Mould risk
What mould needs
Section titled “What mould needs”Three things: moisture, nutrient and the right temperature. The nutrient is almost always present — dust, paint, adhesive, organic material — and so is the temperature. So moisture is what we can control.
And moisture appears wherever the surface is colder than the dew point of the air.
Where it typically arises
Section titled “Where it typically arises”At thermal bridges
Section titled “At thermal bridges”Wall corners, the floor junction, window installation, the foundation junction. These points are colder than the rest of the surface. The steel thermal bridge · Slab edge.
In poorly ventilated rooms with a high moisture load
Section titled “In poorly ventilated rooms with a high moisture load”Bathroom, kitchen, a room used for drying laundry.
On concealed, unventilated surfaces
Section titled “On concealed, unventilated surfaces”Behind furniture, behind a fitted wardrobe — the air does not move there and the surface is colder.
Where the vapour control layer is damaged
Section titled “Where the vapour control layer is damaged”Vapour entering the structure condenses, and the moisture does its damage behind the lining — where we cannot see it. The principle of vapour control.
Why it is not primarily a ventilation question
Section titled “Why it is not primarily a ventilation question”The common answer is “ventilate more”. Ventilation does reduce the humidity, but:
- if the surface is cold, condensation occurs even at normal humidity,
- the occupant cannot repair a structural fault by airing the rooms several times a day,
- in an airtight building the ventilation has to be designed, not left to the occupant.
The order of prevention
Section titled “The order of prevention”- Thermal-bridge-free junctions — the basis.
- Continuous vapour control, with an intact membrane.
- Controlled ventilation: mechanical or deliberately designed.
- Handling the moisture load where it arises: extraction in the bathroom and kitchen.
- Advice on furniture placement at the critical surfaces.
What counts particularly in light gauge steel
Section titled “What counts particularly in light gauge steel”Moisture is not only cosmetic damage: near the structure it is a corrosion risk too. So a suspected mould patch in this technology always has to be investigated, not just painted over.
The point
Section titled “The point”Mould reveals a fault in the structure, not the habits of the occupant. The solution is to remove the cold surface — everything else treats the symptom.