Why IAQ Matters
People spend 90% of their time indoors. Poor indoor air quality causes headaches, fatigue, respiratory problems, and reduced cognitive performance. Studies show that improving IAQ increases productivity by 8-11% and reduces sick leave by 35%. IAQ is now a central feature of WELL certification and increasingly demanded by tenants and employees.
Applicable Standards
- ASHRAE 62.1 — Ventilation for Acceptable Indoor Air Quality
- WELL v2 Air concept — 14 features covering air quality
- EN 16798-1 — Indoor Environmental Parameters
- WHO Air Quality Guidelines — Global health-based limits
- LEED v4.1 EQ credits — Indoor Environmental Quality
Key IAQ Parameters
| Parameter | Good | Acceptable | Poor | Standard |
|---|---|---|---|---|
| CO2 | Below 600 ppm | 600-800 ppm | Above 1000 ppm | ASHRAE 62.1, WELL |
| PM2.5 | Below 12 ug/m3 | 12-25 ug/m3 | Above 35 ug/m3 | WHO, WELL |
| PM10 | Below 20 ug/m3 | 20-50 ug/m3 | Above 50 ug/m3 | WHO |
| TVOC | Below 200 ug/m3 | 200-500 ug/m3 | Above 500 ug/m3 | WELL, EN 16798 |
| Temperature | 22-24C | 20-26C | Outside 18-28C | ASHRAE 55 |
| Relative humidity | 40-60% | 30-70% | Below 20% or above 80% | ASHRAE 55 |
| CO | Below 2 ppm | 2-9 ppm | Above 9 ppm | WHO, WELL |
| Formaldehyde | Below 27 ppb | 27-50 ppb | Above 100 ppb | WHO, WELL |
CO2 as a Ventilation Indicator
CO2 is the most practical indicator of ventilation adequacy in occupied spaces. It is not toxic at building concentrations but correlates directly with outdoor air supply per person.
- Outdoor air: approximately 420 ppm (rising annually)
- Well-ventilated office: 500-700 ppm above outdoor (Delta-CO2)
- ASHRAE 62.1 target: CO2 below 700 ppm above outdoor in steady state
- WELL certification: CO2 below 800 ppm (absolute, not delta)
- Above 1000 ppm: complaints of stuffiness, drowsiness, reduced cognitive function
- Above 1500 ppm: clear indication of inadequate ventilation
Monitoring Approach
| Level | Scope | Equipment | Cost |
|---|---|---|---|
| Basic | CO2, temperature, humidity at 1-2 points per floor | Standalone sensors with display | Low |
| Standard | CO2, PM2.5, TVOC, temp, humidity at multiple zones | Networked sensors with dashboard | Medium |
| WELL-grade | All parameters including CO, formaldehyde, ozone, PM10 | Lab-grade monitors or accredited testing | High |
Sensor Placement
- Height: breathing zone (1.1-1.7m from floor for seated/standing occupants)
- Location: representative of occupied space, not near supply diffusers, doors, or printers
- Density: minimum 1 sensor per 325 m2 (3,500 ft2) per WELL, or 1 per zone
- Calibration: CO2 sensors require annual calibration. PM sensors require periodic reference comparison.
Ventilation Verification
IAQ monitoring and ventilation are inseparable. Key verification checks:
- Outdoor air damper position: verify minimum outdoor air position matches design intent
- Air handling unit filters: check pressure drop, replacement schedule (MERV 13 minimum for WELL)
- Economiser operation: verify free cooling mode activates when outdoor conditions are suitable
- Demand-controlled ventilation: if installed, verify CO2 setpoints and damper response
- TAB report: last Testing, Adjusting, and Balancing report should confirm outdoor air rates meet ASHRAE 62.1
References
Insights & Guidance
- CO2 below 800 ppm, PM2.5 below 15 ug/m3, TVOC below 500 ug/m3. These are the three critical IAQ parameters.
- CO2 is the most practical ventilation indicator. Above 1000 ppm means inadequate fresh air supply.
- Improving IAQ increases productivity 8-11% and reduces sick leave 35%. It pays for itself.
- Sensor placement: breathing zone (1.1-1.7m), away from diffusers, 1 per 325 m2 minimum.
- WELL certification requires continuous IAQ monitoring with public display of results.
People spend 90% of their time indoors. Poor air quality directly impacts health, productivity, and cognitive function. IAQ is now a competitive differentiator for commercial buildings and a requirement for WELL certification.
- Outdoor air dampers closed — CO2 rises rapidly, occupants experience drowsiness and complaints.
- PM2.5 infiltration — poor filtration allows outdoor pollution into the building.
- Off-gassing — new furniture, carpets, and paint release VOCs for weeks to months.
- IAQ monitoring data (continuous or periodic testing reports)
- HVAC maintenance and filter replacement records
- TAB report confirming outdoor air rates
- Sensor calibration certificates
- Are IAQ sensors installed and displaying readings?
- What does the CO2 level read in occupied spaces?
- Are HVAC filters clean and recently replaced?
- What are the current CO2 and PM2.5 levels in occupied spaces?
- When was the last TAB report completed?
- What filter grade is installed in the AHUs?
- IAQ testing — accredited environmental testing laboratory.
- Ventilation assessment — HVAC engineer with ASHRAE 62.1 expertise.
- WELL certification — WELL Accredited Professional.