Interpreting a Mold Test Result

The purpose of a mold test is to confirm that the air quality inside the home (especially in basements) is not significantly out of range from the outside environment.  Mold thrives on decaying tree and plant matter among many other things which is why it is nearly everywhere.   As Certified Mold Testing Experts we do not expect to see a mold test result with zero spores in the home.  If, however, we find mold in types and numbers inside the home that we do not see in its immediate vicinity, the presence of these spores could indicate an air quality issue.

Indoor Mold: this is a type of fungus sometimes referred to as mildew.  Molds thrive on moisture.  Some Molds are known to have Allergenic and Mycotoxin potential.
Spores: are reproductive ‘seeds’ for mold that travel through the air
Mycotoxins: are toxins produced by fungi that can cause health issues in humans or animals
Aspergillus/Penicillium: these are molds that are very common in basements and crawl spaces.  In large amounts, they can be an indicator of air quality issues.  Known to have mycotoxin and allergenic potential.
Stachybotrus: commonly known as ‘Black mold’ found in basements or crawl spaces or other areas with active water penetration and wet surfaces.  Known to have mycotoxin and allergenic potential.

Interpreting a Mold Test Result

What is an air sample or mold spore trap?  How are these samples taken?

An air sample is taken by using a specialized pump to pull a consistent volume of air through a mold spore trap- the trap is a small plastic container that is approximately the same diameter as a silver dollar.  For small to medium size homes typically we take 3 air samples- one control sample from the outside, another one at the lowest level finished area (where we suspect the most issues), and another one at a higher level or where we suspect the least air quality issues.  For larger homes or for homes that have multiple areas with potential air quality concerns we may take additional samples.  After taking the samples we send the traps with documentation to a lab to be analyzed.  The lab will identify and count the number of spores caught in each trap and send the results back to us in a report.

Mold test results should always be interpreted in relation to a home inspection or a mold inspection- which is why Home Inspectors that specialize in mold testing are among the best professionals to consult for an unbiased evaluation of the air quality in the home.

The Test Result: Types of Spores

The test result will list the number of spores and the types of spores found in each sample.  Different labs will organize and present the information differently.  Our lab separates the types of spores into 3 different categories: PREDOMINANTLY OUTDOOR, INDOOR/OUTDOOR, and WATER INDICATORS.

  • PREDOMINANTLY OUTDOOR: (No color)- as a general rule these spores grow predominantly outdoors and are not good indicators of the general air quality inside the home
  • INDOOR/OUTDOOR: (Yellow row) – These spores often grow in moist environments in the home and are excellent indicators of air quality issues in the home– especially aspergillus/penicillium.  Aspergillus/Penicillium have mycotoxin and allergenic potential.
  • WATER INDICATORS: (Red row) These spores grow on wet/saturated surfaces inside the home and can indicate a more severe/active/long-term air quality issue in the home with more severe mycotoxin and allergenic potential.

Some spores are known to have allergenic and mycotoxin potential while others are not.  A visual guide is presented in our report.

The Test Result: Raw Counts of Spores

When the raw counts of certain spores are significantly out of range from the outdoor sample it may indicate an air quality issue– test results are best interpreted by a professional.  In some cases, only a portion of the spores is counted in the lab as there are too many to count individually.  For example, if the Raw Count says ’60’ and only 10% were analyzed that could indicate that there were 10 times the amount of 600 spores (not 60).  See the video for more information.

The Test Result: Calculated Spores Per Cubic Meter

In the report the raw counts are then used to estimate a calculated number of spores per cubic meter, in other words, how many spores we would expect to find floating around in a cubic meter of air.  These graphics can be helpful but can also be misleading- the test results are best interpreted by a professional.  Keep in mind that these graphs are not to scale, and the maximum amounts can vary per sample-  see the video for more information.

How are Spores Per Cubic Meter calculated?

During our air samples, we pull 75 Liters of air through the trap or 15 Liters per minute for 5 minutes- this is an industry-standard.  75 Liters is about the same volume as a kitchen trash can.  Air quality is typically measured in cubic meters– industrial hygienists want to know how many calculated spores per cubic meter there is.  A cubic meter is about the same volume as a standard-size refrigerator.  There are 1000 liters in a cubic meter which is 13.3 times larger than the 75-liter sample taken on-site.  (1000 liters divided by 75 liters is 13.333)  So in order to discuss our air samples in cubic meters we need to extrapolate the data or estimate how many spores we might find in a much larger sample.

Example:  If we find 1000 spores in a 75 Liter sample we can assume there might be around 13,300 spores in a cubic meter.  (1000 x 13.3= 13,300)

Is Mold Testing a Pass or Fail Test?

Mold testing is not regulated on the federal or state level and therefore it is not a pass-or-fail test.  The EPA has very specific guidelines on other environmental concerns like Radon gas but no Federal guidance currently exists for Mold, Mold testing, or Mold mitigation.  Because mold testing is un-regulated it is important to find an unbiased professional that does not have an invested interest in the repairs– mold tests should only be taken with a full home inspection or mold inspection which is why Home Inspectors that specialize in mold testing are among the best professionals to evaluate the air quality in a home.  The Inspector will interpret the results based on the observations made during the inspection and will use their experience analyzing other results as a reference to help inform the buyer.

Spore Sample results taken from the home are always considered in relation to the outdoor control sample.  If higher than typical spore counts were observed outside then higher than typical counts will be expected in the home because people, pets, and objects are always being brought into the house from the outside.  This is one reason why the test result is always relative.

Most Common Sources of Mold or Air Quality Issues

Air quality issues tend to manifest in the basement or crawl space (moist environments) more than in any other area.  The upper levels of the home tend to exhibit fewer air quality issues because they tend to be dryer than the ground level.

  • Basements: (MOST COMMON) Poor grading and drainage from the outside will force water through the foundation wall which contributes to a wet environment conducive to fungal growth.  Trapped moisture between the foundation wall and finishes can cause air quality issues in Finished Basements
  • Crawl Spaces: (MOST COMMON) Poor grading, drainage, and ventilation will cause a moist/wet environment (especially in the warmer months) conducive to fungal growth.  Moisture can seep upwards into the floor framing, finishes, and walls which, over the long term, can cause air quality issues in the living areas.

Other Causes of Mold or Air Quality Issues

  • Long-term Plumbing Leaks: Unaddressed plumbing leaks or flood events can cause air quality issues over the long term.
  • Roof leaks: Un-addressed roof leaks can cause water penetration through the ceiling and cause air quality issues in the home over the long term.
  • Deck Connections: Missing or improper flashing can cause water penetration into the wall framing and air quality issues over the long term.
  • Patios: Installed over the siding/framing or sloped toward the home can cause water penetration into the wall framing and air quality issues over the long term.
  • Siding/Trim:  Poorly installed or maintained siding and trim can cause water penetration into the wall framing and air quality issues over the long term.
  • Grading: Grading that slopes toward the home or that is above or too close to the siding/framing can cause water penetration and air quality issues over the long term.
  • Drainage: Improperly installed or maintained gutter systems can cause water penetration and air quality issues over the long term.
  • Heating/Cooling Systems: Poorly installed, maintained, un-insulated, or under-insulated ductwork can cause water penetration and air quality issues over the long term.
  • Occupants: Habits of the occupants themselves can contribute to air quality issues over the long term (uncleanliness, neglect, not using AC/dehumidifiers, pet urine, etc…)

Tape Lifts vs Air Samples

What are tape lifts?

If a section of mold was observed in a basement bathroom, for example, a tape lift could be used to identify the mold.  A ‘tape lift’ is just as it sounds, we take a small piece of standard ‘scotch tape’ and ‘lift’ the spores from the surface mold.  We send this sample to a lab to identify the species of molds found.  Here at Builder Buddy we rarely take tape lifts as they are not as useful in evaluating the overall air quality in the home as air samples and the experienced mold inspector or testing technician can often visually identify the most common types of mold.

Air Quality Issues: Surface Molds vs Hidden Moisture Damage

People that have less experience with air quality issues in the home often become fixated on surface molds or mold that can be seen with the eyes.  The mold that we typically see in our kitchens and bathrooms is usually just ‘surface molds’ growing on moist surfaces that need to be cleaned or removed.  Anyone can ‘mitigate’ these kinds of molds with household cleaning materials.  Better cleaning and ventilation of these spaces will typically address these issues- read an article on bathroom fan vents and mold found on bathroom ceilings here.

More serious kinds of mold issues are found in finished basements, for example, where we might see mold growing on the drywall or other finished materials close to the floor.  These molds can’t just be ‘cleaned’ on the surface because the real problem is water penetration entering from the outside and pushing through the foundation wall.  This moisture gets trapped behind the finishes and starts to decay materials and cause air quality issues.  The observable mold found, in this case, is just a symptom of a much deeper and more complicated issue.  Many molds will spore, or become more visible, on drier surfaces meaning that conditions behind the visible surface may be much worse.  In many cases, we don’t see any visual evidence of mold but we still suspect an air quality issue based on smells, water stains, and moisture readings.

Determining the difference between surface molds and molds caused by hidden moisture damage can be difficult.  A home inspector that specializes in mold testing is one of the best resources for homeowners concerned about air quality in the home.

What Can Affect a Mold Test?

We expect higher spore counts during Summer during periods of higher humidity.  We also expect higher spore counts after rainy periods when basements and crawl spaces may experience more water penetration.  We expect spore counts to be lower in the Winter when the air is dryer.  Spore counts in the home can vary depending on the Season, Weather, pets/occupants and their living habits, and many other factors.  Sometimes a wet piece of clothing brought from the outside can significantly affect a test result.  Dehumidification can reduce moisture and the number of spores in the home (which is good) however sometimes dehumidifiers can be placed to intentionally hide moisture issues– unfortunately, this is always a limitation.

Can a Musty Smell Indicate Mold?

Yes, the nose is an excellent tool for diagnosing air quality issues and often alerts us to look closer for other causes and symptoms.  Wet, humid, musty, or mildewy smells could all indicate mold growth or mold conditions.

What Causes Mold?

Fungi grow and reproduce in wet or moist environments.  When an environment becomes dry the fungi die or becomes dormant.  The number of spores in the air will be higher during hot/humid Seasons (like Summer) or during rainy periods.  Mold thrives best in persistently wet environments.

What is the Problem with Mold?

When fungi reproduce they send spores into the air.  The spores of most species of fungus do not have allergenic potential. Some species, however, like Aspergillus Penicillium, Stachybotrys ‘black mold’, and others are known to cause allergic reactions in some people.

Is Some Amount of Mold in the Home Considered Normal?

Yes.  Mold spores are found everywhere and especially in our forested humid subtropical climate with high rainfall (here in Western North Carolina).  Fungi thrive on the decaying matter in our trees/shrubs/plants and it’s normal for many of these spores to be brought into the home.  We haven’t seen a mold test result with zero spores in the home yet and in fact, if I did I would likely retest because I would suspect an issue with the equipment.  Most outdoor mold spores are harmless to people.  We suspect a mold or air quality issue when the indoor samples are significantly out of range from the outside and contain a high number of predominantly indoor species with fungi with high allergenic potential.

Should I Order a Mold Test or a Mold Evaluation?

Start with an Inspection: When there are indoor air quality concerns we recommend starting with a Home Inspection or a Mold Evaluation first.  Anything that causes moisture can cause mold which is why our inspectors look at everything first – grading, gutters/drainage, siding/flashing/decks, plumbing, insulation/ventilation, heating and cooling, appliances, attics, crawl spaces – EVERYTHING!  Most of the time we can identify the causes of moisture and we can make recommendations without the need for mold testing.   

We recommend additional Mold Testing when: we suspect hidden water behind finishes or we believe there may be a possibility of it (finished basements, recently repaired plumbing leaks, recently renovated/painted basements, etc)  or for highly sensitive individuals or families.

See our article on Mold Evaluations for more information.

Asheville Mold Testing and Mold Inspections

Builder Buddy has Certified Mold Testing Technicians on staff and is your resource for Mold Testing, Mold Inspections, Air sampling, Tape lifts, Air Quality Testing, and more.
Schedule online or call with questions.

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