Acoustic Glazing Calculator

Rw is the weighted sound reduction index (BS EN ISO 717-1) measured in decibels (dB). It is a single-figure rating of how well the glazing reduces airborne sound across the standard frequency range. A higher Rw means better noise reduction. Standard 4-16-4 double glazing achieves about 29-30 dB Rw; asymmetric and laminated acoustic units (for example Pilkington Optiphon or Saint-Gobain STADIP SILENCE class) reach roughly 36-41 dB Rw depending on the make-up.

Road, rail and motorway noise is weighted towards low frequencies, where glazing performs less well. BS EN ISO 717-1 provides the spectrum adaptation term Ctr for exactly this kind of source, and the relevant single-figure rating becomes Rw+Ctr. For glazed units Ctr is typically -5 to -8 dB, so a unit rated Rw 41 might only deliver around 35 dB against traffic. Using bare Rw against traffic overstates the real reduction by several decibels, which is why this calculator applies a Ctr deduction to road, rail and motorway sources. Aircraft and amplified-music spectra are flatter and use the C term, which is close to zero, so Rw is used for those.

BS 8233:2014 recommends internal ambient noise levels of 30 dB LAeq,8h for bedrooms at night and 35 dB LAeq,16h for living rooms and bedrooms during the daytime. Planning conditions for new developments near noise sources typically require compliance with these levels, usually demonstrated through a ProPG / BS 8233 assessment by an acoustic consultant.

Yes, laminated glass with a PVB (polyvinyl butyral) or specialist acoustic interlayer significantly improves sound reduction. A 6.4mm laminated pane (two 3mm panes with 0.4mm interlayer) outperforms a single 6mm pane acoustically because the interlayer dampens vibration transmission.

Asymmetric glass (different thicknesses in each pane) shifts the coincidence dip so the two panes do not become acoustically transparent at the same frequency. A 6/16/4 unit therefore performs better acoustically than a symmetric 4/16/4 or 6/16/6. The same physics is why a standard triple-glazed unit with three equal panes only reaches about 33-35 dB Rw and can under-perform a well-specified acoustic double — genuine acoustic triple glazing needs asymmetric and/or laminated panes.

For noise alone, secondary glazing is usually the strongest option because of the large glass-to-glass air gap. A 100mm gap typically gives around 40-43 dB Rw, and 150-200mm gaps push higher still. Standard triple glazing (three equal panes) is only about 33-35 dB and is chosen mainly for thermal performance, not acoustics. Acoustic-spec laminated double glazing sits in between at roughly 36-41 dB depending on the make-up.

As an indicative guide (prices vary by region, installer and year — get quotes for your project): standard acoustic DGUs (6/16/6.4 laminated) are roughly £200-£300/m² supply and fit; high-performance units (10/16/8.8 laminated) around £350-£500/m²; secondary glazing with a 100mm+ air gap is often the most cost-effective acoustic solution at about £150-£250/m². Treat these as ballpark figures only, not a fixed quotation.