Misted Double Glazing: Repair the Glass or Replace the Window?

What has actually gone wrong

Double glazing is two panes of glass held apart by a spacer bar and sealed around the edge. The spacer contains a drying agent that keeps the gap free of moisture. Over the years, sun, rain and temperature swings work at the seal. Once it gives, damp air gets in, the drying agent fills up, and the glass mists from the inside.

It does not happen to every window at once. One or two units often go before the rest, usually on the side of the house that takes the most weather.

Why it is worth fixing

It looks bad, but appearance is not the only cost. A failed unit insulates less well, so that window lets more heat out, and the haze gets worse over time rather than better. Left long enough, it can leave permanent marks on the inside of the glass.

When a glass-only repair is enough

Replacing just the sealed unit is the sensible option when:

• The frame is solid, square and not rotten, warped or split
• The window opens, closes and locks properly
• Only one or a few panes have misted
• You are happy with how the window looks and performs otherwise

When a new window makes more sense

Replacement starts to win when:

• Timber frames are soft, rotten or splitting at the joints
• uPVC frames are bowed, cracked or badly discoloured
• Several units in the same window or house are failing together
• The window is draughty or difficult to lock even with good glass
• You were already planning to upgrade the look, colour or security

Our approach

We look at the frame before quoting. If a new glass unit will do the job, that is what we will quote for. If the frame is the real problem, we will tell you that instead, so you are not paying for glass that goes into a window with only a few years left in it.