Secondary glazing can offer U-values from 1.0 to 2.5 W/m²K, depending on the type and materials used. If combined with double-glazed windows, it can improve the overall U-value by reducing drafts and heat loss.

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How to Know:

Secondary glazing generally doesn’t have as specific energy ratings as other glazing types but you can check with your manufacturer to see how it impacts overall window insulation when installed.