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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.
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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.
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.
Also see MOLD GROWTH on SURFACES for an index of what mold genera/species are frequently found on various building surfaces and materials. To better understand the water entry or leak history of a building - gating factors in mold contamination, see Evidence of the Age & History of Water Entry or Leaks In a Building.
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.
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.
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.
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.
In the extremely mold-contaminated building shown at left, the author tested every surface of every different type of building material found inside the structure. The results were interesting: different mold genera/species had strong preferences for different materials (no surprise).
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.
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 rot sets a probable age of mold
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
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.
Notes about these clues to the age of mold in buildings
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.
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.
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
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.
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.
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