Preliminary Indoor Air Quality Screening
As part of my home inspection, I perform preliminary indoor air quality screening at no additional charge. The purpose is not to provide a laboratory analysis of everything in the air. Instead, these measurements provide useful information about ventilation and general indoor air conditions at the time of the inspection.
I measure carbon dioxide (CO₂), airborne particulate matter and volatile organic compounds (VOCs). These readings can help identify conditions that may warrant improved ventilation, filtration, source control or further investigation.
Carbon Dioxide and Ventilation
Carbon dioxide is produced naturally by people breathing inside the home. As occupancy increases, CO₂ levels normally rise. Ventilation and air exchange help remove that accumulated CO₂ and replace indoor air with outdoor air.
For this reason, CO₂ can be useful as an indicator of how effectively a home is exchanging air.
Health Canada recommends a long-term residential CO₂ exposure limit of 1,000 parts per million (ppm), based on a 24-hour average. A reading taken during a home inspection is only a snapshot and should not be interpreted as a 24-hour exposure test.
Instead, I use the reading as a preliminary indication of the ventilation conditions present at the time of the inspection.
Occupancy, whether windows have recently been opened, operation of exhaust fans or mechanical ventilation, weather conditions and other factors can all affect the reading.
Particulate Matter and VOCs
I also measure airborne particulate matter and VOC levels.
Particulate levels can be affected by many normal activities, including:
- Cooking
- Cleaning
- Showering
- Candles or fireplaces
- Smoking or vaping
- Pets
- Renovation or construction activity
- Outdoor air entering the building
VOC readings can also be affected by cleaning products, paints, adhesives, furniture, building materials, fragrances and numerous household products.
Because I do not know everything that occurred inside the home before arriving for the inspection, these measurements need to be interpreted in context.
A low reading is useful information. It indicates that significant concentrations were not detected by the screening equipment under the conditions present at the time of testing.
An elevated reading does not automatically mean that there is a serious indoor air quality problem. It means we should consider why the reading is elevated.
What If the Readings Are Elevated?
If CO₂, particulate matter and VOC levels are all elevated, inadequate ventilation may be contributing to the conditions.
However, simply increasing ventilation is not always the complete answer.
The first step is to consider:
- Current outdoor air quality
- Occupancy
- Activities taking place inside the home
- Filtration
- Operation of exhaust fans or mechanical ventilation
- Possible indoor sources of pollutants
- Combustion appliances
- Recent renovations, cleaning or other activities
Under typical conditions, bringing clean outdoor air into a home can reduce concentrations of pollutants generated indoors.
However, outdoor air quality also needs to be considered. Wildfire smoke, smog, industrial emissions, nearby construction and other temporary or localized conditions can increase outdoor particulate levels. During poor outdoor air-quality conditions, increasing outdoor ventilation may actually introduce additional contaminants into the home.
For that reason, ventilation recommendations should always be considered together with current outdoor air conditions, filtration and the likely source of the elevated reading.
What If Particulates or VOCs Are Elevated but CO₂ Is Low?
When CO₂ is relatively low but particulate matter or VOC readings are elevated, poor overall air exchange may be less likely to be the primary cause.
The next step is to look for a potential source.
This could include cooking, cleaning products, smoking, fireplaces, construction activity, furnishings, outdoor pollution or another identifiable source.
If no source is apparent, retesting after taking possession of the home may provide more useful information because the conditions inside the house can then be controlled.
What These Tests Do — and Do Not — Tell You
These measurements are best described as preliminary indoor air quality screening.
They measure the amount or concentration of certain categories of airborne contaminants detected by the equipment. They do not identify every individual substance present in the air.
Laboratory air sampling is different. Depending on the type of investigation, air is collected and analyzed to identify or quantify specific materials or contaminants.
That type of testing can be useful when there is a specific question that needs to be answered. However, laboratory testing is not automatically necessary simply because someone is concerned about indoor air quality.
My approach is to start with the building.
If the preliminary readings are low and there are no other indications of a problem, more extensive laboratory testing may provide little additional useful information.
If something unusual is identified, the next step should be targeted toward determining the source rather than automatically ordering every available test.
What About Mould?
My approach to mould concerns starts with moisture.
Mould requires moisture to grow. When mould or suspected mould is observed, the most important step is usually to determine why the area became damp and correct the moisture source.
In most cases, identifying the specific type of mould does not change the required building repair. The moisture problem still needs to be corrected and mould-contaminated materials need to be properly cleaned or removed as appropriate.
Mould swab testing is available when there is a specific reason to identify the material. This may be useful, for example, where an occupant has a particular medical sensitivity and their healthcare professional has requested additional information.
Testing may also be appropriate in unusual situations where mould is suspected but the source has not been identified through a thorough building and moisture investigation.
My preference is not to recommend laboratory testing unless the result is likely to answer a useful question.
Asbestos Testing
Asbestos cannot be reliably identified simply by looking at a building material. When a suspect material is present and confirmation is important, a sample can be collected and submitted to a laboratory for analysis.
The presence of asbestos does not automatically mean that the material needs to be removed.
Non-friable asbestos-containing materials that are in good condition and left undisturbed can often remain safely in place or, depending on the circumstances, be covered or encapsulated rather than removed.
However, materials associated with heating ducts, boots and other air-handling components deserve additional consideration. The exposed surface may appear to be in good condition while portions of the material concealed behind or against the ductwork cannot be inspected. Those concealed areas may be deteriorated or subject to vibration, air leakage or turbulence.
Because the hidden condition cannot always be determined visually, asbestos-containing material located at or around HVAC duct connections should be treated more cautiously, particularly where there is a possibility that deteriorated material could communicate with the air stream.
Testing is also particularly important before renovation, drilling, cutting, sanding or other work that may disturb a suspect material.
If asbestos is confirmed, the appropriate response depends on the material, its condition, location and whether it will be disturbed. In many cases intact material can remain in place. Where deterioration, disturbance or potential exposure to the HVAC air stream is a concern, further assessment or appropriate remediation should be considered.
What About Radon?
Radon is different from the preliminary measurements described above.
Radon levels fluctuate significantly, and a short measurement taken during the limited time available for a home inspection cannot reliably determine the home’s long-term radon exposure.
Health Canada recommends long-term radon testing for a minimum of three months.
For that reason, I recommend that homeowners perform a long-term radon test after taking possession of the home rather than relying on a short-duration reading during the home inspection.
The Goal of Preliminary Screening
The purpose of these measurements is not to convince every client that they need expensive laboratory testing.
The goal is to gather additional information about how the home is performing.
CO₂ can provide information about ventilation conditions. Particulate and VOC readings can identify situations that deserve closer attention. Moisture investigation can help locate conditions associated with mould growth. Laboratory testing can then be used when there is a specific reason to identify a material or contaminant.
It is a practical starting point that adds useful information to the home inspection without automatically adding unnecessary testing or expense.
