It usually starts with a few complaints. Someone in accounting gets headaches every afternoon. A tenant on the third floor says the air feels stale. Several employees mention itchy eyes and fatigue that seem to clear up on the drive home. Individually, each complaint is easy to dismiss. Together, they may point to sick building syndrome.
Pinning down what causes sick building syndrome is rarely simple, and a single pollutant is seldom to blame. But in most cases, HVAC systems are involved, either as the source of the problem or as the defense that isn’t doing its job. Ventilation, humidity control, filtration, and air distribution all shape indoor air quality, and when any of them falls short, building occupants feel it.
This guide explains what sick building syndrome is, why it matters to facility managers, how to connect complaint patterns to HVAC causes, and how monitoring and proactive maintenance keep a building from becoming a sick building.
What SBS Is and What It Isn’t
Sick building syndrome (SBS) describes a situation in which building occupants experience acute health and comfort effects that appear to be tied to time spent in a particular building, but no specific illness or exact cause can be identified. Complaints may cluster in a single room or zone, or they may show up in different places throughout the building.
That lack of a single identifiable cause is what makes SBS frustrating for facility managers. It isn’t a diagnosis. It’s a pattern that suggests something about the indoor environment isn’t right.
Common Symptoms Occupants Report
Sick building syndrome symptoms tend to be nonspecific, which is part of why they are easy to overlook. Common symptoms include:
- Headaches, fatigue, and difficulty concentrating
- Eye, nose, and throat irritation
- Dry cough
- Dry or itchy skin and other skin irritation
- Dizziness and nausea
- Sensitivity to odors
Any one of these possible symptoms could have an everyday explanation. The telling sign is timing: most people who experience them report relief soon after leaving the building.
How SBS Differs From Building-Related Illness
Building-related illness (BRI) is a different category. Occupants report symptoms such as cough, chest tightness, fever, chills, and muscle aches, and those symptoms can be clinically diagnosed and traced to an identifiable source in the building. Examples include Legionnaires’ disease, hypersensitivity pneumonitis, building-related asthma triggered by specific allergens, and carbon monoxide exposure. Unlike SBS, recovery from BRI may take time even after leaving the building.
The distinction matters because the response is different. Suspected BRI calls for medical evaluation, immediate source remediation, and in some cases involvement from public health authorities, particularly with conditions like Legionnaires’ disease. SBS calls for a systematic investigation of building conditions, starting with the HVAC system. Facility managers should also keep in mind that some complaints may have causes outside the building entirely, which is why a structured investigation matters.
Why SBS Is a Facility Management Problem
Sick building syndrome is often treated as a comfort issue. For facility managers and building owners, it is also a business issue, and one that is more common than many assume. EPA has cited a World Health Organization report suggesting that up to 30 percent of new and remodeled buildings may generate excessive indoor air quality complaints.
When buildings suffer from unresolved air quality problems, the effects spread well beyond the occupants who report them:
- Escalating complaints: A few informal comments can turn into formal complaints, increased symptoms reported across more occupants, and pressure on property management to act quickly
- Productivity and attendance: Headaches, fatigue, and difficulty concentrating affect work quality, and occupants who feel unwell at work are more likely to take time off
- Tenant retention: Tenants who associate a building with discomfort or health concerns are less likely to renew, and a building’s reputation for poor air can follow it into future leasing
- Liability exposure: When complaints arise, how a building responded matters. Documented investigations, maintenance records, and corrective actions show that concerns were taken seriously; a lack of records makes that harder to demonstrate
Providing a healthy environment supports occupant well-being, but it also protects occupancy, revenue, and the building’s long-term value. The good news is that many of the conditions behind SBS trace back to building systems that facility teams can measure, maintain, and correct.
Reading SBS Symptoms to Find the HVAC Cause
SBS symptoms rarely point to a single cause on their own, but the pattern behind them often does. When and where complaints occur, and what occupants describe, can help facility teams identify which part of the HVAC system to investigate first.
| Complaint Pattern | Likely HVAC-Related Cause | What to Check |
| Stuffiness, drowsiness, and headaches that worsen as the day goes on | Poor ventilation relative to occupancy | CO2 trends, outdoor air damper position, minimum ventilation settings, ventilation schedules |
| Dry eyes, dry skin, and throat irritation, mostly in winter | Low humidity during the heating season | Relative humidity levels, humidification equipment |
| Musty odors or allergy-like symptoms | Moisture and microbial growth | Drain pans, cooling coils, duct insulation, relative humidity |
| Complaints concentrated in one area | Uneven air distribution | Airflow to the zone, VAV box settings, recent layout or occupancy changes |
| Exhaust, garage, or outdoor odors | Negative building pressure or intake placement | Building pressurization, outdoor air intake locations, nearby pollutant sources |
| Chemical odors or irritation after renovations, new furnishings, or changes in cleaning products | Emissions from new materials not being diluted | Ventilation rates during and after work, flush-out practices |
| General discomfort with hot and cold complaints | Poor temperature control or distribution | Thermostat locations, zone temperatures, system balance |
This kind of mapping won’t confirm a cause by itself, but it narrows the investigation. When one area reports more symptoms than others, or complaints follow a clear daily or seasonal rhythm, the pattern often points directly to a ventilation, humidity, or distribution problem that can be measured and corrected.
How HVAC Systems Create a Sick Building
Many discussions of what causes sick building syndrome focus on the contaminants: volatile organic compounds, dust, mold, and chemical odors. But in most buildings, those contaminants become a problem because the HVAC system isn’t diluting, removing, or keeping them out. These are the HVAC conditions that most often create a sick building.
Ventilation Cutbacks and Tight Building Syndrome
SBS is sometimes called tight building syndrome, a name that traces back to the 1970s. After the 1973 oil embargo, energy conservation measures reduced the outdoor air supplied to commercial buildings, while new construction became tighter and many buildings were designed with sealed windows. Complaints rose, and the American Society of Heating, Refrigerating and Air-Conditioning Engineers later increased its recommended ventilation rates.
The same tradeoff still happens today, usually without anyone deciding it on purpose. Common causes of inadequate ventilation include:
- Outdoor air dampers stuck closed or improperly adjusted
- Economizers disabled or failed
- Minimum outdoor air settings reduced to save on heating and cooling costs
- Ventilation schedules that start after occupants arrive
- Occupancy that has grown beyond what the system was designed to serve
Without enough fresh air, pollutants from people, furnishings, and equipment accumulate throughout the day. Standard 62.1 sets minimum ventilation rates for commercial spaces, and systems that fall below them are a common thread in SBS investigations.
Humidity and Moisture Problems
Humidity that is too low, typically during cold-weather heating seasons, dries out eyes, skin, and airways. Humidity that is too high creates conditions for mold growth and other biological contaminants, which can trigger allergic reactions and respiratory issues in sensitive occupants.
HVAC systems can also become moisture sources themselves. Clogged or poorly draining condensate pans, wet duct insulation, and dirty cooling coils can all support indoor mold within the system, where air passing over it distributes spores throughout the building. Oversized cooling equipment that short-cycles removes less moisture, leaving spaces cool but clammy.
Filtration Gaps
Filters capture dust, pollen, and other particulates before they reach occupied spaces, but only if they are the right efficiency, installed correctly, and replaced on schedule. Gaps around filter frames let air bypass the filter entirely, and overloaded filters reduce airflow. Many commercial air handlers can support higher-efficiency MERV-rated filters, but HEPA filtration usually requires fans and housings that central systems aren’t built for. Matching filter efficiency to what the equipment can handle prevents trading poor air quality for poor airflow.
Stagnant Air Zones
A system that performed well when installed can create poor indoor air quality after a building changes. Tenant fit-outs add walls without rebalancing airflow. Open offices become private offices and conference rooms. Thermostats get relocated, VAV box minimums get turned down, and occupancy rises beyond the original design. The result is a range of pockets where supply air barely reaches, and the presence of stale air in those zones often shows up as localized complaints.
Pressurization and Outdoor Air Intake Problems
When a building operates under negative pressure, it pulls air in through doors, gaps, and shafts, bringing indoor air pollution in with it. Parking garages, loading docks, and nearby exhaust can introduce carbon monoxide and other chemical contaminants. Outdoor air intakes placed near dumpsters, loading areas, or exhaust outlets can draw pollutant sources directly into the supply air. Combined with emissions from new building materials and furnishings, these pathways can keep contaminant levels elevated even when ventilation rates look adequate on paper.
What to Monitor: CO2, Humidity, and Indoor Temperature
Most SBS investigations begin after complaints arrive. Monitoring flips that sequence, giving facility teams a way to spot deteriorating conditions before occupants notice them. A handful of metrics cover most of the HVAC-related causes of poor indoor environmental quality:
| Metric | What It Indicates | General Guidance |
| Carbon dioxide (CO2) | Whether outdoor air ventilation is keeping up with occupancy | Not a direct health concern at typical indoor levels; in typical offices, levels about 700 ppm above outdoor air (roughly 1,000 to 1,200 ppm) suggest ventilation may be falling short |
| Relative humidity | Moisture balance for comfort and mold prevention | Below 60%, ideally 30% to 50% |
| Indoor temperature | Thermal comfort and system control | Stable temperatures within the comfort range for the season, with minimal swings between zones |
| Particulates (PM2.5) | Filtration performance and infiltration | Indoor levels consistently at or below outdoor levels; spikes point to filtration gaps or indoor sources |
| Total VOCs | Chemical emissions from materials, furnishings, and products | No single standard; track trends and investigate sharp increases |
CO2 deserves a note of caution. It is a useful indicator of ventilation relative to the number of people in a space, but it doesn’t measure other contaminants, so low CO2 alone doesn’t guarantee healthy indoor air.
Spot checks with handheld meters are useful during investigations, but continuous sensors connected to the building automation system provide far more value. Trend data shows how conditions change through the day and across seasons, reveals which zones drift out of range, and can trigger alerts before small problems become complaints. It also creates a record of indoor air quality that supports tenant communication and documentation.
Proactive Maintenance That Prevents SBS
Most HVAC-related risk factors for sick building syndrome develop gradually. Dampers drift, drain pans clog, filters load up, and sensors lose accuracy long before occupants start to complain. A maintenance program built around indoor air quality catches these conditions early.
| Maintenance Task | Typical Frequency | SBS Risk It Addresses |
| Verify outdoor air damper operation and economizer function | Quarterly, and after controls changes | Inadequate ventilation |
| Inspect filters for loading, fit, and bypass; replace as needed | Monthly inspection, replacement based on pressure drop or schedule | Particulates and airflow restriction |
| Inspect and clean drain pans and cooling coils | Quarterly during cooling season, cleaning as needed | Mold and microbial growth |
| Check humidification and dehumidification equipment | Before each heating and cooling season | Dry air or excess moisture |
| Calibrate CO2, humidity, and temperature sensors | Annually or per manufacturer guidance | Controls acting on inaccurate data |
| Inspect outdoor air intakes and surroundings | Semiannually | Re-entrainment of exhaust and nearby pollutants |
| Rebalance airflow | After layout, occupancy, or tenant changes | Stagnant air zones |
Frequencies should be adjusted for the building’s equipment, climate, and occupancy, and many teams align their programs with ASHRAE Standard 180 for inspection and maintenance of commercial HVAC systems.
Just as important as the maintenance itself is the record of it. Documented inspections, readings, and corrective work show that a building’s systems are being actively managed, which helps address occupant concerns quickly and demonstrates diligence if complaints escalate. Consistent records also reveal patterns, such as a zone that repeatedly drifts out of range, that contribute to recurring problems.
Responding to Occupant Complaints
When complaints do arrive, a consistent process helps facility teams find the cause faster and shows occupants their concerns are being taken seriously:
- Log every complaint: Record the person’s location, the time, the symptoms described, and whether they improve after leaving the building
- Map the pattern: Plot complaints on a floor plan to see whether they cluster by zone, floor, time of day, or season
- Check the likely causes: Use the complaint pattern to prioritize what to measure, such as CO2 and damper position for stuffiness, or humidity and drain pans for musty odors
- Escalate when warranted: Symptoms such as fever, chest tightness, or lingering effects after leaving the building may indicate building-related illness and call for medical evaluation and immediate investigation of potential sources
- Communicate and follow up: Share findings and corrective actions with occupants, then verify with follow-up readings and check-ins that conditions have improved
Documenting each step creates a clear record of the building’s response and helps identify recurring issues over time.
Improve Your Indoor Air Quality With Ambient Enterprises
Sick building syndrome is rarely solved by a single fix, but the HVAC system is almost always part of the answer. Ambient Enterprises provides indoor air quality assessments that trace occupant complaints to their HVAC causes, from ventilation shortfalls and humidity problems to filtration gaps and stagnant air zones.
From there, we handle the remediation, including damper and economizer repairs, rebalancing, humidity control improvements, filtration upgrades, and monitoring systems that keep conditions on track. The result is a healthy environment for occupants and fewer complaints for your team to manage.
Contact our team to schedule an indoor air quality assessment for your building.