Worked Example: French Classroom — NRA 2000 Acoustic Compliance
RT60 calculation for a French école primaire classroom under NRA 2000 (Nouvelle Réglementation Acoustique). Mineral wool wall panels supplement the acoustic ceiling to achieve the 0.4-0.8s target range.
A 189 m³ classroom designed to NRA requires RT60 ≤ 0.8s. With Rockfon Sonar 25mm on the ceiling and Mineral wool 50mm on walls, the calculated RT60 is 0.43s — 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 | 86.0 | 0.04 |
| walls-treatment | Mineral wool 50mm | 10.0 | 0.75 |
| floor | Vinyl/linoleum floor | 63.0 | 0.03 |
| 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 + 86.0 + 10.0 + 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: 86.0 m² × 0.04 = 3.44 Sabins
walls-treatment: 10.0 m² × 0.70 = 7.00 Sabins
floor: 63.0 m² × 0.03 = 1.89 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 + 3.44 + 7.00 + 1.89 + 0.48 + 0.29 = 64.76 Sabins
- 5
Sabine RT60 at 500 Hz
RT60 = 0.161 × V / A = 0.161 × 189 / 64.76 = 0.47s
- 6
Compare to Target
Mid-frequency RT60 (avg of 500, 1k, 2k Hz) = 0.43s. Target: 0.4--0.8s per NRA. Verdict: PASS
Octave Band Results
| Frequency | 125Hz | 250Hz | 500Hz | 1kHz | 2kHz | 4kHz |
|---|---|---|---|---|---|---|
| Total Absorption (Sabins) | 24.8 | 50.0 | 64.8 | 73.9 | 71.8 | 70.5 |
| RT60 (s) | 1.23 | 0.61 | 0.47 | 0.41 | 0.42 | 0.43 |
| Target (s) | — | — | 0.80 | 0.80 | 0.80 | — |
| Verdict | — | — | PASS | PASS | PASS | — |
Compliance Verdict
Reference: NRA 2000, Arrêté 25/04/2003 Art. 5
NRA 2000 (Arrêté du 25 avril 2003) specifies Tr = 0.4-0.8s for teaching spaces in educational buildings. The target Aire d'absorption équivalente Aeq must meet minimum thresholds at 500, 1000, and 2000 Hz.
STI result: 0.71 (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 (0.8s).
Open CalculatorField Story
A newly built école primaire in Lyon must submit acoustic compliance documentation before the Préfecture issues the occupancy permit. The architect favoured polished concrete floors throughout for easy maintenance, leaving acoustic treatment limited to ceiling tiles. Initial calculations show the RT60 at 0.75 seconds — compliant but with no margin. The acoustic bureau recommends adding mineral wool panels behind perforated timber on the rear wall, bringing the RT60 comfortably within the NRA range and providing resilience against future furniture changes that might alter the room's acoustic response.
Frequently Asked Questions
What RT60 does a French Classroom — NRA 2000 Acoustic Compliance achieve?
With the specified materials and dimensions (9m x 7m x 3m, volume 189m3), the calculated mid-frequency RT60 is 0.43s using the Sabine equation. The target under NRA is 0.4--0.8s. 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), Mineral wool 50mm on the walls-treatment (NRC 0.75), 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 64.8 Sabins.
How much does acoustic treatment cost for this room?
The estimated treatment cost is €3,504 for 73 m2 of absorptive material at approximately €48/m2. Actual costs vary by region, supplier, and installation complexity.
Related Examples
UK Primary Classroom — BB93 Acoustic Compliance
UK Secondary Classroom — BB93 Marginal Result
US Classroom — ANSI S12.60 Acoustic Compliance
German Classroom — DIN 18041 Acoustic 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.