Photograph of thick hairy fungal mycelia extending below a wooden subfloor in a home - how old is this mold and how long did it require to grow in this pattern?

How to Estimate the Age of Mold Contamination in buildings
InspectAPedia^® -

How to Estimate the Age of Mold Contamination in buildings
How to evaluate mold samples for indications of active mold growth
Evidence of Mold History in buildings
Evidence of Mold Age in Laboratory Samples
Common causes of mold in buildings
Conditions that cause mold growth in buildings
Insurance claims and mold damage causation analysis
Rapidity or speed of mold growth in buildings
Time between building flooding and mold growth
Questions & answers about how to determine how old mold growth is in buildings

This building mold contamination assessment article discusses how we can estimate the age and history of mold contamination in a building and how we can find evidence suggesting that a given mold contamination case is new, old, or includes both old and new fungal growth.

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers nor with topics or services discussed at this website.

Also see MOLD GROWTH on SURFACES for an index of what mold genera/species are frequently found on various building surfaces and materials.

© Copyright 2012 InspectAPedia.com, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use page top links to major topics or use links at the left of each page to navigate within topics and documents at this website. Green links show where you are in a document series or at this website.

How Old is This Mold? Is it Possible to Determine the Age of Mold in buildings?

For insurance adjusters, building investigators, and building owners, a common question that arises when reviewing building mold contamination is "when did this happen" or "did the recent building leak or problem cause all this mold?". Here we explain how an experienced forensic investigator can find visual evidence that a mold problem in a building is of recent origin or if on the other hand the mold contamination in an area has been most likely present for a much longer time.

A Single-leak event mold example

The mold photos above show the extent of fungal growth in a home which had no previous mold nor leak history but which experienced a burst-pipe flood followed by six months of inattention before an insurance claim was filed.

Thick fungal growth was present on some surfaces, and some fungal growth was present on most materials and surfaces with genera/species varying considerably depending on just what surface we examined.

For example, the edge of a door hosted a different genera/species than the face of the same door (different woods). (We conducted a survey to study just what fungal genera/species preferred just which building materials in this home.)

Was this mold due only to the burst pipe? The absence of other indications of recurrent water entry or rot supported the view that although the fungal growth was extensive, it was in response to a single event.

A multi-event long-standing leak condition mold example

The mold photos above show thick dense fungal growth on rotted wood in a second building. At the top of this page, a photo of similar-looking fungal growth as that shown in the "single-leak" case cited just above (by size, thickness, and extent below a wood subfloor) was was taken in a second building which had suffered decades of water entry. It was much less likely that the mold growth we saw in the second building was due only to a single event flood.

Data like this can assist building owners and insurance claims adjusters in forming a reasonable opinion about the cause and age of mold contamination in a building. In turn, that opinion can assist in setting priorities for building repair since if we do not correct the underlying causes for mold contamination in a building, mold growth is likely to recur and the investment in a given mold remediation project may be wasted.

A mycologist's view on setting an age on mold in buildings

Mycologists indicate and field experience by property inspectors confirms that fungal growth can occur in a building over a broad surface and quite rapidly, in as short a time as 2-3 days in some conditions and they add that it is not very reliable to guess at the "age" of a given mold colony.

Of course there are exceptions: some fungal growth such as "tree ears" and hard fungi produce slow-growing and durable structures over many years - the larger their size the older they are. But in general, mycologists are precisely correct: looking at a sample mold itself does not easily permit us to guess how long mold has been present on that surface.

A building scientist's view on setting an age on mold in buildings

But the good news for building forensic analysis is that other accompanying observations in a mold-contaminated building can provide compelling evidence regarding the age of mold infection there.

A building scientist, particularly if s/he has also some training in mycology, can in some cases sort out the probable history of mold contamination in a building by using evidence from a variety of supporting sources. Most buildings more than just a few years old are likely to have experienced an occasional spill, leak, or other source of water entry which could, in turn, have been a gating factor in developing problematic mold growth in the structure.

buildings more than 20 years old, particularly wood-frame structures and structures which use interior materials which are "mold friendly" such as drywall, fiberglass insulation, and carpeting, often have had more than one leak, wetting or flooding event and may have more than one location and source of mold growth.

In fact a careful inspection of most homes, even ones which have never reported a flood or mold problem, can quite often, perhaps usually, find some spot of fungal growth in the structure. (That does not necessarily mean that the building has a "mold problem".

In all but the most egregious and uncommon cases such as brand new construction which has been flooded, a hasty, superficial scan of a building or of visible mold in it should not alone be a basis for deciding whether or not a mold problem has been long-standing or has occurred only as the result of a single most-recent building leak or flood.

However, thoughtful observation and recording of certain building conditions along with careful, thorough site and laboratory work can provide insight into the probability that mold found indoors at a particular building and at a particular time is probably due to a specific building wetting event or, on the contrary, that mold in a building, or at least some of it, probably pre-dates the specific wetting or flooding event.

Conditions affecting the genera, species, and rate of fungal growth in buildings

The appearance of mold genera/species varies widely as a function of the growth substrate (paper, wood, cloth) and moisture conditions.

Different species prefer different moisture levels and thus may appear on the same material such as drywall but at different heights from the floor if that section of drywall was wet from the floor level. (Stachybotrys chartarum prefers very wet conditions and appears low on the wall.

Cladosporium and Ulocladium are often found somewhat higher on the same wall. Aspergillus sp. or Penicillium sp. often prefer still less wet conditions and may be found higher still or more uniformly spread over a drywall surface as they may grow more readily in conditions of high humidity even if the drywall was not actually wet to the touch.

What produces mold growth on a building surface is the combination of this presence of omnipresent fungal spores available in the general environment, the presence of a building material that a particular fungus will grow on (its food), and the presence of appropriate conditions of moisture and, to a lesser degree, temperature and perhaps light or darkness.

If these mold-conducive conditions have been present in a building for months or years, the probability that a fungal growth has appeared suddenly and as a sudden and brand-new mold colony is rather low.

Conditions permitting an assessment of probable age of mold growth in buildings

All of these mold-producing conditions are likely to pertain and should always considered in both field and laboratory examinations of moldy conditions in any building where mold contamination is present. Of course for any specific case of mold contamination in a building, only some of these conditions will actually be present and determinant of mold growth in a particular building and case.

Water leak history sets a probable age of mold

Evidence of a history of recurrent water entry in a building will establish that mold-producing conditions have been present since the beginning of those water or wet conditions in and at the property. These include both:

Evidence of water-entry producing conditions (missing gutters, in-slope grade, improper ventilation, history of plumbing leaks, multiple flood lines in a building) and
Evidence of the effects of water entry (water stains, damage from rot or insects, visible mold). Mold spores are available in the environment nearly all of the time under all conditions.

Evidence of rot sets a probable age of mold

Photograph of moldy floor trim wall interior.

Evidence of rotted wood components such as flooring, framing, floor joists, sill plates, or posts. While water entry can occur suddenly and can be extreme (flooding, burst piping, sudden severe roof leaks), the conditions produced by a first-time and one-time event, if inspected days, weeks, or even several months after the event, will not include rotted components.

The floor trim in the left hand photo above is not only moldy, a closer examination shows that it has rotted. The rotted condition of the trim indicates long-term exposure to water and makes it less likely that the mold on the trim is due only to a single recent leak event. The right hand photo above examines the wall cavity behind this rotted floor trim, showing additional wood debris and mold growth on the cavity side of drywall in this building.

Evidence of exfoliating rust sets a probable age of mold

Photograph of light rust on a steel lally column.

Photograph of exfoliating rust on a steel lally column.

Evidence of exfoliating rust on steel components such as steel Lally columns, teleposts, or steel heating furnaces or boilers, is evidence of recurrent or protracted wet conditions which are also mold-conducive. "Exfoliating" or thick flaking rust, or even rust penetration of components, is to be distinguished from light, superficial rust that appears readily on unprotected metal surfaces after a single wet event.

The photo at above left shows no building-related rust on a steel lally column in a dry crawl space. This area has not been subject to severe recurrent water entry. The second photo at above right shows exfoliating rust on a steel lally column, clear evidence that this space has been subject to recurrent and/or prolonged (many months) water entry.

Indirect evidence of moist conditions can suggest probable age of mold

Evidence of wood destroying insect activity is suggestive of moist or wet conditions as those invite insects into a building; other conditions such as wood-soil contact are also factors in the development of insect damage.

Evidence of age of mold in the forensic microscopy laboratory

Condition of the mold or fungal colony itself, examined microscopically, may be suggestive of the length of time a mold infection has been present on a surface.

Dry desiccated fungal material is consistent with prior, currently inactive fungal growth on the surface which was sampled.
Fresh, hydrated fungal hyphae or fungal fruiting bodies (conidiophores or other sporulating bodies) are consistent with ongoing, current fungal growth. Some fungal bodies such as thick woody structures grow much more slowly and if present, almost certainly have been developing over a long time.
Of course, both types of fungal presence may be found on a surface, thus indicating that there is both a pre-existing moldy condition and current or renewed fungal growth.

Notes about these clues to the age of mold in buildings

In nature fungal growth can appear outdoors even more rapidly: some species of mushrooms may appear after a rainy night
Rotted components from a single event leak may be present if the building has remained wet for more than a month or two, but that case can still be visually distinguished from prolonged water exposure, recurrent water exposure, multiple flooding events, and extensive deep rot in wood members by visual observation and experience.

Unambiguous, Ambiguous and Overlapping Mold Colonies in buildings

Especially in older buildings where there has been a recent sudden leak event associated with mold growth, it is often possible to identify pre-existing mold as well as mold-producing conditions. In unambiguous cases, the "new" mold associated with the building leak event may, by luck, appear in a limited area of the building which maps the area wet by the recent leak, and separated by distance or building area from other moldy areas which in turn are associated with other building leaks or conditions. The physical separation of wet areas and wet conditions may be sufficient to make a clear assignment of mold causation in such cases.

In ambiguous cases, there is fresh, active fungal growth, probably associated with a recent leak or flooding event in the building, which has grown entirely or partly overlapping pre-existing mold growth. In this case the assignment of cause and age of mold in the building can be ambiguous. If an insurance claim is involved, insurance company policy details and internal claims adjustment guidelines will determine the extent to which insurance coverage will address building remediation and repair for these overlapped-occurrence mold conditions.

Determining Whether or Not a Mold Test Sample Shows Active Mold Growth

Question: how do we determine whether or not mold in a building is active vs. inactive?

Would you please let me know how an individual (or lab) would test for whether a mold found on attic sheathing is active vs. inactive?

Research on-line has told me the test for active vs inactive is whether it smears when you rub it. Is there a more technical test that can be done? Should a lab be able to tell me this when I supply a sample? - M.O.

Answer:

The question of how we determine whether or not mold in a test sample is "active" is a bit misleading, although some surface test samples of mold do indeed give compelling evidence of recent active fungal growth. Our site photograph of moldy roof sheathing (above left) is an example. Is this mold growth "active" or "inactive", and does activity make much difference in risk to building occupants?

At MOLD AGE - Old is the Mold? we discuss visual clues that help determine the age of mold contamination in buildings or on building surfaces. There we explain what dried, desiccated, "old" mold growth may look like on a surface, in a test sample, and under the microscope. Among other factors, we distinguish between

Dry desiccated fungal material is consistent with prior, currently inactive fungal growth on the surface which was sampled. Very desiccated sample materials are almost certainly not indicators of active current fungal growth.
Fresh, hydrated fungal hyphae or fungal fruiting bodies (conidiophores or other sporulating bodies) are consistent with ongoing, current fungal growth. Some fungal bodies such as thick woody structures grow much more slowly and if present, almost certainly have been developing over a long time.

Aureobasidium pullulans (C) Daniel Friedman

Often we can confirm recent fungal growth in a tape sample by the presence of certain growth structures, hyphal buds, or even the state of a conidiophore.

Our photo of Epicoccum sp. fungal spores and hyphae (above left) collected from a building surface shows intact, fragile hydrated complete spores still connected to hyphae - this mold growth is recent and might indeed be considered "active mold growth" as would the intact, hydrated, and budding Aureobasidium pullulans spores shown in our second lab photo (above right). This burst of Pleospora spores is clearly active. Similarly, for certain species that produce long fragile spore chains, the presence of long mold spore chains is certainly indicative of nearby active fungal growth, as these chains break up rapidly into individual spores when airborne.

Conversely, highly desiccated, fractured, or damaged fungal material that lacks budding hyphae or sporulating intact conidiophores are almost certainly "inactive" mold growth in the spot where sampled.

Watch out: "mold activity" or "mold inactivity" can be misleading conclusions about the risks associated with mold growth in buildings.

The moldy books in a college library (photo at left) were in the opinion of some people "an old inactive mold problem" but when workers began dehumidifying the area in preparation for a mold cleanup, visible clouds of Aspergillus sp. spores were released into the air by small air currents caused by simply walking down the aisle between stacks of books.

Mold test sample size: Because a sample represents a small area of a building and of time, and because other materials may be present that the sampler did not see, detect, or test, a single sample is an indicator, not a conclusion about a building's condition.
Multiple mold genera/species: Next, the conditions that produced fungal growth that was seen and tested mean that building conditions were ripe for mold growth, perhaps on other surfaces or in cavities or in less visible locations. For example we may see one species of mold on an attic roof underside, say Cladosporium cladosporioides, perhaps even desiccated by the heat of sun beating on the roof, while the conditions that produced that growth also produced a non-visible but more troubling Aspergillus sp. contaminating growth in building insulation in the attic floor. So at a given time, some mold on building surfaces may be "inactive" while nearby another genera/species may be growing like mad, or releasing spores like mad, i.e. "active".
Dead toxic mold: Next, we suspect an underlying faulty premise that the salient question is whether or not a fungal growth is active or not in a building. In fact even currently inactive (no apparent recent fungal propagation) fungal presence on a surface can be a hazard since spores and fungal hyphal fragments may be toxic, pathogenic, or allergenic even in that state. That point remains true even if some misinformed "mold remediator" tries to "kill" the fungus with a fungicide or bleach.
Smearing mold?: Further, he claim that smearing mold with a finger determines whether or not it is active or not is nonsense. A mold growth on a surface could be very desiccated and may not have actively propagated for a long time but still can be "smeared" with a finger wipe. But we agree that if you cannot smear suspected-mold or better, if you cannot obtain particles on an adhesive tape sample, then the surface may have been previously cleaned, and what remains may be no more than a cosmetic stain.
Inoculation of mold: Finally, even if mold is "not actively growing" at the time that a sample is obtained from a surface (or in dust or air), the presence of a large amount of fungal material in a building can lead to rapid mold re growth and propagation when building conditions change to those more conducive to growth of the fungi already present.

All mold is everywhere all the time in the form of spores ready to inoculate a material or surface. So when building conditions are ripe for mold growth, it is likely to occur. Predominantly, it is the building conditions that determine whether or not we will have a building mold problem, not the presence or absence of mold in general. But the presence of a large reservoir of pre-existing (inactive) mold can speed both the recurrence and the extent of a future mold contamination. "Inactive" does not mean "non-viable".

Watch out however: using a swab or culture test for "viable mold" in buildings can give very misleading results since what grows in the culture is what likes the culture, not necessarily what is present or dominant in the building. See MOLD TESTING METHOD VALIDITY and in particular Mold Culture Plate Test Errors.

These reasons explain why in addition to testing to confirm the presence of mold growth, and to confirm that it is not simply cosmetic, in cases of possibly costly mold cleanup or diagnosing a possible building contribution to indoor air quality complaints, is important to have an expert perform a competent inspection of the building.

Questions & Answers regarding this article

Questions & answers about how to determine how old mold growth is in buildings

Ask a Question or Search InspectAPedia

HTML Comment Box is loading comments...

Recommend / Share this Article

...

Technical Reviewers & References

InspectAPedia.com^® - Daniel Friedman - Publisher & Editor.
InspectAPedia Bookstore lists recommended books, organized by topic & available for purchase. Most of our articles also include a list of recommended books for the specific article topic as well as other references, and information sources.
Critique, contributions wanted: Contact Us to suggest corrections or additions to articles at this website, and if you wish, to receive online listing and credit as a contributor. Particular thanks are due to the many experts and also consumers who read and critique technical articles at InspectAPedia.com.
Additional technical contributors & reference sources for this article are listed below.

Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

MOLD ACTION GUIDE - WHAT TO DO ABOUT MOLD
MOLD ACTIVITY in buildings
MOLD AGE - Old is the Mold?
  Single-leak mold
  Multi-event mold
  Mycologists' view on age of mold
  Building scientists' view on age of mold
  Conditions affecting fungal growth
  Conditions permitting mold age assessment
  Determine if Mold Contamination is Active?
MOLD APPEARANCE - WHAT MOLD LOOKS LIKE
  Black Mold
  Brown Mold
  Green Mold
  Red Mold
  Yellow Mold
  White Mold
  Invisible Mold
  Meruliporia Mold Photographs
  Mildew Photographs
  Recognize Cosmetic Mold
  Recognize Harmless Black Mold
  MOLD GROWTH ON SURFACES, PHOTOS
MOLD APPEARANCE - STUFF THAT IS NOT MOLD
  HARMLESS INDOOR PARTICLES
    Black stains from soot/thermal tracking
    Black stains from animals
    Black cosmetic mold
    Efflorescence & white or brown deposits
    House dust
    MYCOPHOBIA, STAINS MISTAKEN for MOLD
    Pollen
    Sprayed foam insulation
    White stuff that is not mold
    Wood sap

MOLD ATLAS & PARTICLES INDEX
MOLD BY MICROSCOPE
MOLD in the PETRI DISH, PHOTOS
Mold on Books, Book Conservation
MOLD CLASSES, HAZARD LEVELS
  Cosmetic mold
  Allergenic mold
  Common Mold-Allergic Responses
  Pathogenic, Toxic, or "Infectious" Mold
  Attempts to "kill" mold using bleach
  Effective mold cleanup
MOLD CLEANERS - WHAT TO USE

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
Environmental Health & Investigation Bibliography - our technical library on indoor air quality inspection, testing, laboratory procedures, forensic microscopy, etc.
Adkins and Adkins Dictionary of Roman Religion discusses Robigus, the Roman god of crop protection and the legendary progenitor of wheat rust fungus.
Kansas State University, department of plant pathology, extension plant pathology web page on wheat rust fungus: see http://www.oznet.ksu.edu/path-ext/factSheets/Wheat/Wheat%20Leaf%20Rust.asp
"A Brief Guide to Mold, Moisture, and Your Home", U.S. Environmental Protection Agency US EPA - includes basic advice for building owners, occupants, and mold cleanup operations. See http://www.epa.gov/mold/moldguide.htm
US EPA - Mold Remediation in Schools and Commercial Building [Copy on file at /sickhouse/EPA_Mold_Remediation_in_Schools.pdf ] - US EPA
US EPA - Una Breva Guia a Moho - Hongo [Copy on file as /sickhouse/EPA_Moho_Guia_sp.pdf - en Espanol
"A Brief Guide to Mold, Moisture, and Your Home", U.S. Environmental Protection Agency US EPA - includes basic advice for building owners, occupants, and mold cleanup operations. See http://www.epa.gov/mold/moldguide.htm
"Disease Prevention Program for Certain Vegetable Crops," David B. Langston, Jr., Extension Plant Pathologist - Vegetables, University of Georgia (PDF document) original source: www.reeis.usda.gov/web/crisprojectpages/209797.html
"Disease Prevention in Home Vegetable Gardens," Patricia Donald, Department of Plant Microbiology and Pathology, Lewis Jett
Department of Horticulture, University of Missouri Extension - extension.missouri.edu/publications/DisplayPub.aspx?P=G6202
"Management of Powdery Mildew, Leveillula taurica, in Greenhouse Peppers," Ministry of Agriculture and Lands, British Columbia - Original source: www.agf.gov.bc.ca/cropprot/peppermildew.htm
Fifth Kingdom, Bryce Kendrick, ISBN13: 9781585100224, is available from the InspectAPedia online bookstore - we recommend the CD-ROM version of this book. This 3rd/edition is a compact but comprehensive encyclopedia of all things mycological. Every aspect of the fungi, from aflatoxin to zppspores, with an accessible blend of verve and wit. The 24 chapters are filled with up-to-date information of classification, yeast, lichens, spore dispersal, allergies, ecology, genetics, plant pathology, predatory fungi, biological control, mutualistic symbioses with animals and plants, fungi as food, food spoilage and mycotoxins.
Fungi, Identifying Filamentous, A Clinical Laboratory Handbook, Guy St-
US EPA: Mold Remediation in Schools and Commercial Building [Copy on file at /sickhouse/EPA_Mold_Remediation_in_Schools.pdf ] - US EPA
Mycology, Fundamentals of Diagnostic, Fran Fisher, Norma B. Cook, W.B. Saunders Co. 1998, ISBN 0-7216-5006-6 (buy this book at Amazon)
...

Free Encyclopedia of Building & Environmental Inspection, Testing, Diagnosis, Repair

Ask a Question or Search InspectAPedia

How Old is This Mold? Is it Possible to Determine the Age of Mold in buildings?

A Single-leak event mold example

A multi-event long-standing leak condition mold example

A mycologist's view on setting an age on mold in buildings

A building scientist's view on setting an age on mold in buildings

Conditions affecting the genera, species, and rate of fungal growth in buildings

Conditions permitting an assessment of probable age of mold growth in buildings

Water leak history sets a probable age of mold

Evidence of rot sets a probable age of mold

Evidence of exfoliating rust sets a probable age of mold

Indirect evidence of moist conditions can suggest probable age of mold

Evidence of age of mold in the forensic microscopy laboratory

Notes about these clues to the age of mold in buildings

Unambiguous, Ambiguous and Overlapping Mold Colonies in buildings

Determining Whether or Not a Mold Test Sample Shows Active Mold Growth

Question: how do we determine whether or not mold in a building is active vs. inactive?

Answer:

Questions & Answers regarding this article

Ask a Question or Search InspectAPedia

Technical Reviewers & References

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair