Empty houses
Mould and humidity in an empty villa in Phuket
Ask an owner who leaves a villa here what worries them most and it is rarely the roof or the pool. It is opening a wardrobe in November. This is what is really happening in the house while you are away, what stops it, and what to demand as proof that somebody has been inside.
The mechanism
What actually happens inside a house nobody opens.
Mould is not bad luck and it is not dirt. It is a few conditions occurring at the same time, and a closed house on this island supplies every one of them.
The spores are already in the house
They are in every house on earth: in the dust, in the fabric of the sofa, on the walls. Nothing you do keeps them out and no product removes them for good. They are simply waiting for water. What is different here is the dose. A villa sits in a garden that stays wet six months of the year, with a roof void open to the outside air and leaf litter a few metres from the doors, so the load arriving through every opening has nothing in common with a European apartment. You are not going to win this by cleaning. The whole subject is moisture.
Surface humidity is the number, not room humidity
Mould does not read the hygrometer on the wall. It responds to the thin layer of air touching a surface, and that layer can be far wetter than the room it sits in. The cool surfaces here are not the ones a European owner expects. The ground floor slab and the bottom of the walls sit a few degrees below room air because they are coupled to the earth. A masonry wall that has just taken a downpour is cooler again, and gives that water back inwards for days. And if a room is being air conditioned, the direction reverses: the cooled inner face of the wall becomes the cold surface, and the vapour arrives at it from outside. Any of the three puts the air against that surface far closer to saturation than the reading in the middle of the room. That is why a single wardrobe goes and the rest of the bedroom does not.
A closed house wets itself every night
Nothing has to leak for a shut villa to reach a dangerous number. The water in the air stays where it is while the building cools overnight, and relative humidity is a ratio, so it climbs as the temperature falls. Air sitting at 70% at thirty one degrees in the afternoon is above ninety per cent by four in the morning, in every room, every night of the year. Growth starts when the air touching a surface holds above about 80% for long enough, which is why a target of 55 to 60% in the room leaves real margin, and why a reading taken by a visitor at midday tells you very little about what the house did at dawn.
Still air is the accelerator
In a house with people in it, air is dragged around all day by doors, fans, cooling and bodies. In a closed house it stops moving. Warm and cool surfaces stop exchanging with the room, damp boundary layers sit undisturbed against timber and plaster, and moisture settles where it lands. Air movement removes no water at all, but it prevents the local wet spots where growth begins.
There is food on every surface
Mould does not eat concrete. It eats what is lying on the concrete: settled dust, skin oils, the sizing in cotton, the glue in plywood and bookbindings, the finish on tanned leather, soap film on tiles. That is why the first things to go are usually the things you would describe as clean, and the structure of the house comes second.
Nothing here has an off season
In a temperate country growth pauses for a few months of the year. Under a closed roof in Phuket the temperature sits in the range where these organisms are most active, all year round. A colony inside a wardrobe is usually the work of a couple of weeks, not of a whole season away.
The part owners find strange
An empty house goes faster than a full one.
People generate moisture. Showers, cooking, wet towels, a pool in constant use. And yet the villa with a family in it is the one that stays clean. An occupied house is not dry. It is ventilated, and it is watched.
Doors get opened, for no particular reason
Nobody living in a house opens it in order to control humidity. They open it because they are walking through it. Every opening breaks up the still layers, and every fan left running for comfort does the same. None of it is deliberate and all of it works.
The cooling runs because somebody is hot
This is the important one. An air conditioner removes water only while its compressor is actually turning, and in an occupied house it turns for hours. People are a wet load: bodies, showers, cooking, wet towels, a door held open onto a hot garden. The machine has to keep working through all of that, and every one of those hours sends water down the condensate pipe and out of the building. Take the people out and the wet load leaves with them. What remains is heat coming through the roof and the glass, which the machine deals with quickly, so it satisfies the thermostat and stops long before it has taken much water out of the air. Same unit, same setting, a fraction of the water removed.
Things get turned over, not just looked at
Clothes come out of the wardrobe, a book comes off the shelf, cushions get moved, a sheet is pulled off a bed. What that does is not ventilation. It breaks the still layer against the object and exposes the face that never sees air. Anything stored has a permanent hidden face: the underside, the back, the fold. That face never dries, and that is where it starts. So the useful instruction for anybody visiting a closed house is not to open the wardrobe, it is to turn over what is inside it. Looking at the front of a stack of folded linen proves nothing about the bottom of the stack.
Somebody smells it in week one
Mould announces itself by smell long before it is visible. A person in the house notices on day three and opens the cupboard. An empty house has no witness, so the first person to detect it is you, on arrival, at the point where it has stopped being a job and become a bill.
Small failures run for months
A dripping mixer, a slow leak under a sink, a split in the insulation on a refrigerant line above a false ceiling, a roof that lets water past during one storm in June. In an occupied house each of those is found within a day. In a closed house each one runs into the same square metre of plaster until somebody arrives.
Ventilation
When opening the house helps, and when it makes things worse.
The instinct is that a house needs to breathe. Here that is true at some moments and actively wrong at others, because the outside air often carries more water than the air you are trying to replace.
The test is the dew point, not the hour
Outside air on this island sits at a dew point of 23 to 25°C almost every day of the year. Any surface colder than that pulls water out of the air the moment you open the doors: a ground floor slab, a wall that has just taken a downpour, a room that was air conditioned yesterday. So do not open within a few hours of rain, and do not open a house that has just been cooled. Night is worth avoiding too, but not for the reason people repeat: night air here is cooler than the building, not warmer, and it will not condense on a warm wall. The problem is that it arrives close to saturation and chills the fabric of the house, which is exactly how you set up the condensation you get the next morning.
The right moment is a dry season afternoon
In the dry months the outside air genuinely carries less water: a February afternoon can sit near 60% at 33°C, which is as dry as this island gets. That is the window. If somebody is on site, that is when to open everything, wardrobes and store room included, and let air run through for a couple of hours. The dry season here is also the calm season, so do not count on a breeze to do the work. Put a fan in a doorway pushing air out of one end of the house and the rest follows. It costs nothing and does more good than a week of an air conditioner idling on a low setting.
Moving air is not the same as exchanging it
Circulating the air already inside removes not one gram of water. It still matters, because it breaks up the damp layer sitting against cool surfaces and evens out the temperature between rooms. A ceiling fan on its lowest speed, or a small fan pointed into the corner that always goes first, does real work for very little electricity.
Permanent openings are a security question, and half of it is already built
Most houses here already have part of this: ventilation blocks in a service wall, a turbine ventilator turning on the tile roof, a louvred back door that locks behind a grille. What makes any of it work is a low opening on one side and a high one on the other, not two grilles side by side. That is what gets the roof void and the store room moving instead of sitting still. Whether it is acceptable depends on the wall around the house and the road outside, but it is worth pricing a grille and a roof ventilator before buying a machine to solve a problem the building could partly solve on its own.
The spaces no air ever reaches
Inside a shut wardrobe, and behind it. The store room with its door closed, the void above a false ceiling, the space under a bed pushed against a wall. Whatever you do to the main rooms, these keep their own private climate. Opening them is a separate action, and unless it sits on somebody’s list by name it never happens.
Machines
Air conditioning, dry mode, and the dehumidifier.
This is where most of the wasted electricity goes, and most of the false comfort. The three are not interchangeable and only one of them is designed for this job.
Leaving the air conditioning on does less than you think
The machine chases a temperature, and in an empty house that is the wrong target. There is plenty of heat to remove here, arriving through the roof and the glass all afternoon, but almost no water arriving with it, so the thermostat is satisfied by cooling the air long before much has been wrung out of it. The compressor then runs in short bursts, and on many units the fan carries on across a coil that is still wet between them, which puts part of the water it just collected straight back into the room. You pay for a machine that is running and receive a fraction of the drying you assumed you had bought.
Dry mode is better, and still not the answer
On an inverter unit a proper dry cycle holds the compressor at a low, continuous output behind a slow fan, which favours condensation over cooling. That one is worth leaving on in a single room of a closed house. On an older on/off unit, still common in villas here, dry mode is closer to a short compressor cycle behind a low fan speed, and it does much less. Find out which you have. Either way it is governed by a temperature sensor rather than a humidity sensor, it serves only the room it is mounted in, and it stops when that room is cool enough. Check as well that the setting is a real dry cycle at all: on some units it amounts to little more than a low fan speed.
A dehumidifier is the machine built for this
Same physics, different control. It pulls air across a cold coil, the water runs off into a tank or a drain, and it aims at a humidity setpoint instead of a temperature. The heat it produces goes back into the room, which warms the air slightly and pushes the relative humidity down further. In a closed room it will hold a steady reading that no air conditioner will hold in an empty house.
The drain hose, and then the power cut
The failure we find most often is a good machine, correctly set, sitting with a full tank and a warning light. Every unit stops when its tank fills, and in the wet season a tank fills in a day or two. Unless it is plumbed to a permanent drain, a floor waste or a hose run into a bathroom, it protects the house for about two days and then does nothing for three months. The second failure is the one nobody plans for. Power cuts are routine here through the wet months, and most domestic dehumidifiers do not restart on their own: they come back to standby and wait for somebody to press the button. Buy one that resumes its last setting after a power failure, or accept that the machine is only ever as good as the next visit.
What to set it to, and what it really costs to run
A target of around 55 to 60% suits a stored house. Chasing a very low reading is not better: it costs more, works the compressor harder and can dry out timber and instruments for no benefit. The room has to be shut, or the machine spends the season dehumidifying the garden. To know the running cost, read the wattage on the rating plate, estimate the hours a day it will actually run, and multiply by the unit rate on your own electricity bill. That gives you a real number instead of one from a website, and it is usually smaller than owners fear.
Where it starts
The places it always begins, in the fabric of the house.
After enough closed-up villas you stop looking everywhere and go straight to five places. They are the same five every time.
The wardrobe against an exterior wall
A shut door, no air movement, a back panel a centimetre off the plaster, and clothing that is ideal food. If a house has one problem, this is it. What decides it is the wall behind: a ground floor room, an elevation that takes the afternoon rain, or a bedroom that gets air conditioned whenever anybody is in it. Any of those makes that back panel the coldest thing in the room. Worth marking on a plan which wardrobes back onto an outside wall and which sit on internal ones. The internal ones usually behave.
Bathrooms, silicone joints and floor traps
Owners assume an unused bathroom is a dry bathroom. It is not. The floor trap holds standing water, the room is often the darkest and least ventilated in the house, and the door is shut. Add old soap film in the grout and you have something that started in June and gets noticed in October. Once silicone has gone black, it stays black: that is a replacement, not a cleaning.
The void above a false ceiling
This is the one that costs money. Refrigerant lines, condensate trays and duct runs sit in a dark, unventilated space between a hot roof and a cooled ceiling board. A split in the rubber insulation on a suction line, a tray with a slow blockage, a drain pipe off its spigot. The first evidence is usually a stain spreading on the ceiling, by which time it has been running for weeks. Anyone inspecting a closed villa properly opens an access hatch and looks up with a torch.
Under and behind the furniture
The underside of a rattan sofa, the back of a headboard pressed against a wall, the base of a cupboard sitting flat on tile, the underside of a dining table. Unfinished timber or cane, in still air, with no light on it. Pulling furniture a few centimetres off the wall before a house is closed sounds too simple to matter and prevents a surprising amount.
The air conditioning units themselves
An indoor unit that has not turned for months has a dusty coil, a damp tray and a drain line that blocks: dust and biofilm inside it, ants, geckos or a wasp nest at the outlet on the facade. On the ducted units above a false ceiling the trap dries out as well, and the pan starts drawing air instead of draining. Either way the unit becomes a source of smell and a distributor of spores the moment somebody switches it on for arriving guests. A unit that stood idle through a wet season should be serviced before the house is used, not after the first complaint.
Where it starts
And in the things that are not simply replaced.
The building usually survives. What owners actually lose in a closed house is the contents, and almost always the same categories.
Mattresses
The underside is the problem, never the top. A mattress on a solid platform base has no air beneath it, and it is the one cool, still, enclosed surface in the room that also happens to be made of foam and cotton. Strip the bed before the house is closed and get air underneath: on its side against a wall, or lifted clear of the base. Wrapping it in plastic sheeting is worse than leaving it alone.
Leather
Sofas and chairs, but also belts, shoes and bags left in a wardrobe. Tanned hide carries oils and finishes that mould feeds on directly, so leather is often the first thing in a house to bloom, before anything structural shows. A grey or white surface bloom caught early wipes off and the piece survives intact. After months, the staining is in the hide and so is the smell.
Stored linen and clothing
Anything put away has to be dry before it is put away, and dry in Phuket means dry rather than nearly dry. Linen folded slightly damp into a closed cupboard in May is a certainty by August. Sealed boxes with desiccant work well for what you truly want to protect, open shelving in the dry room is the next best thing, and an airtight cupboard with damp contents is the worst of every option.
Books and paper
Paper takes up and gives back moisture with the room, the binding glue is food, and the brown spotting that appears across the pages does not come back off. Books stacked flat on a low shelf against an outside wall are the classic loss. If a house is being closed for a season, the books belong in the room with the dehumidifier, standing upright with space around them.
Paintings, photographs and anything on canvas
These want a conservator, not a household product, and the mistake owners make is trying first and asking afterwards. Wiping a canvas pushes the growth into the paint layer and takes the surface with it. Get art off exterior walls before closing the house. It wants the dry room, but not the hot corner of it: a dehumidifier heats the room it stands in, so keep canvases away from the machine, or leave that room its air conditioning as well. If something has already gone, photograph it and ask a professional before touching it.
Damage
What comes back, and what is gone.
Owners want a rule for this. There is one, and it turns on two things: whether the material is porous, and how long it ran before anyone looked.
Hard surfaces almost always come back
Tile, glass, painted concrete, sealed timber, laminate, stainless steel. Growth on a non-porous surface sits on top of it, and cleaning genuinely removes it. What matters afterwards is the moisture, because on a hard surface it will return to the same square of wall. A stain that comes back in the same place is a diagnosis, not a cleaning failure.
Silicone is a replacement job, and grout usually is
Silicone always. Growth gets below the surface and holds there, bleach lightens it for a few weeks and it comes back darker than before. On a house being prepared for guests, cutting the bead out and running a fresh one is quick, cheap and the only thing that works. Cement grout behaves the same way unless it was sealed, and there the fix is to rake it out and re-grout rather than to keep scrubbing it. Epoxy grout, if the house has it, is not porous: it cleans properly and stays clean. Find out which one is in the bathroom before anybody quotes you for taking it out.
Plasterboard, gypsum ceilings and chipboard do not recover
Once water and growth are inside the board, cleaning the face of it is cosmetic. The board comes out, along with whatever was feeding it, and it should not go back until the leak has been found. A carcass in particle board that has swollen is finished: it will never sit square again, whatever it is treated with.
Textiles usually, leather sometimes, foam almost never
Cottons and linens survive a proper commercial wash unless the stain has set into the fibre. Leather depends entirely on how early it was caught. Mattresses and upholstered foam are the honest bad news: once growth is through the ticking and into the foam, no cleaning reaches it, and the right decision is to replace the piece rather than pay twice.
The smell is the last thing to leave
A house that has been shut and damp holds an odour in the textiles, the wardrobes and the air conditioning long after the visible growth has gone. Guests notice it in the first thirty seconds and write it down. Clearing it means removing the source rather than spraying over it, and it is one of the few problems that is genuinely far cheaper to prevent than to repair.
The protocol
Closing a villa for three months.
This is what we do to a house before it is left, in the order it happens. None of it is expensive. The sequence is what makes it work.
Two weeks before: find the water
Fix the dripping mixer, look under every sink, check the roof and clear the gutters before the rain, and have the air conditioning serviced with every condensate drain cleared and tested. Everything else on this list is defence, and defence loses to an active leak. If the house has a damp patch with a history, that is where to start rather than where to finish.
Empty, dry and open everything soft
Launder all the linen and dry it completely, then store it sealed with desiccant or on open shelving in the dry room. Strip the beds and lift the mattresses off their bases. Take the leather, the books and the art out of the wardrobes and off the exterior walls. Then leave every wardrobe and every internal door standing open: a house closed on the outside should be open on the inside.
The appliances and the drains
Empty the fridge, defrost it, clean it, dry it and prop the door open. Do the same with the washing machine drum and its detergent drawer. Pour water into the floor traps and the sinks nobody uses, then add a spoonful of mineral oil to each, baby oil does the job and cooking oil goes rancid, so that the seal cannot evaporate and let the drains breathe back into the house. Over three months an unoiled floor trap in a Phuket bathroom is dry long before you return, and the smell an owner blames on mould is often the septic tank. Decide deliberately about the water main: leaving it on risks a failed hose flooding the house for weeks, turning it off means somebody has to think about the pool and the planting.
One dry room, one honest machine
Pick the room that will hold the vulnerable contents, and do not pick the one under the hottest part of the roof. A dehumidifier is a heater as well as a dryer: every watt it draws comes back into the room, and a shut room in Phuket settles several degrees above the rest of the house, which is fine for linen and hard on canvas and instruments. Plumb it to a permanent drain, set it to around 55 to 60%, and keep the door and the windows shut. Leave a fan on a timer for the rest of the house so the air is not completely still. If you would rather use what is already installed, run a dry cycle in one room rather than a low temperature across the whole house, and go in knowing it will do less.
Measure it, and have somebody actually come
Leave a hygrometer in the room that always goes first, and better still a small logger that records while nobody is there: the peak matters more than the reading at the moment a person walks in. Then set a visit interval and hold to it, weekly through the wet months. A visit means going in, reading the hygrometer before anything is opened, confirming the dehumidifier is still draining, looking inside the wardrobes and behind the furniture, and putting a torch into the ceiling void. Then one of two things, never both: open the house up if the weather allows it, dry, sunny and not just after rain, or leave it shut and run the air conditioning hard for an hour or two. Nobody cools a house with the doors open.
Proof
What to demand as evidence that somebody was really in your house.
This is the easiest part of the job to invoice and the easiest not to do. A tick in a box proves that a box was ticked. Ask for these five things instead, of us or of anyone else.
Dated photographs, from the same angles every visit
Not a wide shot of a tidy living room. The inside of the wardrobe on the exterior wall, the corner behind the sofa, the underside of a mattress, the bathroom joints, the open ceiling hatch. The same frames each month, so two months can be put side by side and a change becomes obvious. A photograph taken from a fresh angle every time is decoration, not a record.
A humidity reading, taken on arrival
Before the doors are opened, not after. Forty minutes of an open house makes any figure meaningless. A photograph of the hygrometer with the number legible, in the same room every time, gives you a series rather than an anecdote. A series is the only thing that tells you whether the house is drifting or holding.
Who was there, at what time, and for how long
A name and a time, not “the team”. Fifteen minutes is a walk through a closed villa, not an inspection of one. Running the machines properly and looking into the places that fail first takes closer to an hour, and a report should make it plain which of the two happened.
One thing that was wrong
This is the test we would apply to any manager, ourselves included. A monthly report that has carried nothing but good news for six months is not a report from a house, it is a template. Anyone who genuinely walks a property finds a bulb, a mark, a stiff lock, a tray that needed emptying. If none of that ever reaches you in writing, ask why not.
The right to ask for one photograph, unannounced
On a Tuesday, of one corner that you choose, with no notice given. Somebody who is in your house regularly can send it the same afternoon and thinks nothing of the request. The reply you get to that question tells you more about a company than any inspection form it prints.
Straight answers
What owners ask us about damp and mould.
Should I leave the air conditioning running while I am away?
Is a dehumidifier expensive to run in Phuket?
How often does someone need to visit an empty villa?
Can I just seal the house up completely?
There is already mould on the clothes in the wardrobe. What now?
Is empty house care part of management, or a separate service?
Reviewed . We update these pages when the practice on the ground changes, not on a schedule.
Where to go next
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Guides for owners
- Employing villa staff in Phuket
- Off-plan villa handover in Phuket: the snagging inspection
- How to choose a property management company in Phuket
- Self-managing versus hiring a property manager in Phuket
- Short-term rental rules in Phuket: the 30-day question
- Your rental guarantee is ending. What now?
- Switching property manager in Phuket
- Property management fees in Phuket
- The true cost of running a villa in Phuket
- Property management in Phuket for foreign owners
- Water in a Phuket villa: the tank, the pump and the day it runs dry
- Salt corrosion in a coastal villa in Phuket
- Villa air conditioning in Phuket: servicing, faults and who pays
- Villa pool maintenance in the Phuket rainy season
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