Mold and Damp in Your Apartment: Causes, Health Risks and How to Get Rid of Them for Good
Volodymyr SydorenkoAugust 13, 2026
Why mold appears in apartments, how it affects health, what humidity is ideal, how to remove mold properly, fix the causes — from condensation to leaks — and who is responsible in a rental or when neighbors flood you.
Mold and Damp in Your Apartment: Causes, Health Risks and How to Get Rid of Them for Good
Black spots in corners, a musty smell, wallpaper peeling behind the wardrobe, condensation on windows — familiar signs of excess moisture. Mold isn't just a cosmetic problem. It destroys finishes, furniture and building structures and harms health. The good news: in most cases mold can be beaten if you fix the cause, not just the stain. Here's where damp comes from and what to do about it.
Why Mold Is Dangerous
The World Health Organization's guidelines on dampness and mould state that living in damp, moldy homes is associated with an increased risk of respiratory symptoms, asthma and allergic reactions. WHO stresses that the best strategy is to prevent damp and quickly fix its causes. The same position is reflected in the WHO Housing and health guidelines.
Children, older people, people with asthma or allergies and those with weakened immunity are especially vulnerable.
What Humidity Is Ideal
The US Environmental Protection Agency (EPA) recommends keeping indoor relative humidity below 60%, ideally between 30% and 50%. Buy an inexpensive hygrometer — it will show whether there's a problem. In winter, at humidity above 60%, condensation on cold surfaces is almost inevitable.
The Main Causes of Damp
1. Condensation on Cold Surfaces
The most common cause in apartments. Warm moist air meets a cold surface — the corner of an external wall, a window reveal, a lintel — and moisture condenses. Signs: mold in the corners of external walls, around windows and behind furniture pushed against external walls.
2. Insufficient Ventilation
Modern airtight windows have stopped the natural inflow of air. Without trickle vents or regular airing, moisture from breathing, cooking, showering and drying laundry builds up. More in window replacement.
3. Thermal Bridges
Panel joints, balcony slabs, lintels above windows and corners are places where the wall is colder than its surroundings. A thermal imaging survey quickly reveals them. The solution is insulation, ideally external. See apartment insulation.
4. Leaks
The roof, panel joints, risers, upstairs neighbors and internal pipes. Stains with clear outlines that grow after rain or in specific places indicate a leak rather than condensation.
5. Rising Damp
On ground floors and in private houses, moisture can rise from the ground through the foundation and walls if waterproofing is damaged.
6. Household Habits
- drying laundry indoors without ventilation;
- cooking without a hood;
- keeping the bathroom door closed with no ventilation after showering;
- lots of plants and aquariums in a small space;
- furniture pressed against external walls.
How to Find the Cause: A Simple Test
Before spending money on repairs, find out where the moisture is coming from. A simple home test: tape a piece of kitchen foil about 30×30 cm to the problem area of the wall, sealing the edges tightly, and leave it for 1–2 days.
- Moisture on the room side (the outer face of the foil) — the cause is condensation: high air humidity and a cold surface. Solutions: ventilation, heating, insulation.
- Moisture on the wall side (under the foil) — moisture is coming from the wall: a leak, rising damp or wet panel joints. The solution is to find and eliminate the water source.
Additional clues:
- mold appears only in winter — most likely condensation;
- stains grow after rain — a roof or joint leak;
- damp near the floor on the ground floor — rising damp or the basement;
- stains under the bathroom ceiling — weak ventilation.
A Seasonal Checklist
In autumn:
- check the ventilation draft and clean the grilles;
- switch window hardware to winter mode;
- assess the condition of panel joints and the roof (through the OSBB);
- have a hygrometer and, if needed, a dehumidifier ready.
In winter:
- monitor humidity — keep it below 60%;
- air rooms regularly in short bursts;
- don't cover radiators or push furniture against external walls.
In spring:
- inspect corners, reveals and the space behind furniture;
- remove mold while it's still small;
- plan repairs and insulation for the warm season.
How to Remove Mold Properly
The EPA guide Mold Cleanup in Your Home advises:
- Fix the moisture source first — otherwise the mold will return.
- Small areas (roughly up to 1 m²) can be cleaned yourself; for large areas or mold in ventilation, call professionals.
- Protect yourself: gloves, goggles and an N95/FFP2 respirator.
- Hard surfaces (tiles, glass, plastic, painted walls) — clean with water and detergent and dry thoroughly.
- Porous materials (plasterboard, wallpaper, ceiling tiles, carpets) that are heavily affected often have to be removed and replaced.
- Dry wet materials within 24–48 hours after a leak so mold doesn't have time to grow.
- Don't paint over mold — it will grow through the paint.
After removal, you can treat the surface with a professional antiseptic and use paints with antifungal additives for humid rooms.
How to Prevent Mold: A Systematic Approach
Ventilation
- air rooms 2–3 times a day for 5–10 minutes with windows wide open — more effective than a window permanently on micro-ventilation;
- install extractor fans in the bathroom and kitchen with a timer or humidity sensor;
- check natural ventilation draft — a sheet of paper should be drawn to the grille;
- leave a gap under interior doors for air to flow;
- consider trickle vents or a ventilation system with heat recovery.
Heat
- keep a stable temperature — sharply cooling rooms increases condensation;
- don't cover radiators with heavy curtains or wide sills;
- move furniture 5–10 cm away from external walls.
Moisture Control
- dry laundry on the balcony or in a dryer;
- cover pots with lids and use the hood;
- wipe walls after showering and leave the bathroom door open;
- use a dehumidifier in problem rooms;
- don't keep wet shoes and clothes in closed wardrobes.
Repair Solutions
- insulating the facade or problem areas;
- replacing windows with proper installation and a vapor-barrier joint;
- bathroom waterproofing — see bathroom renovation;
- repairing panel joints and the roof — through the OSBB or manager.
Mold in a Private House
In private houses, typical causes include:
- damaged foundation waterproofing — moisture rises through walls from the ground;
- no drainage apron or faulty gutters — rainwater runs under the foundation;
- an uninsulated attic — condensation on the underside of the roof;
- an unventilated basement — constant damp and smell;
- dense planting next to walls — walls don't dry out.
Solutions: diverting water from the foundation, repairing gutters, waterproofing and insulating the plinth, and ventilating the basement and attic. Check these points when buying — see buying a country house.
Mold in a Rented Apartment
Who's responsible — the landlord or the tenant? Under the Civil Code, major repairs are generally the landlord's duty and routine repairs the tenant's. So:
- if the cause is structural (roof leaks, freezing walls, faulty building ventilation) — it's the owner's responsibility;
- if the cause is household habits — no airing, drying laundry in rooms — it's the tenant's responsibility.
Inspect the apartment carefully before moving in — see how to rent an apartment safely. Owners should fix the problem before renting out — see how to rent out your apartment. Spell these issues out in the lease agreement.
Flooded by Neighbors: What to Do
- Shut off the water (or ask the neighbors or emergency service).
- Switch off power to wet areas.
- Photograph and film the damage.
- Call an OSBB or manager representative to draw up a flooding report describing the cause and damage.
- Dry the room as quickly as possible — fans, dehumidifiers, open windows.
- Assess the damage (with an independent appraiser if needed) and demand compensation from whoever caused it. Damage to property is compensated by the person who caused it (Article 1166 of the Civil Code). If you can't agree, go to court.
- If the apartment is insured, notify the insurer.
Mold When Buying an Apartment
Signs of mold are a signal to check the cause: it could be poor ventilation or serious problems with the facade or roof. A fresh repair of just one corner or a smell of paint in a single room is a reason to be cautious. Include these points in your inspection — see how to check an apartment before buying.
Frequently Asked Questions
Will bleach help? Chlorine products bleach stains but don't solve the moisture problem and can harm health if misused. The EPA doesn't recommend bleach as the main product for routine mold cleanup.
Can I live in an apartment with mold? Small areas quickly removed along with their cause don't pose a significant threat. But living long-term in a damp, moldy home is harmful, especially for children.
Dehumidifier or air conditioner? An air conditioner in dry mode helps in summer, while a dehumidifier works year-round, especially in spring and autumn.
Why did mold appear after replacing windows? The new windows stopped uncontrolled air inflow. You need to set up ventilation — airing, vents, fans.
Do anti-mold paints solve the problem? They slow mold growth on the surface but don't remove the moisture that feeds it. Use them as a final step after the cause has been fixed.
Conclusion
Mold is the effect; the cause is excess moisture, cold surfaces or leaks. Measure humidity, find the source, set up ventilation and heating, insulate cold areas and only then remove the mold and redecorate. That way you protect both your family's health and the money invested in renovation.
Sources
- WHO guidelines for indoor air quality: dampness and mould.
- WHO Housing and health guidelines.
- EPA: A brief guide to mold, moisture and your home.
- EPA: Mold cleanup in your home.
- Civil Code of Ukraine — Articles 819, 1166.