Worked Example: School Gymnasium — BB93 Non-Compliant Case
RT60 calculation for a school sports hall that fails BB93 requirements. The metal deck roof and concrete block walls create excessive reverberation despite partial wall treatment, demonstrating why gymnasiums are among the hardest rooms to treat acoustically.
A 2520 m³ gymnasium designed to BB93 requires RT60 ≤ 1.5s. With Metal deck roof on the ceiling and Fabric-wrapped panel 50mm on walls, the calculated RT60 is 3.08s — FAIL.
Room Setup
Total surface area: 1214.0 m². Calculation method: Sabine equation (ISO 3382-2:2008 Annex A).
Surface Materials
| Surface | Material | Area (m²) | NRC |
|---|---|---|---|
| ceiling | Metal deck roof | 360.0 | 0.05 |
| walls-main | Painted concrete block | 390.0 | 0.07 |
| walls-treatment | Fabric-wrapped panel 50mm | 60.0 | 0.80 |
| floor | Rubber sport floor | 360.0 | 0.08 |
| windows | Double glazing 6mm | 36.0 | 0.04 |
| door | Solid timber door | 8.0 | 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 = 24 × 15 × 7 = 2520 m³
- 2
Total Surface Area
Stotal = 360.0 + 390.0 + 60.0 + 360.0 + 36.0 + 8.0 = 1214.0 m²
- 3
Absorption per Surface at 500 Hz
ceiling: 360.0 m² × 0.05 = 18.00 Sabins
walls-main: 390.0 m² × 0.06 = 23.40 Sabins
walls-treatment: 60.0 m² × 0.78 = 46.80 Sabins
floor: 360.0 m² × 0.08 = 28.80 Sabins
windows: 36.0 m² × 0.04 = 1.44 Sabins
door: 8.0 m² × 0.08 = 0.64 Sabins
- 4
Total Absorption at 500 Hz
Atotal = 18.00 + 23.40 + 46.80 + 28.80 + 1.44 + 0.64 = 119.08 Sabins
- 5
Sabine RT60 at 500 Hz
RT60 = 0.161 × V / A = 0.161 × 2520 / 119.08 = 3.41s
- 6
Compare to Target
Mid-frequency RT60 (avg of 500, 1k, 2k Hz) = 3.08s. Target: ≤ 1.5s per BB93. Verdict: FAIL
Octave Band Results
| Frequency | 125Hz | 250Hz | 500Hz | 1kHz | 2kHz | 4kHz |
|---|---|---|---|---|---|---|
| Total Absorption (Sabins) | 104.9 | 101.3 | 119.1 | 137.6 | 140.9 | 137.6 |
| RT60 (s) | 3.87 | 4.01 | 3.41 | 2.95 | 2.88 | 2.95 |
| Target (s) | — | — | 1.50 | 1.50 | 1.50 | — |
| Verdict | — | — | FAIL | FAIL | FAIL | — |
Compliance Verdict
Reference: BB93:2015 Table 1.3
BB93 allows RT60 up to 1.5s for sports halls, but this untreated gymnasium far exceeds the limit. Ball-impact resistant treatment is required on walls and ceiling soffit.
STI result: 0.42 (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 (24m × 15m × 7m) and RT60 target (1.5s).
Open CalculatorField Story
A PE teacher reports that instructions during indoor sports are nearly unintelligible, and whistle blows create painful reverberant build-up. The school gymnasium has a profiled metal deck ceiling at 7 metres height, painted concrete block walls, and a rubber sports floor — all hard, reflective surfaces enclosing a 2,520 m³ volume. The limited fabric panels installed on the end walls during construction were a token gesture that barely dents the excessive RT60. A proper solution requires hanging acoustic baffles from the roof structure and impact-resistant absorptive wall panels — a project costing upward of £80,000.
Frequently Asked Questions
What RT60 does a School Gymnasium — BB93 Non-Compliant Case achieve?
With the specified materials and dimensions (24m x 15m x 7m, volume 2520m3), the calculated mid-frequency RT60 is 3.08s using the Sabine equation. The target under BB93 is 1.5s or less. The result is a FAIL.
What materials are used in this education acoustic example?
This example uses Metal deck roof on the ceiling (NRC 0.05), Painted concrete block on the walls-main (NRC 0.07), Fabric-wrapped panel 50mm on the walls-treatment (NRC 0.8), Rubber sport floor on the floor (NRC 0.08), 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 119.1 Sabins.
How much does acoustic treatment cost for this room?
The estimated treatment cost is £31,500 for 420 m2 of absorptive material at approximately £75/m2. Actual costs vary by region, supplier, and installation complexity.
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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.