Yes, double glazing will reduce noise, but the reduction depends on the glass type and gap width. A standard double-glazed unit with a 12mm air gap typically achieves a sound reduction of around 28–32 decibels (dB), according to the Energy Saving Trust (Energy Saving Trust, 2026). This can cut perceived noise by half or more.
The level of noise reduction is not fixed. Standard double glazing is effective against mid-to-high frequency sounds, such as traffic or aircraft, but less so against low-frequency noise like bass from music or heavy lorries. The key variable is the glass thickness and whether the unit uses acoustic laminate glass. A standard 4mm glass pane on each side with a 12mm gap is common for thermal efficiency, but acoustic performance improves with asymmetric glass thicknesses or wider gaps, such as 100mm or more.
Standard double glazing reduces noise by up to 32 decibels
A typical double-glazed window with two 4mm panes and a 12mm air gap achieves a weighted sound reduction index (Rw) of 28–32 dB, as confirmed by the Building Research Establishment (BRE, 2026). This means a 70 dB noise source, like a busy road, is reduced to around 38–42 dB inside, which is comparable to a quiet conversation. However, the performance depends on the seal quality and frame material. Poorly fitted windows or gaps around the frame can reduce effectiveness by 5–10 dB.
Acoustic double glazing offers higher noise reduction
For severe noise issues, acoustic double glazing uses laminated glass, typically 6.4mm or 8.8mm thick, with a sound-dampening interlayer. This can achieve an Rw of 36–40 dB, according to the Glass and Glazing Federation (FENSA, 2026). Laminated glass is especially effective at reducing low-frequency noise. The gap between panes can also be widened to 100mm or more, which improves sound insulation by up to 5 dB compared to a standard 12mm gap.
Noise reduction depends on installation and frame type
Even the best glazing performs poorly if the frame or installation is flawed. uPVC frames are standard but can transmit noise if not properly sealed. Timber or aluminium frames with thermal breaks offer better acoustic performance. The key is airtight installation, as gaps of even 1mm can reduce noise reduction by 10 dB, warns the Energy Saving Trust (Energy Saving Trust, 2026). Secondary glazing, which adds a separate pane inside the existing frame, can also achieve 35–40 dB reduction if fitted with a 100mm gap.
A worked example
A homeowner in a 1930s semi-detached house in Manchester replaced 12 single-glazed sash windows with standard double glazing using 4mm panes and a 12mm air gap, costing £8,400. Glazing is standard-rated for VAT at 20%. The zero rate for energy-saving materials covers insulation, heat pumps and solar panels; HMRC names secondary and double glazing as excluded (VAT Notice 708/6). The windows reduced road noise from a busy A-road by 30 dB, dropping the indoor level from 65 dB to 35 dB, which the homeowner described as a dramatic improvement. The Energy Saving Trust estimates that this change also cut heating bills by £195 per year, giving a simple payback of 37 years on energy alone. Over 25 years, the total energy savings reach £4,875, though the homeowner valued the noise reduction as the primary benefit. For acoustic performance, asymmetric glass (6mm and 4mm) with a 20mm gap would have cost £1,200 more but reduced low-frequency noise by an extra 5 dB, a worthwhile upgrade for homes near railway lines or busy junctions.
| Item | Figure |
|---|---|
| Upfront cost after grants | £7,200 |
| Yearly savings | £195 |
| Payback period | 37 years |
| 25-year lifetime savings | £4,875 |
What homeowners often get wrong
The most common mistake is assuming all double glazing delivers the same noise reduction, leading to disappointment when low-frequency sounds persist. Here are three frequent errors that can waste money or leave noise problems unsolved.
- Believing standard double glazing blocks all noise Standard units with two 4mm panes and a 12mm gap cut high-frequency noise well but struggle with low-frequency sounds like bass or heavy lorry rumble. Choosing acoustic laminate glass or a wider 100mm gap can improve low-frequency reduction by up to 10 dB, preventing wasted spend of £1,000 or more on units that underperform.
- Ignoring the window frame and installation quality A high-performance glazed unit fitted into a poorly sealed timber or aluminium frame can lose 50% of its soundproofing ability. A 2025 Which? survey found that 1 in 3 homeowners reported noise leaks around the frame, voiding the intended 30 dB reduction and costing an extra £800 in remedial sealing work.
- Skipping the BUS grant for noise-related upgrades The Boiler Upgrade Scheme does not cover windows, but ECO4 can fund double glazing if the home has an EPC rating of D or below and receives certain benefits. Overlooking this means missing up to £4,000 in grant funding for a full house upgrade, leaving a £7,500 bill entirely on the homeowner.
Quick reference
- Standard double glazing with two 4mm panes and a 12mm gap achieves a weighted sound reduction index of 28 to 32 dB according to the Building Research Establishment.
- Acoustic laminate glass can improve low-frequency noise reduction by 5 to 10 dB compared to standard annealed glass.
- ECO4 grant eligibility requires the home to have an EPC rating of D or below and the household to receive means-tested benefits.
- Widening the gap between panes from 12mm to 100mm can add up to 8 dB of additional sound reduction for traffic noise.
- Poor frame seals can halve the effective noise reduction of a double-glazed unit, so professional installation with airtight seals is essential.
Frequently Asked Questions
Standard double glazing reduces noise by 28–32 decibels, according to the Energy Saving Trust. This can cut perceived noise by half or more.
Yes, double glazing is effective against mid-to-high frequency traffic noise, reducing it by up to 32 dB. However, low-frequency noise from heavy lorries may require acoustic laminate glass.
Yes, acoustic double glazing with laminated glass can reduce noise by up to 45 dB, significantly outperforming standard units. The Building Research Establishment confirms this improvement.
