Older homes were built to “breathe.” They let air and moisture escape, which reduced damp but made them draughty and cold. Modern windows and insulation fix the heat loss, but if you only upgrade one area you can accidentally cause condensation and mould.
Here are the questions people ask most when retrofitting:
Condensation happens when warm, damp air inside a house touches a cooler surface. The water vapour turns into droplets, leaving wet patches on walls or misted windows. Every home produces moisture from cooking, showers, drying clothes and even breathing, so without proper ventilation and insulation it builds up quickly.
Condensation is when warm, damp air hits a cold surface and turns into water droplets. Think of a bathroom mirror steaming up, or a cold pint glass dripping on a summer day.
This is the most common place it shows up, because glass surfaces cool faster than walls. It might appear inside (from high humidity), outside (a sign of efficiency) or even between panes (a failed seal).
This is usually a good sign. It shows your windows are holding heat in, so the outer glass cools and attracts moisture.
With efficient glazing that has low U-values, this is normal and harmless.
This points to high indoor humidity and not enough ventilation, not a window fault. Everyday activities such as cooking, showers and even breathing raise moisture levels.
Our Classic and Frontier ranges include trickle vents as standard, and our Heritage windows can have concealed vents if needed. These allow fresh air in without losing heat.
That means the sealed unit has failed and moisture has leaked inside. It is different from surface condensation, and it will not clear on its own.
With standard double glazing, this usually means replacing the unit. At Gowercroft, all our glazing options (double, triple or vacuum) are built to last, with robust seals designed for decades of performance. Our LandVac vacuum units even carry a 25-year warranty against fogging.
If you notice damp patches on plaster or paint, that is condensation too. Cold corners and poorly insulated walls are especially prone to it, since they reach dew point before the rest of the room.
Older homes used to be draughty, so moist air escaped naturally. New energy-efficient glazing makes the house warmer and more airtight, which is great for comfort but means you need planned ventilation to keep humidity under control.
This is the hidden kind. It happens inside walls, roofs or floors when moisture seeps into cooler layers and condenses there. You cannot see it, but over time it damages insulation, rots timber and breeds mould.
Traditional buildings coped better because breathable materials like lime mortar let moisture escape. Modern airtight retrofits need careful planning so water does not get trapped.
Yes, if you only upgrade the windows. The dew point is the temperature where moisture becomes condensation. Energy-efficient glazing keeps rooms warmer, but if the walls stay cold, that dew point can shift into the wall, causing hidden damp.
That is why retrofit should always be a whole-house plan: upgrading insulation and ventilation alongside efficient glazing.
Yes. The more efficient the glazing (the lower the U-value), the warmer the inner glass surface will be. This makes it harder for condensation to form indoors.
At Gowercroft, we offer advanced double glazing, triple glazing and vacuum glazing. Each option is chosen based on the project, whether that is heritage sensitivity, energy performance, or both.
This usually means a thermal bridge. These are cold spots around frames or reveals where insulation is weak. The colder surface drops below the dew point, leading to damp and mould.
Our installation teams are trained to reduce thermal bridging with precise fitting, insulation around frames and careful detailing.
A thermal bridge is a weak point in insulation where heat escapes and surfaces cool. It is common in older buildings with irregular structures. If only the windows are upgraded, these weak spots stand out and create damp.
Aim for 40–60 %. Higher levels encourage mould, while lower levels feel uncomfortably dry. A small digital hygrometer is a simple way to check.
The easiest way is with a digital hygrometer. These small devices show the relative humidity in real time, usually alongside room temperature. You can buy one online or in DIY shops for under £15. Keeping one in living areas and another in bedrooms helps you keep track and adjust ventilation or heating when needed.
Yes. They provide constant background ventilation, letting moist air escape and fresh air flow in. They are not the full solution (you still need extractor fans in kitchens and bathrooms) but they are simple and effective.
In older homes, replacing draughts with controlled ventilation like trickle vents is especially important.
The right choice depends on how airtight your retrofit is and how much control you want over humidity.
Condensation does not mean your windows are failing. It is your home telling you it needs balance between warmth, ventilation and insulation. Efficient glazing with low U-values helps, but the best results come when you think about the whole house.
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