WELL v2 Feature 74 (Sound) Complete Guide: Every Requirement, Threshold, and Compliance Path

Why Feature 74 Matters More Than Any Other WELL Feature for Acoustics

WELL Building Standard v2, administered by the International WELL Building Institute (IWBI), is the dominant wellness certification framework for commercial buildings worldwide. Among its ten concepts — Air, Water, Nourishment, Light, Movement, Thermal Comfort, Sound, Materials, Mind, and Community — the Sound concept is the one that directly governs acoustic design. Feature 74 (Sound) is the original and most widely referenced feature number within this concept, and its three-part structure remains the framework that architects, acoustic consultants, and WELL assessors use to evaluate acoustic performance in offices, educational facilities, healthcare buildings, and multi-tenant commercial spaces.

Feature 74 is not optional background reading. Part 1 (Sound Mapping) is a Precondition — it must be satisfied for any level of WELL certification. Parts 2 and 3 are Optimizations that earn points toward Silver, Gold, or Platinum certification levels. In practice, most projects pursuing WELL certification must address all three parts because acoustic performance is audited holistically during performance verification.

This guide presents every requirement, every threshold value, every applicable space type, and every compliance pathway for all three parts of Feature 74 — structured as a reference that an acoustic consultant can hand to a design team and say: "This is what we need to achieve."

Feature 74 Structure: Three Parts, Two Compliance Tiers

Feature 74 organizes acoustic requirements into three distinct parts. Each part addresses a different acoustic phenomenon, uses different metrics, and applies to different space types.

Preconditions must be met for any WELL certification level. A project cannot achieve WELL Silver, Gold, or Platinum without passing every applicable Precondition. Optimizations earn points that contribute to the certification level. Each Optimization has a defined point value, and projects accumulate points across all WELL concepts to reach certification thresholds.

The distinction matters for project planning. Part 1 is non-negotiable. If the design cannot achieve the RT60 limits in Part 1, the project cannot be WELL certified at any level. Parts 2 and 3 are strategic — a project team can choose to pursue acoustic Optimizations or earn equivalent points through other WELL features. However, in practice, acoustic Optimizations are among the most cost-effective points available, and most serious WELL projects pursue all three parts.

Part 1 — Sound Mapping (L07.1): Reverberation Time Limits

Part 1 is the foundation of WELL acoustic compliance. It requires that enclosed spaces used for communication, concentration, or confidential work achieve reverberation times below specified thresholds. The logic is straightforward: excessive reverberation degrades speech clarity, increases vocal effort, causes listener fatigue, and reduces productivity.

RT60 Thresholds by Space Type

The following table presents the maximum permissible RT60 for each space type covered by Part 1. These values apply across the frequency range 125 Hz to 4000 Hz — all six standard octave bands must comply individually, not just the mid-frequency average.

Critical Detail: "Furnished, Unoccupied" Condition

The measurement condition is frequently misunderstood. Furnished, unoccupied means the room must contain all its intended furniture, finishes, and fixtures — desks, chairs, carpet, curtains, acoustic panels — but no occupants should be present during measurement. This condition is specified because:

• Furniture absorbs sound. A conference table, twelve upholstered chairs, and a carpet contribute 15-25 m squared Sabine of absorption to a meeting room. An empty shell room with bare floors and no furniture will measure 0.2-0.4 seconds higher RT60 than the same room furnished. Measuring an unfurnished room is not valid evidence for WELL compliance.

• Occupants are variable. People absorb sound — a seated adult contributes approximately 0.4-0.5 m squared Sabine of absorption. A 12-person meeting room gains roughly 5-6 m squared Sabine from full occupancy. But occupancy varies from meeting to meeting. The "furnished, unoccupied" condition removes this variable and provides a repeatable, conservative measurement.

• HVAC must be operating. During measurement, all mechanical systems should run at normal operating conditions. This ensures the measurement captures the acoustic environment as occupants actually experience it.

Frequency Range: Every Octave Band Must Pass

WELL Part 1 requires compliance across 125 Hz, 250 Hz, 500 Hz, 1000 Hz, 2000 Hz, and 4000 Hz. A room that achieves RT60 of 0.55 seconds averaged across 500-2000 Hz but measures 0.75 seconds at 125 Hz does not comply. Low-frequency reverberation control is the most common challenge because:

• Bass frequencies require thicker, heavier absorbers. A standard 15 mm mineral fiber ceiling tile provides excellent absorption above 500 Hz (alpha 0.70-0.90) but minimal absorption at 125 Hz (alpha 0.10-0.25).
• Room modes at low frequencies create spatial variation in RT60. A measurement at one position may yield 0.5 seconds at 125 Hz while a position 2 meters away yields 0.9 seconds.
• Effective low-frequency absorption strategies include: suspended acoustic baffles with 200 mm+ air gap, membrane absorbers tuned to 125-250 Hz, thick fabric-wrapped panels (50 mm minimum) mounted with a 50-100 mm air gap behind.

Verification Methods

WELL accepts two verification approaches for Part 1:

1. Design-stage acoustic modeling: Submit Sabine or Eyring RT60 calculations with material absorption coefficients for all surfaces. The calculation methodology must follow ISO 3382-2:2008 Annex A. Sabine's formula (Section A.1) is acceptable for rooms with average absorption coefficient below 0.3. Eyring's formula (Section A.2) should be used for rooms with higher average absorption, particularly large conference rooms with extensive acoustic treatment.

1. Post-construction measurement: On-site RT60 measurement per ISO 3382-2:2008 using the interrupted noise method or the integrated impulse response method. Minimum three source-receiver combinations per room, with receivers at 1.2 m height and at least 1.5 m from any room surface.

Part 2 — Sound Barriers (L07.2): Background Noise and Sound Insulation

Part 2 addresses two related but distinct requirements: controlling the level of background noise within spaces, and ensuring adequate sound insulation between adjacent spaces. Both requirements target the same goal — preventing noise intrusion from degrading the acoustic quality of workspaces.

Background Noise Limits by Space Type

Background noise is measured as L_Aeq (the A-weighted equivalent continuous sound pressure level) over a representative measurement period, typically one hour during normal building operation. All mechanical systems — HVAC, lighting, electrical — must be running at their standard operating condition during measurement.

HVAC Noise: The Primary Source

In most commercial buildings, the HVAC system is the dominant source of background noise. WELL Part 2 requires that HVAC noise alone does not exceed the background noise limit with HVAC operating at its normal design condition — not minimum fan speed, not nighttime setback, but the condition that represents typical occupied-hours operation.

Common HVAC noise sources and their typical contributions:

For conference rooms (35 dBA limit), the HVAC design requires particular attention. A VAV box serving a meeting room should have at least 3 meters of internally lined ductwork between the box and the nearest diffuser. Supply air velocity at the diffuser neck should not exceed 2.0 m/s. Return air should be ducted, not through the ceiling plenum, to prevent cross-talk between adjacent rooms.

Sound Insulation Between Spaces: STC/Rw Requirements

Part 2 also specifies minimum sound insulation ratings for partitions between different space types. Sound insulation is expressed as STC (Sound Transmission Class, per ASTM E413) or Rw (Weighted Sound Reduction Index, per ISO 717-1). The two metrics are approximately equivalent for most partition constructions.

Critical construction detail: These STC ratings apply to the complete partition assembly as built, not just the wall panel. A partition with an STC-50 rated wall panel but a door with STC 28 will have a composite STC of approximately 35-38, depending on the door-to-wall area ratio. The composite STC of a partition with a weak element (door, window, pass-through) is dominated by the weakest element.

For partitions to achieve their rated STC, they must extend from the structural slab below to the structural slab above. Partitions that stop at the suspended ceiling grid — a depressingly common construction shortcut — bypass the insulation path entirely. Sound travels through the ceiling plenum void, over the partition, and down into the adjacent room. This flanking path reduces the effective STC by 10-15 points.

External Noise Intrusion

Part 2's background noise limits include noise from external sources — road traffic, aircraft, construction, neighboring buildings. The facade must provide sufficient sound insulation to keep the total background noise (HVAC plus external intrusion) below the specified limits. For buildings near major roads (>60 dBA L_den external), this typically requires:

• Laminated acoustic glazing: minimum 10.76 mm (6 mm + 0.76 mm PVB + 4 mm) for STC 34-36
• High-performance glazing for high-noise sites: 12.76 mm laminated or insulated glass units with dissimilar pane thicknesses for STC 38-42
• Sealed facade construction with acoustically rated ventilation openings if natural ventilation is part of the building design

Part 3 — Sound Masking and Speech Privacy (L07.3): The Most Commonly Failed Requirement

Part 3 is where the majority of WELL acoustic failures occur. The requirement targets speech privacy — the degree to which conversation in one workspace is unintelligible to occupants in adjacent workspaces. The metric is the Speech Transmission Index (STI), calculated per IEC 60268-16:2020.

STI Thresholds

The STI < 0.50 threshold is the standard privacy criterion. Below 0.50, a listener perceives that someone is speaking but cannot reliably determine what is being said. Above 0.50, individual words become discernible — this is distracting in an open plan environment and a confidentiality concern for private offices.

The STI < 0.20 threshold for confidential spaces is significantly more demanding. Achieving this level of speech privacy without sound masking requires partitions with STC 55+ and careful treatment of every flanking path. In practice, most projects targeting STI < 0.20 use a combination of high-STC partitions (STC 50+) and sound masking in the corridor or reception area outside the confidential space.

Sound Masking System Requirements

If a sound masking system is installed to achieve Part 3 compliance (and in most open plan offices, it is), the system must meet the following specifications:

• Overall level: 40-48 dBA broadband, adjustable in 1 dBA increments
• Spectrum: Pink noise or contoured spectrum optimized for speech masking (higher energy in the 500-2000 Hz range that carries speech intelligibility)
• Spatial uniformity: The masking level must not vary by more than plus or minus 2 dBA across the zone, measured at 1.2 m height on a 3 m by 3 m grid
• Adjustability: The system must allow zone-by-zone level adjustment to accommodate different space types and occupant preferences
• Temporal stability: The masking level must remain constant during occupied hours — systems that ramp up and down based on occupancy sensing must maintain a minimum masking floor

Why Part 3 Fails So Often

Part 3 is the most commonly failed component of WELL Feature 74. The failure pattern is predictable:

1. The design team calculates RT60 and achieves Part 1 compliance. The room has good absorption, short reverberation time, low background noise. Everyone is satisfied.

1. Nobody calculates STI. The acoustic consultant addresses reverberation but does not perform the STI calculation required for Part 3. The design proceeds without verifying speech privacy.

1. The WELL Performance Testing Agent measures STI on site. At a typical 2.5 m desk-to-desk spacing with background noise of 34 dBA and no sound masking, the measured STI is 0.52-0.58 — a fail.

1. Remediation is expensive. Retrofitting a sound masking system after construction costs two to three times more than installing it during fit-out, primarily due to the need to access the ceiling plenum and run new cabling.

Compliance Pathways: Design Stage Through Performance Verification

Design-Stage Submission

For initial WELL certification, acoustic compliance can be demonstrated through design documentation:

1. RT60 calculations for every enclosed space type using Sabine's formula (ISO 3382-2:2008 Section A.1) or Eyring's formula (Section A.2). Calculations must show absorption coefficients for every surface material across all six octave bands (125 Hz through 4000 Hz), the total room absorption, and the resulting RT60 for each band.

1. Material specifications with manufacturer-certified absorption coefficients. Generic "acoustic ceiling tile" specifications are not sufficient — the specific product, thickness, mounting condition, and published NRC/alpha values must be documented.

1. Background noise analysis showing predicted noise levels from HVAC systems, referencing equipment sound power data from manufacturer submissions and duct attenuation calculations per ASHRAE Handbook — HVAC Applications.

1. STI calculations (for Part 3) showing the Speech Transmission Index between representative source-receiver pairs. The calculation must follow IEC 60268-16 and account for room geometry, absorption, background noise spectrum (including masking if specified), and source-receiver distance.

Performance Verification (Post-Construction)

WELL Performance Verification requires on-site measurement by an accredited WELL Performance Testing Agent (PTA). The acoustic measurement protocol includes:

Equipment requirements:

• Class 1 integrating-averaging sound level meter per IEC 61672-1
• Omnidirectional loudspeaker per ISO 3382-2 (for RT60)
• STIPA signal generator and analyzer per IEC 60268-16

• Room furnished with all intended furniture and finishes
• No occupants present during measurement
• All HVAC systems at normal operating condition
• Sound masking (if installed) at calibrated operating level
• Doors and windows to enclosed rooms closed
• No construction activity or unusual external noise events

• RT60: minimum 3 source-receiver combinations per room, receiver height 1.2 m, minimum 1.5 m from walls, minimum 2 m from source
• Background noise: 5 positions per zone at 1.2 m height, at least 2 m from supply diffusers
• STI: minimum 3 source-receiver pairs per open plan zone at actual workstation locations, source at 1.5 m (standing), receiver at 1.2 m (seated)

• Instrument calibration certificates (current within 12 months)
• Annotated floor plan showing all measurement positions
• Octave-band RT60 data for each source-receiver pair
• L_Aeq and octave-band noise levels at each background noise position
• STI value at each measurement pair
• Pass/fail comparison against WELL thresholds for each Part

WELL Performance Rating (Ongoing)

The WELL Performance Rating is a recertification program that requires periodic re-measurement. Acoustic parameters must be re-verified at intervals specified by IWBI (typically annually or biennially). This means the acoustic design must be robust to changes over time — replacement of ceiling tiles with different products, changes to HVAC operation, reconfiguration of open plan layouts, or decommissioning of sound masking systems can all cause a previously compliant space to fall out of compliance.

Common Compliance Strategies by Space Type

Open Plan Offices

The standard compliance package for a WELL-compliant open plan office:

• Acoustic ceiling tile: NRC 0.85 or higher, full coverage, mineral fiber or fiberglass. Budget: $25-40/m squared.
• Carpet tile: NRC 0.25-0.35, standard in most office fit-outs. Budget: included in base fit-out.
• Sound masking system: Plenum-mounted speakers on a 3 m by 3 m grid, calibrated to 42-45 dBA. Budget: $2-4/m squared ($3-6/ft squared).
• Workstation screens: 1.2 m minimum height, NRC 0.80+, between adjacent desks. Budget: $250-400 per screen.
• HVAC design: NC-30 maximum at desk level, ducted returns, lined supply ductwork.

Meeting Rooms and Conference Rooms

• Acoustic ceiling tile: NRC 0.85+, full coverage
• Wall-mounted acoustic panels: 25-40% of wall area, NRC 0.90+, particularly on the wall opposite the display/presentation wall
• Carpet or carpet tile: NRC 0.25-0.35
• Sealed doors: STC 35+ minimum, with drop seals and compression gaskets. For conference-to-conference adjacencies, STC 40+ doors.
• Full-height partitions: Slab-to-slab construction, not ceiling-height. STC 50+ for rooms adjacent to open plan areas.
• HVAC: NC-25 or lower at seated head height. Ducted supply and return. VAV box with 3 m+ lined duct run to room.

Teleconference Rooms

Teleconference rooms have the most stringent RT60 requirement (0.4 seconds) because remote participants experience the room acoustic directly through the microphone. Excessive reverberation degrades voice pickup quality and triggers echo cancellation artifacts.

• Acoustic ceiling tile: NRC 0.90+, or suspended acoustic cloud with 200 mm air gap
• Wall treatment: 60-80% of wall area treated with NRC 0.90+ panels
• Floor: Carpet (mandatory — hard floors create reflections at microphone level)
• Background noise: 30 dBA or lower — more stringent than the WELL minimum of 35 dBA to avoid microphone pickup of HVAC noise
• Door: STC 40+ with acoustic seals on all four edges

Cost of Compliance

The incremental cost of achieving WELL Feature 74 compliance varies by baseline design quality and space type. For a typical commercial office fit-out where the base specification includes a standard suspended ceiling and carpet:

For a 2,000 m squared office floor plate, the acoustic compliance package adds approximately $16,000-$30,000 to the fit-out budget. This represents 1.5-3% of a typical commercial fit-out cost of $800-$1,200 per m squared.

The cost of failing and remediating after construction is three to five times higher: $50,000-$120,000 for the same 2,000 m squared floor plate, plus weeks of disruption to occupied spaces.

Relationship to Other Standards

WELL Feature 74 does not exist in isolation. It references and is compatible with several international acoustic standards:

Projects pursuing both WELL certification and compliance with national building codes (BB93 for UK schools, DIN 4109 for German buildings, NCC for Australian buildings) should note that WELL thresholds are generally achievable within national code requirements, but the measurement conditions and verification procedures may differ. A coordinated acoustic design that addresses both WELL and national code requirements simultaneously is more efficient than treating them as separate compliance exercises.

AcousPlan Automates All Three Parts of WELL Feature 74

Calculating RT60 across six octave bands, verifying background noise against space-type-specific thresholds, and computing STI for every source-receiver pair in an open plan layout is time-consuming when done manually. AcousPlan automates the complete workflow:

1. Model your room with actual dimensions, ceiling height, and surface materials from a database of 5,600+ acoustic products with manufacturer-certified absorption coefficients.
2. Select the WELL Feature 74 compliance check and AcousPlan automatically applies the correct thresholds for your space type across all three Parts.
3. View pass/fail results for RT60 (every octave band), background noise, sound insulation, and STI — with specific identification of which parameters fail and by how much.
4. Generate a WELL-ready PDF report that includes all calculation methodology references (ISO 3382-2, IEC 60268-16), material specifications, and pass/fail determinations formatted for WELL submission.