Secondary Glazing vs Triple Glazing
Triple glazing squeezes the last few percent of thermal performance from a modern window; secondary glazing exists to solve the problems triple glazing can't touch.
What triple glazing does
Adds a third pane inside a sealed unit, typically taking U-values from 1.4 to 0.8 W/m²K — a marginal gain unless you're building to Passivhaus or facing an unheated northern elevation.
What secondary glazing does
Adds an independent second pane with a 100 mm cavity — the same total glass count, but a very different acoustic and heritage story. And it works on windows you legally can't replace.
When triple glazing wins
New-build to Passivhaus, or full replacement projects where the frontage has no historic value and the budget can absorb the 30% uplift over standard double glazing.
When secondary glazing wins
Listed properties, conservation areas, noise-dominated locations, retrofit projects targeting acoustic and thermal gains together, and any budget-sensitive job.
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