What causes mould in a house? The 6 real culprits

Mould is always a moisture problem

There is one rule that makes sense of every mould problem: mould cannot grow without moisture. If you have mould, you have unwanted moisture somewhere. Clean the mould and the moisture stays, the mould comes back. Find and fix the moisture source and the mould stops returning for good.

In Cyprus homes, almost every mould problem traces back to one of six culprits. Sometimes it's more than one — a sealed apartment with a slow leak and poor ventilation can have three sources at once. An inspection finds which ones are at work in your home.

1. Condensation

The single most common cause of mould in Cyprus homes. Warm, damp air from cooking, showering, drying laundry and simply breathing hits cold surfaces — windows, outside walls and ceilings — and turns back to water. That film of moisture is exactly what mould needs.

Condensation peaks in winter, when windows are closed and walls are cold, and in sealed apartments where there's no trickle ventilation. It shows up as black mould around windows, in corners and on outside walls.

2. Rising damp

Ground moisture travelling up through the masonry of a ground-floor or basement wall. It leaves a characteristic tide-mark, blown plaster and sometimes a salty deposit near the floor. Rising damp won't respond to cleaning or paint — the moisture keeps coming up through the wall until the damp-proof layer is restored.

It's more common in older properties and ground-floor rooms, and it's a different fix entirely to condensation mould.

3. Poor ventilation

Moisture has to leave the home, or it builds up. Windowless bathrooms, kitchens with no extractor, drying laundry on radiators, and rooms kept closed for days all trap humidity indoors. In modern sealed apartments, the lack of natural air changes is a major reason mould takes hold.

Poor ventilation doesn't create moisture on its own, but it guarantees that whatever moisture you produce stays inside long enough to cause mould.

4. Leaks and water damage

A slow pipe leak, a roof or window leak, or a past flood that wasn't fully dried can keep materials wet behind the surface. Mould can follow within 48 hours of a leak. Because the moisture is hidden, the mould often grows out of sight — behind a wall, under a floor, or above a ceiling — and you smell it before you see it.

Any mould that appears suddenly, or in a line along a ceiling or wall, should make you suspect a leak.

5. Humidity

Coastal Cyprus — Limassol, Larnaca and Paphos — sits in high humidity year-round. Add air-conditioning, which can create its own condensation on warm ducts and coils, and the indoor environment easily stays damp enough for mould even without an obvious leak. In these areas, managing indoor humidity is a constant job, not a one-off fix.

6. Closed-up rooms

Holiday homes and rentals shut up for weeks or months between lets have almost no air movement. Any moisture left inside — from a last shower, rain through an open vent, or just trapped humid air — has nowhere to go. Mould can bloom across walls, furniture and soft furnishings surprisingly fast in a closed, dark property. This is a top cause for owners in Protaras and Ayia Napa.

Why cleaning alone never works

Every one of these culprits shares the same truth: the moisture keeps coming until you fix the source. Wiping mould off a wall is like mopping a floor with the tap still running. The mould will be back within days, because the conditions that grew it haven't changed.

The right fix depends on the cause. Condensation needs ventilation and humidity control. Rising damp needs a new damp-proof course and re-plastering. A leak needs the leak repaired and the wet materials dried. There is no single mould treatment that solves all six.

How to find your culprit

Start with where the mould is growing. Around windows and high on outside walls points to condensation. Low down with a tide-mark points to rising damp. In a line or patch on a ceiling points to a leak. In a windowless bathroom or behind furniture points to ventilation. Across a closed-up room points to trapped humidity.

An inspection from €75 measures the moisture in your walls, identifies the source, and gives you a clear report and a fixed quote for the right fix — with the inspection fee credited toward any removal work.