Support Condensation and why it forms

Condensation why?

Condensation forms when warm, moisture‑laden air cools down on a cold surface and turns from invisible vapour into liquid water droplets.

Condensation forms when warm, moisture-laden air comes into contact with a surface that is colder than the air itself. When this happens, the air cools down rapidly and can no longer hold as much moisture, so the excess water vapour turns into liquid water droplets. This is the same basic process that causes dew to form on grass in the morning or mist on a cold bottle taken out of the fridge. With double glazing, condensation can appear in three different places, and each has a different cause and meaning: Condensation on the outside of the window This happens when the external air is warm and humid, while the glass pane remains cool. High-quality double glazing is very good at keeping heat inside your home, so the outer pane stays close to the outside temperature. When warm, damp air hits this cold surface, it turns into water droplets. This is actually a sign that your windows are working extremely well—they are insulating effectively, so very little heat is escaping through the glass to warm up the outer pane. It usually clears up as the day warms up or the wind picks up, and it causes no damage or problems. Condensation on the inside of the window. This is the only type that means something is wrong with the window itself.

Condensation cont...

Condensation between the two panes of glass

This occurs when there is too much moisture inside your home, and the inner surface of the glass is cool enough to make that moisture condense. Everyday activities like cooking, showering, drying clothes indoors, breathing, and even having lots of houseplants release water vapour into the air. If your home is well-sealed and draught-proof (which saves energy), that moist air gets trapped inside. When the weather turns cold outside, the inner pane of glass becomes cooler than the air in the room. Once the warm, damp air touches that cooler glass, it turns into water. This does not mean the windows are broken—it means the humidity level in your home is too high, or there is not enough ventilation to let moist air escape. If left untreated, this can lead to mould growth or damage to window frames and sills. Condensation between the two panes of glass Double glazing units are sealed airtight, and the space between the panes is filled with dry air or an insulating gas. When the seal around the edge of the glass breaks or degrades over time, that airtight barrier fails. Moist air from outside or inside can then get trapped between the panes. Because the gap is sealed, that moisture cannot escape, and it turns into mist, fog, or water droplets that stay permanently inside the window. This happens because the seal has aged, been damaged, or failed due to weather changes, and it means the window has lost its insulating ability. It cannot be wiped away or fixed by ventilation, and usually requires the glass unit to be replaced.