![[HERO] 5 Reasons Your New Windows Have Condensation (And How to Fix Your Ventilation)](https://cdn.marblism.com/vWObavXjMj9.webp)
It is one of the most common phone calls we receive at Inspired Glazing. A homeowner in Windsor or West London has just invested in high-quality replacement windows, only to wake up a few weeks later and find a layer of mist or water droplets on the glass.
The immediate reaction is often frustration. “Are my new windows faulty?” “Did the installers miss a seal?”
The truth is usually the opposite. In many cases, condensation on new windows is a sign that your home is now significantly more airtight and energy-efficient than it was before. However, while it proves your windows are working, persistent moisture can lead to mould and damp if not managed correctly.
At Inspired Glazing, we believe in technical precision and long-term performance. In this guide, we will break down exactly why condensation occurs and how you can master your home’s ventilation to protect your investment.
1. The “Airtightness” Paradox
Old, draughty windows were actually quite good at one thing: unintentional ventilation. Because the seals were worn or the frames didn’t fit perfectly, air was constantly escaping and entering your home. This “leakiness” meant that moist air inside the house was regularly replaced by drier outside air.
When you install modern upvc-windows-and-doors or aluminium-windows-and-doors, you are effectively sealing those gaps. Your home becomes a “sealed box.” While this is excellent for reducing energy bills and eliminating cold spots, it means that the moisture we create every day: through breathing, cooking, and showering: has nowhere to go. It stays trapped inside until it hits a surface cold enough to turn it back into liquid.
2. High Humidity Levels in Modern Living
Condensation is a direct result of humidity levels. According to building science, a healthy indoor humidity level should sit between 40% and 60%. In many London households, especially during the winter months, this level can easily spike to 70% or higher.
Common contributors include:
- Drying clothes indoors: A single load of washing can release up to two litres of water into the air.
- Cooking: Boiling pasta or steaming vegetables without an extractor fan active.
- Showering: Even a short shower creates a massive amount of steam that travels through the house.
- Houseplants: Large indoor jungles contribute significantly to moisture levels through transpiration.
If your humidity is high, that moisture will seek out the “dew point”: the temperature at which air can no longer hold water vapour. Even with energy-rated windows, the glass is often the coolest surface in the room, making it the primary target for condensation.
3. Understanding Trickle Vents (Part F Compliance)
Many homeowners find the look of trickle vents (the small horizontal slots at the top of a window frame) unappealing, or they worry they will let in cold air. However, under current UK Building Regulations (Part F), most replacement windows must be fitted with them.
Trickle vents are designed to provide “background ventilation.” They allow a small, controlled amount of air to circulate constantly, helping to equalise the humidity without the massive heat loss associated with opening a window fully.
The most common mistake: We often visit homes in Maidenhead or Ascot where the residents have permanently closed their trickle vents to “keep the heat in.” By doing this, you are effectively turning off your home’s primary defence against damp.
- Actionable advice: Keep your trickle vents open at all times, even in winter. They are engineered to prevent draughts while ensuring your home can “breathe.”
4. The “Drying Out” Phase (New Builds & Extensions)
If you have recently moved into a new build or finished a major extension in areas like Beaconsfield or Gerrards Cross, your condensation might not be a lifestyle issue at all.
New construction materials: such as plaster, concrete, and timber: contain thousands of litres of water. It can take up to a year (or longer) for a new home to fully “dry out.” During this period, the moisture from the walls and floors evaporates into the air, leading to heavy condensation on your new glass.
5. External Condensation: The Sign of High Performance
This is the one that surprises people the most. Sometimes, you will see condensation on the outside of the glass.
This is actually a badge of honour for your windows. It happens when the thermal performance of your double-glazing-aluminium-vs-upvc-windows is so high that virtually no heat is escaping from inside the room to warm up the outer pane of glass. When the outer pane stays cold and the outside air temperature rises or humidity is high (like a misty morning in Windsor), dew forms on the exterior surface.
Result: If your condensation is on the outside, your windows are working perfectly. There is nothing to “fix”: it will usually evaporate as soon as the sun hits the glass.
Practical Advice: How to Fix Your Ventilation
If you are experiencing internal condensation, you don’t necessarily need new windows; you need a new approach to ventilation. Here is how to manage it:
1. The “Purge” Method
Every morning, open your windows wide for just 10 to 15 minutes. This is called purge ventilation. It allows the heavy, moist air accumulated overnight to be replaced with fresh, dry air. Because the walls and furniture are still warm, the room will return to a comfortable temperature very quickly once the windows are closed.
2. Manage the Source
- Use your kitchen extractor fan during and for 15 minutes after cooking.
- Keep bathroom doors closed while showering and leave the extractor fan running until the steam has cleared.
- If you must dry clothes indoors, use a dehumidifier in the same room.
3. Check Your Furniture Placement
In many older properties in West London, we see mould forming behind wardrobes or sofas placed against external walls. This is because air cannot circulate. Ensure there is a small gap (at least 50mm) between furniture and walls to allow air to flow.
4. Professional Inspection
If you notice condensation between the two panes of glass, this is a sign that the “sealed unit” has failed. The desiccant inside the frame is saturated, and the unit is no longer energy-efficient. At Inspired Glazing, we provide window-repairs-replacements to address failed units without necessarily needing to replace the entire frame.
Case Study: Solving Condensation in a Windsor Extension
Challenge: A client in Windsor contacted us after installing a set of large sliding-bi-fold-doors. They were experiencing heavy pooling of water on the bottom tracks every morning.
Solution: Upon inspection, we found the client was drying laundry in the extension with the underfloor heating turned up high, and they had kept the trickle vents closed. We advised them on the “Purge” method and ensured all trickle vents were functional.
Result: Within 48 hours, the condensation had vanished. The thermal performance of the doors was excellent; the issue was simply an imbalance in indoor humidity that the new, airtight seals were highlighting.
FAQs about Windows and Ventilation
Q: Do I need to replace my windows if I have condensation?
A: Not if it’s on the inside or outside of the glass. If it is between the panes, the unit has failed and needs replacing.
Q: Will trickle vents make my house cold?
A: No. They are designed to allow a minimal amount of air to move, which is essential for air quality. The heat loss is negligible compared to the damage that dampness and mould can cause.
Q: Why is condensation worse in the winter?
A: Cold air outside makes the glass colder, while we tend to keep windows closed and heating up inside. This creates the perfect “temperature cliff” for moisture to drop out of the air.
Protect Your Home with Inspired Glazing
Choosing the right replacement windows is only half the battle; understanding how they interact with your home’s environment is the other half. Whether you are looking for bespoke-energy-efficient-windows-doors-in-beaconsfield-gerrards-cross or need expert advice on ventilation for your current installation, our team is here to help.
We pride ourselves on clean workmanship and precise fitting. If you are concerned about the performance of your glazing or are planning a new project in London, Windsor, or the surrounding areas, get in touch for a professional consultation.
Request a call back or call us today at 01753 965 005.
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