Double Glazing Condensation: What It Means and How to Fix It
Condensation on windows is one of the most common complaints from homeowners in {location}. But not all condensation is the same — where it forms tells you very different things about your windows and your home. Here's how to tell the difference and what to do about each type.
Condensation on the Inside Surface
Water droplets on the room-facing surface of your windows — typically noticed in the morning — is caused by excess moisture in the air meeting a cold surface. This is the most common type and it's not a fault with your windows. It's a ventilation and humidity issue.
Common causes include:
- Drying clothes indoors on radiators or airers
- Cooking without using an extractor fan
- Showering or bathing without adequate ventilation
- Blocked or closed trickle vents in window frames
- Lack of background ventilation throughout the property
To reduce internal condensation:
- Open trickle vents on your windows — they're there for a reason
- Use extractor fans in kitchens and bathrooms, and leave them running for 15 minutes after cooking or showering
- Dry clothes outside or in a vented tumble dryer where possible
- Keep internal doors closed when cooking or showering to contain moisture
- Maintain a consistent background temperature — allowing rooms to get very cold overnight creates the perfect conditions for condensation
Condensation Between the Panes
This is the one that means your sealed unit has failed. If you see misting, fogging or water droplets between the two panes of glass in a double-glazed unit, the perimeter seal has broken down and moist air has entered the cavity.
Once a seal fails, the unit cannot be repaired — it must be replaced. The good news is that in most cases, you only need to replace the glass unit itself, not the entire window frame. A glazier in {location} can remove the failed sealed unit from the frame and fit a new one, typically for between £50 and £150 per unit depending on size.
Failed sealed units are common in double glazing that's 15 to 25 years old. The seal gradually degrades with UV exposure and thermal cycling. If one unit has failed, others of the same age may follow, so it's worth inspecting all your windows.
Condensation on the Outside Surface
Water on the external face of your windows — often seen on cool mornings — is actually a sign that your glazing is working well. It means the outer pane is cold because very little heat is escaping through the glass. This is most common with modern, energy-efficient double and triple glazing with low-emissivity coatings.
External condensation is harmless and will clear as the day warms up. No action is needed.
When to Call a Professional
Call a FENSA-registered glazier in {location} if:
- You have misting between panes — the sealed unit needs replacing
- You notice water pooling at the base of the frame — this could indicate failed drainage holes in the frame
- Condensation persists on the inside despite improving ventilation — the window may not meet current thermal standards
- Frames are showing signs of rot (timber) or distortion (uPVC) — this can compromise the seal
Building Regulations
If you're replacing sealed units or full windows, the work must comply with Part L of the building regulations (conservation of fuel and power). Replacement windows must meet minimum U-value standards. A FENSA-registered installer will self-certify compliance, saving you the cost and hassle of a building control application.
Don't ignore condensation between panes — failed sealed units reduce your home's energy efficiency and can eventually cause moisture damage to window frames.