Worked Example: Law Firm — Premium WELL F74 Acoustic Plaster
RT60 calculation for a premium law firm's open plan area using acoustic plaster ceiling for an upscale finish. Demonstrates WELL v2 Feature 74 compliance while maintaining the refined aesthetic expected in professional services environments.
A 680.4 m³ open plan office designed to WELL-F74 requires RT60 ≤ 0.5s. With Acoustic plaster 15mm on the ceiling and Fabric-wrapped panel 50mm on walls, the calculated RT60 is 0.34s — PASS.
Room Setup
Total surface area: 724.0 m². Calculation method: Sabine equation (ISO 3382-2:2008 Annex A).
Surface Materials
| Surface | Material | Area (m²) | NRC |
|---|---|---|---|
| ceiling | Acoustic plaster 15mm | 252.0 | 0.70 |
| walls-main | Plasterboard on studs | 122.4 | 0.07 |
| walls-treatment | Fabric-wrapped panel 50mm | 50.4 | 0.80 |
| floor | Carpet (heavy) | 252.0 | 0.30 |
| windows | Double glazing 6mm | 40.0 | 0.04 |
| door | Solid timber door | 7.2 | 0.08 |
Absorption coefficients sourced from manufacturer datasheets and ISO 354 test reports. Browse the full acoustic materials database.
Step-by-Step Calculation
- 1
Room Volume
V = L × W × H = 18 × 14 × 2.7 = 680.4 m³
- 2
Total Surface Area
Stotal = 252.0 + 122.4 + 50.4 + 252.0 + 40.0 + 7.2 = 724.0 m²
- 3
Absorption per Surface at 500 Hz
ceiling: 252.0 m² × 0.65 = 163.80 Sabins
walls-main: 122.4 m² × 0.05 = 6.12 Sabins
walls-treatment: 50.4 m² × 0.78 = 39.31 Sabins
floor: 252.0 m² × 0.14 = 35.28 Sabins
windows: 40.0 m² × 0.04 = 1.60 Sabins
door: 7.2 m² × 0.08 = 0.58 Sabins
- 4
Total Absorption at 500 Hz
Atotal = 163.80 + 6.12 + 39.31 + 35.28 + 1.60 + 0.58 = 246.69 Sabins
- 5
Sabine RT60 at 500 Hz
RT60 = 0.161 × V / A = 0.161 × 680.4 / 246.69 = 0.44s
- 6
Compare to Target
Mid-frequency RT60 (avg of 500, 1k, 2k Hz) = 0.34s. Target: ≤ 0.5s per WELL-F74. Verdict: PASS
Octave Band Results
| Frequency | 125Hz | 250Hz | 500Hz | 1kHz | 2kHz | 4kHz |
|---|---|---|---|---|---|---|
| Total Absorption (Sabins) | 80.3 | 148.5 | 246.7 | 344.4 | 420.7 | 408.0 |
| RT60 (s) | 1.36 | 0.74 | 0.44 | 0.32 | 0.26 | 0.27 |
| Target (s) | — | — | 0.50 | 0.50 | 0.50 | — |
| Verdict | — | — | PASS | PASS | PASS | — |
Compliance Verdict
Reference: WELL v2 Feature 74, L07
Premium law firms demand invisible acoustic solutions. Acoustic plaster provides a seamless monolithic ceiling that absorbs sound without the grid-and-tile appearance. WELL Feature 74 compliance supports the firm's wellness programme and recruitment marketing.
Cost Estimate
Costs are indicative and vary by region, supplier, and installation complexity. For a detailed cost breakdown, use the AcousPlan calculator.
Open the AcousPlan calculator pre-loaded with the exact room dimensions (18m × 14m × 2.7m) and RT60 target (0.5s).
Open CalculatorField Story
An international law firm relocating to a new London headquarters insists on WELL Building Standard Gold certification for recruitment purposes — top graduates increasingly choose employers based on workplace quality. The managing partner vetoes visible acoustic ceiling tiles as looking too corporate. The acoustic consultant specifies a spray-applied acoustic plaster system that creates a seamless white ceiling surface with NRC 0.70 — visually indistinguishable from conventional plaster but absorbing five times more sound. At £110 per square metre it costs three times more than standard tiles, but the firm considers it essential for their brand image. The WELL assessment confirms Feature 74 compliance.
Frequently Asked Questions
What RT60 does a Law Firm — Premium WELL F74 Acoustic Plaster achieve?
With the specified materials and dimensions (18m x 14m x 2.7m, volume 680.4m3), the calculated mid-frequency RT60 is 0.34s using the Sabine equation. The target under WELL-F74 is 0.5s or less. The result is a PASS.
What materials are used in this office acoustic example?
This example uses Acoustic plaster 15mm on the ceiling (NRC 0.7), Plasterboard on studs on the walls-main (NRC 0.07), Fabric-wrapped panel 50mm on the walls-treatment (NRC 0.8), Carpet (heavy) on the floor (NRC 0.3), Double glazing 6mm on the windows (NRC 0.04), Solid timber door on the door (NRC 0.08). The total absorption at 500 Hz is 246.7 Sabins.
How much does acoustic treatment cost for this room?
The estimated treatment cost is £60,984 for 554 m2 of absorptive material at approximately £110/m2. Actual costs vary by region, supplier, and installation complexity.
Related Examples
Open Plan Office — BS 8233 Acoustic Design
Small Meeting Room — BS 8233 Acoustic Design
Co-working Space — Industrial Conversion Acoustics
Call Centre — BS 8233 Speech Privacy Design
Explore More
All calculations are advisory and based on the Sabine equation (ISO 3382-2:2008 Annex A). Results require professional verification for compliance submissions. Absorption coefficients are sourced from manufacturer datasheets and ISO 354 test reports.