Who Pays for Winter Condensation and Mold in a Japanese Rental? Where Responsibility Divides and What to Do
Written by：SUMIMOTO Inc.Editorial Policy
As temperatures drop, many renters in Japan struggle with condensation on windows, damp closets, and mold on wallpaper. Is it a building problem or a lifestyle problem? And will I be billed when I move out?
This article explains in general terms how responsibility is divided between landlord and tenant, what to do day to day, and how to contact the management company. Individual outcomes depend on the lease and the building, so treat this as a guide, not a definitive answer.
Why do condensation and mold become issues in rentals?
Condensation forms when warm, humid indoor air touches a cold window or wall. Poor ventilation, drying laundry indoors, heavy humidifier use, and heating habits all add up. Left alone, it leads to mold, mites, and damaged wallpaper and window frames.
In rentals, the same symptom can come from poor insulation or ventilation in the building, or from moisture built up through daily living. Which factor dominates changes how responsibility is viewed, and it is hard to tell apart, so recording the problem early and sharing it with the manager matters.
Numbers to keep in mind
- Indoor humidity guide
- 40–60%
- 24-hour ventilation standard
- 0.5times/hr
- Wallpaper depreciation period
- 6years
A range generally considered helpful against condensation and mold
Guide for ventilation systems required in houses built since 2003
Guide in the MLIT guidelines used when calculating restoration costs
How is responsibility divided between landlord and tenant?
Under the Civil Code, the landlord has a duty to carry out the repairs needed to keep the unit usable. The tenant must use the unit with the care of a prudent manager, and the landlord's repair duty does not apply when the repair is needed because of a cause attributable to the tenant.
Condensation itself often depends on the building, such as window structure and insulation, so it cannot simply be blamed on the tenant. However, if a tenant knows condensation is forming, does not wipe it or ventilate, and lets mold spread, this may be treated as a breach of the duty of care.
How responsibility tends to divide (general guide)
| Situation | General view | What the tenant does |
|---|---|---|
| Condensation or mold from poor insulation or faulty ventilation | Often a landlord repair matter | Take photos and contact the manager early |
| Small amounts of condensation in normal life | Often within normal use | Wipe it regularly and ventilate |
| Condensation ignored and mold spread | May be a breach of the duty of care | Act early and report before it spreads |
| Indoor drying or over-humidifying | May be seen as the tenant's management issue | Review humidity control and ventilation |
Legal basis
- Civil Code, Art. 606
- The landlord must make repairs needed for use of the property, excluding repairs needed through the tenant's fault.
- Civil Code, Art. 607-2
- In some cases the tenant may carry out repairs, for example when notified repairs are not done within a reasonable period or in urgent situations.
- Civil Code, Art. 615
- The tenant must promptly notify the landlord when repairs are needed.
- Civil Code, Art. 621
- Wear from ordinary use and aging is outside the tenant's restoration duty.
What can you do today to prevent it?
The basics are: (1) wipe windows in the morning, (2) run the fan after bathing and cooking, (3) keep furniture a few centimeters from walls, (4) avoid indoor drying or add a dehumidifier, (5) do not over-set the humidifier.
Light mold can be wiped with a store-bought disinfectant, but mold behind wallpaper or over a wide area can worsen with amateur work. Take photos and consult the manager.
How does this relate to restoration at move-out?
At move-out, dirt and wear from ordinary use are in principle not the tenant's cost. But if mold spread through poor upkeep and damaged wallpaper or flooring, the tenant may be charged. Wallpaper costs are generally reduced according to years of occupancy.
Keep dated photos from move-in and daily life, and save your contact history with the manager (emails and chats). It makes the settlement easier to discuss.
Common slips and fixes
✕Left condensation thinking it would dry, and mold spread.
→Wipe it daily and report to the manager with photos before it spreads.
✕Reported only by phone, so no record remained.
→Use email or chat and keep the date and content.
✕Replaced wallpaper or redid sealant on their own.
→Get the manager's approval before any work.
✕No move-in photos, so the tenant was told to pay at move-out.
→Photograph closets, windows, and north-facing walls with dates right after moving in.
Condensation and mold checklist
- I wiped window and frame droplets this morning
- I ran the fan after bathing and cooking
- I left gaps behind closets and furniture
- I checked indoor humidity
- I photographed any mold I found
- I contacted the manager by email and kept a record
FAQ
- Q. Is condensation the tenant's responsibility?
- A. Condensation often depends on the building's structure and insulation, so it is not necessarily the tenant's fault. Ignoring it until mold spreads can be treated as a breach of the duty of care.
- Q. Will I be charged for mold removal?
- A. Generally not within normal use, but if poor upkeep is judged to be the cause, the tenant may bear it.
- Q. Who pays electricity for dehumidifiers and humidifiers?
- A. Usually the tenant. Whether to buy or install equipment can be discussed with the manager.
- Q. What if repairs are slow after I ask?
- A. If notified repairs are not done within a reasonable time, the tenant may be able to repair. Re-request in writing (email) and keep a record.
In the SUMIMOTO Hub app, the 24-hour AI advisor explains lease terms and how to write to your management company in multiple languages. Please also confirm individual cases with a qualified professional.
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References & Sources
This article provides general information as of its publication date and is not individual legal, tax or investment advice. It was written with the help of generative AI.Editorial Policy
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