Which buildings are most at risk?

Sealed, mechanically ventilated buildings constructed between the 1980s and early 2000s carry the highest historical burden. Modern airtight buildings without correctly sized mechanical ventilation are emerging as the new at-risk category, particularly where post-occupancy commissioning was incomplete.

How is SBS investigated?

Through a structured pathway: occupant symptom survey across affected and control zones, walk-through audit of HVAC and finishes, multi-day measurement of CO₂, PM, VOCs, humidity and temperature, and targeted laboratory sampling where the survey points to a specific source.

How long does remediation usually take?

Targeted ventilation upgrades and source removal typically resolve symptoms within two to eight weeks. Cases requiring AHU replacement or full ductwork cleaning can take a season. Verification re-measurement is essential before declaring an investigation closed.

Can SBS recur after remediation?

Yes, particularly where the underlying engineering cause is addressed but the operational regime is not. Filters revert to a previous grade, demand-controlled ventilation is overridden, or a new material is introduced without checking emissions. Continuous monitoring is the standard guard against recurrence.

How does sick building syndrome usually present in a modern UK office?

Sick building syndrome typically presents as a cluster — more than 20% of occupants in one zone reporting two or more symptoms (headache, eye irritation, fatigue, throat irritation) that resolve on leaving the building. The pattern, not the individual symptom, is the diagnostic signal. Continuous indoor air monitoring, a ventilation assessment and speciated VOC testing together identify the engineering cause behind the cluster.

Health publication

Sick Building Syndrome

A cluster of acute symptoms experienced by occupants of a building that improve when they leave. Recognising, diagnosing and remediating SBS is one of the most impactful interventions in occupational health.

Reviewed by IAQ specialists Updated 2026 Based on WHO and CIBSE guidance

Definition

What sick building syndrome actually describes

Sick building syndrome describes a recognisable cluster of acute symptoms — headache, fatigue, eye and throat irritation, difficulty concentrating, dry skin — that appears in a significant proportion of occupants of a particular building and resolves when those occupants leave. It is an environmental health phenomenon rather than a medical diagnosis. The symptoms are real and reproducible; the mechanism is the building, not the individual.

The WHO formalised the concept in 1983, setting a threshold of 20% or more of occupants reporting two or more relevant symptoms that resolve on leaving. That threshold remains the working trigger for a formal investigation today.

SBS sits at the intersection of building services, occupational health and HR. Left unaddressed it produces persistent absenteeism, declining engagement, and — increasingly — formal grievance processes. Addressed early, it usually traces to a small number of correctable engineering causes.

Recognising SBS

Six symptom clusters to watch

If two or more of these symptoms appear in a significant share of occupants, and resolve when leaving the building, SBS should be investigated.

Cognitive

Difficulty concentrating, mental fatigue, brain fog.

·Drop in productivity
·Headaches by mid-afternoon

Sensory irritation

Dry, itchy or burning eyes; throat irritation.

·Often worse near printers
·Improves outdoors

Respiratory

Coughing, congestion, asthma exacerbation.

·Linked to filter quality
·Worse in winter

Allergic-like

Skin rash, sinus pressure, sneezing.

·Often dust and humidity related
·May indicate mould

General malaise

Drowsiness, nausea, lethargy without cause.

·Common with high CO₂
·Resolves on leaving

Cluster signal

Over 20% of occupants report two or more symptoms.

·Triggers formal investigation
·Map by zone

“

A building is considered 'sick' when more than 20% of its occupants experience symptoms that resolve on leaving, with no specific medical diagnosis identified.

— WHO classification, 1983

Sealed 1990s office building with mirrored glass facade

Causes

Why buildings make people sick

SBS rarely traces to a single agent. It emerges from compounding stressors: under-ventilation, elevated CO₂ and VOCs, dry or damp air, dusty HVAC systems, irritating lighting and acoustic load. Each contributor is below the threshold that would trigger an individual complaint; together, they produce the symptom cluster.

The historical preconditions are well documented. Sealed buildings constructed in the 1980s and 1990s with fixed-rate mechanical ventilation, internal finishes that off-gas formaldehyde and other VOCs, and HVAC maintenance regimes that lapsed within the first decade of life. The modern equivalent is an airtight building with under-sized ventilation, where the engineering response to one problem (heat loss) has created another (poor dilution of indoor sources).

Occupant density has become the new amplifier. Hot-desking and hybrid working compress occupancy into two or three days a week, on which the original ventilation design is asked to do more than it was sized for. The pattern of complaints — quiet Mondays and Fridays, symptomatic Tuesdays through Thursdays — is now a recognisable diagnostic signal.

Engineering causes

The five recurring root causes

Under-ventilation is the most common single cause. Where outdoor air supply falls below 10 l/s/person, CO₂ climbs through the day, bioeffluents accumulate, and the perception of stale air becomes universal.

Contaminated AHUs — dirty cooling coils, biofilm in drip trays, dust in supply ducts — push microbial and particulate exposure into the supply air itself. The signature is symptoms that worsen when the AHU runs, not when it stops.

Material off-gassing from recent refurbishment produces a formaldehyde and VOC peak that takes weeks to months to decay. Symptom onset that maps to a fit-out date is the strongest single indicator.

Humidity extremes below 30% or above 60% RH drive sensory irritation directly and amplify other contaminants. Low humidity is the dominant pattern in heated UK offices in winter.

Source proximity — printer banks, kitchenettes, photocopier rooms vented into the open-plan area — concentrates exposure for nearby desks without affecting the building average. Symptom mapping by desk location reveals it quickly.

Diagnostic pathway

How specialists investigate SBS

1
Stage 01
Occupant survey
Standardised symptom questionnaires across affected and unaffected zones to establish prevalence and rule out clustering by team rather than location.
2
Stage 02
Walk-through audit
Visual inspection of HVAC plant, supply terminals, finishes, water damage, refurbishment history and pollutant sources. Often identifies the root cause before measurement begins.
3
Stage 03
IAQ measurement
Multi-day continuous monitoring of CO₂, PM2.5, VOCs, humidity, formaldehyde and temperature in the affected zone. Sorbent-tube sampling for laboratory speciation where TVOC is elevated.
4
Stage 04
Targeted remediation
Ventilation increase, source removal, AHU clean, filter upgrade and material substitution — sequenced by impact and cost. Verification re-measurement closes the investigation.

Bright renovated office with fresh air and plants

Remediation

What actually fixes SBS

Most SBS cases resolve once two or three of the underlying causes are addressed. Bringing outdoor air supply up to BS EN 16798-1 Category II is the single intervention with the largest effect. AHU cleaning and filter upgrade to ISO ePM1 50% follows. Source removal — venting printer banks, switching cleaning chemistry, replacing a recently installed material — closes the gap.

The pattern of recovery is consistent. CO₂ and symptom reports respond within days. VOC levels fall over weeks as the material reservoir is depleted. Mould-related cases require the moisture source to be eliminated before any IAQ improvement is measurable.

What does not work: standalone air purifiers used as a substitute for ventilation; aromatherapy and odour-masking products that add to the VOC load; cosmetic responses such as repainting that introduce fresh emissions. SBS is engineering theatre's most reliable trap.

See how a structured IAQ investigation is run →

FAQ

Common questions about SBS

No. SBS is an environmental health phenomenon, not a clinical diagnosis. Symptoms are real and measurable, but they cannot be attributed to a specific pathogen or chemical. The defining feature is that they correlate with occupancy of the affected building and resolve when occupants leave it.

Suspect SBS in your building?

Independent IAQ investigation is the fastest path from suspicion to evidence-led remediation.

Request an investigation

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