Worked Example: Townhouse Stairwell — BS 8233 Flutter Echo Control
30 m³ stairwell with painted plaster walls, timber treads, and carpet runner
A 30 m³ residential living designed to BS-8233 requires RT60 ≤ 0.8s. With Single glazing on the ceiling, the calculated RT60 is 0.82s — MARGINAL.
Room Setup
Total surface area: 64.2 m². Calculation method: Sabine equation (ISO 3382-2:2008 Annex A).
Surface Materials
| Surface | Material | Area (m²) | NRC |
|---|---|---|---|
| Ceiling — skylight | Single glazing | 2.0 | 0.16 |
| Ceiling — plaster | Painted plaster | 3.0 | 0.04 |
| Floor — landing | Timber floor (sealed) | 5.0 | 0.09 |
| Walls — plaster | Painted plaster | 26.0 | 0.04 |
| Walls — plasterboard | Plasterboard on studs | 12.0 | 0.07 |
| Carpet runner on stairs | Heavy carpet | 8.0 | 0.29 |
| Doors (ground + landing) | Solid timber door | 3.2 | 0.09 |
| Stair treads — timber | Timber floor (sealed) | 5.0 | 0.09 |
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 = 2 × 2.5 × 6 = 30 m³
- 2
Total Surface Area
Stotal = 2.0 + 3.0 + 5.0 + 26.0 + 12.0 + 8.0 + 3.2 + 5.0 = 64.2 m²
- 3
Absorption per Surface at 500 Hz
Ceiling — skylight: 2.0 m² × 0.18 = 0.36 Sabins
Ceiling — plaster: 3.0 m² × 0.04 = 0.12 Sabins
Floor — landing: 5.0 m² × 0.10 = 0.50 Sabins
Walls — plaster: 26.0 m² × 0.04 = 1.04 Sabins
Walls — plasterboard: 12.0 m² × 0.05 = 0.60 Sabins
Carpet runner on stairs: 8.0 m² × 0.14 = 1.12 Sabins
Doors (ground + landing): 3.2 m² × 0.08 = 0.26 Sabins
Stair treads — timber: 5.0 m² × 0.10 = 0.50 Sabins
- 4
Total Absorption at 500 Hz
Atotal = 0.36 + 0.12 + 0.50 + 1.04 + 0.60 + 1.12 + 0.26 + 0.50 = 4.50 Sabins
- 5
Sabine RT60 at 500 Hz
RT60 = 0.161 × V / A = 0.161 × 30 / 4.50 = 1.07s
- 6
Compare to Target
Mid-frequency RT60 (avg of 500, 1k, 2k Hz) = 0.82s. Target: 0.4--0.8s per BS-8233. Verdict: MARGINAL
Octave Band Results
| Frequency | 125Hz | 250Hz | 500Hz | 1kHz | 2kHz | 4kHz |
|---|---|---|---|---|---|---|
| Total Absorption (Sabins) | 6.6 | 4.2 | 4.5 | 6.1 | 8.1 | 8.8 |
| RT60 (s) | 0.73 | 1.16 | 1.07 | 0.79 | 0.60 | 0.55 |
| Target (s) | — | — | 0.80 | 0.80 | 0.80 | — |
| Verdict | — | — | FAIL | PASS | PASS | — |
Compliance Verdict
Reference:
Open the AcousPlan calculator pre-loaded with the exact room dimensions (2m × 2.5m × 6m) and RT60 target (0.8s).
Open CalculatorField Story
A Georgian townhouse in Edinburgh has a central stairwell connecting four floors — a 2 m by 2.5 m shaft rising 6 m. The parallel painted plaster walls create textbook flutter echo: a handclap produces metallic ringing that persists for seconds, and every footstep echoes throughout the house. The tall narrow proportions make this acoustically similar to a reverberant corridor stood on end. A fitted stair carpet runner provides absorption on horizontal surfaces at each tread. A section of plasterboard on the party wall provides low-frequency panel absorption. The skylight acts as a panel absorber. BS 8233 does not set specific stairwell targets, but controlling flutter echo is essential to prevent sound transmission between floors via the open stairwell — a flanking path undermining floor sound insulation.
Frequently Asked Questions
What RT60 does a Townhouse Stairwell — BS 8233 Flutter Echo Control achieve?
With the specified materials and dimensions (2m x 2.5m x 6m, volume 30m3), the calculated mid-frequency RT60 is 0.82s using the Sabine equation. The target under BS-8233 is 0.4--0.8s. The result is a MARGINAL.
What materials are used in this residential acoustic example?
This example uses Single glazing on the Ceiling — skylight (NRC 0.16), Painted plaster on the Ceiling — plaster (NRC 0.04), Timber floor (sealed) on the Floor — landing (NRC 0.09), Painted plaster on the Walls — plaster (NRC 0.04), Plasterboard on studs on the Walls — plasterboard (NRC 0.07), Heavy carpet on the Carpet runner on stairs (NRC 0.29), Solid timber door on the Doors (ground + landing) (NRC 0.09), Timber floor (sealed) on the Stair treads — timber (NRC 0.09). The total absorption at 500 Hz is 4.5 Sabins.
How much does acoustic treatment cost for this room?
Cost data is not available for this example. Use the AcousPlan calculator to estimate treatment costs for your specific room configuration.
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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.