How to Read Your Mould Air Test Results, A Homeowner’s Guide to Lab Reports in Winnipeg
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- 17 min read
Introduction
Why Mould Lab Reports Are Confusing
Receiving a mould air test lab report can be stressful, especially if you are already dealing with moisture issues, health concerns, or visible mould in your home. Most lab reports are written for inspectors, industrial hygienists, or remediation professionals trained in the terminology and process, not for homeowners. They are filled with scientific names, numerical spore counts, abbreviations, and technical notes that are difficult to interpret without experience. Many people are left wondering if their home is “safe,” whether they need remediation, or if the numbers mean something serious.
One of the biggest challenges with mould air testing is that mould spores exist naturally in outdoor air. It is normal for mould to be present indoors at low levels, even in clean and well-maintained homes. A lab report does not give a simple yes or no answer. Instead, it provides data that must be interpreted in context. This includes how indoor spore levels compare to outdoor levels, what types of mould spores are present, whether the building is occupied or unoccupied, recent water damage history, visible mould, odours, humidity levels, and construction details that may allow moisture to build up inside wall cavities.
Homeowners also tend to assume that air testing alone can diagnose a mould problem. In reality, mould air testing is only one tool in a broader assessment process. Without understanding moisture conditions, building materials, airflow patterns, and potential hidden growth areas, air results can be misleading. Low numbers do not always mean there is no mould problem, and higher numbers do not automatically mean a home is unsafe. The value of the report comes from proper interpretation and pairing the data with what is happening inside the building.
A Relief Restorations Winnipeg mould air testing lab report is designed to support informed decision-making. It does not stand alone. Our standard reporting includes a summary of findings written in plain language, a picture index so clients can visually reference areas of concern, and practical recommendations based on what we observed during the inspection and testing process. This approach helps homeowners understand not just the numbers on a page, but what those numbers actually mean for their specific property and next steps.
Relief Restorations provides detailed reports when completing mould inspections or testing. Lab results will come with a report summary and include any recommendations to make things easy to interpret.
Mould Test Results, What This Report Is Actually Telling You
Mould test results are not a diagnosis on their own. They are a snapshot of airborne spore levels at the time and location of sampling. Air samples capture spores that are present in the air during a short sampling window, which means results can be influenced by airflow, recent cleaning, recent disturbances, weather conditions, and how the building is being used. This is why results must be interpreted carefully and in context.
A mould air test measures the concentration and types of airborne spores in a specific area. These results are then compared to outdoor air samples and to established internal criteria used to flag potentially elevated mould conditions. The purpose is to identify abnormal indoor mould patterns that may indicate hidden growth, moisture problems, or contamination following water damage.
We use specific criteria to assess whether mould spore levels are elevated based on whether a space is occupied or unoccupied. This distinction matters because unoccupied spaces such as crawlspaces, mechanical rooms, or vacant areas often tolerate higher background spore levels than living spaces.
Our criteria for elevated mould counts are as follows:
For occupied areas:
Cladosporium is considered elevated at 300 spores per cubic metre plus 3 times the outdoor level.
Alternaria is considered elevated at 100 spores per cubic metre plus 3 times the outdoor level.
Aspergillus/Penicillium is considered elevated at 200 spores per cubic metre plus 2 times the outdoor level.
Stachybotrys, Chaetomium, and Ulocladium are considered elevated at 35 spores per cubic metre plus 2 times the outdoor level.
Other moulds are considered elevated at 100 spores per cubic metre plus 2 times the outdoor level.
For unoccupied spaces:
Cladosporium is considered elevated at 600 spores per cubic metre plus 3 times the outdoor level.
Alternaria is considered elevated at 200 spores per cubic metre plus 3 times the outdoor level.
Aspergillus/Penicillium is considered elevated at 400 spores per cubic metre plus 2 times the outdoor level.
Stachybotrys, Chaetomium, and Ulocladium are considered elevated at 70 spores per cubic metre plus 2 times the outdoor level.
Other moulds are considered elevated at 200 spores per cubic metre plus 2 times the outdoor level.
These criteria are used to identify patterns that suggest indoor mould amplification, meaning mould is likely growing somewhere within the building. The presence of certain water-damage indicator moulds such as Stachybotrys, Chaetomium, or Ulocladium indoors is more concerning than the presence of common outdoor moulds like Cladosporium or Basidiospores. However, even common outdoor moulds can indicate an indoor issue if indoor levels are significantly higher than outdoor levels.
It is also important to understand that mould test results can vary from room to room. A basement may show elevated counts while upper floors do not, or one bedroom may show abnormal levels due to hidden moisture behind a wall. This is why sampling locations are selected strategically based on building layout, moisture patterns, odours, and reported concerns. A single sample rarely tells the full story in larger homes or complex buildings.
What is an unoccupied space?
An unoccupied space is any area of a building that is not regularly used as a living or working space and is not intended for daily occupancy. These areas typically have different ventilation patterns, temperature conditions, and background mould levels compared to living spaces, which is why mould spore count criteria are higher for unoccupied areas.
Common examples of unoccupied spaces include:
Crawlspaces and subfloors
Mechanical rooms and utility rooms that aren't in frequent use
Furnace rooms that aren't in frequent use
Attics that are not finished living space
Storage rooms that are not regularly occupied
Vacant units or rooms not currently being lived in
Unfinished basements that are not used as living areas and rarely accessed
Service shafts and enclosed utility chases
Occupied spaces are areas where people spend regular time, such as bedrooms, living rooms, kitchens, offices, and finished basements used as living space.
What Is a Mould Air Test and When Is It Useful
A mould air test is a method of collecting airborne particles using a calibrated pump and spore trap cassette. Air is drawn through the cassette for a set period of time, and particles are captured on a collection surface. The cassette is then sent to a laboratory where a trained analyst identifies and counts mould spores under a microscope. The results provide a breakdown of spore types and concentrations for each sampled location.
Air testing is useful when there is a reason to suspect hidden mould growth, such as persistent musty odours, a history of water damage, unexplained health symptoms that appear to worsen indoors, or moisture conditions that are difficult to visually assess. It can also be helpful when confirming whether mould contamination is isolated to a specific area or potentially affecting multiple rooms.
However, air testing has limitations. It does not tell you where mould is growing, only that spores are present in the air. Spores may originate from hidden wall cavities, damp building materials, HVAC systems, or even outdoor air infiltration. Air testing alone cannot identify the moisture source that allowed mould to grow, which is the most critical part of preventing future problems.
This is why a mould inspection is an important first step, either before air testing or at the same time. A proper mould inspection includes a visual assessment of building materials, targeted invasive checks when appropriate, moisture mapping using moisture meters, and thermal imaging to identify temperature differences that may indicate damp areas. These tools allow us to locate moisture sources and potential mould growth zones that air testing alone cannot pinpoint.
Control samples are also essential, especially when outdoor temperatures are above 0°C. A control sample is an outdoor air sample taken at the same time as indoor samples. This establishes the baseline mould levels in the surrounding environment. Because mould spores are naturally present outdoors, comparing indoor samples to outdoor levels allows us to determine whether indoor mould levels are elevated or abnormal. Without a control sample, it becomes much harder to interpret whether indoor results reflect indoor mould growth or simply normal outdoor spore infiltration.
In many cases, more than one indoor sample is needed. Buildings are not uniform environments. Airflow, moisture conditions, and construction details vary from room to room. Taking multiple samples allows for pattern recognition. If elevated mould counts appear in one area but not others, this can help narrow down the likely location of hidden growth. If elevated counts appear in multiple areas, this may indicate a more widespread moisture issue.
In some situations, testing behind walls using a cassette with tubing and a small drilled access hole can provide more targeted information about hidden cavities. The benefit of this approach is that it can help confirm whether mould spores are present within a specific wall cavity without removing large sections of drywall. This can be useful when moisture meters or thermal imaging suggest damp conditions behind finishes. The downside is that this method only samples a very small area and can still miss growth located elsewhere in the cavity. It also involves creating a small opening in the wall, which must be properly sealed afterward. It can also produce debris contaminated results when the cassette is overloaded with debris from the creation of the small hole. Another downside is the need to repair the 1/4" hole once the test is complete. Behind-wall air sampling should be used selectively and as part of a broader inspection strategy, not as a standalone diagnostic method.
Ultimately, mould air testing is most effective when combined with a thorough mould inspection and moisture assessment. Air testing alone does not provide the full picture. When used properly, it supports informed decisions about whether further investigation or remediation is warranted and helps confirm whether mould growth is likely occurring within a building.
How to Read the Lab Report Step by Step
A mould air test lab report can look overwhelming at first, but once you understand what each section represents, the information becomes much easier to interpret. The report is structured to show where samples were taken, what mould types were identified, and how many spores were detected in each area.
Sample locations and identifiers
Each sample is labelled with a unique identifier and a location name. This tells you exactly where in the building the air sample was collected. Common locations include bedrooms, basements, living areas, mechanical rooms, and an outdoor control sample. The location matters because spore levels are compared between rooms to identify abnormal patterns.
Indoor versus outdoor comparison
The outdoor control sample establishes the baseline mould levels in the surrounding environment. Indoor samples should generally be similar to or lower than outdoor levels for common outdoor mould types. When indoor levels are significantly higher than outdoor levels, or when water-damage indicator moulds are present indoors but not outdoors, this suggests indoor mould amplification. Indoor mould levels are typically lower than outdoors due to our furnace/HVAC systems filtering the air, the building being somewhat air tight and the unfavorable growth conditions (dry, bright, frequently cleaned).
Spore types listed
The report will list different mould genera such as Cladosporium, Aspergillus/Penicillium, Alternaria, Basidiospores, and sometimes water-damage indicator moulds such as Stachybotrys or Chaetomium. Some moulds are commonly found outdoors, while others are more closely associated with damp building materials. The type of mould present is often more meaningful than the raw number alone.
Spore counts and units
Spore concentrations are typically reported as spores per cubic metre of air. These numbers show how many mould spores were captured during the sampling period and extrapolated to a standardized air volume. Higher numbers do not automatically mean a serious problem. The numbers must be compared to outdoor levels, to other rooms in the building, and to whether the space is occupied or unoccupied.
Laboratory notes and detection limits
Lab reports often include notes about low detection limits, overloaded samples, or potential interferences. These notes explain limitations of the sample and whether counts may be under- or over-represented. Understanding these notes helps avoid misinterpreting results as definitive when there may be technical limitations in the sample itself.
What Different Mould Spore Types Generally Indicate
Not all mould spores mean the same thing. Some are primarily outdoor moulds that enter buildings naturally through doors, windows, and ventilation. Others are more closely associated with damp or water-damaged building materials.
Cladosporium and Basidiospores are common outdoor moulds. Elevated indoor levels often indicate outdoor air infiltration, open windows, or high airflow bringing spores indoors. However, if indoor levels are significantly higher than outdoor levels, this may suggest indoor growth on damp materials.
Alternaria is commonly found outdoors and on decaying organic matter. Elevated indoor levels may be associated with moisture-damaged materials, potted plants, or building envelope leaks that allow organic debris to remain damp.
Aspergillus and Penicillium are commonly grouped in lab reports because their spores look similar under microscopy. These moulds are frequently associated with damp building materials, dust, and indoor amplification. Elevated indoor levels often indicate moisture issues in wall cavities, basements, crawlspaces, or HVAC systems.
Stachybotrys, Chaetomium, and Ulocladium are considered water-damage indicator moulds. Their presence indoors is more strongly associated with chronic moisture conditions and wet cellulose-based materials such as drywall, wood framing, or insulation. These moulds are not typically abundant in outdoor air, so indoor detection is more likely to reflect indoor growth.
Understanding what mould types generally indicate helps shift the focus away from fear and toward practical building-related causes. The goal is to identify moisture sources and affected materials, not to focus solely on spore names.
What Are Black Moulds?
“Black mould” is a general, non-technical term people use to describe dark-coloured mould growth, but it does not refer to a single mould type. Several different moulds can appear black or very dark in colour, including Stachybotrys, Ulocladium, Chaetomium, and some species of Cladosporium. The colour alone does not indicate how serious a mould issue is. What matters more is whether the mould is growing due to ongoing moisture problems and whether it is affecting building materials and indoor air quality.
List of Common Mould Spores Found in Water or Moisture Damaged Buildings
Aspergillus/Penicillium, commonly found on damp drywall, insulation, dust, and building materials affected by moisture.
Chaetomium, strongly associated with chronically wet drywall, wood framing, and cellulose-based materials.
Stachybotrys, typically found on materials that have been wet for extended periods, such as drywall, paper backing, and wood products.
Ulocladium, often found on water-damaged walls, window frames, and areas with recurring moisture intrusion.
Trichoderma, commonly associated with wet wood, paper, and building materials affected by leaks or flooding.
Acremonium, frequently found in areas with chronic moisture, including around plumbing leaks and condensation-prone surfaces.
What Is Considered “Normal” Versus a Concern
There is no universal safe or unsafe number for mould spores in indoor air. Mould is part of the natural environment, and low-level presence indoors is normal. What matters most is the pattern of results and how they compare to outdoor levels and building conditions.
Indoor spore levels should generally be similar to or lower than outdoor levels for common outdoor moulds. When indoor levels exceed outdoor levels by a meaningful margin, especially in occupied living spaces, this suggests indoor amplification.
The presence of water-damage indicator moulds indoors is more concerning than elevated levels of common outdoor moulds. These moulds are more strongly linked to damp building materials and long-term moisture issues.
Context matters. A basement with elevated Aspergillus/Penicillium and high humidity following a recent flood may require a different response than a single room with slightly elevated Cladosporium on a windy spring day. This is why air test results must be interpreted alongside moisture readings, visual observations, odours, and building history.
Occupied versus unoccupied spaces are also treated differently. Higher background spore levels are more tolerable in crawlspaces or mechanical rooms than in bedrooms or living areas. This distinction is built into the criteria used to flag elevated mould conditions and helps prioritize areas that may affect occupant comfort and indoor air quality.
Common Misinterpretations of Mould Air Test Reports
One of the most common misunderstandings is assuming that low numbers mean there is no mould problem. Air samples are taken at a single point in time and may miss spores released at other times. Hidden mould growth behind walls may not always release spores into the sampled air, especially if the area is sealed or not actively disturbed.
Another frequent misinterpretation is panicking over any mould detected. Mould spores are always present in outdoor air and often present indoors at low levels. The presence of mould spores alone does not mean a home is unsafe or requires remediation. The pattern, type, and context of mould spores matter far more than their mere presence.
Some homeowners assume air testing is a clearance test or proof that remediation is complete. Clearance testing requires a controlled process and specific criteria, and air testing alone is not a reliable way to confirm that all mould has been removed. Clearance is based on visual inspection, moisture control, proper cleaning, and verification that affected materials have been addressed.
Another common mistake is ignoring moisture sources. Air test results may show elevated mould, but without addressing the moisture source that allowed mould to grow, any remediation efforts are temporary. Moisture control is the foundation of effective mould management.
What To Do After You Receive Your Mould Test Results
Once you receive your mould test results, the next step is to interpret them in context. If results suggest indoor mould amplification, the focus should shift to identifying where moisture is present and what materials may be affected. This may involve targeted inspection, moisture mapping, and in some cases limited invasive checks to confirm hidden growth.
If results do not indicate elevated mould levels but you are still experiencing odours, moisture issues, or visible mould, further investigation may still be warranted. Air testing does not rule out all mould problems, particularly when growth is contained within wall cavities or concealed spaces.
When elevated mould levels are identified, remediation should be based on the extent of affected materials and the source of moisture. Proper remediation involves controlled containment, removal or cleaning of affected materials as appropriate, and correcting the moisture issue that allowed mould to grow. Ongoing monitoring of moisture conditions helps prevent recurrence.
Throughout this process, clear documentation matters. A Relief Restorations Winnipeg Mould Air Testing standard report includes a summary of findings written in plain language, a picture index to visually reference areas of concern, and any practical recommendations tailored to the specific building conditions. This helps homeowners understand what was found, why it matters, and what steps make sense moving forward.
When to Seek Professional Guidance in Winnipeg
There are situations where professional interpretation and guidance are especially important. If anyone in the home is experiencing ongoing respiratory symptoms, headaches, or sensitivities that appear to worsen indoors, it is important to have mould results interpreted alongside a proper building assessment. Air test numbers alone do not explain whether building conditions are contributing to indoor air quality concerns.
Visible mould growth, persistent musty odours, or a history of water damage are also strong indicators that professional involvement is warranted. In these situations, mould air testing should be paired with a full mould inspection to identify moisture sources, affected materials, and the extent of any hidden growth. Relying on air testing alone can miss localized problems that are contained within wall cavities or under flooring.
Ongoing moisture issues, such as repeated dampness in basements, condensation on windows and walls, or recurring leaks, should be professionally assessed even if mould test results are not clearly elevated. Moisture conditions are the underlying driver of mould growth, and addressing them early helps prevent more extensive damage later.
Professional guidance is also helpful when planning remediation or preventative upgrades. Understanding containment needs, material removal scope, and moisture correction strategies ensures that work is done properly and that mould does not return due to unresolved underlying issues.
Common Terms and Definitions for Reference
Many lab reports and inspection notes include technical terms that can be confusing without context. Understanding a few common definitions makes it easier to follow your report.
Air sample refers to a collected air volume used to measure airborne mould spores at a specific location and time.
Swab sampling is used to collect visible mould from a surface for lab identification of the mould type present on that material.
Tape lift sampling uses adhesive tape to lift mould or debris from a surface to identify what is growing on that specific area.
Bulk sampling involves removing a small piece of material to confirm mould growth within building materials.
Control sample refers to an outdoor, or other air sample used to establish baseline mould levels for comparison.
Spores per cubic metre refers to the standardized unit used to report mould concentrations in air samples.
Indoor amplification refers to mould growth occurring within the building that increases indoor spore levels above outdoor levels.
Water-damage indicator moulds are mould types more strongly associated with chronically damp building materials.
Moisture mapping refers to using moisture meters and thermal imaging to identify damp areas within building materials.
Containment refers to isolating affected areas during remediation to prevent the spread of mould spores and debris.
Remediation refers to the controlled removal or cleaning of mould-affected materials and correction of moisture sources.
Why a Mould Inspection Comes First or Should Happen at the Same Time
A mould inspection provides critical context that air testing alone cannot. Visual inspection identifies visible mould growth, water staining, and building defects that allow moisture intrusion. Moisture meters detect damp building materials that may not show visible signs of water damage. Thermal imaging highlights temperature differences that can indicate moisture behind walls or under floors.
When air testing is performed without an inspection, results may be misinterpreted because the underlying cause of elevated spores is unknown. A mould inspection allows sampling locations to be selected strategically based on building conditions and reported concerns. This improves the usefulness of the air test results and helps avoid unnecessary testing in areas that are unlikely to be affected.
In many cases, inspection findings guide whether air testing is even needed. If visible mould growth and moisture intrusion are already confirmed, remediation decisions can often be made without air testing. Air testing becomes more valuable when hidden growth is suspected, when confirming the extent of contamination, or when comparing multiple areas within a building.
Why DIY Mould Test Kits and Some Testing Methods Are Limited
DIY mould test kits often provide misleading results because mould spores are naturally present in indoor and outdoor air. These kits usually lack outdoor control samples, do not measure standardized air volumes, and cannot be interpreted in context with building conditions or moisture sources. As a result, they tend to confirm that mould exists in the environment without indicating whether there is an actual indoor mould problem.
Why Typically Air Testing Over Other Methods?
Professional air testing is typically used because it captures airborne spores in a controlled, measurable way and allows indoor results to be compared to outdoor control samples and established criteria. This makes it more useful for identifying abnormal indoor mould patterns and potential hidden growth. Other methods such as vacuum sampling or surface sampling can be helpful in specific situations, but they only show what is present on a surface or in dust, not what occupants are actually breathing, and they do not provide the same building-wide context as air testing when paired with a proper mould inspection.
Tape lifts and other surface sampling methods are sometimes used when there is visible growth and the goal is to identify what is present on a specific material. These methods can be helpful to confirm the type of mould on a surface or to support documentation when visible contamination is present, but they do not measure overall indoor air quality or indicate whether mould is present elsewhere in the building. For this reason, surface sampling is typically used as a targeted tool alongside a mould inspection and, when appropriate, air testing, rather than as a standalone method.
Conclusion and Practical Next Steps
Mould air testing is a useful tool when it is used as part of a broader assessment process. It provides data that helps identify abnormal indoor mould conditions, but it does not diagnose the cause of mould growth or replace a proper inspection. Understanding mould test results requires context, including outdoor control samples, building conditions, moisture sources, and how the space is used.
The most important step in addressing mould concerns is identifying and correcting moisture issues. Without moisture control, any cleanup or remediation is temporary. Pairing mould air testing with a thorough mould inspection provides a clearer picture of what is happening inside the building and helps guide appropriate next steps.
If you have received mould test results and are unsure what they mean, professional interpretation can help you understand whether further investigation or remediation is warranted. Clear reporting, visual documentation, and practical recommendations make it easier to move forward with confidence and address mould concerns properly rather than relying on guesswork or incomplete information.
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At Relief Restorations, we specialize in providing comprehensive restoration services, including mould remediation, water damage restoration, fire and smoke damage restoration, asbestos removal, light demolition, inspection and testing services across Winnipeg and Manitoba, Canada.
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