In clear language: why moisture and mould appear on a wall and whether insulation will help. How to check where condensation forms in your wall before you even start the repair.
What you'll learn
Wet patches appear on a wall, black mould grows in the corner, the wallpaper peels off. That's almost always condensation — moisture that settles inside or on the surface of the wall. In this article, with no complicated terms, we explain why this happens, what the "dew point" is and how to check whether insulation will fix the situation.
Where the moisture comes from
The warm air in your room always contains water vapour — from breathing, cooking, laundry. While the air is warm, the vapour is invisible. But if it touches a cold surface, part of the vapour turns into droplets of water. It's the same effect as a fogged-up glass holding a cold drink.
The temperature at which vapour starts to fall out as droplets is called the dew point. If a wall surface (or a layer inside it) is colder than the dew point, moisture forms there.
Why a cold wall = a damp wall
A poorly insulated wall is cold on the inside. Its inner surface drops below the dew point — and condensation settles on it. Then: moisture → damp wallpaper → mould in the corners (where it's coldest).
Mould isn't just a cosmetic problem. It ruins the finish and harms health. But you have to tackle the cause — the cold surface — not just the symptom.
Will insulation help
Most often — yes. Insulation makes the inner surface of the wall warmer, so it stops dropping below the dew point. The condensation disappears.
But it matters where exactly the dew point sits in your wall. If insulation is done wrongly (for example, a thin layer on the wrong side), moisture may form inside the structure — between the layers. Then everything looks dry on the outside while the wall slowly gets wet from within.
How to check your wall
The thermal conductivity calculator builds the temperature profile through the full thickness of the wall and shows where the dew point lies and whether there's a condensation risk. You enter the wall layers, the room and outdoor temperatures — and immediately see whether the wall will be dry.
- Enter your wall's layers.
- Set the indoor temperature (usually +20 °C) and the outdoor one.
- See whether a condensation-risk mark appears, and where.
- Add insulation and check whether the risk disappears.
Безкоштовно · без реєстрації
Example
An uninsulated wall with an inner surface at +12 °C, at +20 °C in the room and 55% humidity, falls into the risk zone — the dew point is around +10.7 °C and the surface is cold. We add insulation — the inner surface warms up to +18 °C, and the risk disappears.
Frequently asked questions
Is the wall always to blame? A cold surface is the main reason condensation forms. The calculator shows exactly this side of the question: whether your wall is warm enough.
Which standard describes this? The assessment of moisture in structures is governed by ДСТУ Б EN ISO 13788.
How much insulation does it take to remove the moisture? Enough to make the inner surface warmer than the dew point. How to choose the thickness — in the article how much insulation a wall needs.
Теги: