A Story from the Field: Our House Is Clean, but the Smell Comes Through the Wall

Nid is forty-five and lives in a two-storey townhouse in a small housing estate off Lat Phrao Road with her husband and their nine-year-old daughter, who has allergies. During the 2026 floods, water entered every house in the row to a depth of about forty centimetres. Once it went down, Nid's family spent nearly two weeks shovelling mud, throwing out a sofa and wooden cabinets that had swollen, scrubbing floors, and finally booking a team to disinfect and ozone-treat the house. By the end, their home smelled fresh again.

Less than a week later, the musty smell came back. This time it was not coming from the floor. It was coming from the living-room wall that the family shares with the house next door. Nid noticed a damp ring forming low in one corner and small black dots appearing along the skirting board. The upstairs bedroom on the same wall began to smell like laundry that had not dried properly. Her daughter started sneezing every morning again.

The house next door belongs to an elderly man in his seventies who lived alone. When the water came, his son took him to stay in another province. The house was locked up with mud, a mattress and waterlogged furniture still inside. Through the front gate you could see tide marks on the walls and a pile of belongings that had never been carried out.

Nid did not want to fall out with a neighbour she had known for ten years. She also did not want her daughter to keep getting ill. She needed a way to protect her family that would also respect her neighbour, and she was far from alone. Across Bangkok's townhouse estates, many families who restored their homes quickly are now discovering that a home is only as dry as the house on the other side of the wall.

How Odor and Mold Travel from Next Door into Your Home

Townhouses and semi-detached houses share a party wall, and many also share a continuous roof structure, connected drainage and back yards that sit side by side. Moisture and odor have several routes to cross from one home into another.

• The shared wall. Brick or lightweight concrete block walls that absorbed water on your neighbour's side slowly pass that moisture through to yours, especially in the lower section that was underwater. If mud and wet belongings are still piled against the wall on their side, it will never dry out.
• A continuous roof space. In many older townhouses, the party wall stops at the ceiling and does not continue up to the roof tiles. Damp, musty air from one house can drift across the roof space into the next.
• Drains and inspection chambers. If your neighbour's drains or inspection chamber are still blocked with mud, wastewater can stagnate and the smell can reach you through connected pipes or a front inspection chamber that sits right beside yours.
• Cracks and service penetrations. Cracks along the wall, cable holes and pipe openings that pass through the party wall are direct paths for air.
• Adjoining back yards. Rubbish, wet mattresses and furniture dumped behind the house next door are a source of odor, mosquitoes and rats, often just a few metres from your kitchen window.

The Effects You Should Not Ignore

Your family's health. More mold spores inside your home can trigger allergies, asthma, a blocked nose, sneezing and coughing, particularly in young children, older people and anyone with a weakened immune system. A house that still contains mud and standing water may also harbour bacteria such as E. coli, and rats moving in can spread the bacteria that cause leptospirosis.

Work you have already done goes to waste. If the source is still on the other side, the wall you have just repainted may grow mold again. The money and effort you put in will not deliver what you expected.

Mosquitoes and rats. A locked house with standing water and wet rubbish is an ideal breeding place for Aedes mosquitoes and a shelter for rats that can cross into your home over the roof or the fence.

Your relationship with your neighbour. Problems left unspoken tend to turn into resentment. Starting a polite conversation early protects both your health and the goodwill between your households.

The value of the whole row. Anyone who views a house in the same row, to buy or to rent, will notice the smell and the condition of the houses on either side.

Common Reactions That Don't Fix the Source

• Painting damp-proof paint on your side of the wall. It helps for a while, but if the wall is still taking on moisture from the other side, the paint will blister and mold will return.
• Keeping the room shut with the air conditioner running. It reduces humidity in the air, but the smell keeps seeping in through the wall every day.
• Air fresheners or charcoal bags. They mask the odor briefly and do nothing about mold or germs.
• Climbing over to clean your neighbour's house yourself. Never do this without the owner's permission. Apart from violating their rights, you risk electrical hazards, unstable structures and exposure to contaminated mud.
• Staying quiet and waiting for the neighbour to return. The longer you wait, the further mold spreads on both sides of the wall.

A Friendly, Step-by-Step Approach: From Conversation to Restoring Both Homes

1. Record what is happening. Photograph the damp patches and mold spots, and note the dates and times when the smell is strongest. This is not about building a case. It is so you can talk with clear, calm information.
2. Contact the owner politely. If you do not have a phone number, ask the estate's juristic person, the estate manager or another neighbour to help you get in touch. Explain the problem honestly and ask how they are doing too. Very often, owners simply do not know that their house is affecting anyone else.
3. Offer an easy solution. For example, offer to help arrange a team to remove damaged items and a team to disinfect, so that the owner only needs to give permission and send someone to unlock the house. Treating both houses on the same day also makes planning simpler.
4. Let the owner decide. Every step inside their home requires the permission of the owner or someone they appoint. The WHD team only enters a property when a person with the right to do so opens it for us.
5. Protect your side at the same time. You do not need to wait for the other side to be ready. You can reduce the impact inside your home straight away, as described in the next section.
6. If you really cannot reach the owner. Talk to the estate's juristic person, or ask your local district office, which handles sanitation and community nuisance issues, for advice on what to do next.

How to Start the Conversation: A Simple Message You Can Adapt

Many people delay contacting a neighbour simply because they do not know how to begin. A short, warm message that focuses on shared interests usually works far better than a complaint. Here is an example you can adapt to your own words:

Notice what the message does: it opens with concern for the other family, describes the problem without blame, offers practical help and leaves the decision with the owner. If the owner lives far away, offering to coordinate can be the most valuable thing you do for them.

Protecting Your Side While You Wait: What You Can Do Right Now

• Move furniture away from the shared wall. Leave a gap of five to ten centimetres so air can circulate and you can spot new damp patches easily.
• Seal openings through the party wall. Have a builder seal cable holes, pipe openings and cracks with suitable materials to reduce air coming from next door.
• Wipe small mold spots. Use CHEMGENE HLD4H spray on small areas, wear gloves and a mask, and keep windows open while you work.
• Ventilate in the right direction. Open windows on the side away from your neighbour and use extractor fans to push air out, rather than blowing air towards the shared wall.
• Ozone-treat rooms along the shared wall. This reduces musty odors and airborne mold spores in your home while you wait for the source next door to be dealt with.
• Look after your own front inspection chamber. Clean it, and pour water into floor drains regularly so the traps stay filled and block sewer smells.

How WHD Helps: Disinfection and Ozone Treatment for Homes That Share a Wall

World Health Disinfection (WHD) provides ozone treatment and disinfection fogging for homes after floods. We take single-house jobs as well as two-house or whole-row jobs when owners agree to treat their homes together.

• Disinfection fogging with CHEMGENE HLD4H. We use CHEMGENE HLD4H, a professional-grade disinfectant, applied with ULV equipment as a very fine mist. It reaches lower walls, skirting boards, room corners and the space under the stairs.
• Ozone treatment. Ozone helps reduce airborne mold spores and breaks down the molecules behind musty, muddy and drain-like odors, both in a house that has not yet been restored, once damaged items have been removed, and in your own home that has been affected.
• Treating both sides together. If your neighbour agrees, treating both houses in one round breaks the cycle of moisture and odor passing back and forth through the wall.

How We Work

1. Survey the party wall, roof space, drains and inspection chambers of the houses involved.
2. Advise on removing mud, mattresses and damaged furniture from a house that has not yet been restored.
3. ULV disinfection fogging of areas that were flooded.
4. Ozone treatment with controlled dose and duration, with sensitive electronics covered or moved out first.
5. Ventilation, a re-check of odors and mold spots, and advice on long-term moisture control.

Understanding Your Party Wall: Why It Dries So Slowly

A party wall in a typical Bangkok townhouse is a single masonry wall, often plastered on both sides. When floodwater sits against it, water is drawn into the bricks or blocks and the mortar joints, then slowly moves upward and sideways. Drying works in reverse: moisture has to travel back to the surface and evaporate. If one side of the wall is painted with a dense coating and the other side is blocked by wet belongings, there is almost nowhere for the water to go.

That is why a party wall can stay damp for weeks after the floor is dry. Lightweight concrete blocks, which are common in newer townhouses, hold even more water than traditional red bricks. While the wall is wet, mold grows readily on its surface, behind skirting boards and behind furniture placed against it.

The practical lesson is that both faces of the wall need to be cleared, cleaned and allowed to breathe. You can do your part by moving furniture away and keeping air moving on your side. Your neighbour's part is equally important, which is why a cooperative approach almost always gives the best and fastest result.

It also helps to know that a damp wall is not always a sign of a leak or a structural problem. In most homes we visit after a flood, the moisture is simply water that soaked in while the street was underwater and has not yet had a chance to escape. Once the source is removed and air can move freely on both sides, most party walls dry steadily. If damp patches keep growing after several weeks, ask a builder to check for a leaking pipe or a gutter problem along the shared roof line.

A Realistic Timeline When Neighbours Work Together

Week 1: Talk and agree. Contact the neighbour, explain the situation and agree a date. Arrange for someone to unlock the house and for a team to remove mud and damaged furniture. Have an electrician check the electrics in the neighbour's house before power is switched back on.

Week 2: Disinfect and deodorize both homes. Once the damaged items are out, book disinfection fogging and ozone treatment for both houses on the same day. Seal any openings through the party wall at the same time.

Weeks 3 to 6: Let the wall dry. Keep air moving on both sides and avoid repainting until a builder confirms the wall is dry. Check regularly for new damp patches or mold spots and wipe them promptly.

After that: Repair and maintain. Repaint, replace skirting boards if needed and agree a simple arrangement with your neighbour, such as checking the back yards and drains together after heavy rain.

If your neighbour cannot act straight away, follow the steps to protect your side and repeat ozone treatment in affected rooms if needed until the source has been removed.

Checklist: Where to Look on Your Side of the Wall

• ☐ The lower thirty to sixty centimetres of the party wall in every room
• ☐ Behind sofas, wardrobes and bookcases standing against the shared wall
• ☐ Skirting boards and the corners where the party wall meets the floor
• ☐ The ceiling near the party wall, and the roof space if you can access it safely
• ☐ Cable holes, pipe openings and cracks through the party wall
• ☐ The front inspection chamber and floor drains next to your neighbour's
• ☐ The boundary fence and back yard, for standing water and dumped items
• ☐ Bedrooms on the upper floor that share the same wall

10 Reasons Shared-Wall Homes in Lat Phrao Choose WHD

1. Ozone treatment reduces musty odors in rooms along the shared wall.
2. ULV disinfection fogging reaches lower walls and damp corners.
3. We use CHEMGENE HLD4H, a professional-grade disinfectant.
4. Two houses can be treated together when both owners agree.
5. We trace odor routes through the wall, roof space and drains.
6. We only enter a property with the owner's permission.
7. Ozone dose is controlled, and electronics are covered before treatment.
8. Practical advice on long-term moisture control for party walls.
9. A mosquito spraying service for back yards with standing water.
10. A dust mite removal service for mattresses in affected rooms.

Before and After Solving an Odor Problem from Next Door

Customer Voice (Example Scenario)

"I hesitated for a long time before calling our neighbour's son. I was worried he would think we were complaining. I got his number from the estate office and just explained honestly. He actually thanked us, because he had no idea the house was in that state. He arranged a day to unlock it and the team disinfected and ozone-treated both houses together. Our living-room wall is drying out now, the smell has mostly gone, and my daughter is sleeping much better."

— Nid, townhouse owner in Lat Phrao (example scenario)

Frequently Asked Questions

Q: If my neighbour is not ready, can I have only my house ozone-treated?
A: Yes. Ozone-treating your home reduces musty odors and airborne mold spores. However, while the source remains next door, some smell may return, so combine it with sealing openings in the party wall and contacting the neighbouring owner.

Q: Can your team work in the house next door if the owner is away?
A: No. Our team only enters a property when the owner or their appointed representative gives permission and opens it for us.

Q: Why is treating both houses at once better?
A: It cuts off the routes by which moisture and odor pass back and forth in a single round, and the estate office only needs to coordinate once.

Q: If one house is ozone-treated, will ozone drift into the house next door?
A: The team controls dose and time to suit the space and recommends informing neighbours in advance. If the party wall has many openings, we assess and seal them before starting.

Q: How long before a damp party wall can be repainted?
A: Wait until the wall is truly dry on both sides, which depends on its thickness and the weather. Ask a builder to measure moisture before painting.

Q: I cannot contact the neighbouring owner at all. What should I do?
A: Ask the estate's juristic person or your local district office for advice. In the meantime, protect your side of the wall using the steps above.

Q: Will ozone damage anything in my home?
A: Dose and duration are controlled. Sensitive electronics, artworks and items containing natural rubber are covered or removed beforehand as a precaution.

Stop Musty Odors Crossing the Wall. Talk to WHD Today.

We serve townhouses, semi-detached and detached homes in Lat Phrao, Wang Thonglang, Chok Chai 4 and nearby areas.

Book Ozone Treatment – Click Here

View Disinfection Service – Click Here

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

Related Links

• Residential ozone disinfection
• Ozone treatment for odors and chemical residue
• Master Ozone Generator
• All articles
• External sources: WHO: Floods and health and Thailand Department of Health