Preparing Your Hong Kong Home for Rainy Season
Between May and September, Hong Kong receives the bulk of its annual rainfall — over 2,400 millimetres on average, among the highest for any major city. Typhoons can dump 100mm or more in a single hour, while prolonged rain pushes humidity above 95 percent for days. Inadequate preparation leads to water ingress, mould growth, and costly repairs. The time to prepare is March or April.
Window Sealing and Maintenance
Windows are the most common rainwater entry point in Hong Kong flats, especially during typhoons when wind drives rain sideways.
- Inspect window seals: Check silicone sealant around every frame for cracks, gaps, or peeling. Deteriorated sealant must be fully removed and replaced — applying new over old will not create a lasting seal.
- Clear drainage holes: Sliding windows have small weep holes at the bottom of the track. These frequently clog with dirt. Clean them with thin wire or compressed air.
- Test operation: Every window should close and lock tightly. Windows that do not seal properly will leak on higher floors where wind pressure is greater. Replace worn gaskets and adjust hinges as needed.
Roof and External Wall Checks
Top-floor and village house residents should inspect roof membranes for cracks or blistering. Flat roofs common in Hong Kong are vulnerable because water pools on them. Ensure roof drains are clear and waterproofing extends up parapet walls. Professional roof waterproofing for a typical village house costs HK$15,000 to HK$40,000.
Check external walls for cracks around windows, AC sleeve holes, and pipe penetrations. Even hairline cracks admit significant water during prolonged rain. Fill small cracks with flexible exterior sealant; consult a professional for larger ones.
Drainage System Clearing
- Floor drains: Pour water into each bathroom and kitchen drain to ensure flow. Clear slow drains with a plunger or drain snake. Ensure U-traps are filled with water — dry traps allow backflow during heavy rain.
- Balcony and roof drains: Clear leaves and debris. Install mesh guards to prevent future blockages. Check that balcony floors slope toward the drain.
- Building downpipes: If external downpipes overflow during light rain, report to your building management or Owners' Corporation immediately.
Dehumidifying Strategies
During rainy season, indoor humidity regularly exceeds 80 percent, promoting mould, warping furniture, and damaging electronics. A compressor dehumidifier rated to remove 12 to 20 litres daily suits a typical 400 to 600 square foot flat. Popular brands in Hong Kong include Mitsubishi Electric, Panasonic, and Sharp, priced HK$2,000 to HK$5,000.
- Moisture absorbers: Place calcium chloride boxes (吸濕盒, available at Aeon, Donki, or Japan Home) in wardrobes and shoe cabinets.
- Strategic ventilation: Open windows on drier days; keep them closed and run the dehumidifier on humid days. Check the Hong Kong Observatory's humidity forecast.
- AC dry mode: Most split-type units have a dry mode (除濕模式) that dehumidifies without aggressive cooling — effective and energy-efficient.
Flood-Prone Areas
The Drainage Services Department maintains a list of flooding black spots. Residents in Sheung Wan, Tai O, Yuen Long, and low-lying New Territories areas should take extra precautions: keep sandbags ready (distributed by Home Affairs before typhoon season), elevate valuables off ground floors, and install non-return valves on ground-floor drains.
When to Call a Professional
If you discover active water ingress, persistent damp patches, or mould growth, do not wait — damage worsens with each rainfall and mould doubles within 48 hours. A professional waterproofing assessment costs HK$500 to HK$1,500 and can identify the water entry path before extensive damage occurs. Prevention always costs less than repair.