WELL v2 Air Quality: Indoor PM2.5, VOC, and Ventilation Thresholds Explained (2024)

15 µg/m³. That is the maximum PM2.5 concentration WELL v2 feature A01 allows in occupiable spaces under its standard option (35 µg/m³ in commercial kitchens and industrial spaces). Here is what all four WELL v2 Air preconditions require, and where the optimization points come from.

What thresholds does WELL v2 Air require?

WELL v2 Air is one of 10 WELL v2 concepts, structured around 4 mandatory preconditions under §A01 through §A04 and 10 optional optimizations under §A05 through §A14. Selecting the wrong compliance option in §A01 costs certification level, not just optimization points: Option 2 PM thresholds cap certification at Gold, and Option 3 caps at Silver.

WELL v2 §A01 Part 5 requires the pollutants in Parts 1-3 to be monitored in regularly occupied spaces at intervals no longer than once per year, with results submitted annually through the WELL digital platform. Dwelling units are excluded from this ongoing-monitoring part. The table below shows every pollutant threshold from §A01. Commercial kitchen and industrial exceptions appear in the third column. Each value reflects a tested indoor concentration in the occupied building, not a design target or modeled prediction.

Source: WELL v2, §A01

What are the precondition thresholds for PM2.5 and PM10?

PM2.5 is fine particulate matter measuring 2.5 microns or smaller, required by WELL v2 §A01 to stay at or below 15 µg/m³ in all regularly occupied spaces except commercial kitchens and industrial areas. PM10, coarser particles at 10 microns, must remain at or below 50 µg/m³. Both thresholds are verified after occupancy, not modeled at design.

WELL v2 §A01 offers three compliance options. Option 1 sets PM2.5 at 15 µg/m³ and PM10 at 50 µg/m³. Option 2 applies where outdoor annual average PM2.5 reaches 35 µg/m³ or higher: indoor PM2.5 rises to 25 µg/m³, but certification caps at Gold. Option 3 ties indoor concentrations to outdoor conditions, capping PM2.5 and PM10 at 30% of the 24- or 48-hour outdoor average on the test day; certification caps at Silver.

How do VOC and inorganic gas limits apply to occupied spaces?

VOC refers to volatile organic compounds, a broad class of chemicals that off-gas from finishes, adhesives, and furnishings, required by WELL v2 §A01 to remain below specific concentrations in all regularly occupied spaces. Lab-based testing (Option 1) limits benzene to 10 µg/m³, formaldehyde to 50 µg/m³, and toluene to 300 µg/m³.

Sensor-based monitoring (Option 2) requires at least one total VOC sensor per 325 m² (3,500 ft²), with sensor accuracy of 20 µg/m³ plus 20% across the 150–2,000 µg/m³ range. Total VOC must remain at or below 500 µg/m³ for at least 90% of regularly occupied hours.

Inorganic gas limits under §A01 cap carbon monoxide at 10 mg/m³ (9 ppm) and ozone at 100 µg/m³ (51 ppb) in standard occupied spaces. Results from all pollutant categories must be submitted annually to the WELL digital platform (§A01 Part 5).

What does the smoke-free environment precondition require?

The smoke-free environment precondition is §A02 of WELL v2, prohibiting smoking and e-cigarette use in all interior spaces within the project boundary. The prohibition extends outdoors: no smoking or vaping within 7.5 m (25 ft) of any entrance, operable window, or building air intake per §A02 Part 2a.

Occupied outdoor areas above grade, including decks, patios, balconies, and rooftops, are entirely smoke-free under §A02 Part 2b. Where outdoor areas at grade do allow smoking, §A02 requires signage along walkways at intervals no greater than 30 m (100 ft), describing the health hazards of secondhand smoke.

Building owners often treat §A02 as a lease or policy matter rather than a design matter. The 7.5 m buffer from air intakes (or the maximum extent local codes allow) requires site planning. Intakes placed near outdoor smoking areas put tobacco smoke into the supply air, which can show up as a §A01 PM2.5 problem.

How do ventilation design requirements connect to ASHRAE 62.1?

Ventilation design is the §A03 precondition in WELL v2. Mechanically ventilated systems must meet or exceed ASHRAE 62.1-2010 supply and exhaust rates for at least 90% of the project area. Equivalent standards include ASHRAE 62.2-2016, EN 16798-1, AS 1668.2-2012, and CIBSE Guide A. Systems must be tested and balanced after occupancy.

For naturally ventilated spaces, §A03 requires outdoor air PM2.5 below 15 µg/m³ (annual average) and PM10 below 30 µg/m³ before the natural ventilation pathway qualifies. Where outdoor PM2.5 is 15 µg/m³ or higher but below 35 µg/m³ (and PM10 below 70 µg/m³), natural ventilation is allowed only under Option 3, which caps certification at Silver.

Mixed-mode buildings must switch to mechanical ventilation whenever outdoor PM2.5 at a monitoring station within 4 km exceeds 15 µg/m³ per §A03. Optimization points under §A06 reward exceeding the ASHRAE 62.1-2010 outdoor air supply rate by 30% (1 point) or 60% (2 points), or deploying demand-controlled ventilation to hold CO₂ below 900 ppm (1 point) or 750 ppm (2 points).

How does radon testing work under WELL v2?

Radon testing is the §A01 requirement that all regularly occupied spaces at or below grade be measured by an independent professional and shown to contain radon at or below 0.15 Bq/L (4 pCi/L). The independent-professional clause eliminates self-testing by project team members.

One test covers up to 2,300 m² (25,000 ft²) of regularly occupied below-grade space per §A01. Larger footprints require proportionally more tests. The test must be completed before WELL certification is granted, and results are submitted to the WELL digital platform.

Radon originates from uranium decay in soil and rock beneath buildings. The 4 pCi/L limit equals the U.S. EPA action level. §A01 Part 4 offers an alternative to testing: all regularly occupied spaces at or below grade can instead meet the mechanical-ventilation requirements of §A03 Part 1 Option 1.

Why do WELL v2 Air thresholds use these specific numbers?

WELL v2 air thresholds are numeric limits that WELL sets from public health references and cites in the standard, not arbitrary design targets. The PM2.5 precondition of 15 µg/m³ per §A01 equals the WHO 2021 24-hour guideline value for PM2.5; the WHO 2021 annual guideline is 5 µg/m³ (the 2005 annual value was 10 µg/m³), so the WELL threshold is not an annual-mean guideline.

The 4 pCi/L radon ceiling per §A01 mirrors the U.S. EPA action level for residential mitigation.

The smoke-free buffer in §A02 is 25 ft (7.5 m), or the maximum extent local codes allow, from entrances, operable windows and air intakes. The formaldehyde limit of 50 µg/m³ per §A01 is stricter than the WHO indoor air guideline of 100 µg/m³ (30-minute average).

What optimization points are available for improved air quality scores?

Air quality optimization in WELL v2 refers to the §A05 and §A06 point pathways, offering up to 4 points for tighter pollutant thresholds and 3 more for ventilation improvements.

Under §A05, tighter PM2.5 earns 1 point at 12 µg/m³ or 2 points at 10 µg/m³. Tighter PM10 earns 1 point at 30 µg/m³ or 2 points at 20 µg/m³. Meeting tighter VOC limits, including formaldehyde at 9 µg/m³, benzene at 3 µg/m³, and acetaldehyde at 140 µg/m³, earns 1 additional point per §A05. CO at 7 mg/m³ (6 ppm) and NO₂ at 40 µg/m³ (21 ppb) earn 1 more point for inorganic gases.

Under §A06, exceeding ASHRAE 62.1 outdoor air supply by 30% earns 1 point; by 60%, 2 points. Demand-control ventilation holding CO₂ below 750 ppm earns 2 points. CO₂ sensors must be placed at return air diffusers or in the breathing zone, at least 1 m from doors, windows, and occupants per §A06.

What exceptions apply to commercial kitchens, multifamily, and WELL Core?

Exceptions in WELL v2 Air apply to three project types, each with modified compliance pathways per §A01 notes.

Commercial kitchen and industrial spaces face a higher PM2.5 ceiling per §A01: 35 µg/m³ instead of 15 µg/m³. The CO limit for commercial kitchens and industrial areas rises to 34 mg/m³ (30 ppm), reflecting the combustion loads from cooking equipment.

Multifamily residential projects have a dwelling unit testing exception. Bronze and Silver certification do not require air quality testing inside individual dwelling units. Gold and Platinum certification require dwelling unit testing, and all pollutant thresholds, including PM2.5, PM10, VOCs, and inorganic gases, must be met in tested units.

WELL Core projects must satisfy air quality requirements in non-leased spaces representing at least 2.5% of total project area per §A01 Core notes. When non-leased space falls below 2.5%, the project team supplements testing with leased space to reach the threshold.

What do teams consistently get wrong about WELL v2 Air?

Three points deserve early attention because they are fixed by design, not by testing.

1. Testing before finishes cure. Measurements taken before adhesives, sealants and finishes have off-gassed can differ from later readings. Plan the test date with the performance testing agent and the Performance Verification Guidebook.

2. Natural ventilation in high-PM markets. Annual outdoor PM2.5 of 15 µg/m³ or higher (or PM10 of 30 µg/m³ or higher) disqualifies the standard natural ventilation pathway (Option 2) under §A03. Check the outdoor annual average at design stage, because switching to mechanical ventilation after construction documents are complete is a major change.

3. Air intakes within the §A02 buffer. The 7.5 m smoke-free buffer is a site design constraint. Intakes below outdoor terraces or near service entries can fall inside the buffer. Tobacco smoke infiltration shows up in §A01 PM2.5 readings, not §A02. The failure is harder to trace.

What belongs on the WELL v2 Air pre-submission checklist?

• PM2.5 tested at or below 15 µg/m³ in all regularly occupied spaces (§A01)
• PM10 tested at or below 50 µg/m³ in all regularly occupied spaces (§A01)
• Benzene at or below 10 µg/m³ per lab test (§A01)
• Formaldehyde at or below 50 µg/m³ per lab test (§A01)
• Toluene at or below 300 µg/m³ per lab test (§A01)
• Carbon monoxide at or below 10 mg/m³ (9 ppm) (§A01)
• Ozone at or below 100 µg/m³ (51 ppb) (§A01)
• Radon at or below 0.15 Bq/L (4 pCi/L); 1 test per 2,300 m² of below-grade occupied space (§A01)
• Smoking and e-cigarettes prohibited in all interior spaces (§A02)
• No smoking within 7.5 m of all entrances, operable windows, and air intakes (§A02)
• Occupied outdoor areas above grade designated smoke-free (§A02 Part 2b)
• Mechanical ventilation rates meet or exceed ASHRAE 62.1-2010 for 90% of project area (§A03)
• Ventilation system tested and balanced after occupancy (§A03)
• Ducts sealed or cleaned before registers installed (§A04)
• MERV 8 or higher construction filters replaced before occupancy (§A04)
• Annual monitoring results submitted to WELL digital platform (§A01)
• For multifamily Gold/Platinum: dwelling unit testing completed (§A01)
• For WELL Core: non-leased space testing covers at least 2.5% of project area (§A01)