Air Quality Monitoring in Social Housing: Beyond Humidity

While damp and mould rightly dominate housing discussions, air quality encompasses more than humidity alone. Poor indoor air quality affects tenant health, cognitive function, and wellbeing—and can indicate underlying issues with ventilation and building performance.

Key Air Quality Parameters

Carbon Dioxide (CO2)

CO2 is the primary indicator of ventilation adequacy:

• Outdoor air contains around 400-450 ppm CO2
• Exhaled breath contains approximately 40,000 ppm
• Indoor levels rise as people breathe and ventilation dilutes

What the Levels Mean

Health Effects

Elevated CO2 is associated with:

• Drowsiness and reduced cognitive function
• Headaches
• Difficulty concentrating
• General stuffiness and discomfort

Volatile Organic Compounds (VOCs)

VOCs are chemicals that evaporate at room temperature:

• Sources: Paints, cleaning products, furniture, flooring, air fresheners
• Newly decorated: Properties often have elevated VOCs
• Health effects: Eye, nose, throat irritation; headaches; in some cases more serious effects

Common VOCs in Housing

• Formaldehyde (composite wood products, some textiles)
• Benzene (tobacco smoke, car exhaust)
• Toluene (paints, adhesives)
• Limonene (cleaning products, air fresheners)

Particulate Matter (PM2.5 and PM10)

Tiny particles suspended in air:

• PM10: Particles under 10 micrometers (dust, pollen)
• PM2.5: Particles under 2.5 micrometers (smoke, combustion)
• Sources: Cooking, smoking, candles, outdoor pollution infiltration

Health Effects

Particulates are associated with:

• Respiratory problems
• Cardiovascular effects
• Particular risk for vulnerable groups

Why Air Quality Matters for Housing

Tenant Health

People spend 90% of their time indoors. Indoor air quality directly affects:

• Respiratory health
• Sleep quality
• Cognitive function and productivity
• General wellbeing

Ventilation Assessment

CO2 monitoring provides objective evidence of ventilation performance:

• Validates whether ventilation systems are working
• Identifies properties with inadequate fresh air supply
• Informs decisions about ventilation improvements

Retrofit Verification

When improving building airtightness:

• Reduced air infiltration should be compensated by mechanical ventilation
• CO2 monitoring confirms ventilation strategy is adequate
• Identifies properties where retrofit has created problems

Monitoring Approaches

CO2 Sensors

Relatively mature and affordable technology:

• NDIR (non-dispersive infrared) sensors are accurate and stable
• Can be included in multi-parameter sensors
• Real-time readings enable immediate feedback

VOC Sensors

More complex than CO2:

• Usually measure total VOC (TVOC) not individual compounds
• Metal oxide sensors are common but need calibration
• PID sensors more accurate but more expensive

Particulate Sensors

Available in various forms:

• Optical sensors can detect PM2.5 and PM10
• Lower-cost sensors have accuracy limitations
• Useful for indicating relative levels and trends

Practical Applications

Ventilation System Verification

CO2 monitoring can confirm:

• MVHR systems: Delivering expected air change rates
• PIV systems: Achieving adequate dilution
• Natural ventilation: Whether it's sufficient
• Extractor fans: Making meaningful difference

Occupancy Pattern Analysis

CO2 correlates with occupancy:

• Indicates when property is occupied
• Helps understand usage patterns
• Useful for void property monitoring

Post-Retrofit Monitoring

After fabric improvements:

• Confirm ventilation is adequate in more airtight property
• Identify if mechanical ventilation is needed
• Track VOC levels after decoration works

Interpreting Results

Contextual Factors

Consider when interpreting data:

• Occupancy: More people = higher CO2
• Time of day: Bedrooms higher overnight
• Season: Winter typically worse (windows closed)
• Outdoor conditions: Urban areas may have higher baseline PM

Trends vs. Absolutes

Don't over-react to single readings:

• Peaks during cooking are normal
• Recovery time matters more than peak level
• Persistent elevation indicates systematic issue

The Link to Damp and Mould

Ventilation Connection

High CO2 and high humidity often go together:

• Both indicate inadequate ventilation
• Addressing ventilation helps both problems
• CO2 can be an earlier indicator of ventilation problems

Comprehensive Assessment

Multi-parameter monitoring provides fuller picture:

• Temperature and humidity for damp risk
• CO2 for ventilation adequacy
• Together they inform root cause diagnosis