Worked Example: Apartment Bathroom — NBR 15575 Acoustic Reality
12 m³ bathroom with tiled walls and floor — the worst-case residential scenario
A 12 m³ residential living designed to NBR-15575 requires RT60 ≤ 0.6s. With Painted plaster on the ceiling, the calculated RT60 is 1.14s — FAIL.
Room Setup
Total surface area: 32.6 m². Calculation method: Sabine equation (ISO 3382-2:2008 Annex A).
Surface Materials
| Surface | Material | Area (m²) | NRC |
|---|---|---|---|
| Ceiling | Painted plaster | 6.0 | 0.04 |
| Floor — tile | Terrazzo/marble floor | 6.0 | 0.01 |
| Walls — tile | Exposed concrete | 16.0 | 0.02 |
| Shower screen | Single glazing | 2.0 | 0.16 |
| Door | Solid timber door | 1.6 | 0.09 |
| Towels + bath mat | Curtains (medium weight) | 1.0 | 0.56 |
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 = 3 × 2 × 2 = 12 m³
- 2
Total Surface Area
Stotal = 6.0 + 6.0 + 16.0 + 2.0 + 1.6 + 1.0 = 32.6 m²
- 3
Absorption per Surface at 500 Hz
Ceiling: 6.0 m² × 0.04 = 0.24 Sabins
Floor — tile: 6.0 m² × 0.01 = 0.06 Sabins
Walls — tile: 16.0 m² × 0.02 = 0.32 Sabins
Shower screen: 2.0 m² × 0.18 = 0.36 Sabins
Door: 1.6 m² × 0.08 = 0.13 Sabins
Towels + bath mat: 1.0 m² × 0.49 = 0.49 Sabins
- 4
Total Absorption at 500 Hz
Atotal = 0.24 + 0.06 + 0.32 + 0.36 + 0.13 + 0.49 = 1.60 Sabins
- 5
Sabine RT60 at 500 Hz
RT60 = 0.161 × V / A = 0.161 × 12 / 1.60 = 1.21s
- 6
Compare to Target
Mid-frequency RT60 (avg of 500, 1k, 2k Hz) = 1.14s. Target: 0.3--0.6s per NBR-15575. Verdict: FAIL
Octave Band Results
| Frequency | 125Hz | 250Hz | 500Hz | 1kHz | 2kHz | 4kHz |
|---|---|---|---|---|---|---|
| Total Absorption (Sabins) | 1.3 | 1.3 | 1.6 | 1.8 | 1.7 | 2.0 |
| RT60 (s) | 1.52 | 1.47 | 1.21 | 1.07 | 1.13 | 0.95 |
| Target (s) | — | — | 0.60 | 0.60 | 0.60 | — |
| Verdict | — | — | FAIL | FAIL | FAIL | — |
Compliance Verdict
Reference:
Open the AcousPlan calculator pre-loaded with the exact room dimensions (3m × 2m × 2m) and RT60 target (0.6s).
Open CalculatorField Story
Every acoustic consultant knows bathrooms are the most reverberant rooms in any dwelling — this 3 m by 2 m bathroom in a Sao Paulo apartment is a textbook example. Floor-to-ceiling ceramic tiles on all walls, porcelain floor tiles, and a painted plaster ceiling create near-total absence of absorption. The glass shower screen adds another reflective surface. The only absorbers are towels on rails and a bath mat — providing negligible absorption against 32 m² of hard surfaces. This Sabine calculation reveals the true condition: a highly reverberant environment amplifying every water splash, toilet flush, and conversation to levels clearly audible in adjacent bedrooms. NBR 15575 does not set RT60 targets for bathrooms, but the result demonstrates why partition STC ratings between bathrooms and bedrooms must be exceptionally high.
Frequently Asked Questions
What RT60 does a Apartment Bathroom — NBR 15575 Acoustic Reality achieve?
With the specified materials and dimensions (3m x 2m x 2m, volume 12m3), the calculated mid-frequency RT60 is 1.14s using the Sabine equation. The target under NBR-15575 is 0.3--0.6s. The result is a FAIL.
What materials are used in this residential acoustic example?
This example uses Painted plaster on the Ceiling (NRC 0.04), Terrazzo/marble floor on the Floor — tile (NRC 0.01), Exposed concrete on the Walls — tile (NRC 0.02), Single glazing on the Shower screen (NRC 0.16), Solid timber door on the Door (NRC 0.09), Curtains (medium weight) on the Towels + bath mat (NRC 0.56). The total absorption at 500 Hz is 1.6 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.