What the WELL Building Standard requires for air data

The WELL Building Standard requires two things for air: a space must test below fixed limits for pollutants like PM2.5, carbon monoxide and radon, and it must run continuous air quality monitoring that keeps records, not a single day of testing.

A facilities team heading into a WELL assessment, or renewing one, usually has the first half handled: a test report from a few months ago. What they are missing is the second half, a record of what the air has actually done since.

This post covers what the WELL Building Standard requires, number by number, where WELL's own numbers differ from ASHRAE's, and what a building needs to track between assessments.

Key Takeaways

• WELL's Air Quality Standards precondition requires PM2.5 under 15 µg/m³, PM10 under 50 µg/m³, carbon monoxide under 9 ppm, ozone under 51 ppb and radon under 4 pCi/L at the lowest occupied level.
• In larger, denser spaces, WELL's ventilation effectiveness feature also requires carbon dioxide under 800 ppm, a number ASHRAE's own ventilation standard does not set.
• WELL's monitoring feature asks for at least one monitor per floor, tracking two of particle count, CO₂ or ozone, with a reading no less often than once an hour and records kept for a minimum of 3 years.
• The precondition can be met with a single day of testing. The monitoring feature cannot.
• A continuous reading is a record a facilities team can show between assessments. It is not a WELL certification by itself, and only a WELL assessor can confirm what counts toward points.

What the WELL Building Standard actually covers

The International WELL Building Institute (IWBI) administers the WELL Building Standard, scored across concepts that include air, water, light and movement. Inside the air concept, one precondition is mandatory for every project, and a separate feature covers ongoing monitoring. This post covers both: the fixed limits in WELL's Air Quality Standards precondition, and the ongoing air quality monitoring and feedback feature.

The air quality limits every WELL project must hit

WELL's Air Quality Standards precondition sets fixed thresholds that a regularly occupied space must test below. The main limits are:

• PM2.5 under 15 µg/m³
• PM10 under 50 µg/m³
• Carbon monoxide under 9 ppm
• Ozone under 51 ppb
• Formaldehyde under 27 ppb
• Total VOCs under 500 µg/m³
• Radon under 4 pCi/L at the lowest occupied level

That radon limit is the same action level the EPA uses for homes. A project can miss any other optimization and still certify, but it cannot pass WELL without clearing every part of this precondition.

What WELL counts as continuous air quality monitoring

Hitting the precondition once is not the same as monitoring. WELL's monitoring feature asks for at least one monitor per floor in regularly occupied or common space, measuring at least two of particle count, CO₂ or ozone, mounted roughly 4 to 6 feet above the floor. Readings have to come in no less often than once an hour, and the project has to keep those records for a minimum of 3 years. A real-time display also has to show temperature, humidity and CO₂ to the people in the room, not just to the facilities team.

Why a single test does not satisfy WELL

The precondition and the monitoring feature ask for different things, and a passing test does not cover both. A test report proves what a room measured on one day. The monitoring feature proves what a room has done every hour since, which is a different kind of evidence and the kind most buildings are missing when an assessment comes up for renewal.

A monitor only ever tells you what the air is doing. It does not raise the ventilation rate, swap a filter or fix a damper schedule by itself. What it gives a facilities team is the record WELL's monitoring feature actually asks for, and a number to act on before the next test instead of after it.

How WELL's carbon dioxide standard compares to ASHRAE's

In larger, denser spaces, roughly 500 square feet or more with over 25 people per 1,000 square feet, WELL's ventilation effectiveness feature adds a carbon dioxide limit of 800 ppm, tied to demand controlled ventilation.

That is a firmer number than the one most people assume ASHRAE sets. ASHRAE's own position document on indoor carbon dioxide states plainly that ASHRAE Standard 62.1 "does not provide a limit value for indoor CO2." ASHRAE treats CO₂ as one signal among several, not a pass or fail number. WELL, by contrast, writes 800 ppm into the standard itself for these spaces, which is one reason a building can meet ASHRAE's ventilation guidance and still need to address CO₂ for a WELL point.

What to track between WELL assessments

A facilities team does not need to wait for the next assessment to find out where a space stands. The same parameters WELL asks about are worth watching continuously: CO₂ in the rooms that fill up fastest, PM2.5 during wildfire season or near a loading dock, and radon at the lowest occupied level, which needs months of data to mean anything rather than a single test.

When a reading climbs, the fix is usually ventilation first, not equipment. If particle counts are the problem, a HEPA room purifier or a MERV 13 filter is the usual next step to test, run again after the change, and confirm it moved the number.

None of this is a WELL certification by itself. A continuous record is evidence a facilities team can bring to its own review, the same way an OSHA indoor air quality complaint benefits from a number instead of a one-time test. Whether a specific monitor or dataset qualifies toward WELL points is a question for a WELL assessor, not a monitoring vendor.

FAQ

What is the WELL Building Standard? The WELL Building Standard is a building certification administered by the International WELL Building Institute that scores a project across concepts including air, water, light and movement. The air concept includes a mandatory precondition with fixed pollutant limits and a separate feature for ongoing monitoring.

What CO2 level does the WELL Building Standard require? WELL's ventilation effectiveness feature requires carbon dioxide under 800 ppm in larger, denser spaces as part of demand controlled ventilation. That is a firmer number than ASHRAE sets: ASHRAE's own position document says its ventilation standard does not set a CO2 limit at all.

Does the WELL Building Standard require a radon test? Yes. WELL's Air Quality Standards precondition requires radon under 4 pCi/L at the lowest occupied level, the same action level the EPA uses for homes. It is mandatory, not an optional point.

How long does WELL require air quality data to be tracked? WELL's monitoring feature asks for readings no less often than once an hour and for those records to be kept for a minimum of 3 years. A single day of testing satisfies the precondition but not this feature.

Does continuous air quality monitoring count toward WELL certification by itself? It supports the monitoring feature's record keeping, but whether a specific dataset or device qualifies toward points is decided by a WELL assessor, not by a monitoring vendor. A continuous reading is evidence a facilities team can bring to that review.

The next step for a facilities team

The WELL Building Standard asks for more than a passing test: fixed limits on PM2.5, carbon monoxide, ozone and radon, a firmer CO₂ number than ASHRAE sets in larger spaces, and a monitoring feature that wants hourly data kept for years. Most buildings have the test. What they are missing is the record in between.

A facilities team that wants that record before the next assessment, not scrambled together the week of it, can start with a short form on Measured Air's page for commercial buildings. Measured Air replies within a business day.