Humidity and Mould in a Phnom Penh Apartment: How to Protect Your Home

Prepared by the NovAsia Editorial Team

Mould in a Phnom Penh apartment is not just a normal consequence of living in the tropics. It usually appears when high outdoor humidity combines with cooled air-conditioned surfaces, small leaks, weak ventilation and furniture pushed tightly against walls. The solution is not fragrance spray or repeated repainting. The practical defence is moisture control: measure relative humidity, remove water quickly, keep air moving inside wardrobes and bedrooms, and investigate repeated stains before they become part of the apartment’s normal background.

For day-to-day control, a simple hygrometer is enough. U.S. EPA guidance recommends keeping indoor relative humidity below 60%, ideally around 30-50%, while CDC guidance suggests keeping it as low as practical and preferably no higher than 50%. In Phnom Penh, the lower end of that range may not be realistic without continuous equipment, so the practical warning sign is sustained humidity above 60%, visible condensation, a musty smell, or stains that return after cleaning or paint.

This article is about the behaviour of a specific apartment, not general weather. The important questions are: does the facade leak during heavy rain, where does the air conditioner drain, does the bathroom dry after showers, does the extractor actually move air, and what happens when the home is closed for several days?

Why mould appears even in a new apartment

Mould needs moisture. Fungal spores are present in the environment, but active growth needs a surface that stays damp long enough. In a tropical city, the source is not always a visible leak. A wall may feel dry in the middle of the room while the local humidity behind a wardrobe stays high for weeks.

Cambodia’s wet monsoon season usually runs from around May to October, when much of the annual rainfall occurs. During long rainy periods, outdoor air holds more moisture, laundry dries more slowly, shoes and balconies stay wet, and opening windows is not always a drying strategy. If the air outside is already humid, long ventilation may bring in more water vapour rather than remove it.

Air conditioning adds a second mechanism. It cools air and surfaces. When warm humid air enters through a balcony door, a loose window frame, the corridor or an unsealed gap, water can condense on cold glass, aluminium frames, pipes, walls near the indoor unit or furniture close to an exterior wall. A correctly operating air conditioner removes some moisture, but not every mode, unit size or installation gives stable dehumidification.

A unit that is too powerful can cool the room quickly and cycle off before removing enough water vapour. Dirty filters, icing, a blocked drain or fan-only operation after the compressor stops can also worsen humidity control. A cold apartment can still be a damp apartment.

New buildings are not automatically safe. Concrete, render and screed can retain construction moisture. If a newly finished apartment is closed quickly, fitted with built-in wardrobes against external walls and rarely conditioned, the first months may produce smells and spots. That does not make mould acceptable. The developer or building management should check leaks, facade joints and building systems, while the owner should support drying and airflow.

The most vulnerable places are areas with weak air movement: the back of wardrobes, corners behind beds, under sinks, behind curtains, closed storage rooms, bathrooms with weak extraction, mattresses on solid bases and suitcases placed directly against walls. Humidity at the surface can be much higher than a sensor reading in the middle of the living room.

Humidity, condensation or a leak: how to tell the difference

A stain does not always reveal its source immediately. The same grey or black growth may be caused by general humidity, a cold corner, a leaking pipe or rainwater entering the facade. The fix depends on the cause.

General high humidity usually shows up in several poorly ventilated places. Wardrobes smell musty, shoes and leather items develop surface growth, small spots appear on the backs of furniture, and towels stay damp for too long. Hygrometer readings remain high not only after a shower, but for much of the day.

Condensation is usually linked to a cold surface. It appears on glass, aluminium frames, cold-water pipes, walls in the direct path of cold air, or corners where an external wall is colder than the rest of the room. Stains may worsen when the indoor temperature is very low and the balcony door is opened often. In that case, the surface keeps receiving new moisture.

Leaks are usually more local and connected to rain, plumbing use or an upstairs unit. After a storm, a window reveal darkens, paint bubbles near a balcony door or a wet stripe appears on a ceiling. Under a sink, the issue may worsen after water use. A bathroom ceiling stain may point to an upstairs pipe or waterproofing problem.

A simple first read:

This table is only a starting point. Water can travel inside walls and emerge far from the defect. Repeated or large damage needs a technician with a moisture meter and an understanding of the building.

Musty, earthy odour matters even without a visible stain. Damp-building guidance treats visible mould, water marks and characteristic odour as warning signs. Growth may be behind wardrobes, wallpaper, gypsum board, ceiling panels or inside air-conditioning components.

When inspecting, do not look only at the open wall. Check lower corners, skirting boards, bathroom silicone, the inside of wardrobes, under the mattress, ceilings near risers and the air-conditioner drain outlet. Fresh paint on one patch, new sealant over old sealant and a locally replaced skirting board all deserve questions about previous water damage.

Testing is usually not the first step. EPA guidance notes that if mould is visible, sampling is often unnecessary because there is no universal household safe spore count, and test results do not remove the need to clean growth and fix moisture. Testing can help in disputes or complex hidden cases, but it should not replace repair.

Controlling humidity without turning the home into a sealed refrigerator

Measurement comes first. Put one hygrometer in a bedroom or problem room and another in the living area or wardrobe. A single reading after a shower is less important than the level several hours later. If humidity regularly remains above 60%, the routine needs to change.

Air conditioning helps when it runs long enough and drains properly. For daily living, moderate stable cooling is usually better than extreme cooling for short bursts. Very low temperature settings increase the difference between outdoor air and indoor surfaces, which can make condensation more likely when humid air enters.

Dry mode can help on a rainy day or in a room with modest heat load, but each model behaves differently. It is not a universal replacement for a dehumidifier. Use the hygrometer, not the icon on the remote, as the test.

A separate dehumidifier is useful when the room is cool enough but still humid, or when the apartment is empty and does not need strong cooling. It removes moisture without primarily cooling the room, but it adds heat and needs a reliable water path. A small tank may fill quickly and stop the unit. For a long absence, continuous drainage must be tested and secured so water cannot return or spill.

Ventilation should be deliberate. A short cross-ventilation period can remove odour and moisture when outdoor air is drier. During a hot, humid storm, long-open windows may add moisture. If the air conditioner is running, an open balcony door forces it to cool and dehumidify a constant stream of humid air.

Bathrooms must dry after each use. The door can stay open after a shower if that does not spread moisture into an already damp apartment, and the extractor should actually move air rather than merely make noise. A piece of light paper near the grille can show whether there is pull, but the duct route and condition need a technician if there are doubts.

Kitchen extraction matters too. A recirculating hood reduces odours and grease, but it does not remove all water vapour from boiling, washing and cooking. In a small apartment, cooking can raise humidity quickly, so either proper extraction or short, well-timed ventilation is needed.

Do not push furniture tightly against cold external walls. A small gap lets air move and allows early inspection. Pay attention to heavy wardrobes, solid bed bases and upholstered headboards. Lift the mattress occasionally and check the underside, especially if the bed base has no slats.

Wardrobes should not be packed with damp clothes. Silica gel and small moisture absorbers can help in enclosed spaces, but they do not fix a damp room. If a container fills quickly, it is a signal to measure humidity and inspect the moisture source.

Air-conditioner filters should be cleaned according to the manufacturer’s instructions, while coils and drains should be serviced by a competent technician. A dirty indoor unit can hold moisture, smell on start-up and spread contaminants. Spraying harsh chemicals into a unit without correct cleaning may damage parts and fail to clean hidden surfaces.

A HEPA air purifier can reduce airborne particles and may be a helpful addition after the source is fixed, especially for sensitive residents. But it does not solve mould or moisture. Devices that deliberately generate ozone should not be used as a household mould solution: ozone can irritate lungs and is not a safe substitute for removing damp materials.

What to do when mould is already visible

The first step is to stop the moisture. If you only wipe the stain or paint over it, it will return. Check for leaks, blocked air-conditioner drainage, window seals, pipework, grout, bathroom extraction and overall humidity. After repair, the area must dry fully before new finishing.

A small patch on a hard non-porous surface may sometimes be cleaned by a resident. EPA uses roughly 10 square feet, about 0.9 square metres, as a practical threshold below which household clean-up may be possible in many cases. That is not a guarantee. Material type, health status, hidden damage and water source matter.

For a small job, limit spread, wear gloves, eye protection and at least an N95 respirator, clean the surface with detergent and water, then dry completely. If using a chlorine product, follow the label, ventilate properly and never mix it with ammonia or other cleaners. Dangerous gases can form.

Bleach is not a universal answer. It may be suitable for some smooth sealed surfaces when used correctly, but porous materials are much harder to clean. Mould can penetrate gypsum board, ceiling tiles, carpet, chipboard, upholstered furniture and mattresses. Lightening the surface does not prove that the contamination has been removed.

Wet porous materials may need removal and replacement, especially if they stayed wet, lost strength, smell after drying or show growth on both sides. Saving a cheap panel at the cost of repeated growth is rarely sensible.

Do not point a normal fan directly at a mouldy surface before cleaning; airflow can spread particles. Do not dry-scrub, sand or scrape growth without containment. Removed material should be bagged before being carried through common areas, and surrounding surfaces should be cleaned afterwards.

Professional help is needed if the affected area is large, hidden, recurring, linked to flooding, inside a wall or HVAC system, spread across several rooms, or accompanied by a strong smell without a visible source. A credible contractor should look for moisture, remove or clean material under control and verify drying, not simply spray fragrance or chemical fog.

Contaminated floodwater or sewage requires special caution. In that case the concern is not only mould; bacteria and other contaminants may be present. Cosmetic cleaning is not enough.

Success means four things: the source of water is fixed, damaged material is cleaned or removed, the area is fully dry, and growth does not return. Dead mould can still be allergenic, so physical removal matters more than simply killing growth.

In a rental, document the issue before cleaning: photographs, dates, hygrometer readings and conditions. Inform the landlord or building management in writing, especially if the suspected source is a facade, pipe, roof or upstairs apartment. This helps distinguish tenant use from building defects and makes it easier to confirm that the source was actually fixed.

How to inspect before renting or buying

Mould is easier to avoid than to fight after moving in. In Phnom Penh, try to inspect not only on a bright dry day. After heavy rain, weak window seals, balcony drainage and damp ceiling patches are easier to spot.

Start with smell. Ask for the air conditioner and fragrance diffusers to be turned off before the viewing. A heavy musty odour that returns after a few minutes needs investigation.

Open all built-in wardrobes. Look at the back panel, lower corners and floor. Check skirting boards, under sinks, bathroom ceilings, silicone, grout, ventilation grilles, the bed base and the air-conditioner service area.

At windows, look beyond visible stains. Repeated sealant, local repainting, swollen board, rusted fixings and discoloured reveals can point to old leaks. On the balcony, water should drain away and not sit against the door. Sliding-door thresholds should not show signs of repeated overflow.

Run the air conditioner for at least 15-20 minutes. Check odour at start-up, stable airflow, no dripping from the indoor unit and sensible drainage. If no water appears from the drain on a humid day, that is not automatically a fault, but it is worth asking where the drain runs and when the unit was serviced.

Ask the owner or manager whether there have been facade leaks, upstairs leaks, waterproofing repairs, window resealing or air-conditioner drainage complaints. "It has been repainted" does not explain the cause.

For a new project, check how long the building has been occupied. Real facade weaknesses sometimes show only after one or two rainy seasons. That does not mean a new unit should be rejected, but warranty procedures and management response should be clear.

For furniture, removable wardrobes with a small wall gap are often easier to manage than built-in units sealing a cold corner. A bed base that allows air circulation is better for mattresses. Natural light and controlled ventilation help, but open windows are not a substitute for dehumidification in the wet season.

A short pre-contract check:

1. Is there musty odour without fragrance and active cooling?
2. Are there water marks near windows, ceilings, wardrobes or skirting?
3. Do extraction, air conditioning and drainage work?
4. Who repairs facade and plumbing leaks?
5. What happens when the apartment is closed for several days?

This is not a building survey, but it prevents many common misses.

Health effects: what to take seriously

This article is general information, not medical advice. If symptoms are significant, persistent or include breathing difficulty, seek medical assessment.

The World Health Organization treats dampness and microbial growth as an important indoor air-quality issue. Research links damp buildings with respiratory symptoms, cough, wheeze, asthma aggravation, allergic rhinitis and other complaints. This does not mean every dark spot causes severe illness in every person, but chronic dampness should not be treated as cosmetic only.

Sensitivity varies. One resident may notice only odour; another may develop blocked nose, irritated eyes, cough or skin symptoms. People with asthma, chronic lung disease, strong allergies or weakened immune systems need more caution. CDC materials also identify some people with serious immune suppression or chronic lung disease as at higher risk of severe fungal infections.

If symptoms become worse at home and improve away from the apartment, record that pattern and discuss it with a doctor. Do not diagnose "black mould poisoning" from colour alone. Many moulds look similar, and household testing rarely helps treatment without clinical context.

Seek medical advice for persistent cough, wheeze, shortness of breath, recurrent asthma flare-ups, severe eye or skin irritation, fever, or symptoms in a person at higher risk. Breathing difficulty requires urgent care.

Sensitive residents should stay away during clean-up. A person with severe asthma, immune compromise or chronic lung disease should not dismantle a major affected area. A mask reduces particle inhalation during minor work; it does not make a complex remediation project safe.

When the apartment will be empty

A Phnom Penh apartment should not simply be closed, fully powered off and ignored for several weeks or months. In a tropical climate, stagnant air and inactive dehumidification can encourage growth on furniture, clothing and walls.

Before leaving, remove damp textiles, dry shoes, move dense items away from walls, clean air-conditioner filters and check drainage. Store bedding and clothes fully dry. If using a dehumidifier, test continuous drainage and power recovery before departure. A full tank will stop the unit, and some models do not restart after a power cut.

Remote plugs and sensors can help, but they do not replace a person with access. A leak, blocked drain or failing air conditioner needs someone on site. For a long absence, arrange inspections after heavy rain and at regular intervals.

Bottom line

Mould in Phnom Penh is not an unavoidable tropical tax. Outdoor humidity raises the risk, especially in the wet season, but indoor growth usually points to a specific combination of leaks, condensation, weak extraction, poor air-conditioner performance, stagnant air or long closure.

Prevention is a routine: measure humidity, keep sustained levels below the danger range where practical, remove water fast, dry wet materials within 24-48 hours when possible, keep air moving behind furniture, and fix leaks instead of painting over them. A returning stain is a building or moisture problem, not a decorating problem.

When choosing a home, focus on smell, wardrobes, window reveals, balcony drains, bathrooms and air-conditioning performance. A good apartment should stay dry not only during a viewing, but also after heavy rain, several hours without cooling and short periods of absence.

Sources

1. World Health Organization — WHO Guidelines for Indoor Air Quality: Dampness and Mould. Evidence review on dampness, microbial growth and health risks.
2. U.S. Environmental Protection Agency — A Brief Guide to Mold, Moisture and Your Home; Mold Cleanup in Your Home. Guidance on humidity, porous materials and household clean-up limits.
3. Centers for Disease Control and Prevention — Mold: About, Clean Up Guidelines and Health Problems. Prevention, protection and higher-risk groups.
4. ASHRAE — Damp Buildings, Human Health, and HVAC Design; Humidity Control Resources. Damp-building signs and hot-humid climate moisture control.
5. U.S. Department of Energy — Advanced HVAC Humidity Control for Hot-Humid Climates. Cooling versus water-vapour removal.
6. World Bank Climate Change Knowledge Portal — Climate Risk Country Profile: Cambodia. Monsoon seasonality and climate context.
7. World Meteorological Organization — Phnom Penh-Pochentong Climatological Information, averages for 1982-2024. Reviewed 27 June 2026.

Frequently asked

What humidity level should worry me in an apartment?

If relative humidity stays above 60% for long periods, or if you notice a musty smell, condensation or recurring stains, you need to change the ventilation and dehumidification routine and look for the moisture source.

Can I simply paint over mould?

No. The moisture source must be fixed first. Paint over a damp area is usually only a cosmetic cover-up and the staining often returns.

What should I check before renting an apartment in Phnom Penh?

Check wardrobes, corners, ceilings, window frames, bathrooms, air-conditioner drainage, indoor odour and signs of fresh localised repainting. Ask directly about leaks and air-conditioner maintenance.