Secondary Glazing for Heritage Sash Windows — The Complete Guide

If you own a listed building or live in a conservation area, replacing your original sash windows may not be an option. Secondary glazing offers a planning-approved route to improved comfort without touching your originals.

What is secondary glazing?

Secondary glazing is an internal panel fitted to the room-side of your existing window reveal. It creates a sealed air gap between the original window and the new panel — which is where the thermal and acoustic performance comes from.

Unlike replacement windows, secondary glazing doesn't alter the external appearance of your property. This is why planning authorities and conservation officers approve it even for Category A listed buildings.

Is secondary glazing effective?

Yes — significantly so. A well-fitted secondary glazing system can:

• Reduce heat loss through windows by up to 60%
• Cut noise levels by up to 80% with acoustic glass
• Eliminate draughts completely
• Reduce condensation on original frames

Secondary glazing vs replacement windows for listed buildings

In most cases, you cannot replace windows in a Category A or B listed building without Listed Building Consent — and even with consent, your conservation officer will typically require like-for-like replacement that closely matches the original.

Secondary glazing sidesteps this entirely. Because it's an internal addition that doesn't alter the fabric of the building, it typically doesn't require planning permission at all — though we always recommend checking with your local planning authority first.

What types of secondary glazing are available?

We offer six configurations to suit different window types and access requirements:

• Lift-out panels — simplest and most affordable
• Horizontal sliding — most popular, allows ventilation
• Vertical sliding — mirrors the operation of sash windows
• Side-hung casement — for wider openings
• Acoustic grade — laminated glass for maximum noise reduction
• Thermal grade — argon-filled for maximum heat retention

Edinburgh-specific approvals

We are an approved supplier of secondary glazing to Edinburgh City Council, and our products are pre-approved for use in the city's listed buildings and conservation areas. This simplifies the process considerably for Edinburgh homeowners and contractors.

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