Condensation and Black Mould on Windows in Derby
Soaking wet window sills every morning are one of the most common winter problems in Derby homes. Here is what causes it, how we clean the resulting mould, and what we can and cannot fix.
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Why Derby homes get so much condensation
From late October through to early March, we get calls every week from people in Allestree, Normanton and Chaddesden whose window sills are wet through every morning. The water itself is one issue. The black mould that grows in the silicone and along the frames is the bigger problem.
The cause is almost always the same combination: warm, moist indoor air meets cold glass. A four-person household in a typical Derby semi produces around ten litres of water vapour a day from cooking, washing, breathing and drying clothes. With the heating cycling on and off and the windows shut tight against the cold, that moisture has nowhere to go.
Bedrooms tend to be worst because two people breathing for eight hours produces a lot of moisture, and bedroom windows are usually shut overnight in winter. Bathrooms and kitchens come a close second.
What the mould looks like and where it grows
The first sign is usually a thin black line along the silicone where the glass meets the frame. Within a few weeks it spreads up the rubber seals and into the corners. On older wooden frames it can lift paint and get into the timber itself.
On window sills, watch for a brown or yellow tideline where water has pooled and dried repeatedly. This is mineral residue from the water and is much harder to remove once it has set in.
For tenants approaching a checkout, this is exactly the kind of thing inventory clerks flag. A quick wipe with a sponge will not get rid of it, and trying to scrub it off with a kitchen scourer can scratch the silicone or paintwork, making it worse. See our guide on deposit deductions for cleaning for more on what landlords look for.
How we clean condensation mould
- Treat the silicone first
We apply a non-bleach mould treatment, leave it to penetrate for 10 to 15 minutes, then work it in with a soft brush. Bleach lightens the surface but does not always kill the mould underneath. Our products do.
- Clean the frames and rubber seals
Frames get wiped with a cleaner that lifts mould residue without damaging the paint or vinyl. Rubber seals are gently scrubbed with a soft toothbrush style brush to get into the recess where mould collects.
- Restore the sills
Window sills are cleaned and the brown water tideline is treated. On most painted sills the mark lifts. Heavily damaged paint may show through and need refreshing by a decorator afterwards.
- Polish the glass
We finish with a streak-free glass polish so the windows actually look clean again, not just mould-free.
What cleaning will not solve
We will be honest. If your windows are streaming wet every single morning, no amount of cleaning will stop the mould coming back within weeks. The underlying issue is ventilation and heating, and that needs different fixes:
- •A trickle vent on each window opened during winter, even though it feels counter-intuitive
- •Running the bathroom extractor for 20 minutes after every shower
- •Drying laundry outside or in a vented tumble dryer rather than over radiators
- •Keeping bedroom doors slightly ajar overnight so air can circulate
- •If the property has no extractors and single-glazed windows, this is a landlord maintenance issue
Keeping it under control between cleans
Once we have removed the mould, a five-minute morning routine in winter keeps it from coming back: wipe the windows with a microfibre cloth or a cheap window vac, leave the trickle vents open during the day, and air the room out for ten minutes after waking up. If keeping on top of it is hard, our regular cleaning visits include window-frame and sill maintenance every visit.
Have questions?
We are happy to help. Call us or send an enquiry and we will get back to you.