WELL Building Standard air requirements for offices

The WELL Building Standard's Air concept sets evidence-based thresholds for the airborne factors that most affect occupant health and cognition: carbon dioxide, particulate matter (PM2.5 and PM10), total and speciated volatile organic compounds, formaldehyde, ozone, carbon monoxide and radon. It also defines minimum ventilation rates, filtration standards, source control measures and operational verification.

For UK office and facilities teams, WELL Air is useful even without pursuing formal certification — the thresholds give a defensible target to design, commission and operate against, and align with CIBSE TM40 and BS EN 16798-1 in most respects.

• CO₂: below 900 ppm in regularly occupied spaces, measured at breathing-zone height during normal occupancy.
• PM2.5: below 15 µg/m³ annual mean, with stricter thresholds (≤10 µg/m³) for higher scoring.
• PM10: below 50 µg/m³ annual mean.
• TVOC: below 500 µg/m³.
• Formaldehyde: below 27 ppb (≈33 µg/m³).
• Ozone: below 51 ppb.
• Carbon monoxide: below 9 ppm (8-hour mean).

Lower scoring tiers add tighter targets, particularly on particulates and VOCs. Our office CO₂ monitoring, particulate monitoring and VOC testing services map directly to these thresholds.

WELL Air requires outdoor air supply meeting or exceeding ASHRAE 62.1 (broadly equivalent to BS EN 16798-1 Category II), with demand-controlled ventilation in densely occupied or variable-occupancy zones. Filtration is specified at MERV 13 or higher for particulates, with activated carbon stages where outdoor air or internal sources warrant it.

Source control is treated as a first-line measure: low-emission materials and finishes, entryway dirt-walk-off systems, separately exhausted printing and cleaning areas, and smoking restrictions. Most UK office refurbishments need targeted attention to formaldehyde from MDF and adhesives and TVOCs from paints, sealants and carpets.

Independent ventilation testing and HVAC hygiene reviews are the most common way UK occupiers evidence compliance with these requirements.

WELL Performance Verification combines on-site spot measurements with continuous monitoring across a representative sample of regularly occupied zones. Sensors must be calibrated against reference instruments, and data must cover normal operating hours rather than cherry-picked windows.

In practice that means a mix of laboratory-grade spot tests (formaldehyde, speciated VOCs, particulate gravimetric checks) and continuous wireless sensors for CO₂, PM2.5, PM10, TVOC, temperature and humidity. We deliver both as part of an office air quality testing engagement.

WELL's Thermal Comfort and Sound concepts complement the Air concept. Relative humidity is expected to sit between 30% and 60%, with operative temperature controlled to ASHRAE 55 / BS EN 16798-1 Category II ranges. Persistent excursions outside these bands are a strong predictor of comfort complaints and absenteeism, independent of the headline pollutant data.

We capture humidity and temperature alongside CO₂ and particulates so that wellbeing recommendations are grounded in the same dataset.

Across the UK office portfolios we have measured, headline CO₂ and PM2.5 thresholds are achievable with disciplined ventilation tuning and MERV 13+ filtration. The recurring failure modes are: residual formaldehyde and TVOCs after recent fit-out works; under-supply of outdoor air in dense meeting rooms; humidity excursions in shoulder seasons; and unverified BMS CO₂ control signals that do not match breathing-zone reality.

If you are reviewing your office against WELL Air, the fastest path to a defensible position is a baseline survey followed by targeted continuous monitoring. Request a quote or contact us to scope an assessment.