Worked Example: Government Office — IBC Open Plan Compliance
RT60 calculation for a US government agency open plan office meeting IBC 2021 requirements. Standard acoustic ceiling and carpet specification demonstrates that compliant offices need not be expensive when treated from the design stage.
A 259.2 m³ open plan office designed to IBC requires RT60 ≤ 0.6s. With Armstrong Ultima+ on the ceiling and Fabric-wrapped panel 50mm on walls, the calculated RT60 is 0.28s — PASS.
Room Setup
Total surface area: 319.2 m². Calculation method: Sabine equation (ISO 3382-2:2008 Annex A).
Surface Materials
| Surface | Material | Area (m²) | NRC |
|---|---|---|---|
| ceiling | Armstrong Ultima+ | 96.0 | 0.80 |
| walls-main | Plasterboard on studs | 75.6 | 0.07 |
| walls-treatment | Fabric-wrapped panel 50mm | 32.0 | 0.80 |
| floor | Carpet (heavy) | 96.0 | 0.30 |
| windows | Double glazing 6mm | 16.0 | 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 = 12 × 8 × 2.7 = 259.2 m³
- 2
Total Surface Area
Stotal = 96.0 + 75.6 + 32.0 + 96.0 + 16.0 + 3.6 = 319.2 m²
- 3
Absorption per Surface at 500 Hz
ceiling: 96.0 m² × 0.85 = 81.60 Sabins
walls-main: 75.6 m² × 0.05 = 3.78 Sabins
walls-treatment: 32.0 m² × 0.78 = 24.96 Sabins
floor: 96.0 m² × 0.14 = 13.44 Sabins
windows: 16.0 m² × 0.04 = 0.64 Sabins
door: 3.6 m² × 0.08 = 0.29 Sabins
- 4
Total Absorption at 500 Hz
Atotal = 81.60 + 3.78 + 24.96 + 13.44 + 0.64 + 0.29 = 124.71 Sabins
- 5
Sabine RT60 at 500 Hz
RT60 = 0.161 × V / A = 0.161 × 259.2 / 124.71 = 0.33s
- 6
Compare to Target
Mid-frequency RT60 (avg of 500, 1k, 2k Hz) = 0.28s. Target: ≤ 0.6s per IBC. Verdict: PASS
Octave Band Results
| Frequency | 125Hz | 250Hz | 500Hz | 1kHz | 2kHz | 4kHz |
|---|---|---|---|---|---|---|
| Total Absorption (Sabins) | 55.5 | 91.3 | 124.7 | 152.9 | 173.9 | 173.8 |
| RT60 (s) | 0.75 | 0.46 | 0.33 | 0.27 | 0.24 | 0.24 |
| Target (s) | — | — | 0.60 | 0.60 | 0.60 | — |
| Verdict | — | — | PASS | PASS | PASS | — |
Compliance Verdict
Reference: IBC 2021 §1207; GSA P100 §5.8
IBC 2021 §1207 focuses primarily on sound isolation (STC ratings) rather than RT60, but GSA P100 federal standards require acoustic treatment for government workspaces. This design meets both requirements.
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 (12m × 8m × 2.7m) and RT60 target (0.6s).
Open CalculatorField Story
A federal agency is fitting out leased commercial office space in Washington DC. The General Services Administration (GSA) requires compliance with P100 facilities standards, which mandate acoustic treatment for all occupied spaces. The base building provides a concrete slab ceiling and concrete floors. The tenant improvement budget must cover suspended acoustic ceiling, carpet, and wall treatment. By specifying acoustic materials from the start rather than retrofitting, the project achieves compliance at 30% lower cost than a neighbouring agency that attempted to add treatment after occupancy.
Frequently Asked Questions
What RT60 does a Government Office — IBC Open Plan Compliance achieve?
With the specified materials and dimensions (12m x 8m x 2.7m, volume 259.2m3), the calculated mid-frequency RT60 is 0.28s using the Sabine equation. The target under IBC is 0.6s or less. The result is a PASS.
What materials are used in this office acoustic example?
This example uses Armstrong Ultima+ on the ceiling (NRC 0.8), 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 124.7 Sabins.
How much does acoustic treatment cost for this room?
The estimated treatment cost is $10,080 for 224 m2 of absorptive material at approximately $45/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.