InspectAPedia ^®

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

This website discusses how we can estimating 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. Also see MOLD GROWTH on SURFACES for an index of what mold genera/species are frequently found on various building surfaces and materials.

© Copyright 2009 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links 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.

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

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

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.

• 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.

Share this Article      

...

Technical Reviewers & References

Search InspectAPedia

• Daniel Friedman - principal author/editor of the InspectAPedia^® Website
• 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.

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

• Our recommended books about building design, inspection, and repair, and about indoor environment testing, diagnosis, and cleanup are at the InspectAPedia Bookstore.
• ...

More Information on Building Diagnostic Inspections and Repairs

...

InspectAPedia® Home & Site Map - Building & Environmental Inspection, Testing, Diagnosis, Repair, & Problem Prevention Advice: In-depth research & advice on diagnosing, testing, correcting, & preventing building defects & indoor environmental hazards. Unbiased information, no conflicts of interest.

The Mold Information Center: What to Do About Mold in Buildings, When and How to Inspect for Mold, Clean Up Mold, or Avoid Mold Problems

Use this simple, economical mold test kit by following our instructions on how to collect and mail mold samples to our lab

Environmental Inspection, Testing, & Diagnosis On-Site IAQ, Gas, Air Testing, Mold Investigation, Sick Building Diagnosis, Lab Services, & Remediation Plan Preparation - indoor air quality testing, problem source determination, supporting lab work, written remediation plan addressing removal of environmental and other hazards and prevention of their recurrence.

Building Inspection, Problem Diagnosis, Forensic Investigation & Testing, Repair Consulting

Contact Daniel Friedman for website content suggestions or for fee-paid consulting