A typical scenario (an illustrative story based on common situations, not a review from a specific customer)

A two-storey townhouse in Lam Luk Ka and the under-stair door nobody wants to open

Ton and his wife have been paying off a two-storey townhouse in a housing estate in Lam Luk Ka, Pathum Thani, for five years. The house is four and a half meters wide. Downstairs there is a living room, a small toilet under the stairs, a separate under-stair storage cupboard, and a kitchen extension built out the back right up to the fence. Their six-year-old daughter loves playing hide-and-seek in the under-stair cupboard, which is packed with boxes of old toys, a spare fan, bags of winter clothes and a box of house documents.

That year it rained hard for several days in a row. The canals could not drain fast enough and the estate's roads turned into rivers. Water entered the house to about thirty centimeters, and because the estate sits lower than the main road, it stayed for almost two weeks before pumps cleared it. The family moved upstairs, and whatever could not be lifted in time stayed underwater.

Once the water was gone, Ton spent two days off scrubbing the living room floor, washing the kitchen and hauling soggy boxes out of the under-stair cupboard. The house looked much better. But within weeks, a musty smell rushed out every time someone opened the under-stair door. The gypsum wall inside had a black band reaching half a meter above the floor. The kitchen extension smelled stale and faintly of drains even though it was washed every day, and some floor tiles had lifted and sounded hollow when tapped. Their daughter started coughing at night, and Ton sneezed every morning when he came downstairs.

This picture is very common in townhouses across housing estates in Pathum Thani, Nonthaburi, Bang Bua Thong, Rangsit, Khlong Luang and the eastern outskirts of Bangkok. Townhouses have a particular layout that makes some corners much harder to dry than in a detached house, and unless you understand those damp spots, no amount of washing will solve the problem.

Why townhouses have damp corners that mold and bacteria love

A townhouse is a row house that shares walls with neighbors on both sides (except for end units). It has windows only at the front and back, so air can flow in just one direction, front to back. If the back has been closed in as a solid kitchen extension and the front has security grilles and a roller shutter, the ground floor gets almost no airflow at all. Post-flood moisture therefore lingers far longer than in a detached house that can open windows on every side.

The under-stair room: the dampest space in the house

The space under the stairs is usually a storage cupboard or toilet. It has no window, one side is often the party wall with the neighbor, and many houses partition it with gypsum board or plywood. When floodwater gets in, these materials wick water tens of centimeters above the actual flood line, and with the door shut, the moisture has nowhere to go. That is exactly what mold likes best. In homes with a toilet under the stairs, daily showering adds even more humidity.

Storerooms and cardboard boxes

Cardboard, fabric bags, books and clothes stored on the ground floor are excellent food for mold. Once soaked and left piled up for days, spores multiply quickly and billow into the air every time someone moves them. Clearing out a storeroom after a flood without a mask is the moment of heaviest spore exposure.

Kitchen extensions and sinking floors

Most townhouse kitchen extensions are built on shallower foundations than the main house, so they tend to settle and open a crack between the original floor and the extension. Floodwater seeps in and sits under the slab and tiles, making tiles lift, sound hollow and release a musty smell through the grout for months. Kitchens also have waste pipes, grease traps and, in some homes, a septic or treatment tank nearby. In a flood, sewage from these systems can back up and contaminate the kitchen area.

Germs commonly found in damp corners after a flood

• Mold growing on gypsum, plywood, paper and fabric, releasing spores that trigger allergies and asthma and cause most musty odors.
• Bacteria from sewage and wastewater, such as E. coli, carried by floodwater and overflowing septic systems, which cause stomach illness and diarrhea when they get from hands to mouth.
• Leptospira bacteria (leptospirosis) from the urine of rats that sheltered from the water in storerooms and under kitchens.
• Cockroaches and rats, which love damp corners and stacked boxes and spread germs throughout the house.

Symptoms to watch, and who is most at risk

People living with damp corners may develop congestion, morning sneezing, night-time coughing, itchy eyes, skin rashes, headaches, or diarrhea after touching contaminated surfaces. Those who need extra care are:

• Young children, who crawl and play on the ground floor and in hidden corners such as the under-stair cupboard.
• Older people, who often sleep downstairs because stairs are difficult, so they spend the whole night near the moisture.
• Pregnant women, who should avoid handling moldy items and contact with wastewater.
• People with chronic illness, including diabetes, lung disease, people on immune-suppressing medicine, and those with allergies or asthma.

If anyone who waded through floodwater develops a high fever, calf pain, red eyes or severe diarrhea, they should see a doctor immediately and mention their flood exposure. Ozone treatment manages the home environment. It is not medical treatment.

What townhouse families have to deal with

Health

Townhouses are compact. The ground floor is living room, dining room and children's play area all at once, so odors and spores from the under-stair room or kitchen reach everyone quickly. Allergies and coughs that start after a flood are often dismissed as an ordinary cold until they have dragged on for a month.

Money

Most families are still paying their mortgage. Tearing out gypsum under the stairs, replacing kitchen cabinets, retiling and throwing away stored belongings is already a heavy burden. If recovery is done in the wrong order and mold returns, the repairs must be paid for again, pushing the budget even further.

Time

Working parents only have weekends for cleaning. Scrubbing mold again every week in a cramped space under the stairs eats into time that should be spent resting with the children.

Property value and neighbors

A house with musty odors and mold stains is hard to sell or rent. And because townhouses share walls, damp and mold from one home can spread to the neighbor's side of the wall, or the other way around. Restoring a townhouse therefore sometimes means talking with the neighbors too.

Family life

When a child is afraid to play in her favorite corner, a grandparent cannot sleep because of the smell, and everyone retreats upstairs, a house that should be a place to rest becomes somewhere everyone wants to escape from.

Why common fixes do not solve townhouse problems

1. Emptying the under-stair room without removing the soaked walls

Gypsum and plywood that have been underwater hold moisture inside the material and behind the board. Wiping the surface and closing the door simply creates a small mold incubator under the stairs.

2. Keeping the under-stair door shut so the smell stays in

The more you close it, the more moisture builds up and the more mold grows. Every time the door opens, a burst of spores flows into the living room.

3. Washing the kitchen every day without knowing water is trapped under the tiles

The smell coming from the grout and from tiles that sound hollow comes from water and mud trapped below. Washing the surface will not help. The floor and the crack at the extension joint must be fixed.

4. Pouring bleach across a poorly ventilated ground floor

In a townhouse with little airflow, the chlorine smell lingers for a long time and irritates the airways of children and older people. More importantly, bleach does not penetrate to mold inside porous materials.

5. Relying on charcoal bags or moisture absorbers under the stairs

These help a little in normal times, but after a flood the amount of moisture far exceeds what they can absorb, and they do nothing to the mold that is already growing.

6. Painting anti-mold paint over walls that are still damp

Anti-mold paint works on walls that are dry and clean. Applied over damp, moldy walls, it blisters and peels, and black spots return within weeks.

WHD ozone disinfection for townhouses

The Residential and Building Ozone Disinfection service from World Health Disinfection (WHD) uses ozone gas (O₃), which has strong oxidizing power. In a closed space, ozone spreads into the gaps under the stairs, behind kitchen cabinets, under the sink, between storage shelves and into corners a cloth cannot reach. It breaks down the cell structures of viruses, bacteria and mold and breaks apart musty odor molecules, then reverts to oxygen (O₂), so there is no chemical residue in a home where small children crawl on the floor.

According to the test results certified for the company by Thailand's Department of Medical Sciences and Intertek (UK), the WHD system eliminates viruses, bacteria and mold by 99.99%. Details are on the certification page.

The right order: ozone treatment comes after removing damaged belongings, tearing out soaked materials, cleaning and drying the house. It does not replace removing moldy gypsum, repairing a kitchen floor with water trapped underneath, or rodent and cockroach control. It is the finishing step that deals with germs and odors in the air and in spaces you cannot see.

Safety and neighbors: ozone treatment must take place in a closed space with no people, pets or plants inside. Everyone must leave the house, including anyone upstairs, because a townhouse staircase connects the air of every floor. Re-entry is allowed only after the rest and ventilation period set by the team. Because townhouses share walls, the team checks cracks, pipe openings and roof-space gaps that might connect to the house next door, seals them properly, and advises owners to let their neighbors know in advance.

How the WHD team works in townhouses

1. Survey the damp spots. The team checks the under-stair room, storerooms, kitchen extension, ground-floor bathroom and party walls, finds the strongest odor sources and identifies materials that should be removed.
2. Plan zones and seal leaks. The house is divided into zones such as the main ground floor, the under-stair room and the kitchen, and any openings to the neighboring house are sealed.
3. Preparation. Food, plants and pets are removed. The under-stair door, kitchen cabinets and storage cupboards are opened, and the team confirms that nobody remains inside.
4. Ozone release and contact time. About 30 minutes per zone, depending on size and severity.
5. Rest and ventilation. Ozone reverts to oxygen, doors and windows are opened, and the team checks before the family returns.
6. Aftercare advice. Guidance on ventilating a row house, storing items under the stairs and watching for recurring damp spots.

Ozone jobs of 15,000 baht or more include a free medical-grade disinfectant spray. If the house still smells of strong cleaning chemicals after the big clean-up, see the chemical residue odor removal service as well.

10 reasons to finish townhouse flood recovery with ozone

1. It reaches windowless under-stair rooms where natural airflow never gets in.
2. It tackles musty odors from kitchen extensions and storerooms at the source instead of masking them with fragrance. See the ozone disinfection service.
3. No chemical residue on floors, safe for children who crawl and play downstairs after the ventilation period.
4. Fewer mold spores in ground-floor air, which in many homes is both the living room and a grandparent's bedroom.
5. It helps reduce germs in areas once contaminated by wastewater, such as around drains and under the sink, after they have been cleaned.
6. Done in a single day. About 30 minutes per zone plus rest time, so the family only needs to be out for half a day.
7. A team that understands row houses checks and seals openings that might connect to the neighbors, for everyone's safety.
8. Certified testing by the Department of Medical Sciences and Intertek (UK), according to the test results certified for the company.
9. It protects your repair budget by preventing mold from returning on new walls and newly installed cabinets. Read more about the residential ozone service.
10. It helps get the house ready to sell or rent, so buyers and tenants are not greeted by a musty smell at the door. Ask us via Contact us.

Before and after: a townhouse restored step by step

Example case: a Bang Bua Thong townhouse where Grandma sleeps downstairs

Example case (an illustrative scenario to explain the process, not a real customer review)

Prae lives in a three-storey townhouse in a housing estate in Bang Bua Thong, Nonthaburi, with her husband and her 78-year-old grandmother, who sleeps in a ground-floor room converted from the guest lounge because she can no longer climb stairs. Floodwater entered the house to about twenty-five centimeters and stayed for ten days.

After the water drained, the family cleaned the house themselves and hired a carpenter to replace Grandma's bed and wardrobe. Still, Grandma complained that her room smelled musty at night, and she began coughing more often. Prae first took her to a doctor, who advised reducing exposure to damp and mold in the bedroom alongside her treatment.

The team's survey found that the under-stair storeroom next to Grandma's room had a gypsum wall that was still damp and moldy on the back, and soaked cardboard boxes had been lifted onto shelves instead of thrown away. The team recommended removing the lower, water-soaked gypsum, discarding all the cardboard boxes, running a dehumidifier continuously for about a week, and having a builder seal cracks in the party wall shared with the neighbor.

Once the house was properly dry, ozone treatment was booked for a Saturday. The family took Grandma to a nearby shopping mall, and Prae told the neighbors on both sides in advance. The team treated three zones: Grandma's room, the under-stair storeroom and the back kitchen. After the rest and ventilation period, the family returned in the evening. Prae said the musty smell in Grandma's room was gone, and the family kept taking Grandma to her follow-up appointments with the doctor.

Townhouse flood recovery checklist

Safety first

• Switch off ground-floor power at the breaker and have an electrician check any sockets that were submerged before use.
• Wear gloves, boots and an N95 mask while clearing storerooms and the under-stair room.
• Watch for rats, snakes and insects hiding in boxes and dark corners.
• See a doctor immediately for fever, calf pain or diarrhea after wading.

Sort and remove

• Discard cardboard, books and fabrics soaked in muddy water that smell. Photograph them for insurance first.
• Remove soaked gypsum, plywood and insulation to a sensible height above the flood line, as your builder advises.
• Check kitchen extension tiles that sound hollow and have a builder assess the floor and the joint crack.

Wash and dry

• Wash floors and walls with water and detergent, especially around drains, under the sink and anywhere sewage may have backed up.
• Open front and back doors for cross-ventilation, point fans into the under-stair room and run a dehumidifier continuously. WHO and CDC advise cleaning and drying within 24 to 48 hours to limit mold.
• Do not repaint or install new walls until the structure is completely dry.

Ozone day

• All people, pets and plants must leave the entire house, including the upper floors.
• Tell neighbors on both sides in advance and let the team check and seal shared openings.
• Open the under-stair door, kitchen cabinets and internal storage cupboards.
• Seal food in closed containers or take it out of the house.

After ozone and long-term care

• Re-enter only when the team confirms the rest and ventilation period is complete.
• Store items under the stairs in lidded plastic boxes on raised shelves, away from the walls.
• Add an exhaust fan or vent to the under-stair room if possible.
• Watch for new stains or smells in the first one to three months and fix any moisture source right away.

Frequently asked questions about townhouses after floods and ozone

1. The houses are joined. Will ozone leak into my neighbor's home?

The team checks possible connections such as cracks in the party wall, pipe openings and roof-space gaps and seals them before starting. We also recommend telling your neighbors in advance so everyone feels comfortable.

2. Can you treat only the ground floor while we wait upstairs?

No. Townhouse staircases are open and connect the air on every floor. Everyone must leave the house during treatment and return only after the rest and ventilation period.

3. The gypsum under the stairs is already moldy. Can ozone fix it without tearing it out?

If the gypsum soaked up water and has mold on the back, it should be replaced, because the moisture inside the board will let mold return. Ozone treatment follows removal and drying, to deal with remaining spores and odors in the space.

4. The kitchen extension smells of drains. Will ozone help?

If the smell comes from water trapped under the tiles or a broken pipe, fix the cause first. After repair and cleaning, ozone is very effective at dealing with remaining odors and germs in the space.

5. How long does it take?

About 30 minutes per zone, plus preparation, rest and ventilation. Most townhouses are finished within a single day.

6. Price and promotions

Price depends on house size, number of floors and number of zones. Call or message on LINE for an assessment. Jobs of 15,000 baht or more include a free medical-grade disinfectant spray.

Make every corner of your townhouse livable again, even under the stairs

The WHD team is ready to survey the damp corners of your townhouse after the flood and finish recovery with ozone treatment that leaves no chemical residue.

See the Ozone Disinfection Service

Call 065-556-6294  |  LINE @whd268  |  worldhealthdisinfection@gmail.com

Related pages

• Residential and Building Ozone Disinfection
• Chemical residue odor removal with ozone
• Ozone disinfection machines
• Certification documents
• Contact us

References

• CDC: Floods (cleanup guidance)
• World Health Organization fact sheets