A Story from the Field: Three Weeks on the First Floor

Khru Nid is a 45-year-old primary school teacher. She lives in a two-storey detached house in a housing estate in Rahaeng subdistrict, Lat Lum Kaeo district, Pathum Thani, together with her husband, their two children and her 78-year-old mother. When flood warnings went out in 2026, the whole family spent a night carrying their belongings upstairs: sofa cushions, the television, sacks of rice, boxes of documents, baskets of clothes, the children's schoolbooks and her mother's mattress.

The water came into the house almost half a metre deep and stayed for nearly three weeks. Five people lived together in two bedrooms and a small landing upstairs. They boiled water and cooked rice in an electric pot on a table. Because it rained almost every day, laundry was dried indoors. Clothes soaked from wading out to buy supplies hung from curtain rails. The belongings they had carried up were stacked against the walls, half covering some of the windows, and most of the windows stayed shut to keep out mosquitoes.

When the water went down and the family started carrying things back downstairs, Khru Nid realised the upper floor had a problem of its own. The wall behind the stacked boxes had a band of black mold. The underside of the mattresses that had been laid on the floor was covered in white mold. The wooden wardrobe smelled strongly musty. Some document boxes had gone soft and smelled stale. Her mother was coughing more every night, and her younger child had developed an itchy rash in the creases of the elbows and knees.

"We went upstairs to keep our things safe," she said to our team. "How did the upstairs end up growing mold?" The answer is that during the flood, the upper floor became the most crowded, closed-up and humid space in the house, even though the water never reached it.

Why a Floor the Water Never Reached Still Turns Damp and Moldy

• Moisture rises up the stairwell. A ground floor standing in water for weeks releases humidity constantly. The staircase acts like a chimney, carrying damp air straight to the upper floor.
• Many people in a small space. Breathing, cooking, boiling water and bathing for five people add far more moisture to a room than most of us imagine. In a closed room, that moisture has nowhere to go.
• Drying laundry indoors. Wet clothes hung in a closed room are one of the largest moisture sources in any home, especially during weeks of rain with no sunshine.
• Some belongings were already damp. Items carried up as the water began to enter, such as table legs, the bottoms of boxes or cushions that touched the water, carried moisture and germs upstairs with them.
• Stacks block the airflow. Boxes and furniture pushed against walls and in front of windows create pockets of still air. The wall behind a stack is almost always the first place mold appears.
• Windows closed against mosquitoes and rain. Mosquitoes multiply quickly during floods, so many families keep windows shut all day. The humidity inside the room simply builds up.

Put all of this together and you have a warm, crowded, humid upper floor full of fabric, paper and wood, which is exactly what mold needs.

The Impacts Families Often Overlook

Health. The upper floor is where everyone sleeps, so mold spores in the bedrooms affect the family directly: allergy symptoms, a persistent cough, a blocked nose and asthma flare-ups. Older people and young children are usually affected first. Damp conditions also make skin rashes and fungal skin infections worse. Meanwhile, the ground floor that has just dried out still holds mud and flood residue that may carry bacteria, and there is a risk of leptospirosis from floodwater and mud. Always wear rubber boots and gloves when cleaning downstairs, and see a doctor if anyone develops a fever after contact with floodwater.

Belongings. The very things you carried upstairs to protect, such as important documents, books, mattresses and clothes, may have started to grow mold. If you carry them back down without checking, you take the mold with you into cupboards and shelves you have just cleaned.

Time. Restoring the house one floor at a time without a plan often means cleaning the same spaces two or three times as spores move between floors.

Family wellbeing. After weeks of living in cramped conditions, everyone wants their home back. Getting the order right means the family returns to normal life sooner and with fewer setbacks.

Sort Your Belongings Before Moving Them Back Down

The key is not to rush everything back downstairs. The ground floor still needs to be cleaned, disinfected and dried, and some of the items upstairs need checking first.

1. Divide everything into three piles. Dry with no smell; damp or smelly but cleanable; and heavily molded or falling apart, which should be thrown away.
2. Important documents. Separate any damp papers and let them dry in a shaded, airy spot. Photograph or scan them first. If official documents are damaged beyond use, ask the issuing agency about replacements.
3. Mattresses and pillows. Anything that lay on the floor for weeks should be checked underneath. If there is mold or a strong smell, consider replacing it, especially for older relatives and children.
4. Clothes and curtains. Rewash everything that smells, and dry it fully in the sun before putting it away.
5. Rice and dry food. If a sack smells stale, shows mold or has clumped together, do not eat it.
6. Keep items that are not ready upstairs for now, until the ground floor has been disinfected and is dry enough.

A Room-by-Room Checklist for the Upper Floor

Before you call anyone, walk through the upper floor with this checklist. It helps you see the full picture and gives our team useful information when you send photos.

• Bedrooms. Lift every mattress and check the underside and the floor beneath it. Look at the skirting boards and the lower part of the walls, especially in corners. Check behind headboards and under beds where boxes were pushed in.
• Walls where items were stacked. Once the boxes are moved, look for black or green spots, a fuzzy white film, peeling paint or a damp, cool feel to the touch. Photograph anything you find.
• Wardrobes and drawers. Open them and smell. Look at the back panels and the corners at the bottom. Check leather shoes, bags and belts, which often grow mold before clothes do.
• Windows and curtains. Check the frames and the bottom of the curtains, where condensation collects. Curtains that hung over wet laundry are often the first to smell.
• The upstairs bathroom. With five people using it for weeks and little ventilation, check the ceiling, the grout and the exhaust fan, if there is one.
• The landing and staircase. The top of the stairs receives damp air rising from below. Look at the walls along the stairwell and the underside of the handrail.
• Ceiling and roof space. If you see stains on the upstairs ceiling, there may be condensation or a roof leak as well. That needs a builder to look at, separately from mold treatment.

Looking After Older Relatives and Children During Recovery

In many Thai homes, grandparents and young children spend the most time indoors, and they are also the most sensitive to mold and damp. While you are clearing and sorting, try to keep them away from the dustiest work. If possible, let them stay with relatives or in the cleanest room of the house on the days when boxes are being moved and mud is being washed out. Keep the room they sleep in as dry and well ventilated as you can, and wash their bedding in hot water if the fabric allows. If an older person's cough gets worse, a child's rash spreads, or anyone has difficulty breathing, see a doctor rather than waiting for the house to be finished. Mention that the family has been living in a flood-affected home, as that information helps the doctor.

Why the Usual Approaches Are Not Enough

• Cleaning only the ground floor. It feels logical because the upstairs never flooded, but spores from the upper floor drift back down and settle on the surfaces you have just cleaned.
• Wiping walls with bleach. Stains on the wall may fade, but spores in the air, inside the wardrobe and in fabrics remain untouched. In a bedroom, the fumes are unpleasant too.
• Air fresheners and odour absorbers. They mask the bedroom smell for a while but do nothing about the cause.
• Running fans on their own. Fans help things dry faster, but once mold is present, they also blow spores around the whole house.

The Solution: Ozone Treatment Upstairs, Disinfection Fogging on Both Floors

The World Health Disinfection (WHD) team plans the restoration of a two-storey house as one job, not room by room, so that germs and spores do not simply move between floors.

Ozone treatment service. Ozone is particularly well suited to the upper floor, where the main problems are musty odour and spores in the air, in wardrobes and in fabrics. Ozone gas spreads into every gap in a closed room, helping to deal with mold spores and breaking down the molecules that cause musty smells.

Disinfection fogging service. Using CHEMGENE HLD4H disinfectant through ULV fogging equipment, we treat the ground floor that was directly flooded as well as moldy surfaces upstairs, such as the walls where boxes were stacked, the floor under mattresses and the staircase.

Treating both floors in one visit, in the right order, means the house is restored as a whole and the family can move back into every room with confidence.

Why the Order Matters: A Simple Sequence for the Whole House

Families often ask whether they should start upstairs or downstairs. The answer is that each step makes the next one work better, so the order matters more than the starting point.

1. Get an electrician to check the ground floor before using power downstairs.
2. Wash out mud and remove soaked items from the ground floor.
3. Sort belongings upstairs into the three piles and throw out what cannot be saved.
4. Let both floors dry with as much airflow as you can safely provide.
5. Have both floors treated together: fogging first, then ozone, then ventilation.
6. Move clean, dry belongings back downstairs, using closed plastic boxes where possible.
7. Keep an eye on the corners that had mold for the next few weeks, and keep humidity down.

Following this sequence means germs and spores are dealt with once, in the whole house, rather than being carried backwards and forwards between floors.

How the WHD Team Works in a Two-Storey House

1. Survey both floors. We assess mold and odour on the flooded ground floor and the damp upper floor.
2. Advise on clearing. Before treatment day, we explain how to wash out mud downstairs and sort belongings upstairs.
3. Fog the ground floor with CHEMGENE HLD4H across floors, walls, the kitchen, the bathroom and under the stairs.
4. Fog the high-risk areas upstairs, including walls where items were stacked, bedroom floors and the inside of open wardrobes.
5. Controlled-dose ozone treatment for the whole house. Doors and windows are closed. No people, pets or plants may be inside. Sensitive electronics are covered or removed.
6. Ventilate and re-check. The house is opened up to clear the ozone until it is safe. We check the smell and the risk areas, then advise when it is a good time to carry belongings back downstairs.

What Ozone Can and Cannot Do

Ozone is very effective at reaching the places a cloth or spray cannot, and at breaking down the musty odour that soaks into fabrics and wardrobes. It is not a replacement for basic cleaning, though. Visible mold growth on walls should still be cleaned off, soaked mattresses that cannot dry still need to go, and a wall that is still wet will keep feeding mold until the source of moisture is removed. Think of ozone as the finishing step that deals with what is left in the air and in soft materials once the obvious work is done. Used that way, together with disinfection fogging and good ventilation, it gives the most reliable result.

Ozone Safety

• No people, pets or plants may be inside the house during ozone treatment. Plan for the family to be out during the treatment window.
• The house must be fully ventilated before anyone goes back in. The team will tell you when it is safe.
• We use a controlled dose, because very high concentrations over long periods can age rubber and some plastics more quickly.
• Older relatives' medicines, food and baby supplies should be kept in sealed containers or taken out of the house during treatment.

10 Reasons to Treat the Upper Floor Together with the Ground Floor

1. The upper floor is where everyone sleeps, and clean bedroom air has a direct effect on health.
2. Ozone treatment tackles musty smells in wardrobes and fabrics that washing alone cannot remove.
3. Disinfection fogging on both floors at the same time stops germs moving between floors.
4. CHEMGENE HLD4H disinfects surfaces without relying on harsh-smelling bleach in bedrooms.
5. It reduces the risk that the belongings you worked so hard to save are damaged further.
6. Older relatives and young children get back to sleeping in rooms where they can breathe freely.
7. One whole-house job means you do not have to clean the same rooms again and again.
8. You get clear advice on when to move belongings back downstairs.
9. It helps the family return to normal life sooner after weeks of crowded living.
10. You get long-term care advice, including on residential ozone disinfection and our dust mite removal service for mattresses.

Before and After

Next Time: How to Move Belongings Upstairs Without Making the Upper Floor Damp

Many homes in Lat Lum Kaeo sit close to canals and low-lying land. Planning ahead for moving your belongings can reduce the damage next flood season.

• Prepare lidded plastic boxes in advance. Use them instead of cardboard, which absorbs moisture and collapses. Label each box so you can find things easily.
• Leave a gap of at least a hand's width from the walls and keep windows clear, so air can flow behind the stacks.
• Raise things off the floor. Use shelving or plastic pallets. Do not leave mattresses flat on the floor for weeks; stand them up to air from time to time.
• Keep wet and dry items apart. Wipe anything that got wet during the move before stacking it with other belongings.
• Choose a drying corner near a window or balcony, and use mosquito screens or nets rather than keeping windows shut all day.
• Have a fan or dehumidifier ready for the upper floor, as long as electricity can be used safely.

None of this will keep a house completely free of humidity during a flood, but it greatly reduces the places where mold can take hold and makes recovery afterwards much easier.

Customer Voice

"At first we only asked the team to look at the ground floor, but they showed us the mold behind the boxes in the upstairs bedroom. Doing the whole house at once settled it. My mother sleeps much better now, and the children's room doesn't smell musty anymore." Khru Nid, two-storey house in Lat Lum Kaeo (a representative scenario from our field work)

Frequently Asked Questions (FAQ)

Q: The upper floor never flooded. Does it really need ozone treatment?
A: If there is a musty smell, mold behind stacked items, or someone in the household has allergies, ozone treatment upstairs helps deal with odour and spores in the bedrooms. Our team will assess first and only recommend what is needed.

Q: Should belongings go back downstairs before or after fogging?
A: After fogging and once the ground floor is dry enough, so clean items do not meet leftover moisture and germs.

Q: Can a moldy mattress still be used?
A: If the mold has penetrated deeply or the smell is strong, it is better to replace it, especially for older relatives and children. If there are only surface marks and it is fully dry, it may be cleanable. Judge each item on its own condition.

Q: How long do we need to leave the house during ozone treatment?
A: It depends on the size of the house and the strength of the odour. The team will give you a clear time, including the ventilation period, after assessing the house.

Q: What about electrical safety on the ground floor?
A: Have an electrician inspect sockets, switches and wiring that were under water before switching power back on downstairs. A disinfection team cannot certify electrical safety.

Q: How should we prepare for the next rainy season?
A: Use lidded plastic boxes on raised shelving, keep a gap from the walls, do not block windows, and ventilate whenever you can.

Let Your Two-Storey Home in Lat Lum Kaeo Breathe Again, Top to Bottom

Talk to the World Health Disinfection team about ozone treatment for musty upper floors and disinfection fogging for the whole house. We are available every day.

Book Ozone Treatment, Click Here

View Disinfection Service, Click Here

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

Related Links

• Residential ozone disinfection
• Dust mite removal service
• Master Ozone Generator
• All articles
• External sources: WHO: Floods and health and Department of Health, Thailand