More Places to Look for Hidden Mold in Buildings - Looking for Mold
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Description and photos of oft-forgotten places to look for hidden mold
Guide to finding hidden mold in buildings, under carpets, at ceiling penetrations and air or water leak points
Guide to finding mold hidden on or in furniture
Finding mold in air conditioning systems

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This article provides suggestions for where else to look for mold in buildings - places that are often forgotten but places that can harbor significant toxic or allergenic mold reservoirs. The fact that mold is said by some inspectors to be "hidden" in buildings does not mean one cannot find it by careful inspection and testing.

Also see FIND MOLD in BUILDINGS, HOW TO and see MOLD GROWTH on SURFACES for an index of what mold genera/species are frequently found on various building surfaces and materials, and see Mold Related Illness: Index of Symptoms and finally, for an atlas of building molds and for more microphotographs of building mold samples observed in our laboratory, see Mold Atlas of Indoor Clinical Mold, Pathogens, Allergens & Other Indoor Particles. And MOLD BY MICROSCOPE shows what mold looks like under the microscope.

We look for mold in buildings where it is not obvious by using context: where do we see leak stains, or where do we see building practices most likely to have produced a hidden leak or moisture problem? Ice dam leaks in walls, hidden plumbing leaks, roof spillage by the foundation, are all common clues that often track to a wet building wall or ceiling cavity and from there to a hidden mold problem which may need to be addressed.

This procedure helps identify the presence of or locate the probable sources of mold reservoirs in buildings, and helps decide which of these need more invasive, exhaustive inspection and testing.

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Other Places to Look for Hidden Mold Contamination or Mold Growth

There are many places to look for mold growth. Here are a few others that you might not have considered:

Underside of carpets or carpet padding that have been wet - check for moldy or water-stained carpet tack strips;
Previously wet cardboard boxes and their contents;
Ceiling penetrations like 120-V smoke detectors;
Top of poorly-insulated exterior walls; behind wallpaper below windows which had a one-time or recurrent leak.
Furniture: we often find extensive mold on the un-finished side of drawers, tables, game tables, and chairs that have been in a wet or damp environment.
Imported Mold: Sometimes mold is imported into a "dry" building on furnishings or contents that were previously stored in a wet location or in another moldy building.
Building Insulation is often moldy even if it looks clean.
Appliances: Don't forget to clean your refrigerator, including gaskets, coils, and evaporator tray.
Air Conditioning Systems: take a careful look at your window or wall-mounted air conditioner and be sure to make a complete inspection of central air conditioning system ductwork, registers, and air handlers, as well as any heating air handlers and duct work. Check especially downstream of the air handler on cooling systems since condensation there may promote mold growth.
Have You Found Other Places to look for mold? Send us your own discoveries - your tips may help other people who are bothered by indoor mold but who have not been able to find its source.

Here are photos of more places to look for hidden mold in buildings

Here we provide a photo tour of mold which was hidden at least from some investigators and occupants, with photo and text tips on spotting problem mold in air conditioning systems, behind and under bath and other cabinets, mold under and in wall to wall carpeting, mold on stored paper files, file folders, and books, mold on, in, and under furniture, and mold behind wallpaper.

Where to look for hidden mold in air conditioning equipment interiors and in HVAC duct work

Photo of mold inside of a Florida Air Conditioning air handler unit - Mark Cramer, Tampa, FL.

Mold may be found growing on insulation or even on metal surfaces inside of an air handler unit, such as on the blades of the squirrel cage fan in the blower compartment.

Anywhere that house dust and debris are deposited on the surfaces of an HVAC system we may find mold growth - that's because house dust contains lots of skin cells and often other organic debris that can support fungal growth.

But mold growth in an air handler or air duct is more likely where moisture is present at problematic levels, such as where condensate is blowing onto the fan assembly or duct interior when it should be captured and drained away by the condensate drain system.

So also look for mold inside of ductwork or air handler sections that are downstream in the air pathway from the blower assembly itself.

And pay particular attention to air handler equipment or ductwork that has been wet from leaks, condensate leaks, or other moisture sources such as building flooding.

How We Find Hidden mold behind bathroom and other cabinets

Photo of mold behind a bahtroom vanity cabinet - a small area of toxic mold

Photo of mold behind a bahtroom vanity cabinet - a small area of toxic mold fully exposed after removal of the cabinetry

Photos of mold behind a bathroom vanity cabinet base - shower water leaked across the bath floor, under the vanity, and into the wall cavity.

This was a small mold cleanup area, less than 10 sq .ft. and suitable for handling by a homeowner or handyman. The second photo shows the extent of mold after the cabinet was removed.

When we rebuilt this bathroom, since the tile floor slopes slightly down from tub towards the vanity base, as precautions against future mold growth we sealed all of the new vanity underside surfaces to reduce moisture and thus mold growth, and we caulked the vanity carefully at the floor level to prevent water from passing below.

Tips for Finding Hidden Mold Below Built-in Bureau Drawers

The previously-hidden toxic black mold (Aspergillus niger) shown in this photograph was found beneath a built-in bathroom storage drawer - shower water leaked across the bath floor, under the built-in, and into the wall cavity. I found this incompletely cleaned area during a post-remediation mold clearance inspection and test.

This was a small mold cleanup area, less than 10 sq .ft. and suitable for handling by a homeowner or handyman had there not already been a costly mold remediation project at this property. In this case the remediator returned to complete the work.

Failing to simply pull out a drawer to look into the built-in cavity is an indication of superficial workmanship on a mold cleanup job. Here is a mold test lab photo of Pen/Asp spore chains that we had found in our mold clearance inspection sample of settled dust taken near this bathroom.

Here is a mold test lab photo of the actual Aspergillus niger colony sample I collected from the pine tongue and groove subflooring in the moldy area shown above - this is a probable source of the spore chain found in our screening sample.

How to Find Hidden mold below wall to wall carpeting:

Photo of moldy carpet tack strips indicating moldy wall to wall carpeting and prior leaks or flooding

Photo of clean carpet tack strips confirming that there has been no water entry at this location since carpets were installed

Hidden mold in and under wall to wall carpeting is notorious and widespread in areas which have been subject to wet conditions such as basements or floors on leaky slabs.

The first photo at left shows moldy carpet tack strips which confirms a history of water entry and makes the carpeting highly suspect of serving as a problem mold reservoir. (We tested the carpeting further using a special vacuum mold test method.) The second photo shows clean carpet tack strips, indicating that at least since this wall to wall carpeting has been installed there has been no water below the carpet in this area, and suggesting that the risk of mold in this carpeting is low.

Of course mold may be visible on the surface of carpeting too, such as in this closet.

In this case we suspected that the visible carpet mold was the "tip of an iceberg" of hidden mold below.

How to Spot Hidden mold on stored papers and files in cabinets:

Photo of moldy paper files in a law office basement

Photo of moldy file folders in a law office file cabinet subject to prior flooding

Paper files and documents and file folders, even stored in metal file cabinets, can become quite moldy when left in a damp basement. In these photos the file cabinet was never itself wet, but the floor beneath it had been wet several times leading to extensive mold growth on these law office files.

There are procedures for cleaning and salvaging moldy books and paper files, but the cost is high, making it appropriate only in special circumstances such as the preservation of works of art or valuable books or historic papers.

How to Recognize Hidden Mold on and in Furniture:

Photo of moldy upholstered chair from a lakefront cottage

Upholstered furniture can be quite moldy if it has been exposed to flooding (photos above).

Only in unusually severe circumstances will upholstered furniture be visibly moldy. Don't forget to look on the underside of couches, tables, and chairs, especially since the un-finished but hidden surfaces such as raw wood under a table or cabinet more easily take up moisture and support mold growth.

The condition of the moldy green chair in the photo (left), from a lakefront cottage in Elk Lake Michigan, was pretty obvious after it had spent a decade in the damp cottage. Moldy furniture like this must either be discarded or stripped to its bare frame for cleaning before reupholstering.

Remember to use your light (as we describe here and in other articles) to look along finished wood surfaces as often light colored problem mold is hard to see but may be quite extensive.

How to Find Mold Hidden Behind Wallpaper

Building wallpaper may include problematic molds such as Aspergillus sp. and Stachybotrys in areas subject to leaks such as below the window in the condominium in New Jersey, or in bathrooms where wallpaper was applied.

We suspected mold and convinced our daughter to peel down the wallpaper below this window because she had told us that there had been a history of wind-blown rain leaks at this particular opening.

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Mark Cramer Inspection Services Mark Cramer, Tampa Florida, Mr. Cramer is a past president of ASHI, the American Society of Home Inspectors and is a Florida home inspector and home inspection educator. (727) 595-4211 mark@BestTampaInspector.com 11/06 and 04/2008

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Other Places to Look for Hidden Mold

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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
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Other Places to Look for Hidden Mold Contamination or Mold Growth

Here are photos of more places to look for hidden mold in buildings

Where to look for hidden mold in air conditioning equipment interiors and in HVAC duct work

How We Find Hidden mold behind bathroom and other cabinets

Tips for Finding Hidden Mold Below Built-in Bureau Drawers

How to Find Hidden mold below wall to wall carpeting:

How to Spot Hidden mold on stored papers and files in cabinets:

How to Recognize Hidden Mold on and in Furniture:

How to Find Mold Hidden Behind Wallpaper

Questions & Answers regarding this article

Ask a Question or Search InspectAPedia

Technical Reviewers & References

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