Fog/condensation inside my double glazing — can it be fixed?

Replaced two failed units this way — kept the frames, just new glass. Way cheaper than I feared.

Adding a note since this one comes up seasonally: the reason foggy double glazing can't be wiped clean is that the spacer and desiccant sealed inside the unit have saturated — so it's a whole-unit replacement, which I've broken down in can just the glass unit be replaced. And while you're replacing a sun-facing unit anyway, it's the ideal moment to upgrade to Low-E glass to cut the heat — same labour, better glass.

For anyone whose windows also feel draughty or let heat in (not just fogged): that's a different failure from a fogged sealed unit — it's the perished rubber gaskets/seals around the frame, and there's a newer thread on whether just the window seals can be re-done without new windows. Foggy-between-the-panes = glass-unit job; draughty with cracked rubber = a reseal. Useful to tell them apart before anyone quotes you whole new windows.

One thing that ties into this: when you're choosing new windows, the glazing and frame spec is exactly what governs condensation and heat, not just the opening type. A good insulated double-glazed unit with a thermal-break frame runs warmer on the inside face and resists the surface condensation you get on cheap single glazing or a non-broken frame. There's a thread on choosing aluminium window types — casement vs sliding vs tilt-and-turn — and the glazing to pair with them. (Condensation BETWEEN the panes, as in this thread, is a failed sealed unit and separate — but specifying good sealed units + thermal breaks up front avoids the surface-condensation version.)

Adding the mechanism for anyone finding this later, because it changes the fix. Fog that appears BETWEEN the two panes — the kind you can't wipe off from either side — means the sealed unit's edge seal has failed. Once humid outside air has leaked into that sealed gap, then any time the inner pane drops below the trapped air's dew point the moisture condenses inside the cavity — which is exactly why it clouds up on a cool morning and clears again as the day warms. Because the water is sealed inside the unit, there is genuinely nothing to clean: the fix is replacing the glass unit itself (the sealed IGU), not the frame or the handles. If a few units around the villa are misting up around the same time, they're usually the same age and it's worth replacing them together rather than one a month.