns (typically follows gravity/structural paths)
- Ventilation deficiencies (moisture accumulation in specific zones)
Phase 3: Responsibility Allocation
| Cause | Primary Responsibility |
|---|---|
| AC differential (cooling party) | Unit owner running AC below 22°C |
| Structural defect | HDB (if common area) or Town Council |
| Water leakage | Source unit owner |
| Ventilation | Affected unit owner (internal ventilation) |
Phase 4: Remediation
- Short-term: Mould removal and surface treatment
- Medium-term: Insulation installation or AC adjustment
- Long-term: Monitoring and maintenance protocols
Key Recommendations
- Avoid AC settings below 22°C in units with shared walls
- Consider thermal insulation panels for chronic cases
- Establish communication channels with neighbours early
- Document conditions with photos and humidity readings
- Engage neutral third-party assessment when disputes arise