Ask anyone who has opened up a Japanese house after a summer away: the smell comes first. Mould is the most common — and most avoidable — damage to empty homes in Japan.
Why it happens
The rainy season (梅雨) brings weeks of rain from early June to mid-July across most of the country (earlier in Okinawa; Hokkaido barely has one), followed by hot, humid summers. Relative humidity regularly sits above 70–80%. Mould grows readily above about 60–65%, and a closed house with no airflow traps that moisture in tatami, futons, wooden ceilings and the space under the floor.
Where it starts
- Tatami mats and the floorboards beneath them
- Futons and cushions in closets (押し入れ)
- Bathroom ceilings and corners
- North-facing rooms and walls against the hillside
- Under-floor space where ground moisture rises
A care routine that works
- Air it regularly. Open windows and closets for a couple of hours on dry days.
- Run a dehumidifier. Set to keep around 50–60%, draining continuously so it doesn't stop when the tank fills.
- Lift and store soft furnishings. Futons in breathable covers, off the floor; closet doors left ajar.
- Check the bathroom fan and treat early spots before they spread.
- Measure. A cheap hygrometer reading at each visit shows whether the routine is working.
How we help
Work through the rainy-season checklist before June. Moisture checks are part of every Standard and Premium visit, and our moisture management add-on places and services dehumidifiers. Each visit report records the humidity reading — see the sample report.
