TLDR: What WELL v2 Sound Requires
WELL v2 Feature S01 (Sound) is the acoustic component of the WELL Building Standard, administered by the International WELL Building Institute (IWBI). It has seven parts covering sound mapping, maximum noise levels, sound barriers (STC/OITC), sound absorption (RT60), sound masking, impact noise, and enhanced audio devices. To earn points toward WELL certification, a project must demonstrate compliance with one or more parts through either prescriptive documentation (manufacturer data, design calculations) or performance verification (field measurement).
The critical calculation requirements are: background noise levels meeting ASHRAE Handbook criteria by room type (typically NC 30–40 for offices), RT60 meeting ANSI/ASA S12.60 or project-specific targets (typically 0.6–0.8 s for open offices), STC ratings meeting minimum thresholds for enclosure walls (typically STC 45–50 for private offices), and sound masking providing 40–48 dB(A) of broadband masking in open-plan areas.
For project teams pursuing WELL certification, S01 is one of the most technically demanding features because it requires acoustic expertise, quantitative evidence, and often post-construction verification. This guide walks through each part's calculation method, identifies the documentation IWBI requires, and uses a London office tower case study to illustrate what happens when the calculation is done wrong.
The Problem: A WELL Re-Certification Failure
A 45,000 m² office tower in the City of London achieved WELL Gold certification in 2022. During the 2025 re-certification audit, the project failed Feature S01.2 (Maximum Noise Levels) when performance verification measurements revealed background noise levels 8–12 dB above the ASHRAE criteria in 14 of 22 measured locations.
The root cause was an HVAC system modification made in 2024. The building management team had increased supply air fan speeds by 15% to address tenant complaints about summer overheating after a refurbishment that increased occupancy density. The higher fan speeds increased duct-borne noise by 6–8 dB(A) in terminal units, pushing background noise from NC 35 (compliant) to NC 43–47 (non-compliant) in affected zones.
The original WELL submission had used HVAC design documentation showing calculated NC values at design fan speeds. Nobody re-measured after the operational change. The re-certification failure triggered a 6-month remediation programme costing £185,000: duct-mounted attenuators at 28 terminal units (£3,200 each), two air handling unit speed controllers (£12,000 each), and acoustic consultancy fees for redesign and verification testing (£25,000).
The lesson: WELL certification is not a one-time achievement. Operational changes to building systems can invalidate the acoustic basis of certification, and re-certification requires current performance data, not historical design values.
S01.1: Sound Mapping
Sound mapping requires documenting the acoustic zones within the project boundary and identifying noise sources, transmission paths, and receiver locations. This is a design documentation requirement, not a measurement requirement.
What IWBI Requires
Per the WELL v2 Standard §S01.1:
- A floor plan annotated with acoustic zones classified by noise sensitivity (quiet zones, collaborative zones, high-noise zones)
- Identification of all significant noise sources (HVAC terminals, lifts, kitchens, print rooms, reception areas)
- Sound transmission paths between zones (walls, floors, ceilings, ductwork cross-talk)
- Design noise criteria for each zone per ASHRAE Handbook — Fundamentals, Chapter 48
Acoustic Zone Classification
| Zone Type | Example Spaces | Target NC | Target dB(A) |
|---|---|---|---|
| Quiet | Private offices, conference rooms, libraries | NC 25–30 | 30–35 |
| Standard | Open-plan offices, break rooms | NC 35–40 | 40–45 |
| Active | Lobbies, cafeterias, collaboration areas | NC 40–45 | 45–50 |
| Noisy | Kitchens, mechanical rooms, print rooms | NC 45–55 | 50–60 |
The sound map must show that noisy zones are not adjacent to quiet zones without adequate sound barriers, and that HVAC zones are designed to deliver the target NC in each space.
S01.2: Maximum Noise Levels
This is the most frequently failed part of S01 because it requires quantitative compliance with specific background noise criteria.
Prescriptive Path
Per WELL v2 §S01.2 Prescriptive:
- HVAC system designed to meet noise criteria per ASHRAE Handbook — HVAC Applications, Chapter 48
- Documentation from MEP engineer confirming calculated NC/RC values at each terminal unit
- Manufacturer sound power data for all air handling units, fan coil units, and terminal devices
Performance Verification Path
Per WELL v2 §S01.2 Performance:
- Background noise measurements per ANSI/ASA S12.2 in representative spaces
- Measurements taken with HVAC operating at normal conditions, space unoccupied
- Results must meet the criteria in the following table:
| Space Type | Maximum NC | Maximum dB(A) |
|---|---|---|
| Private office | NC 30 | 35 |
| Teleconference room | NC 25 | 30 |
| Open-plan office | NC 40 | 45 |
| Conference room | NC 30 | 35 |
| Reception/lobby | NC 40 | 45 |
| Corridor | NC 45 | 50 |
Model your HVAC noise levels. Use the AcousPlan noise criteria calculator to check NC, NR, and RC values against WELL v2 S01.2 thresholds. Input your octave-band sound pressure levels and get instant compliance verdicts.
The Calculation Method
Background noise level in NC is determined by plotting octave-band sound pressure levels (63 Hz to 8 kHz) against the NC curves per ANSI/ASA S12.2. The NC rating equals the lowest NC curve that is not exceeded by any octave band. This means a single octave band exceeding the curve sets the rating — you cannot "average" across frequencies.
For the London office tower, the 500 Hz band was the controlling frequency. The terminal units had sound power levels of 42 dB re 10⁻¹² W at 500 Hz, and the room correction (10 log Q/4πr² + 4/R) added approximately 5 dB, giving an in-room SPL of 47 dB at 500 Hz — which crosses the NC 45 curve. The design had predicted 41 dB at the original fan speed, crossing NC 35.
S01.3: Sound Barriers
S01.3 specifies minimum Sound Transmission Class (STC) or Outdoor-Indoor Transmission Class (OITC) ratings for walls, floors, and ceilings separating acoustic zones.
STC Requirements by Adjacency
| Adjacency | Minimum STC |
|---|---|
| Private office to private office | STC 45 |
| Private office to open-plan | STC 45 |
| Private office to corridor | STC 40 |
| Conference room to open-plan | STC 50 |
| Conference room to conference room | STC 50 |
| Teleconference room to any space | STC 50 |
| Mechanical room to occupied space | STC 55 |
Common STC Pitfalls
The STC rating of a partition wall is only valid if the wall extends from slab to slab (or equivalent structural barrier). A common failure mode in commercial fitouts is walls that terminate at the suspended ceiling — the ceiling void provides a flanking path with an effective STC of 10–15 dB, regardless of the wall's laboratory STC rating.
For the WELL performance path, field-measured Sound Transmission Class (FSTC or ASTC per ISO 16283-1) will typically be 3–7 points lower than the laboratory STC rating due to flanking, penetrations, and junction details. Design to an STC value 5 points above the WELL minimum to provide margin.
S01.4: Sound Absorption
S01.4 requires adequate sound absorption to control reverberation and improve speech intelligibility.
RT60 Targets
| Space Type | Maximum RT60 (s) at 500–1000 Hz |
|---|---|
| Private office (< 50 m³) | 0.6 |
| Open-plan office | 0.8 |
| Conference room (< 100 m³) | 0.6 |
| Conference room (100–500 m³) | 0.8 |
| Lecture hall | 0.8 |
| Cafeteria | 1.0 |
NRC Requirements
Per S01.4 Prescriptive, at least 50% of the ceiling area must have a Noise Reduction Coefficient (NRC) ≥ 0.80, and at least 25% of the combined wall area must have NRC ≥ 0.60 in open-plan offices. These percentages can be adjusted if a Sabine/Eyring calculation demonstrates that the alternative material configuration achieves the target RT60.
Calculation Method
Use the Sabine equation (per ISO 3382-2:2008 §A.1):
RT60 = 0.161 × V / Σ(αᵢ × Sᵢ)
For an open-plan office zone of 20 m × 15 m × 2.7 m = 810 m³:
| Surface | Area (m²) | NRC | Absorption (m²) |
|---|---|---|---|
| Ceiling (acoustic tile) | 300 | 0.85 | 255 |
| Floor (carpet) | 300 | 0.30 | 90 |
| Perimeter walls | 189 | 0.05 | 9.5 |
| Furniture (30 workstations) | — | — | 25 (estimated) |
| Total | 379.5 |
RT60 = 0.161 × 810 / 379.5 = 0.34 seconds — well within the 0.8 s limit.
This illustrates why open-plan offices rarely fail S01.4 if they have acoustic ceiling tiles and carpet. The challenge is in conference rooms and private offices with hard floors and minimal wall absorption.
S01.5: Sound Masking
Sound masking is the controlled introduction of background sound to reduce the intelligibility of unwanted speech. WELL v2 S01.5 requires masking systems to produce:
- 40–48 dB(A) of broadband noise in open-plan areas
- Spectrum matching the ASTM E1573 or equivalent masking contour
- Spatial uniformity within ±2 dB(A) across the masked zone
- No perceptible tonal or temporal variation
S01.6 and S01.7: Impact Noise and Audio Devices
S01.6 requires impact noise management for floors above occupied spaces. The minimum requirement is IIC (Impact Insulation Class) ≥ 50 for floor-ceiling assemblies, with IIC ≥ 55 recommended for spaces above quiet zones. Compliance is demonstrated through manufacturer test data per ASTM E492 or field measurement per ASTM E1007.
S01.7 (Enhanced Audio Devices) requires conference rooms and presentation spaces to have audio systems that maintain speech intelligibility with STI ≥ 0.60 at all listener positions, per IEC 60268-16. This applies to rooms with amplified speech systems and is verified through system commissioning measurements.
Documentation Checklist for WELL S01 Submission
| Part | Document | Source |
|---|---|---|
| S01.1 | Annotated acoustic zone plan | Architect/acoustic consultant |
| S01.2 | NC calculation or measurement report | MEP engineer or acoustician |
| S01.3 | STC test reports for all separating elements | Manufacturer / lab test |
| S01.4 | RT60 calculation (Sabine/Eyring) or measurement | Acoustic consultant |
| S01.4 | NRC certificates for acoustic products | Manufacturer |
| S01.5 | Masking system specification + commissioning report | Masking contractor |
| S01.6 | IIC test reports for floor assemblies | Manufacturer / lab test |
| S01.7 | AV system STI commissioning data | AV contractor |
Common Mistakes in WELL Sound Compliance
1. Using Design NC Values Without Field Verification
HVAC noise predictions based on manufacturer data and duct calculations are typically optimistic by 3–8 dB compared to field measurements due to installation quality, duct breakout, and fan operating points deviating from design. For performance verification projects, always budget for field measurement and potential remediation.
2. Specifying STC Without Addressing Flanking
A wall tested at STC 50 in a laboratory will perform at FSTC 43–47 in the field. Common flanking paths include: ceiling plenum above the wall, raised floor beneath the wall, shared ductwork with inadequate cross-talk attenuators, electrical back-boxes located back-to-back, and penetration seals with gaps.
3. Ignoring Operational Changes Post-Certification
WELL certification is recertified every 3 years. Changes to HVAC operating points, space layouts, or occupancy density between certifications can invalidate acoustic compliance. Maintain an acoustic operations manual documenting the conditions under which certification was achieved.
4. Over-Reliance on Sound Masking
Sound masking addresses speech privacy in open plan but does not reduce actual noise levels. If background noise from HVAC already exceeds NC 40, adding masking pushes the ambient level to NC 45+, creating a noisy environment that masks speech at the cost of comfort and concentration. Masking works best when HVAC noise is NC 30 or lower.
Summary
WELL v2 Feature S01 is a comprehensive acoustic quality standard covering seven aspects of the indoor sound environment. The most technically demanding parts are S01.2 (background noise, requiring NC compliance with ASHRAE criteria), S01.3 (sound barriers, requiring STC-rated construction), and S01.4 (sound absorption, requiring RT60 compliance via Sabine/Eyring calculation). The prescriptive path relies on design documentation and manufacturer data. The performance verification path requires field measurement per ISO 3382-2 and ANSI/ASA S12.2.
The London office tower case demonstrates that WELL certification is a living commitment. Operational changes to HVAC systems invalidated the noise level compliance, costing £185,000 in remediation. The calculation methods are straightforward — Sabine for RT60, octave-band analysis for NC — but the evidence package must be rigorous and must reflect actual operational conditions, not design-stage assumptions.
Verify your WELL S01 compliance. Use the AcousPlan calculator to compute RT60, NC values, and STI for your project — and generate documentation-ready results for your IWBI submission.