Noise Rating (NR) Criteria by Room Type
Ctrl+D to bookmark this toolRecommended maximum background noise levels from building services for UK building types. Data from CIBSE Guide A and BS 8233.
What Is an NR Rating?
NR (Noise Rating) curves are used to assess the acceptability of steady background noise from building services — fans, ductwork, pipework, diffusers. An NR value represents the maximum acceptable sound pressure level across octave bands from 31.5 Hz to 8 kHz. Lower NR = quieter. NR25 is very quiet (suitable for concert halls), NR40 is typical for a busy office.
NR is NOT the same as dB(A), though they are related. As a rough guide, NR ≈ dB(A) - 6 for broadband noise, but this varies with the noise spectrum. Always assess against the octave band NR curve, not just a single number.
Recommended NR Criteria by Room Type
CIBSE Guide A, Table 1.5; BS 8233:2014| Space Type | NR Rating | dB(A) Equivalent (approx) | Category | Source |
|---|---|---|---|---|
| Concert hall | NR 15–20 | 20–25 | Entertainment | CIBSE Guide A |
| Recording studio | NR 15–20 | 20–25 | Specialist | — |
| Theatre (auditorium) | NR 20–25 | 25–30 | Entertainment | CIBSE Guide A |
| Cinema | NR 25–30 | 30–35 | Entertainment | CIBSE Guide A |
| Hospital ward | NR 25–30 | 30–35 | Healthcare | HTM 08-01 / CIBSE |
| Hospital operating theatre | NR 35–40 | 40–45 | Healthcare | HTM 08-01 |
| Consulting room | NR 30–35 | 35–40 | Healthcare | CIBSE Guide A |
| Hotel bedroom | NR 25–30 | 30–35 | Hospitality | CIBSE Guide A |
| Hotel lobby / reception | NR 35–40 | 40–45 | Hospitality | CIBSE Guide A |
| Classroom | NR 25–30 | 30–35 | Education | BB93 |
| Lecture theatre | NR 25–30 | 30–35 | Education | BB93 |
| Library / study room | NR 25–30 | 30–35 | Education | CIBSE Guide A |
| Office (private / executive) | NR 30–35 | 35–40 | Office | CIBSE Guide A |
| Office (open plan) | NR 35–40 | 40–45 | Office | CIBSE Guide A |
| Meeting room / boardroom | NR 25–35 | 30–40 | Office | CIBSE Guide A |
| Retail (general) | NR 35–45 | 40–50 | Retail | CIBSE Guide A |
| Restaurant | NR 35–40 | 40–45 | Hospitality | CIBSE Guide A |
| Kitchen (commercial) | NR 45–55 | 50–60 | Back of house | — |
| Gymnasium / sports hall | NR 40–50 | 45–55 | Sport | CIBSE Guide A |
| Plant room (occupied) | NR 50–60 | 55–65 | Back of house | — |
| Corridor / circulation | NR 40–45 | 45–50 | — | CIBSE Guide A |
| Toilet / WC | NR 40–45 | 45–50 | — | — |
| Car park | NR 50–60 | 55–65 | — | — |
NR criteria apply to the total building services noise contribution, not to background noise from external sources. The specified NR is a MAXIMUM — designing below it is always better. Where a range is shown, use the lower value for higher quality environments.
What These Values Mean in Practice
NR 25 is very quiet — you can hear a clock ticking. This is the standard for hospital wards and bedrooms. Achieving this requires careful duct sizing (low velocities), acoustic attenuation, and vibration isolation of all rotating equipment.
NR 35 is typical for a well-designed office. Normal conversation is comfortable and telephone calls are clear. Most fan coil units and VAV terminals can achieve this without additional attenuation, provided duct velocities are kept within recommended limits.
NR 45+ is only acceptable for noisy spaces like retail, kitchens, and plant rooms. Background services noise is masked by the activity noise in these spaces, so tighter criteria would not improve the acoustic environment.
Common Sources of Building Services Noise
The main noise sources in a building services system are fans (both supply and extract), air terminal devices (diffusers and grilles), ductwork breakout and regenerated noise at fittings, pumps, chillers, and vibration transmitted through the structure. Controlling noise starts at the duct sizing stage — lower duct velocities mean less regenerated noise and lower fan pressures.
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