Why your windows are dripping (and how to stop the mould before it starts)

If you’re wiping water off your windowsills most mornings this winter, you’re not imagining it and you’re not doing anything wrong.

Condensation happens when warm, moist indoor air hits a cold surface. In winter, your windows are the coldest surface in the room, so the moisture in the air collects there as droplets. Where’s that moisture coming from? Mostly:

• Showers and baths
• Cooking
• Drying washing indoors
• Even breathing overnight

Left alone, that water feeds mould on the frames, the seals, and the wall underneath. Here’s how to actually deal with it.

1. Tackle the moisture at the source

Wiping the glass only treats the symptom. The real fix is putting less moisture into the air to begin with:

• Showers — run the exhaust fan during, and for 10 minutes after.
• Cooking — use the rangehood or crack a window.
• Drying clothes inside — that water ends up on your windows and walls. Dry washing in a ventilated room with the door shut and a window open, or use a dehumidifier.

2. Ventilate even when it’s cold

It feels wrong to open a window in July, but it works:

• Open two windows on opposite sides of the house for 10 minutes in the morning.
• This flushes out damp air far faster than you’d expect.
• The room reheats quickly once they’re shut — a sealed-up house just traps the moisture.

3. Wipe condensation early

• Deal with it in the morning, before it sits.
• A dry microfibre cloth or a window squeegee takes 30 seconds.
• Drying the sill stops the pooling water that leads to rot and mould.

4. If mould has already started, clean it properly

For small spots on frames and seals:

• Mix roughly 70–80% white vinegar to water in a spray bottle.
• Spray it on and leave for 10 minutes.
• Scrub with an old toothbrush, then wipe clean.

Vinegar kills mould at the root. Bleach often just lightens the colour while leaving the spores behind. Always wear gloves, open a window, and never mix cleaning products together.

5. Check the spots that hide

Mould loves the places you don’t look:

• Behind curtains
• Top corners of window recesses
• Behind furniture against external walls
• Inside wardrobes on outside walls

Pull furniture a few centimetres off external walls so air can move behind it, and leave wardrobe doors open occasionally over winter.

If mould has spread across a ceiling, into the wall, or through grout and silicone, it’s time for a professional clean rather than fighting it with a spray bottle every week.