Acoustic double glazing: balancing sound performance and natural light

Specifying acoustic double glazing in a partition wall relies on three quantifiable levers, to be weighed up from the design phase before validating the detail drawings.

• Asymmetric thickness: a 10/16/6 mm composition improves sound reduction by 3 to 5 dB compared with a symmetric 8/16/8 mm, by shifting the coincidence frequencies. The trade-off is that light transmission drops by 8 to 12 % according to the EN 410 calculation on the same compositions.
• Acoustic PVB film: a three-layer viscoelastic interlayer adds 2 to 4 dB across the 1000-2000 Hz range compared with standard PVB, which only delivers a 1 to 2 dB gain. Observed additional cost: 15 to 25 EUR/m² according to recent supplier consultations.
• Fill gas: argon optimises thermal insulation, Ug 1.1 W/m²K versus 1.4 for air according to EN 673 values, with no measurable acoustic impact.

Kytom’s contrarian position: industry conventional wisdom often presents argon as an acoustic lever, sometimes on the basis of a 1 to 2 dB gain. Our reading of the tests carried out on supplier technical data sheets differs: at constant thickness and PVB, switching from air to argon produces no measurable acoustic gain beyond the margin of uncertainty. It is a thermal lever, wrongly sold as acoustic.

Common configurations place 8/16/8 standard PVB at around 36 dB Rw with 78 % light transmission, 10/16/6 standard PVB at 40 dB for 68 % LT, and 10/16/6 acoustic PVB at 43 dB for 66 % LT. The choice comes down to the ratio of cost per dB gained to light retained.

When acoustic double glazing is not justified: below an Rw 32 dB target on an isolated partitioned office, with no proven nuisance, standard 44.2 laminated single glazing is sufficient at a significantly lower cost. Beyond a required Rw 45 dB, double glazing reaches its physical limit and you have to switch to a solid partition or a double-skin acoustic lobby, otherwise the additional cost is unjustified.

For the architect and the technical inspector: balance the glazing ratio before specifying the glass

The applicable acoustic insulation levels for offices and tertiary spaces are governed by a dedicated normative framework, supplemented by requirements relating to collaborative spaces.

• Standard closed office: Rw greater than or equal to 32 dB for everyday confidentiality (high-performance level).
• Meeting room: Rw greater than or equal to 35 dB for sensitive exchanges.
• Executive and confidential spaces: Rw greater than or equal to 38 dB (very high-performance level).
• Exposed facades: DnTA,tr greater than or equal to 30 dB in a tertiary office.

Reframing for the architect and the technical inspector: the structuring decision is not the choice of glass, it is the glazing ratio in the detail drawings. On a fully glazed floor-to-ceiling partition, achieving 38 dB DnTA,tr in situ becomes marginal beyond around 80 % glazing ratio on the partition face. Kytom then recommends introducing a solid base of 0.9 to 1.1 m or a solid transom, failing which the executive target is not achievable even with a 10/16/6 acoustic PVB. This constraint is dealt with at the sketch stage, not at tender stage: integrated early, it preserves the architectural language; integrated late, it forces a revision of the detail drawings and an imposed trade-off.

A laboratory Rw 38 dB does not guarantee a DnTA,tr 38 dB in situ. Flanking transmissions through the plenum, raised floor and technical ducts degrade overall performance by 3 to 8 dB. Three recurring defects compromise real acoustic performance: rigid installation without neoprene gaskets on all four faces, discontinuous silicone sealing around the perimeter, and partition profiles not filled with high-density mineral wool. Treating plenums with acoustic baffles up to the upper slab determines the result.

Limits of the framework for glazed partitions: the normative levels are defined for solid walls. Their direct transposition to a glazed removable partition remains an approximation tolerated by the profession, which should be qualified project by project.

Kytom’s 4-step methodology, from diagnosis to handover

On glazed partition wall projects with an acoustic objective, Kytom applies an auditable 4-step sequence, deployed by the design teams since 2006.

• Step 1, in-situ diagnosis: class 1 sound level meter according to NF EN 61672-1, measurements by octave bands from 125 to 4000 Hz, identification of priority sources such as the adjacent open space, circulation, HVAC. Duration 0.5 to 1 day depending on the surface area.
• Step 2, comparative simulation: 3 to 5 glazing configurations assessed on composition, PVB and thickness, with cost-per-dB ratios and light transmission impact.
• Step 3, detailed specification: detail drawings including treatment of singular points (partition/facade junction, plenum, frame connection), installation protocol and hold points on silicone sealing and decoupling.
• Step 4, handover measurements: in-situ DnTA monitoring by sampling 10 to 15 % of the partitions, comparison with the contractual target, lifting of reservations where applicable.

An assumed contrarian position: contrary to the widespread practice of aligning acoustic monitoring with 100 % visual inspection, Kytom observes very low intra-series dispersion of DnTA performance on standardised removable partitions from the same installation sequence, which justifies a handover sampling of 10 to 15 % rather than an exhaustive inspection: beyond this threshold, the marginal cost of inspection exceeds the value of the information provided. This reading differs from certain technical inspector practices that require an exhaustive inspection.

The cumulative lead times generally represent 3 to 5 weeks on a standard tertiary project cycle.

When this method is oversized: on a project of less than 200 m² of glazed partitions with an Rw 32 dB target, step 1 (in-situ diagnosis) and step 4 (handover measurements by sampling) can be streamlined in favour of enhanced visual inspection of the installation and a one-off handover test, reducing the lead time to around 2 weeks.