How uPVC ages
The frame itself is the long-lived part: the plastic slowly chalks and yellows in sunlight, but structurally it usually outlasts everything attached to it. What wears out first is the moving hardware, hinges, locks and handles, and the sealed glass units, whose edge seals give up years before the frame does.
That order matters, because it means a draughty, stiff or misted window is often a window with a worn component, not a dead window. The question to ask is which part has failed, and the answer decides whether you are spending tens of pounds or thousands.
Misted glass: the most misdiagnosed fault
Condensation between the panes means the sealed unit's edge seal has failed and the insulating gas and dryness are gone. It looks terminal and is routinely quoted as a full window replacement, but the sealed unit can usually be swapped inside the existing frame for a fraction of the cost, restoring both the view and the insulation.
The repair route makes sense when the frame is sound and the failures are isolated. It stops making sense when units are failing one after another, because the remaining originals are the same age with the same life expectancy, and serial call-out fees quietly add up to real money.
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Compare window and door quotesRepair or replace: the honest arithmetic
Repair when the problem is one unit, one hinge or one lock on windows younger than their design life. Lean toward replacement when multiple units have misted, hardware is failing across the house, draughts persist after adjustment, or the glazing predates modern energy standards, because at that point every pound spent patching is a pound not spent on windows that will cut the heating bill.
Replacement also resets the clock on performance and paperwork: a standard uPVC casement runs about £500 to £1,250 fitted, the new units come with the building regulations certificate you will need when you sell, and the glass moves to modern standards. When the arithmetic tips that way, compare quotes from trusted window and door installers across the whole house rather than window by window: the per-window price falls as the count rises.
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