Is secondary glazing an effective option for energy efficiency?

Yes, secondary glazing can be an effective option for energy efficiency, particularly for older buildings, listed properties, or homes where replacing original windows isn’t feasible. While less efficient than modern double or triple glazing, it significantly reduces heat loss and noise while preserving historic features—a priority in many UK conservation areas.

How secondary glazing improves energy efficiency

• Reduces heat loss: Creates an insulating air gap between the original window and secondary unit, reducing conductive heat loss by over 60% in some cases.
• Lowers U-values: A single-glazed window (U-value ~5.0 W/m²K) can drop to ~2.7 W/m²K with basic secondary glazing. Adding Low-E glass or sealed units further improves this.
• Minimises draughts: Seals gaps in older windows, reducing air leakage and cold spots.

Key advantages for UK homes and businesses

• Heritage-friendly: Approved for listed buildings in England and Wales where double glazing is often prohibited.
• Cost-effective: Typically 30-50% cheaper than full window replacement.
• Quick installation: Fitted internally without altering original windows, often completed in 1-2 days.
• Noise reduction: Cuts external noise by up to 25%, beneficial for urban properties or offices.
• Condensation control: Reduces moisture buildup on primary windows.

Limitations to consider

• Lower efficiency: Modern double glazing achieves U-values as low as 1.2 W/m²K—secondary glazing rarely matches this.
• Operational compromises: Some designs limit window opening or obscure period features.
• Maintenance needs: Requires regular cleaning of both glazing layers.

Recent UK developments

• Retrofit prioritisation: Included in the PAS 2035 retrofit standards as a priority for historic buildings.
• Energy cost crisis: Rising heating bills have increased UK demand for secondary glazing by 20-30% since 2022, according to industry reports.
• Listed building concessions: Many local councils now actively recommend secondary glazing in conservation area guidance notes.

Practical advice for installation

1. Prioritise critical rooms: Focus on north-facing rooms or spaces with severe draughts first.
2. Choose Low-E glass: Opt for coatings that reflect heat back into the room.
3. Ensure airtight seals: Magnetic or compression-fit frames prevent air leakage.
4. Maintain ventilation: Fit trickle vents if needed to comply with building regulations.

Common mistakes to avoid

• Blocking ventilation: Completely sealing windows risks dampness in older properties.
• Poor spacing: Leaving less than 20mm between glazing layers reduces insulation benefits.
• Ignoring aesthetics: Obtrusive frames can detract from period features—slimline aluminium or acrylic options are less visible.
• DIY errors: Improperly fitted units create thermal bridges—use accredited installers from TrustMark or GGF.

For most UK homeowners, secondary glazing provides a balanced option where traditional double glazing isn’t possible. While it may not be as efficient as full replacements, it offers meaningful energy savings alongside heritage protection—a balance increasingly endorsed by conservation bodies and energy assessors.