Indoor Air Quality Testing for Commercial Buildings

An indoor air quality complaint rarely arrives as a technical question. It arrives as an email from a tenant’s facilities manager saying that four people on the north side of the eleventh floor have headaches, that it has been going on for a fortnight, and asking what the landlord intends to do. The instinct is to hire someone to test the air. That instinct is right, but the order in which the work is done determines whether the money produces an answer or a folder of numbers with no conclusion attached.

This article explains what indoor air quality testing measures, what each number actually indicates, which frameworks give those numbers meaning, and what an owner should do in the first week of a complaint. It is written for owners, developers and asset managers rather than for industrial hygienists, so the emphasis is on decisions and consequences. Budlong provides MEP engineering services across California and spends a great deal of time on buildings where the air is the symptom and the mechanical system is the cause. The wider range of that work is set out on our expertise overview.

1. What Is Indoor Air Quality Testing?

Indoor air quality testing is the measurement of physical and chemical parameters of the air inside an occupied building, compared against an outdoor baseline and interpreted against a published reference framework. It is a diagnostic activity, not a compliance activity. In most commercial buildings in the United States there is no legal requirement to test indoor air at all, which surprises owners the first time they ask.

The confusion arises because several different things travel under the same name. A twenty minute walk with a handheld meter is testing. So is a four week investigation with laboratory analysis, chain of custody documentation and a signed report. So is a permanently installed sensor network reporting to a dashboard. They cost different amounts and carry very different weight if the matter ever reaches a lawyer.

The purpose is almost always one of four things: resolving an occupant complaint, verifying a newly completed building before handover, supporting a voluntary certification such as LEED or WELL, or establishing a record in anticipation of a dispute. Being clear about which of the four you are doing is the single most useful decision an owner makes, because it dictates the method, the cost and the deliverable.

2. How Testing Actually Works

Two families of method sit behind every indoor air quality report, and the difference between them is the difference between a few hundred dollars and a few thousand.

Direct reading instruments

Direct reading instruments give a number on site, in real time. Non-dispersive infrared sensors for carbon dioxide, electrochemical cells for carbon monoxide, optical particle counters or nephelometers for particulate matter, photoionisation detectors for total volatile organic compounds, and thermistors and capacitive sensors for temperature and relative humidity. They are quick, they let an investigator walk a floor and find a gradient, and they are indispensable for locating a source.

Their weakness is specificity. A photoionisation detector responds to a broad mixture of compounds and reports a single index calibrated against a reference gas. It will tell you something organic is present, not whether it is a cleaning product, a printer, a new carpet or a solvent from the fit-out next door.

Laboratory analysis of collected samples

The alternative is to collect the air and analyse it later. Sorbent tubes drawn at a known flow rate for a known duration and analysed by gas chromatography with mass spectrometry give speciated volatile organic compounds, meaning a list of individual compounds with individual concentrations. Passive badges collect over days rather than hours. Formaldehyde is normally collected on a treated cartridge and analysed by high performance liquid chromatography because photoionisation detectors respond to it poorly. Fungal sampling uses spore traps or culture plates, and is only worth doing once a moisture source has been identified.

Laboratory methods cost more and take one to three weeks to return results. What they buy is defensibility: a published method, a documented flow rate, a calibration certificate and a chain of custody form are what allow a conclusion to survive challenge.

Duration, placement and the outdoor baseline

Three procedural details separate a useful survey from a worthless one. Duration must cover the period when the complaint occurs, which usually means starting before occupancy so the overnight build-up and the morning purge are both captured. Placement must be in the breathing zone, roughly three to six feet above the floor, away from supply diffusers and away from the return.

The third is the outdoor baseline, and it is the one most often skipped. Concurrent outdoor measurement with the same instrument is what converts a raw indoor number into a statement about the building. Indoor carbon dioxide of 1,050 ppm means one thing when outdoor air is 420 ppm and something completely different when a loading dock has pushed outdoor air at the intake to 900 ppm. During a wildfire smoke episode, indoor fine particulate can exceed every published guideline while the filtration system is performing better than specified, and only the paired outdoor reading demonstrates that.

3. The Parameters That Get Measured

The table below sets out the core parameter list, what each one genuinely indicates, the framework normally used to interpret it, and what an elevated reading usually turns out to mean in a commercial building. Note carefully which of these frameworks are enforceable and which are not.

4. Which Buildings and Situations Trigger Testing

There is no general obligation to test, but there are five situations where testing is either required by a contract or is the only sensible response.

An occupant complaint

The most common trigger. Symptoms clustered in place and time, resolving away from the building, point to the building. Symptoms that follow individuals home usually do not.

Post-construction handover

New finishes, adhesives, sealants and furniture emit for weeks. Owners taking handover of a fit-out often specify a verification test as a condition of acceptance. This is where a flush-out belongs, before occupancy rather than after a complaint.

Voluntary certification

LEED indoor environmental quality credits, the WELL Building Standard and RESET Air all require measurement. LEED and WELL are point in time verifications with defined analyte lists and thresholds. RESET is a continuous monitoring standard and requires accredited monitors reporting on an ongoing basis rather than a one-off test.

Litigation, insurance or a regulatory inquiry

Once a claim exists, the standard of evidence changes completely. Instruments must be calibrated with documentation, methods must be published methods, samples must have chain of custody, and the report must be signed by someone qualified to defend it. Screening data collected earlier without those controls can be worse than nothing.

Change of use or a known event

Converting an office floor to a medical or laboratory use, a flood, a sewer backup, a wildfire smoke intrusion or a nearby demolition all justify a baseline before and after.

5. What Testing Asks of Each Building System

Indoor air quality is an outcome of the mechanical system, the envelope and the way the building is operated. When a test finds a problem, the fix lands in one of a small number of places.

Outdoor air delivery

The first question in any investigation is how much outdoor air is actually reaching the breathing zone, measured rather than assumed. That means a traverse at the outdoor air intake or a tracer measurement, damper position verification, and a check of the control sequence against what the design intended. Design intent itself comes from ASHRAE Standard 62.1 or, in California, Title 24 Part 6 Section 120.1. A system delivering half its design outdoor air will produce complaints that look chemical and are in fact arithmetic.

Filtration

Filter rating, filter condition and above all filter seal. A MERV 13 filter in a rack with a quarter inch gap around the frame performs closer to MERV 8, because air takes the easy path. Bypass is the most common filtration failure in commercial buildings, and it is invisible on a maintenance record that logs only replacement dates.

Pressure relationships

Buildings that are net negative pull air from wherever they can get it: the car park, the loading dock, the lift shaft, the sanitary system, the soil beneath the slab. A large share of odour complaints and essentially all radon and vehicle exhaust findings are pressure problems rather than source problems. Measuring differential pressure across doors and between floors costs almost nothing and frequently ends the investigation on the first day.

Ductwork and distribution

Leakage in supply ductwork loses conditioned outdoor air into ceiling plenums before it reaches occupants, and leakage in return paths draws unconditioned air in. Both show up as a ventilation shortfall at the breathing zone while the air handler appears to be doing its job. This is why duct leakage testing matters beyond its energy code role.

Moisture control

Condensate pans that do not drain, traps sized wrongly for the fan static, chilled water insulation gaps and envelope leaks all put liquid water where organic material is waiting. Every microbial finding traces back to a moisture source, and remediating growth without fixing the water guarantees a repeat visit.

Capacity and zoning

Where the complaint is comfort rather than contamination, the fault is usually in load and zoning rather than in air quality at all. A tenant who has densified a floor beyond the original design, added a server closet or reglazed a facade has changed the load. Accurate HVAC load calculations and honest zoning are the fix, and they belong in a HVAC design scope rather than in an air quality report.

6. The Codes and Standards Behind the Numbers

Numbers only mean something inside a framework. Six frameworks matter to a commercial building owner in California, and they do very different jobs.

ASHRAE Standard 62.1

Standard 62.1 is the ventilation standard for buildings other than low rise residential. It sets minimum outdoor air rates in the breathing zone as the sum of a rate per person and a rate per unit floor area. For office space the 2022 edition uses 5 cfm per person plus 0.06 cfm per square foot at a default density of five people per thousand square feet. It also requires mechanically cooled systems to limit indoor humidity to a maximum dew point of 60 degrees Fahrenheit, and it permits demand control ventilation with carbon dioxide sensors accurate to within 75 ppm and calibrated at least every five years. The current editions are published by ASHRAE.

ASHRAE Standard 55

Standard 55 defines thermal comfort, and it does not fix a temperature. It defines a comfort zone as a function of operative temperature, humidity, air speed, metabolic rate and clothing insulation, targeting acceptability for 80 percent of occupants. A large proportion of what tenants report as bad air is a Standard 55 problem, and no amount of contaminant sampling will find it.

OSHA and Cal/OSHA

Federal OSHA has no comprehensive indoor air quality standard for commercial buildings. It has permissible exposure limits for individual substances and the general duty clause. California goes further. Title 8 Section 5155 sets the state permissible exposure limits, including 25 ppm for carbon monoxide against the federal 50 ppm. More importantly for owners, Title 8 Section 5142 requires that mechanically driven HVAC systems supply the outdoor air quantity required by the building standards code in force when the permit was issued, that they operate continuously during working hours with narrow exceptions, and that they be inspected at least annually with written records retained for five years. That inspection record is the first document a Cal/OSHA inspector asks for after a complaint.

EPA guidance and CDC or NIOSH methodology

EPA does not regulate indoor air in ordinary commercial buildings. What it publishes is guidance, including its building owner and facility manager material and its ambient standards, which are useful as outdoor reference points. The CDC and NIOSH Health Hazard Evaluation programme is the closest thing to a standard investigation methodology in the United States. Employers, employee representatives and unions can request an evaluation, and the published reports are a genuinely useful library of how similar complaints were resolved elsewhere.

California code: Title 24 Part 6 and CALGreen Part 11

Title 24 Part 6 Section 120.1 sets the minimum ventilation rate for nonresidential buildings and requires MERV 13 particle filtration on most mechanically ventilated systems. The 2025 Energy Code, which applies to permit applications from 1 January 2026, restructures the minimum ventilation calculation around a total outdoor airflow rate per unit floor area, with an exception for spaces of known design occupancy that allows the larger of an occupant based rate and an area based rate. The California Energy Commission publishes the standard and its compliance manuals.

CALGreen, Part 11 of Title 24 and administered through the California Building Standards Commission, carries the indoor environmental quality provisions. Section 5.504 covers pollutant control during construction: temporary ventilation with MERV 8 return filters if the permanent system is used, covering of duct openings from rough-in through startup, MERV 13 filtration before occupancy, and low emitting adhesives, sealants, paints, coatings, carpet, resilient flooring and composite wood tested against the CDPH standard method for chamber emissions testing. Section 5.506 requires outdoor air delivery meeting Energy Code Section 120.1 and carbon dioxide monitoring where demand control ventilation is used.

ASHRAE Standard 241 and voluntary programmes

Standard 241-2023, Control of Infectious Aerosols, is the framework for infection risk management. It requires compliance with the underlying ventilation standard first, then defines an Infection Risk Management Mode with equivalent clean airflow rates per person: 30 cfm per person for office space and 40 cfm per person for classrooms, achievable through any combination of outdoor air, filtration at MERV-A 11 or better, and air cleaning. It also requires a Building Readiness Plan, which is an assessment and commissioning obligation rather than a testing one.

On the voluntary side, LEED indoor environmental quality credits from the U.S. Green Building Council, the WELL Building Standard and RESET Air all set numeric targets. RESET is distinctive in requiring continuous monitoring with accredited monitors rather than periodic testing, with commercial interior targets of 35 micrograms per cubic metre for PM2.5, 500 micrograms per cubic metre for total volatile organic compounds, 1,000 ppm for carbon dioxide and 30 to 60 percent relative humidity.

7. Healthcare, Laboratories, Schools and Data Centres

Four building types change the question enough to deserve separate treatment.

Healthcare

In hospitals and outpatient facilities the governing document is not 62.1 but ASHRAE Standard 170, and the parameters that matter most are pressure relationship, air change rate and filtration efficiency by room type rather than contaminant concentration. Testing in this environment is largely airflow and pressure verification, repeated on a defined interval, with documentation that survives an accreditation survey. Our healthcare facilities work sits inside that regime routinely.

Laboratories

Laboratories invert the usual problem. The concern is containment and exhaust rather than supply, and the measurements that matter are fume hood face velocity, room pressure relative to adjacent corridors, and exhaust stack dispersion so that discharge is not re-entrained at an intake on the same roof. A general purpose IAQ survey in a laboratory answers almost none of the questions that actually matter, which is why laboratory and industrial projects need a different scope from day one.

Schools and universities

Classrooms are the highest occupant density and the lowest floor area per person in ordinary construction, so they generate the largest carbon dioxide signal and the fastest response to a ventilation failure. They are also where continuous monitoring pays back quickest, because the failure mode is frequently a unit ventilator that has been disabled for noise. Education projects benefit more from monitoring than almost any other sector.

Data centres and technical spaces

Occupied areas within mission critical facilities carry an unusual concern: gaseous contamination that attacks electronics rather than people. Corrosion coupon monitoring, using copper and silver reactivity classification, is the relevant test, and it is completely different from an occupant health survey. The two are often confused in scoping, with the result that the wrong test gets bought.

8. Screening, Investigation or Continuous Monitoring

The three approaches are not competing products. They answer different questions at different price points and different levels of evidential weight. The table below sets out how the choice usually resolves.

The pattern that works best for an owner with a portfolio is layered rather than exclusive. Continuous monitoring runs permanently to catch drift and intermittent faults. A screening survey handles routine complaints. A full investigation is held in reserve for the small number of situations that genuinely warrant it. Periodic reference grade testing keeps the sensor network calibrated, because an uncalibrated dashboard that everyone has stopped believing is worse than no dashboard at all. Sensor networks sit naturally alongside other smart building technologies and should be specified with the same rigour.

9. The Complaint Investigation Sequence

The order of operations is what separates a resolved complaint from an open one. Five steps, in this order, and only this order.

Step one: interview and complaint mapping

Before any instrument is unpacked, record who is affected, precisely where they sit, what the symptoms are, when they begin and end, whether they resolve away from the building and whether anything changed recently. Plot the affected workstations on a floor plan and overlay the air handling zones. A cluster confined to one zone points at that zone’s equipment. A cluster along an exterior wall points at the envelope or the perimeter system. A scatter across the floor with no pattern usually points somewhere other than the air.

Step two: walkthrough

Walk the affected space and the areas above, below and adjacent to it. Look for water staining, condensation, unusual odours, recent construction, new furniture, blocked diffusers, ceiling tiles moved for cabling and any local exhaust that has been disabled. Look hardest at what the tenant has changed, because a densified floor plate or a new print room accounts for a large share of complaints.

Step three: HVAC inspection and outdoor air verification

Open the air handling unit. Check the outdoor air damper position against the control command, the mixed air temperature against what the damper position implies, the filter condition and, most importantly, the filter seal. Pull the control trend logs for the affected period. Measure differential pressure between the space and its neighbours, the corridor, the stair and the outdoors.

This is where most investigations end. The finding is an outdoor air damper commanded to minimum and mechanically stuck below it, an economizer sequence overridden years ago during a noise complaint, a supply fan running at reduced speed after an energy retrofit that nobody rebalanced, or a building running net negative and pulling garage air up a lift shaft. None of those are contaminant problems and none of them are found by sampling.

Step four: targeted measurement

Only now does measurement make sense, and by this point it is targeted rather than exploratory. If the walkthrough found new millwork, sample for formaldehyde. If it found a print room, sample speciated VOCs at the room and at the complaint location. If it found garage pressure issues, log carbon monoxide at the affected floor and at the garage. Sample over a period that includes the complaint window, with a concurrent outdoor baseline throughout.

Step five: remediation and verification

Fix the cause, then re-measure to confirm. Where the fault is a control sequence, a damper actuator or a rebalance, the correction is cheap and the verification straightforward. Where it is capacity, the conversation becomes a design conversation. Either way the verification measurement is what closes the complaint with the tenant, and it belongs in the scope from the beginning.

Where flush-out fits

A building flush-out is a construction phase measure, not a complaint response. After finishes are installed and before occupancy, the system delivers a large volume of outdoor air to purge emissions from adhesives, coatings, carpet and furniture. The LEED Indoor Air Quality Assessment credit defines the most widely used version: 14,000 cubic feet of outdoor air per square foot of floor area, with the space held between 60 and 80 degrees Fahrenheit and relative humidity no higher than 60 percent, or a phased alternative allowing occupancy after 3,500 cubic feet per square foot with a minimum 0.30 cfm per square foot continuing until the full volume is delivered. It is voluntary in California. It is also energy intensive, and on a project without a certification driver the better investment is usually in low emitting material selection under CALGreen Section 5.504.4 in the first place.

Key Takeaways

• Decide what decision the testing will inform before you buy it. Complaint resolution, handover verification, certification and litigation support are four different scopes.
• Interview and map before you measure. The complaint pattern tells you where to put the instruments.
• Inspect the air handling unit and the control sequence before sampling. Most commercial complaints end here.
• Measure differential pressure early. Negative buildings import their own contaminants.
• Always take a concurrent outdoor baseline. An indoor number alone cannot separate a building problem from an ambient one.
• Carbon dioxide is a ventilation indicator, not a pollutant threshold. ASHRAE 62.1 sets no limit value for it.
• Know which numbers are enforceable. OSHA and Cal/OSHA PELs are. EPA ambient standards and voluntary programme thresholds are not.
• Continuous monitoring and one-off testing are complements. Monitor for trend, test for defensibility, and calibrate one against the other.

10. Where Budlong Works

Indoor air quality problems are local in a way energy problems are not. Outdoor air quality varies enormously between a Bay Area campus and an inland Southern California site, wildfire smoke exposure differs by region and season, and jurisdictions vary in how they enforce CALGreen construction pollutant control. Budlong maintains teams across California so both the code experience and the climate experience sit behind the work, as set out on our company story page.

Sectors where air quality testing comes up most

Commercial landlords face tenant complaints as a recurring operational cost. Healthcare carries pressure and filtration verification as an accreditation obligation. Education generates the strongest ventilation signal and the fastest complaint response. Laboratories need containment verification rather than an occupant survey.

11. Related Reading

12. Frequently Asked Questions