How secondary glazing reduces road noise
Road noise enters through glass, frame gaps, vents and sometimes the surrounding wall. Secondary glazing adds a second sealed barrier with an air space between the original and inner windows. The separation and airtight perimeter matter as much as the glass choice.
A survey looks at the frequency of the noise, traffic speed, distance from the road, existing frame condition and ventilation. The result should be specified for the room rather than selected from a generic soundproofing claim.
Which glass works for traffic noise?
Acoustic laminated glass can help damp vibration, while a carefully sealed secondary frame provides the independent barrier. We may recommend hinged, sliding or removable access depending on the sash, bay or casement configuration and how the room is used.
The published maximum for suitable systems is up to 54dB noise reduction, described as up to 80% quieter. That is a maximum window-level result, not a promise of silence. Doors, roofs, party walls, vents and open chimneys can remain alternative sound paths.
Road noise and sash windows
Original sash windows can be acoustically weak because the glass is thin and the joinery may have settled. Secondary glazing improves the inner line without removing the outer sash. Slimline frames, careful sightlines and access panels help retain the character and practicality of the room.
For period and listed homes, compare this approach with our sash-window soundproofing guide and listed-building glazing service.
Cost and what to expect
Guide prices including VAT are £675 for a small casement, £1,220 for a Victorian sash and £2,565 for a Georgian bay. Use the secondary glazing calculator for an initial estimate, then arrange a survey so the specification reflects the actual opening.
A suitable installation can often be completed in a single day once the units are made. We explain the likely improvement, the limitations of window-only treatment and any other sound paths before work begins.
Frequently asked questions
Will secondary glazing stop traffic noise completely?
No. It can substantially reduce noise through the window, but walls, vents, roofs, doors and other parts of the building may transmit sound too.
Is secondary glazing better than replacing sash windows for road noise?
It can be a strong option where the original sash is sound and the external appearance matters. A survey should compare refurbishment, replacement and secondary glazing for the property.
How much does road-noise secondary glazing cost?
Guide prices including VAT start around £675 for a small casement, with larger sash and bay windows costing more. The final price depends on size, access, glass, frame and finish.