Which Partition Delivers More Sound Insulation for Less Carbon?
Updated: Sep 23
Introducing ACER: a proposed method for comparing the carbon efficiency of airborne sound insulation constructions
To calculate Acoustic Carbon Efficiency Ratio (ACER) of your construction, use the calculator.
How can we compare the embodied carbon of partitions that provide different levels of sound insulation?
Comparing their Global Warming Potential (GWP) directly is not necessarily fair. A partition achieving Rw 60 dB is providing a different level of acoustic performance from one achieving Rw 40 dB.
One possible approach is to divide GWP by the sound-insulation rating, producing a value in kgCO₂e/m²/dB. Although simple, this is conceptually weak because sound insulation is logarithmic: an additional decibel does not represent a linear increase in construction performance or material demand.
Another approach is to compare constructions within performance bands. The Max Fordham Office Partition Study: Embodied Carbon Assessment, for example, groups partitions into low, medium and high acoustic-performance categories and compares their carbon impacts within each group. This is useful, but the result depends on the selected categories and baseline construction. It is difficult to use the results for wider comparisons between performance levels, product families or regions.
The proposed Acoustic Carbon Efficiency Ratio
I propose a dimensionless descriptor called the Acoustic Carbon Efficiency Ratio (ACER), comparing the global warming potential of a candidate construction with that of the ACER Standard Reference Concrete providing the same airborne sound insulation rating:
where:
s = lifecycle scope, such as A1–A3 or A1–A5 or A1-C etc;
X = acoustic descriptor, such as Rw, Rw+C, or Rw+Ctr;
T = reference study period in years, where time-dependent lifecycle stages are included.
The result is interpreted as follows:
ACER < 1: lower GWP than the acoustically equivalent concrete reference;
ACER = 1: equal GWP;
ACER > 1: higher GWP than the acoustically equivalent concrete reference.
For example:
This means that, over a 60-year reference study period, the candidate construction has 55% of the whole-life embodied GWP of the standard reference concrete providing the same Rw — or 45% less.
For lifecycle scopes that are not time-dependent, the year is unnecessary:
The ACER Standard Reference Concrete
ACER Standard Reference Concrete is a fixed conventional benchmark comprising 1 m² of homogeneous, monolithic and unreinforced concrete of variable thickness.
The proposed reference is based on the Mineral Products Association UK sector Environmental Product Declaration for C28/35 CEM II/C-M (S-L) + SR ready-mixed concrete, registration EPD-IES-0011234:002.
The carbon assumptions include:
A1–A3 GWP-total: 176.0 kgCO₂e/m³;
A1–A5 GWP-total: 183.3 kgCO₂e/m³;
A4: 10 km delivery by Euro 6 concrete mixer truck;
A5: pumped placement, 2.24 kWh/m³ installation energy, 44.78 litres/m³ water and 1.5% construction wastage.
B1 GWP: -5.37 kgCO₂e/m³ RSP 30 years, -7.6 kgCO₂e/m³ RSP 60 years, -9.81 kgCO₂e/m³ RSP 100 years.
The UK origin identifies the provenance of the data. It does not mean that the reference represents typical concrete production in every country. Its purpose is to provide a fixed and transparent denominator that can be applied consistently.
Why use a concrete reference?
A homogeneous concrete element provides a simple and reproducible relationship between thickness, mass, sound insulation and embodied carbon. Its variable thickness allows a reference value to be established across a range of acoustic ratings without placing constructions into arbitrary performance bands.
The proposed method offers four potential benefits:
Meaningful: carbon is compared against equivalent acoustic performance rather than against area alone.
Comparable: constructions with different sound-insulation ratings and from different regions can be assessed within one framework.
Transparent: the reference material, acoustic model, lifecycle boundary and carbon assumptions are fixed and published.
Not sensitive to project location: Ready-mixed concrete is generally produced at a local batching plant and transported over a relatively short distance. This reduces geographical variation in A4 transport impacts compared with products manufactured at a small number of distant factories or imported from other countries. The ACER reference therefore provides a relatively stable transport benchmark, although concrete mix design and production impacts can still vary by region.
Limitations
The reference is an acoustic–carbon benchmarking convention, not a complete structural design or necessarily a practical alternative to the candidate construction.
Reinforcement, finishes, linings, structural connections, supports and junction treatments are excluded. Formwork is excluded from the source EPD under its cut-off rules. Acoustic equivalence is limited to the selected laboratory airborne sound-insulation descriptor and does not imply equivalence in structural capacity, fire resistance, durability, thermal performance, thickness, cost or buildability.
Initial application
I have applied ACER to the double-leaf lightweight constructions presented published in the Max Fordham Office Partition Study: Embodied Carbon Assessment, which examines various board materials and partition configurations. Full construction details are available in the report. The Rw and GWP values are taken from that study. Where Rw+C and Rw+Ctr are assessed, C and Ctr values are obtained from INSUL predictions of the stated constructions.
(The project location is considered in London.
Construction-code example: 2BGSoundbloc12.5_SFR70(MW25)_2BGSoundbloc12.5 denotes two layers of 12.5 mm British Gypsum SoundBloc board on each side of a 70 mm deep steel frame, with 25 mm mineral wool in the cavity. SFR denotes a steel frame, while TFR denotes a timber frame.)
The initial results suggest that lightweight double-leaf partitions generally provide airborne sound insulation with lower upfront carbon than an acoustically equivalent homogeneous concrete reference. However, this advantage reduces substantially over the study’s 60-year whole-life scenario, which assumes that partitions are replaced after 30 years.
The conclusions also depend on the acoustic descriptor. A construction that appears carbon-efficient when assessed using Rw can become less favourable under Rw+C, and particularly under Rw+Ctr, because these terms account more directly for spectral limitations, including low-frequency performance. This demonstrates the value of linking carbon impacts to a clearly defined acoustic requirement. It also shows that service life, replacement, transportation, additional functions and the quality of the supporting acoustic evidence must be reported alongside ACER.
The assessed CLT constructions generally have the highest ACER values. Although timber can have a relatively low carbon intensity, these build-ups use a substantial quantity of material, including two 100 mm CLT panels in the medium- and high-performance options. The CLT is also assumed to be transported from southern Germany, increasing its A4 impact. Importantly, these walls would normally form part of a loadbearing CLT structure. ACER assesses their acoustic carbon efficiency but gives no credit for their structural function, so they should not be compared directly with non-loadbearing partitions without this qualification.
ClayTec boards have relatively low manufacturing impacts at the factory gate. In the study, however, they are assumed to be manufactured in southern Germany. The long-distance transport route to UK projects—particularly the HGV journey to northern European ports—substantially increases their A4 impact and makes them less competitive in the assessed UK scenarios. This reflects the assumed supply chain rather than an inherent disadvantage of clay as a material.
One construction (High-5) produces an exceptionally low ACER and appears to be an outlier. Its reported acoustic performance seems inconsistent with the stated build-up and has not been verified against a corresponding laboratory report. This result should therefore be treated as provisional and excluded from comparative conclusions until its construction and acoustic evidence have been confirmed.
Final words
I would welcome views from architects, acoustic consultants and whole-life-carbon specialists:
Would a common, performance-normalised descriptor such as ACER help you compare sound-insulating constructions during design?
Reference
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