The short answer
Black spotting, damp panel backs and a musty smell in stored clothing almost always mean condensation rather than water coming through the building. Warm, moist bedroom air reaches a cold external or party wall that has been sealed off behind an airtight box, moisture drops out onto that cold surface and mould follows.
The wall behind a wardrobe on an external elevation is frequently the coldest and least ventilated surface in the whole room. Enclose it completely and you have created the ideal conditions for surface mould, whatever the cabinetry is made of.
Why the surface behind a wardrobe goes cold
Room heat normally washes across a wall and keeps its surface temperature above the dew point. A sealed run of wardrobes fixed hard to the plaster stops that circulation and adds an insulating layer of clothing and shelving. The plaster behind sits several degrees colder than the rest of the room.
The moisture is generated in the ordinary way: breathing, drying laundry, bathrooms, cooking. It migrates to the coldest surface available. In a solid nine-inch Victorian wall with no cavity, that surface is behind the furniture, which is why mould appears there and nowhere else.
Ruling out genuine water ingress first
Before treating it as condensation, the pattern should be checked honestly. Condensation typically shows as fine black speckling across a broad area, worse in winter, worse at cold corners and at low level, with clean plaster behind it. Penetrating damp is usually a tide mark or a localised stain, often traceable to a defective gutter, a failed pointing joint, a bridged cavity or a leaking pipe run.
That distinction matters because joinery detailing will manage condensation risk but will not cure a leaking rainwater pipe. Where the pattern suggests ingress, the building fault has to be resolved first and by the appropriate trade.
- Fine black speckling over a wide area, seasonal: condensation.
- Defined stain, tide mark or damp that persists in summer: investigate ingress.
- Damp confined to one corner below a window or gutter: check the external fabric.
- Musty clothing but a dry wall: poor ventilation inside the carcass.
How fitted joinery should be detailed on a cold wall
The principle is to keep air moving and to avoid pressing a sealed panel against cold plaster. That means a ventilated cavity behind the carcass rather than a hard fix onto the wall, a fixing method that maintains that gap, and a plinth and top detail that allow air to enter low and leave high.
Inside the wardrobe, discreet ventilation to hanging and shelved compartments keeps stored clothing dry. Slatted or perforated backs, small vents behind the carcass line and avoiding fully airtight compartments all help. Materials matter too: moisture-resistant board where a run sits against a known cold wall, and finishes applied to all faces including backs and edges so panels are not left able to absorb moisture from one side only.
Where a wall is genuinely cold, the correct sequence is to address the wall before the joinery arrives - insulated plasterboard or an appropriate breathable system specified by whoever is handling the building fabric - then install the run with a ventilated void. Retrofitting that later means dismantling new furniture.
Putting an existing installation right
On an existing run the first step is to open it up and look at how it is fixed. If the carcasses are hard against the plaster with no ventilation path, they can often be brought forward onto a battened line, with the plinth and top adapted to allow airflow. Affected board is treated or replaced, and the plaster is dried and made good before anything is refitted.
The occupant side matters as well: keeping doors ajar occasionally, not overpacking hanging space, avoiding drying laundry in the room and making sure background ventilation and extraction are working. Joinery detailing reduces the risk substantially, but it cannot outrun a room producing more moisture than it can shed.
How we approach it
We survey the wall before designing a run, and where an elevation is exposed or a wall is solid masonry, ventilation and material specification are decided at that point rather than left to chance. Our fitted wardrobe, floor to ceiling wardrobe and dressing room work is detailed on that basis.
If you have inherited a run with mould behind it, the useful step is a proper look at the fixing method and the wall's condition. That determines whether the answer is ventilation detailing, a fabric repair, or both.
Frequently asked questions
- Why is there mould only on the wall behind my wardrobe?
- Because sealing a wall behind furniture stops warm room air from reaching it, so its surface sits colder than the rest of the room. Moisture in the air condenses on that cold surface and mould grows there and nowhere else.
- Should fitted wardrobes have a gap behind them?
- On cold external or party walls a ventilated void behind the carcass is a sensible detail, along with air paths at the plinth and top. It keeps the wall surface warmer and lets any moisture disperse.
- Will moisture-resistant board on its own solve it?
- No. It makes the joinery more tolerant, but the cause is a cold, unventilated surface. Ventilation detailing and, where needed, work to the wall itself are what remove the condition.
- How do I know whether it is condensation or a leak?
- Condensation is usually fine, widespread black speckling that worsens in winter. A defined stain or tide mark that persists through summer suggests water entering the building, which needs investigating before any joinery is installed or refitted.
Planning a project like this?
SH Joinery surveys every room before quoting, so you get a fixed price against a written specification rather than an estimate. Send us your drawings, photographs or rough sizes and we will come back with an honest view of what your project involves.