Worked Example: UK Primary Classroom — BB93 Acoustic Compliance
Step-by-step RT60 calculation for a typical UK primary school classroom demonstrating BB93:2015 compliance. Uses Rockfon Sonar ceiling tiles and fabric-wrapped rear wall panels to achieve the 0.6s target.
A 189 m³ classroom designed to BB93 requires RT60 ≤ 0.6s. With Rockfon Sonar 25mm on the ceiling and Fabric-wrapped panel 50mm on walls, the calculated RT60 is 0.31s — PASS.
Room Setup
Total surface area: 237.6 m². Calculation method: Sabine equation (ISO 3382-2:2008 Annex A).
Surface Materials
| Surface | Material | Area (m²) | NRC |
|---|---|---|---|
| ceiling | Rockfon Sonar 25mm | 63.0 | 0.85 |
| walls-main | Painted plaster | 72.0 | 0.04 |
| walls-treatment | Fabric-wrapped panel 50mm | 24.0 | 0.80 |
| floor | Carpet (heavy) | 63.0 | 0.30 |
| windows | Double glazing 6mm | 12.0 | 0.04 |
| door | Solid timber door | 3.6 | 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 = 9 × 7 × 3 = 189 m³
- 2
Total Surface Area
Stotal = 63.0 + 72.0 + 24.0 + 63.0 + 12.0 + 3.6 = 237.6 m²
- 3
Absorption per Surface at 500 Hz
ceiling: 63.0 m² × 0.82 = 51.66 Sabins
walls-main: 72.0 m² × 0.04 = 2.88 Sabins
walls-treatment: 24.0 m² × 0.78 = 18.72 Sabins
floor: 63.0 m² × 0.14 = 8.82 Sabins
windows: 12.0 m² × 0.04 = 0.48 Sabins
door: 3.6 m² × 0.08 = 0.29 Sabins
- 4
Total Absorption at 500 Hz
Atotal = 51.66 + 2.88 + 18.72 + 8.82 + 0.48 + 0.29 = 82.85 Sabins
- 5
Sabine RT60 at 500 Hz
RT60 = 0.161 × V / A = 0.161 × 189 / 82.85 = 0.37s
- 6
Compare to Target
Mid-frequency RT60 (avg of 500, 1k, 2k Hz) = 0.31s. Target: ≤ 0.6s per BB93. Verdict: PASS
Octave Band Results
| Frequency | 125Hz | 250Hz | 500Hz | 1kHz | 2kHz | 4kHz |
|---|---|---|---|---|---|---|
| Total Absorption (Sabins) | 26.8 | 61.5 | 82.8 | 105.9 | 119.0 | 119.0 |
| RT60 (s) | 1.14 | 0.49 | 0.37 | 0.29 | 0.26 | 0.26 |
| Target (s) | — | — | 0.60 | 0.60 | 0.60 | — |
| Verdict | — | — | PASS | PASS | PASS | — |
Compliance Verdict
Reference: BB93:2015 Table 1.2
BB93:2015 requires RT60 ≤ 0.6s at mid-frequencies for primary classrooms. Full ceiling treatment with supplementary rear wall absorption achieves compliance with margin.
STI result: 0.72 (per IEC 60268-16:2020)
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 (9m × 7m × 3m) and RT60 target (0.6s).
Open CalculatorField Story
A head teacher at a 1970s-built primary school reports that children at the back of the classroom struggle to hear instructions clearly. The room has painted plaster walls, a hard plaster ceiling, and vinyl flooring — all highly reflective surfaces. Background noise from corridor activity adds to the problem. An acoustic survey measures an unoccupied RT60 of 1.8 seconds at mid-frequencies, more than triple the BB93 limit. The solution involves installing suspended mineral fibre ceiling tiles and fabric-wrapped absorbers on the rear wall, bringing the RT60 below 0.6 seconds and transforming speech clarity for every pupil.
Frequently Asked Questions
What RT60 does a UK Primary Classroom — BB93 Acoustic Compliance achieve?
With the specified materials and dimensions (9m x 7m x 3m, volume 189m3), the calculated mid-frequency RT60 is 0.31s using the Sabine equation. The target under BB93 is 0.6s or less. The result is a PASS.
What materials are used in this education acoustic example?
This example uses Rockfon Sonar 25mm on the ceiling (NRC 0.85), Painted plaster on the walls-main (NRC 0.04), 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 82.8 Sabins.
How much does acoustic treatment cost for this room?
The estimated treatment cost is £6,750 for 150 m2 of absorptive material at approximately £45/m2. Actual costs vary by region, supplier, and installation complexity.
Related Examples
UK Secondary Classroom — BB93 Marginal Result
US Classroom — ANSI S12.60 Acoustic Compliance
German Classroom — DIN 18041 Acoustic Design
Australian Classroom — NCC/AS 2107 Compliance
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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.