🏢ASHRAE 189.1-2020 · United States

Open Plan Office Acoustic Design to ASHRAE 189.1-2020

Open plan offices present a unique acoustic paradox: speech must be intelligible within conversation groups but unintelligible beyond the distraction distance to preserve privacy and concentration. ISO 3382-3:2012 defines the key metrics — spatial decay rate D2,S, distraction distance rD, and A-weighted SPL of speech at 4 m (Lp,A,S,4m).

TL;DR

Under ASHRAE 189.1-2020, a open plan office of 400-600 m³ (typical dimensions 20m × 10m × 2.8m) requires an RT60 of ≤ 0.8s at broadband. Background noise must not exceed 40 NC. ASHRAE Handbook Chapter 49 recommends NC 35-40 for open-plan offices.

RT60 Target

≤ 0.8s

Noise Limit

40 NC

STI Minimum

N/A

Frequency Range

broadband

Specific Requirements

Parameter	Target	Clause Reference	Notes
Background Noise Limit	≤ 40 NC	§8.3.4	HVAC + building services, unoccupied
Frequency Range	broadband	—	Octave bands for compliance assessment

Step-by-Step Compliance Calculation

1
Set NC target
Open-plan offices: NC 35-40 per ASHRAE Chapter 49. Lower targets for executive areas or studios.
2
Model mechanical noise
Calculate noise at each octave band from fan, ductwork, terminal units, and diffusers at design airflow.
3
Specify attenuation
Size silencers, lined plenums, and flexible connections to bring each octave band below NC curve.
4
Commission and verify
Measure octave-band noise levels at representative positions with full HVAC operation.

Recommended Materials

Surface	Material Category	Min NRC	Coverage %
Ceiling	Mineral wool ceiling tile	0.85	85%
Duct attenuation	Lined duct and silencers	0.70	100%

Browse the full acoustic materials database for absorption coefficients and product specifications.

Common Failure Modes

⚠️Underfloor air distribution noise

Underfloor air supply plenums with floor diffusers can produce broadband noise exceeding NC 40 at nearby workstations.

⚠️Chilled beam noise

Active chilled beams with high primary air velocities generate turbulent noise at the nozzles, exceeding NC criteria.

Frequently Asked Questions

What RT60 does ASHRAE 189.1-2020 require for a open plan office?

ASHRAE 189.1-2020 requires a reverberation time of ≤0.8s at broadband for open plan office spaces. ASHRAE Handbook Chapter 49 recommends NC 35-40 for open-plan offices. The focus is on HVAC noise control through proper duct sizing, terminal unit selection, and diffuser specification. ASHRAE complements ISO 3382-3 speech privacy design by ensuring mechanical noise does not mask or interfere with communication.

What is the maximum background noise level for a open plan office under ASHRAE 189.1-2020?

ASHRAE 189.1-2020 sets a maximum background noise level of 40 NC for open plan office spaces. This includes noise from HVAC systems, building services, and external intrusion, measured with the room unoccupied. Exceeding this limit degrades speech intelligibility and occupant comfort.

How much acoustic treatment does a open plan office need to comply with ASHRAE 189.1-2020?

A typical open plan office (400-600 m³) requires Mineral wool ceiling tile (NRC ≥0.85) covering 85% of the ceiling as the primary treatment. Additional wall absorption on 1 surface(s) is typically needed. Use the AcousPlan calculator with the pre-loaded dimensions (20m × 15m × 2.8m) to calculate the exact absorption deficit for your room.

Calculate ASHRAE 189.1-2020 Compliance for Your Open Plan Office

Pre-loaded with typical open plan office dimensions (20m × 15m × 2.8m) and an RT60 target of 0.8s per ASHRAE 189.1-2020. Enter your actual dimensions, select materials, and verify compliance instantly.

Open Calculator with Preset