A Story from the Field: Eight Tenants, Eight Different Demands

Khun Kate is forty and manages a four-storey commercial building she took over from her father. It stands in a soi off Pracharat Bamphen Road in Huai Khwang, Bangkok, and is divided into eight small offices for rent. Her tenants include an accounting firm, a small travel agency, a design studio, an insurance agent and an online shop that uses its unit as a packing room. The ground floor has the entrance lobby, shared toilets and two of the leased units.

During the 2026 floods, water in the soi came into the ground floor about thirty centimetres deep and stayed for several days. Power to the ground floor was cut and the building was closed for almost two weeks. When the water receded, it left a thin layer of mud across the lobby floor, a sewer smell coming up from the shared toilets, water stains along the lobby walls, and soaked carpet tiles and fabric partitions in the two ground-floor units.

What Khun Kate did not expect was that tenants on the second, third and fourth floors, where the water never reached, would start messaging her almost every day. The accounting firm said its files smelled. The design studio said the staircase and corridors were so musty that clients did not want to come up. The insurance agent asked for a rent reduction. The ground-floor tenants wanted to know when they could reopen. Every tenant wanted a different answer, and every tenant wanted it this week.

"If we do it room by room, the way each tenant asks, it will never end," Khun Kate told our team, "and the smell from the common areas will just come back into the rooms we have already done." This is exactly the challenge many owners of multi-tenant buildings face once the water goes down.

Why Only the Ground Floor Flooded but Every Floor Smells

• The staircase and lobby are the building's air shaft. Damp air and odours from the ground floor rise up the stairs into every corridor and seep into leased units through the gaps under doors.
• A building closed for days without air conditioning. Sealed office rooms left for days in humid weather accumulate moisture easily, especially rooms full of carpet, fabric partitions and paper files.
• Shared toilets and drains. Floodwater pushes silt and sewage back into the pipes. As the water traps in floor drains and basins dry out, sewer gases escape into the building.
• Air conditioners restarted after a long stop. Units left off in high humidity can grow mold on their coils and drain trays, and when they are switched on again they blow musty air into the office.
• Office contents that absorb moisture. Paper files, boxes of stock, fabric chairs and carpet tiles all hold odours and feed mold.

In other words, a multi-storey building behaves like one connected space. Cleaning one floor or one unit without dealing with the shared air paths rarely solves the problem.

There is also a human factor. When tenants on the upper floors smell something unpleasant on the stairs every morning, they naturally assume the problem is bigger than it is, and complaints multiply. Dealing with the shared spaces first often calms the situation as much as it improves the air.

What It Means for the Owner and the Tenants

Health of the people working there. Staff who sit in a musty office for many hours a day are at risk of allergy symptoms, coughing, a blocked nose, headaches and asthma flare-ups. Mud and flood residue on the ground floor may carry bacteria that cause diarrhoea or skin infections, and cleaners washing out mud should be careful about leptospirosis. Rubber boots and gloves are essential.

Income. Tenants who cannot work may ask for rent reductions or decide not to renew. Vacant units in a building that smells are also harder to let. The longer the problem drags on, the more the building's reputation suffers.

Relationships with tenants. Delays and unclear communication can make tenants feel that the owner does not care, even while the owner is working hard behind the scenes to fix things.

Your tenants' own customers. An accounting firm or a travel agency depends on clients walking in. A musty lobby and staircase reflect badly on your tenants' businesses as well as on the building.

Step One: Communicate with All Tenants at the Same Time

1. Set up one communication channel, such as a building LINE group, so every tenant receives the same information at the same time and you are not answering the same questions eight times.
2. Share the sequence of work and expected dates, for example the electrical inspection, mud clean-up, disinfection fogging and ozone treatment, and the date you expect the building to reopen.
3. Ask for consent to enter leased units. Fogging and ozone inside a tenant's unit require the tenant's permission. State the date and time, and ask tenants to secure valuables, confidential documents and sensitive electronics.
4. Explain what tenants need to do beforehand: shut down computers, unplug equipment, remove food and plants, and make sure nobody is in the building during ozone treatment.
5. Handle rent and lease questions case by case, based on the lease and the facts, and keep photographs of the damage to support the discussion.

Common Areas Versus Leased Units: Who Handles What

One of the most common sources of friction after a flood is uncertainty about responsibility. Setting it out clearly at the start saves a lot of back-and-forth later. The exact split depends on your leases, but a typical arrangement looks like this.

• The owner usually handles the common areas: the lobby, staircase, corridors, shared toilets, the building's electrical system up to each unit, external drains and the roof.
• Tenants usually handle their own contents: furniture, stock, documents, computers and anything they brought into the unit, including deciding what to throw away.
• Grey areas need a conversation: carpet tiles and partitions installed by a tenant, air conditioners supplied with the unit, and damage inside a unit caused by water that came through common areas.

Writing down what you have agreed with each tenant, even in a short message, prevents misunderstandings. When everyone knows who is doing what, the whole building recovers faster. (This is general guidance, not legal advice.)

Supporting Tenants Whose Work Depends on Paper or Stock

Some businesses are hit harder than others. An accounting firm with years of client files, or an online shop with boxes of stock, may be worried about losses that go beyond the smell. As the owner, you cannot solve everything for them, but a few practical suggestions go a long way. Encourage them to separate damp files and let them dry in a shaded, airy place before boxing them again, and to scan anything important. Suggest that stock in cardboard is moved into lidded plastic boxes once it has been checked. Remind them that items with mold or a strong musty smell should not be sent to customers. And make sure they know the date of the building treatment, so they can have their unit included and avoid bringing clean items back into a room that still smells.

A Sample Notice to Tenants

Many owners find it easier to start from a short template. You can adapt something like this for your building group chat or a printed notice in the lobby:

Dear tenants, following the flood, the building will undergo professional disinfection fogging and ozone treatment on Saturday and Sunday. Common areas on every floor will be treated. If you would like your unit treated at the same time, please reply in this group by Thursday. Before Friday evening, please shut down and unplug computers, store important documents in closed cabinets, and remove food and plants. Nobody may enter the building from Saturday morning until we confirm it is safe to return. We expect everyone to be able to return to work on Monday morning. Thank you for your patience.

A clear, friendly notice like this answers most tenant questions before they are asked and shows that the building has a plan.

Why Fixing One Unit at a Time Does Not Work

• Each tenant hires someone separately, but the common areas still hold odour and germs. As soon as the unit door opens, the corridor smell comes straight back in.
• Cleaning only the ground floor leaves moisture and odour trapped in the upper corridors and stairwell.
• Spraying air freshener in the lobby mixes perfume with mustiness and leaves visitors feeling uncomfortable.
• Pouring bleach in the shared toilets creates fumes that bother tenants on every floor, and does nothing about drain odours or spores in the air.

The Solution: Disinfection Fogging and Ozone Treatment for the Whole Building in One Round

The World Health Disinfection (WHD) team plans a multi-tenant building as a single job, so the common areas and every participating unit are cleaned at the same time.

Disinfection fogging service. Using CHEMGENE HLD4H disinfectant through ULV fogging equipment, we cover the ground-floor lobby, shared toilets, staircase, corridors on every floor and every unit whose tenant has given consent. The ultra-fine mist reaches under the stairs, behind filing cabinets and onto shared surfaces such as handrails and door handles.

Ozone treatment service. After fogging, the team runs a controlled-dose ozone treatment to deal with airborne mold spores and break down the musty odour molecules trapped in carpets, partitions and upholstered furniture, so the building is ready to welcome clients again.

How the WHD Team Works in a Multi-Tenant Building

1. Whole-building survey. Together with the owner, we assess the common areas and each unit, separating units that were directly flooded from those that only have odour.
2. Scheduling. We usually work over a weekend or outside office hours so tenants' businesses are not disrupted, and the owner notifies tenants in advance.
3. Preparatory work. We advise on washing out mud, removing damaged carpet and fabric partitions, having an electrician check the ground floor, and having an air conditioning technician clean any units that smell.
4. Fogging with CHEMGENE HLD4H, working from the ground floor upward, through common areas and consenting units.
5. Controlled-dose ozone treatment. Doors and windows are closed, and warning signs are posted at every entrance. No people, pets or plants may be in the building during this stage. Sensitive electronics are covered or removed.
6. Ventilation and re-check. The building is opened up to clear the ozone until it is safe. We check the smell on every floor and let the owner know, so they can tell tenants it is time to return.

What Ozone Can and Cannot Do in an Office Building

Ozone is excellent at reaching every corner of a closed space and at breaking down the musty odour that soaks into carpets, partitions and upholstered chairs. It is not a substitute for removing the source of the problem. Carpet tiles that sat in floodwater, swollen chipboard furniture and soggy cardboard should still be taken out. Walls that are still wet will keep feeding mold until they dry. A sewer smell caused by a blocked pipe needs a plumber. Think of ozone as the final step that deals with what remains in the air and in soft materials once the obvious work has been done. Combined with disinfection fogging and good ventilation, that is what gives tenants a building that genuinely smells clean rather than one that has simply been perfumed.

Ozone Safety

• No people, pets or plants may be in the building during ozone treatment, including security staff.
• The building must be fully ventilated before tenants return. The team will confirm when it is safe.
• We use a controlled dose, because very high concentrations over long periods can age rubber and some plastics. Computers, printers and other sensitive equipment are covered or removed.
• Important documents should be kept in closed cabinets or lidded boxes.

10 Reasons for Building Owners to Treat the Whole Building in One Round

1. Common areas and units are cleaned together, so odour does not drift back into units already treated.
2. Disinfection fogging covers the lobby, shared toilets, staircase and corridors on every floor.
3. Ozone treatment tackles musty smells in carpet, partitions and upholstered furniture.
4. CHEMGENE HLD4H disinfects surfaces without relying on harsh-smelling bleach.
5. Work takes place outside office hours, so tenants' businesses are not interrupted.
6. Every tenant can return on the same day, reducing complaints and rent reduction requests.
7. The owner communicates one plan to everyone and earns tenants' confidence.
8. Tenants' clients no longer meet a musty lobby and staircase.
9. It protects the value of the building and makes it easier to find new tenants.
10. You receive long-term care advice, including on ozone treatment for odours and chemical residue.

Before and After

Checklist Before Reopening the Building to Tenants

• An electrician has checked the ground-floor distribution board, sockets and switches and confirmed they are safe to use.
• Mud has been washed out of the lobby, shared toilets and under the stairs, and floors are dry with no standing water.
• Floor drains in the shared toilets hold water again, so sewer gases cannot escape.
• Air conditioners in units with a musty smell have been cleaned by a technician.
• Damaged carpet, fabric partitions and cardboard boxes have been removed.
• Fogging and ozone treatment are complete and the building has been ventilated for as long as the team advised.
• A message has gone out to tenants confirming the building is ready, with a suggestion to open windows for the first hour.

Preparing the Building for the Next Rainy Season

Many commercial buildings in the sois of Huai Khwang sit in spots where water collects quickly during heavy rain. Preparing in advance reduces damage and lightens the load on the owner.

• Write a simple emergency communication plan for tenants: who coordinates, which channel you will use, and how tenants should protect their belongings.
• Encourage ground-floor tenants to keep stock and documents raised off the floor, in lidded plastic boxes rather than cardboard.
• Consider raising ground-floor power sockets, after consulting an electrician.
• Check the drains in front of the building and the roof gutters before the rainy season starts.
• Schedule periodic disinfection of the common areas, since a building with many visitors benefits from regular care.

Health Advice for Staff Returning to Work

When the building reopens, a few simple habits help everyone settle back in comfortably. Open windows for the first hour of the first few days to bring in fresh air. Ask cleaning staff to wear gloves and boots if any mud remains in hidden corners, and to wash their hands thoroughly afterwards. Encourage anyone with asthma or strong allergies to let their employer know if symptoms return, so the room can be checked again. If a staff member develops a fever, muscle pain or headache after helping with the flood clean-up, they should see a doctor and mention their contact with floodwater, because early treatment matters for infections such as leptospirosis. These steps are not complicated, but they show tenants and their staff that the building takes their wellbeing seriously.

Customer Voice

"What helped most was having one plan to share with every tenant. The team worked on Saturday and Sunday, and by Monday every office was back at work. The complaint messages in the group chat stopped." Khun Kate, owner of a small office building in Huai Khwang (a representative scenario from our field work)

Frequently Asked Questions (FAQ)

Q: Some tenants will not allow access to their units. What then?
A: We treat the common areas and the units we have permission for. Untreated units should keep their doors firmly closed during the ozone stage, and can be scheduled later.

Q: Can the work be done outside office hours?
A: Yes. Office buildings are usually scheduled at weekends or after working hours so tenants can carry on as normal.

Q: Do computers and documents need to be moved out?
A: Sensitive equipment is covered or removed, and important documents should be kept in closed cabinets. The team will give detailed advice before the treatment day.

Q: The shared toilets still smell of sewage. What should we do?
A: Refill dry floor drains with water to restore the trap seal, and have a plumber check for pipes blocked by silt before fogging and ozone treatment.

Q: Who should pay?
A: That depends on each building's leases and agreements. Common areas are usually the owner's responsibility, while leased units are best agreed with each tenant individually.

Q: How soon after the water recedes should we book the treatment?
A: Book as soon as you can, but schedule the treatment itself for after the mud is out, damaged materials are removed and the electrical system has been checked. Fogging and ozone work best in a building that is clean and starting to dry, and that is usually within the first one to two weeks.

Q: Do you serve buildings outside Huai Khwang?
A: Yes. We work with offices, shophouses, condominiums and homes across Bangkok and the surrounding provinces. Contact us by phone or LINE.

Get Every Floor of Your Huai Khwang Office Building Back to Work

Talk to the World Health Disinfection team about office building disinfection and ozone treatment after the flood. We are available every day.

View Disinfection Service, Click Here

Book Ozone Treatment, Click Here

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

Related Links

• Ozone treatment for odours and chemical residue
• Master Ozone Generator
• CHEMGENE HLD4H spray disinfectant
• All articles
• External sources: WHO: Floods and health and Department of Disease Control, Thailand