49dB Secondary for Sash Windows Installation
Prince Albert Road, NW1 – bespoke acoustic secondary windows designed for a restricted 56 mm cavity behind original timber sash windows.
Location context - why this room was noisy
Located close to Regent’s Park, the master bedroom faced Prince Albert Road (A5205), a busy London route carrying regular buses, cars and commercial traffic between Maida Vale and Camden Town. The continuous background murmur, together with louder individual vehicle pass-bys, was disrupting sleep, rest and home working. The property retained its original single-glazed timber sash windows, which provided limited protection from the traffic noise outside.
Historic DfT traffic counts list Prince Albert Road ~21k AADT (well above the 10k vpd threshold often used to flag high-flow urban links). DEFRA’s 2022 strategic noise maps show elevated Lden along London A-roads due to persistent flows, with evening/weekend visitation maintaining levels. Camden’s borough-wide 20mph limit moderates risk, but volumes remain high—creating steady mid-band energy with rush-hour peaks that secondary glazing is designed to address.
Property
Victorian house near Regent’s Park, NW1 – master bedroom
Existing Windows
Original single-glazed timber sash
Challenge
Constant road noise from Prince Albert Road is disrupting rest and home working
Solution
Bespoke inward-opening timber secondary sash windows using 49 dB laboratory-rated acoustic laminated glazing, installed within a 56 mm glass-to-glass cavity
Result
Indoor measurements:
- Average level: Approximately 40.8 dB(A) to below 28.5 dB(A)
- LAeq.15min: ~40.8 dB → < 28.5dB (≈12dB reduction)
- LAFmax: 52.9dB → 32.4dB (≈20.5dB reduction)
- Spectrum: strong cuts across 125Hz–4kHz, taming traffic rumble and tyre/engine noise (Measured with an NTi XL2, same mic position before/after.)
- Instrument: Calibrated NTi Audio XL2 acoustic analyser
Why secondary glazing (not replacement)?
Heritage-conscious solution
The original timber sash windows were retained, preserving the external appearance of the property and avoiding unnecessary changes to the façade.
Improved thermal comfort
In addition to reducing noise, the internal secondary windows improved insulation around the original single-glazed openings, reducing cold draughts and making the bedroom more comfortable during colder weather.
The secondary-window specification had a calculated U-value below approximately 1.1 W/m²K. This figure relates to the internal secondary unit rather than a measured whole-opening U-value for the completed primary-and-secondary arrangement.
Designed for a restricted cavity
Only approximately 56 mm was available between the original and secondary glazing. The new system therefore combined specialist acoustic laminated glass, high-integrity compression sealing and a rigid bespoke timber frame to maximise performance within the limited space.
Original windows retained
The new secondary windows were installed internally, allowing the original sash windows and the building’s external appearance to remain unchanged. The inward-opening design also retained access for operation, cleaning and maintenance. Future-proofed without altering the façade
OUR SOLUTION
We designed and installed bespoke inward-opening timber secondary sash windows, manufactured to fit the existing openings accurately and preserve the proportions of the original sash windows.
The secondary windows were positioned approximately 56mm glass-to-glass from the original single glazing. This was a substantially more restricted cavity than the deep 100–200mm arrangements commonly associated with maximum secondary-glazing laboratory results.
The new system incorporated 49dB laboratory-rated acoustic laminated glazing, continuous compression seals and a multipoint locking mechanism. Together, these features provided acoustic mass, consistent sealing pressure and a substantially more airtight internal barrier.
The system was specifically configured to deliver high acoustic performance within the restricted cavity while retaining the original external sash windows.
Hear the Difference
The recording below demonstrates the difference measured in the bedroom before and after installation. Headphones are recommended.
The recording is provided as an illustration of the change at this property. Playback equipment, volume settings and the listener’s environment will affect how the comparison sounds.
Acoustician Note
“In this relatively large bedroom, the improvement became even more apparent with distance from the window. Around two metres into the room, the road noise had almost completely disappeared into the background, and individual vehicle pass-bys were no longer intrusive.”
– Sebastian, Lead Acoustician, The Soundproof Windows
Specification Snapshot
- System: Bespoke timber secondary sash windows
- Primary windows: Original single-glazed timber sash windows
- Acoustic glazing: Acoustic laminated glazing laboratory-rated at Rw 49 dB
- Installed cavity: Approximately 56 mm glass to glass
- Sealing and locking: Continuous compression seals with a multipoint locking mechanism
- Measured average reduction: At least 12.3 dB, based on the recorded LAeq levels
- Measured maximum reduction: 20.5 dB, based on the recorded LAFmax levels
- Thermal performance: Approximately 5.6 W/m²K for conventional single glazing, compared with less than 1.1 W/m²K for the internal secondary-window unit
- Testing equipment: Calibrated NTi Audio XL2 acoustic analyser
- Guarantee: 10-year CPA insurance-backed guarantee, subject to applicable terms
Does your room face a busy London road?
This Prince Albert Road project demonstrates that substantial real-world noise reduction can be achieved even where the available cavity is restricted.
Every property is different. Installed performance depends on the existing window, available cavity, glass specification, sealing, installation quality, room conditions, noise spectrum and other potential sound-transmission paths.
We assess these factors before recommending a secondary-window specification for your property.
Arrange an acoustic window assessment → Send us photographs and an approximate measurement of your available reveal depth. We will review the existing window, noise source and practical installation options before recommending a suitable system.
SPECIALIST SOUNDPROOF WINDOWS & DOORS
Through specialist manufacturing and precision technology, we can reduce noise pollution by up to 95%. By installing specialist soundproof windows and doors, we provide you with the best products on the market. Don’t compromise on design. Don’t compromise on quality.
PROUDLY SUPPORTING:
Trees for Life is a conservation charity dedicated to rewilding the Scottish Highlands. They currently have 44 tree planting sites and have planted nearly two million trees to date.
10 YEAR INSURANCE BACKED GUARANTEE
All of our products come with up to a 10 Year Insurance Backed Guarantee provided by the Consumer Protection Association. So you can rest assured that your home is in safe hands.
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AWARD-WINNING PRODUCTS & INSTALLATION
Following awards in 2020, and 2021, The Soundproof Windows was announced as the ‘Best Acoustic Window & Door Installation Company – London’ at the SME News Awards 2022.