Condensation on double glazed windows

Question

Hi,

I had new double glazed windows fitted approximately 2.5 years ago but couldn't move in as there were still work going on in the house. Now that we've moved in we've noticed there is significant condensation daily, to the point where water is dripping onto the window sills. Turning on/off the vents hasn’t helped at all.

We tried to get in touch with the guy who fitted the windows but can't get hold of him.

Any ideas the reason behind the condensation and how to resolve this please.

Any advice will be much appreciated.

Regards

Arman · Accepted Answer

Hi Arif,
Speaking to you as if I’m an expert carpenter and joiner who’s seen this many times:

First off, the windows themselves are probably not faulty — the fact that the condensation is on the inside of the glass (not between the panes) suggests it’s an internal moisture problem, not a failure of the double glazing unit.

Here's what’s likely happening:

Your house was probably unoccupied and unheated for a long time while the work was ongoing.

Building materials like plaster, paint, and screed hold a lot of moisture and take months to fully dry.

Now that you’re living there — cooking, showering, breathing — humidity levels are spiking, and the cold windows are the perfect spot for that moisture to condense.

My opinion (based on experience):
It’s almost certainly a ventilation and humidity issue, not a faulty installation.
Turning vents on and off won't solve much because you probably have trapped humid air inside the house.

Solutions I'd recommend:

Get a dehumidifier — a good one (like a 10-20L per day model). Run it constantly for a few weeks to pull the moisture out of the air.

Ventilate — even crack windows open daily for 15–20 minutes, especially after showers and cooking.

Check heating — warm air holds more moisture. If your house is kept cold, the moisture dumps onto cold surfaces like glass.

Longer term — think about extractor fans in bathrooms/kitchen, or even trickle vents if you don’t have enough.

If water is dripping onto sills every day, you’re at risk of mould and damaged timber soon, so don’t ignore it.

My honest opinion:
This isn’t your window fitter’s fault — it's typical in newly renovated houses.
Deal with the humidity aggressively now, and in 2–3 months you should notice a big improvement.
(If the condensation was inside the sealed unit, then you'd have a warranty claim, but that's not your issue.)

Would you like me to also suggest a couple of really reliable dehumidifiers? (Some are much better than others depending on house size.)

Martin · Answer

Your windows are not doing there job, cold air is hitting the warm air in your room causing the condensation, only way to resolve is new windows

Daniel · Answer

Hi Arif. Is this affected all windows or just a couple. I might be the glass is glazed the wrong way round or there’s not enough ventilation in the rooms. If the rooms are really warm and due to the cold days condensation will always appear.

Paul · Answer

There’s a possibility the glass was glazed the wrong way around or the silicone seals have gaps and letting cold air in.

Edward · Answer

Hello & good morning,
When the new glass was fitted there is a possibility that they have put the glass in the wrong way around hence condensation on the internal windows this is just one of the common problems

Oli · Answer

Sounds like the glass is installed the wrong way around so the coated pane is on the interior of the house instead of the exterior

Condensation on double glazed windows

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