Window care
Window Condensation: Inside, Outside or Between the Panes?
Before deciding what a misted window means, establish where the moisture is. Condensation on the room side, on the outside surface and within a sealed glazing unit are different observations. A clear description is the first step towards asking the right question.
Start with the surface, not the conclusion
Condensation forms when water vapour meets a surface cold enough for it to become liquid. The Glass and Glazing Federation explains that temperature, humidity and ventilation all affect this. Seeing moisture is an observation; it does not identify a single cause or remedy for every window.
Note the room, the time and which part of the window is affected. Is it one pane, an edge, several windows or a patch that appears repeatedly? A photograph can help show the pattern, but avoid leaning outside or taking risks to inspect it.
Moisture on the inside surface
Room-side condensation can be influenced by everyday moisture from activities such as cooking and bathing, together with surface temperature and ventilation. Record whether it appears after a particular activity and whether it clears. Keep existing ventilation openings unobstructed and follow guidance for the ventilation system you have.
Do not assume that wiping the surface identifies or solves the underlying problem. Persistent damp or mould needs an appropriate assessment of the building and conditions, rather than a diagnosis made from one photograph. A change in windows is not automatically a complete answer.
Moisture on the outside surface
External condensation can occur when the outer pane is cold relative to the surrounding air. The GGF notes that it can appear on energy-efficient glazing because less heat from inside reaches the outer pane. Its presence alone does not mean the sealed unit has failed.
Observe whether it changes with the weather or clears later. Different windows on the same building may behave differently. Write down what you can see rather than assuming that every pane should look identical at every moment.
Moisture that appears to be between the panes
If the haze cannot be reached on either exposed surface and appears to be within the glazing unit, ask a glazing professional to assess it. Do not dismantle the unit or drill the glass to investigate. Establish which product was installed and gather any relevant paperwork before arranging an assessment.
A useful record distinguishes a recurring internal haze from surface marks or residue. Note when it first appeared and whether it changes. Avoid concluding that an entire frame needs replacement before the actual issue and options have been examined.
Keep a simple observation log
Record the date, the affected surface, the room conditions you noticed and a clear photograph taken safely. Include any recent changes, such as decorating, ventilation adjustments or building work. A few factual entries are more useful than a list of remedies tried at random.
The aim is to give the responsible professional enough context to investigate. Condensation is a reason to look carefully at the conditions and the assembly, not a reliable stand-alone verdict on the quality of a window.
Explore the subject: Glazing guide.
