Worked Example: UK Secondary Classroom — BB93 Marginal Result
RT60 calculation for a larger secondary school classroom with vinyl flooring and partial ceiling coverage. Demonstrates how budget-driven ceiling cuts push results to marginal compliance, highlighting the risk of value engineering acoustic treatment.
A 240 m³ classroom designed to BB93 requires RT60 ≤ 0.6s. With Armstrong Ultima+ on the ceiling, the calculated RT60 is 0.64s — MARGINAL.
Room Setup
Total surface area: 254.6 m². Calculation method: Sabine equation (ISO 3382-2:2008 Annex A).
Surface Materials
| Surface | Material | Area (m²) | NRC |
|---|---|---|---|
| ceiling | Armstrong Ultima+ | 60.0 | 0.80 |
| walls-main | Painted plaster | 96.0 | 0.04 |
| floor | Vinyl/linoleum floor | 80.0 | 0.03 |
| windows | Double glazing 6mm | 15.0 | 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 = 10 × 8 × 3 = 240 m³
- 2
Total Surface Area
Stotal = 60.0 + 96.0 + 80.0 + 15.0 + 3.6 = 254.6 m²
- 3
Absorption per Surface at 500 Hz
ceiling: 60.0 m² × 0.85 = 51.00 Sabins
walls-main: 96.0 m² × 0.04 = 3.84 Sabins
floor: 80.0 m² × 0.03 = 2.40 Sabins
windows: 15.0 m² × 0.04 = 0.60 Sabins
door: 3.6 m² × 0.08 = 0.29 Sabins
- 4
Total Absorption at 500 Hz
Atotal = 51.00 + 3.84 + 2.40 + 0.60 + 0.29 = 58.13 Sabins
- 5
Sabine RT60 at 500 Hz
RT60 = 0.161 × V / A = 0.161 × 240 / 58.13 = 0.66s
- 6
Compare to Target
Mid-frequency RT60 (avg of 500, 1k, 2k Hz) = 0.64s. Target: ≤ 0.6s per BB93. Verdict: MARGINAL
Octave Band Results
| Frequency | 125Hz | 250Hz | 500Hz | 1kHz | 2kHz | 4kHz |
|---|---|---|---|---|---|---|
| Total Absorption (Sabins) | 20.3 | 41.4 | 58.1 | 62.7 | 59.6 | 57.4 |
| RT60 (s) | 1.90 | 0.93 | 0.66 | 0.62 | 0.65 | 0.67 |
| Target (s) | — | — | 0.60 | 0.60 | 0.60 | — |
| Verdict | — | — | MARGINAL | MARGINAL | MARGINAL | — |
Compliance Verdict
Reference: BB93:2015 Table 1.2
With vinyl flooring and only 75% ceiling coverage, this classroom sits at the margin of BB93 compliance. Adding carpet tiles or completing ceiling coverage would provide a necessary safety margin.
STI result: 0.62 (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 (10m × 8m × 3m) and RT60 target (0.6s).
Open CalculatorField Story
A newly refurbished secondary school classroom has Armstrong ceiling tiles installed during renovation, but budget cuts reduced ceiling coverage from 100% to 75% and eliminated the planned carpet and rear wall panels. Teachers notice echo during class discussions and struggle to maintain attention. A post-completion acoustic test reveals RT60 hovering at the BB93 limit. The facilities manager must now retrofit additional absorption — a far more expensive proposition than including it during the original fit-out. This example illustrates why acoustic treatment must be budgeted from the start.
Frequently Asked Questions
What RT60 does a UK Secondary Classroom — BB93 Marginal Result achieve?
With the specified materials and dimensions (10m x 8m x 3m, volume 240m3), the calculated mid-frequency RT60 is 0.64s using the Sabine equation. The target under BB93 is 0.6s or less. The result is a MARGINAL.
What materials are used in this education acoustic example?
This example uses Armstrong Ultima+ on the ceiling (NRC 0.8), Painted plaster on the walls-main (NRC 0.04), Vinyl/linoleum floor on the floor (NRC 0.03), 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 58.1 Sabins.
How much does acoustic treatment cost for this room?
The estimated treatment cost is £2,520 for 60 m2 of absorptive material at approximately £42/m2. Actual costs vary by region, supplier, and installation complexity.
Related Examples
UK Primary Classroom — BB93 Acoustic Compliance
US Classroom — ANSI S12.60 Acoustic Compliance
German Classroom — DIN 18041 Acoustic Design
Australian Classroom — NCC/AS 2107 Compliance
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.