Condensation on Windows in Winter: Stopping Mould in Dublin Homes

Condensation on windows is the first sign of winter in many Dublin homes. From November to March, cold glass and warm, moist air meet every morning, and water runs down onto the sills. Left alone, that moisture feeds black mould on frames, curtains and wall corners. This seasonal guide explains what causes it and what to change.

Why does condensation on windows get worse in winter?

Condensation gets worse in winter because the glass is colder and homes are sealed up to keep heat in. SEAI’s 2026 technical standards describe condensation as moisture in the air depositing on cold surfaces due to reduced ventilation and breathability. Colder glass and less fresh air mean more water.

Everyday life adds the moisture. Showers, cooking, kettles, breathing overnight and wet washing all release water vapour. In a small apartment with windows closed, that vapour has nowhere to go except the coldest surface, which is usually the window or an outside wall corner.

SEAI also notes that cold spots, called thermal bridges, can cause damp cold walls, condensation build-up and mould growth. That is why mould often starts behind wardrobes, in ceiling corners and around window reveals.

How do you know if condensation is causing mould?

Condensation mould shows as black spots on window seals, frames, sills, wall corners and the backs of curtains. It is worst on north-facing and outside walls. SEAI lists stuffiness, odour, mould and condensation as evidence of inadequate ventilation, so mould is a ventilation warning, not only a cleaning job.

The HSE says moulds and fungi grow on walls and windows in damp houses. It lists mould spores among the common triggers of allergic rhinitis, which affects about 1 in 5 people. People with asthma or allergies tend to notice symptoms first.

Damp from a leak or rising damp looks different. It usually appears as a tide mark or a patch that stays wet in dry weather. Where black spots have already spread, our mould cleaning service in Dublin treats one room from €95 or a whole bathroom from €120.

How do you stop condensation on windows?

Stop condensation by removing moisture where it is made and letting fresh air in. Run extractor fans during and after cooking and showering, keep trickle vents open, and air rooms for a few minutes each morning. Keep the heating at a steady, moderate level rather than short blasts.

The HSE gives the same core advice: use an extractor or open a window when cooking or showering to prevent condensation, and keep bathroom curtains clean. SEAI’s standards add that where a kitchen or utility room under 6.5 m² has no outside wall and cannot be aired by a window, the extract fan should run on for 15 minutes after use.

How should you dry clothes indoors in winter?

Dry clothes outside whenever the weather allows, as the HSE advises. Indoors, use one room only, close its door, open the window slightly or run a dehumidifier, and keep the airer away from walls. Avoid bedrooms, where people already add moisture overnight.

Draping wet clothes over radiators puts the most moisture into the air in the shortest time. A tumble dryer vented outside, or a condenser dryer with its water tank emptied, keeps that moisture out of the room. Spin clothes at the highest setting the fabric allows before drying them.

How do you clean condensation mould safely?

Clean small patches of surface mould with a mould spray, following the label, while wearing gloves and with the window open. Wipe, rinse and dry the surface. The HSA’s home chemicals leaflet says to read the label, use the recommended amount and never mix chemicals.

Never mix bleach-based mould sprays with vinegar or other cleaners. Wipe window seals and the bottom rubber gasket carefully, because mould hides in the groove. Wash affected curtains on the hottest setting the label allows.

For larger areas, or mould that keeps returning, fix the moisture first and then clean. The guide to cleaning mould from walls covers painted surfaces and ceilings in more detail.

What should renters do about winter condensation?

Renters should ventilate and heat reasonably, and report broken fans or missing ventilation to the landlord in writing. The RTB’s minimum standards say a rented home must not have damp and must have proper heating and ventilation that tenants can control. Dated photos help if there is a disagreement later.

Mould is a common source of argument at the end of a tenancy. Our guide to mould in a rented house in Ireland sets out who is responsible for what. Cleaning mould off is only half the answer if a fan has failed or vents are blocked.