A blown double-glazed unit is one of the most common window problems in UK homes. That telltale foggy patch between the panes means the seal has failed, moisture has crept in, and the insulating gas has escaped. But does a blown unit mean you need a whole new window? Almost always, no.
What Does “Blown Double Glazing” Actually Mean?
Double glazed units have two panes of glass separated by a spacer bar, with the cavity filled with argon or krypton gas. Over time – typically 15 to 25 years – the seal degrades and humid air enters the cavity, causing condensation between the panes.
50%
reduction in thermal efficiency from a single blown sealed unit – equivalent to heating through single glazing. (Source: British Fenestration Rating Council, 2024)
When Repair Makes Sense
In most cases, a blown sealed unit can be repaired by replacing just the glass unit. A typical sealed unit replacement costs between £80 and £180, compared to £350 to £800 for a complete window replacement including frame.
When Replacement Is the Better Call
If the frame itself is warped, cracked, or discoloured beyond repair, a new unit replacement won’t solve draught or security issues. If the windows are over 20 years old and multiple units have blown, full replacement may be the smarter long-term investment.
Can You Upgrade at the Same Time?
Modern Low-E glass with argon fill offers significantly better thermal performance. FENSA reports that upgrading from standard double glazing to Low-E argon units can reduce heat loss through windows by up to 40% (Source: FENSA, Energy Efficiency Guide, 2024).
How Plastic Doctor Can Help
We specialise in repairing rather than replacing wherever possible. A survey takes around 20 minutes, and we cover all of Essex and Suffolk. Contact us at plasticdoctor.co.uk/contact-us/ for a free assessment.
