Crawlspace Mold: How to Find, Test, & Prevent Mold in Crawl Spaces
InspectAPedia® -
How to find, test, prevent, or remove mold from building crawl spaces
Our site offers impartial, unbiased advice without conflicts of interest.
We will block advertisements which we discover or readers inform us are associated with bad business practices,
false-advertising, or junk science. Our contact info is at
InspectAPedia.com/appointment.htm.
This document gives advice on how to find and deal with mold in building crawl spaces. This is a chapter of "How to Look for Mold" which describes how to find mold and test for mold in buildings, including how and where to collect mold samples using adhesive tape - an easy,
inexpensive, low-tech but very effective mold testing method.
This crawl space inspection procedure for mold 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.
CRAWLSPACE MOLD: finding the problem mold, allergens, or other particles in crawl spaces
The photograph at page top shows extensive fungal growth on the underside of subflooring and on wood framing supporting a wood floor over a very damp
crawl space. Depending on the mold genera/species, if an airborne fungus is present at high levels in a crawl space, spores of that mold
may move easily to upper levels in the building.
We very often find that insulation in crawl spaces has become a problem mold reservoir. Some of these molds move easily from the crawl area up into the living space.
For example, Penicillium sp. or Aspergillus sp. spores, which can be as
small as about one micron in diameter, are so tiny and light that they can move much like a gas in a building. These tiny spores rise
in upwards-moving air currents as warm air, rising to upper building levels, creates a slightly lower air pressure in lower building
areas such as basements and crawl spaces.
Depending on the tightness of construction, and the presence or absence of hot air or central
air conditioning systems which themselves may increase indoor air particle movement, the rate of movement of particles from a moldy
crawl space can vary widely.
In some instances we have found rather high levels of airborne mold spores and mold spores in settled dust
that tracked directly to the moldy crawl space.
In other instances we found that there was not much air and particle movement upwards from
a crawl space or basement, until specific triggering conditions occurred.
These included opening of a basement door, or in the case of crawl spaces,
opening upper floor windows or turning on a whole house exhaust fan. These conditions led to a significant increase in movement of
crawl space (or basement) mold from lower building areas into the living space.
First aid for moldy crawl spaces
Do not enter or work in a moldy area without wearing proper respiratory and other personal protection. See Crawl Space Safety Advice
Evaluate the history of water entry, dampness, ventilation, listing the factors conducive to fungal growth such as:
Present or past wet conditions, whether "once", episodic, or recurrent water entry
Marginal or no ventilation. Actually I prefer to stop trying to vent crawl spaces since when we want venting it's usually inadequate, and depending on weather conditions venting a crawl space can actually increase its moisture level and make matters worse. A preferred approach is to dry out, enclose, and seal a crawl space under a building, making it into conditioned space.
Exposed dirt. If the crawl space has a dirt floor, put down 6-mil plastic over the dirt to reduce moisture movement from the soil into the crawl space. Also see MOLD ON DIRT FLOORS
Presence of fiberglass or other fibrous insulation
Fix outside conditions that are causing wet crawl space conditions such as roof gutter or downspout spillage by the building foundation.
Fix inside conditions that wet crawl spaces, such as plumbing leaks or improper ventilation.
Look for visible mold:
Inspect the exposed sides of all framing, joists, girders, posts
Inspect the exposed under-side of subflooring of the floor overhead. See our warning about mold growth on pine boards discussed at Attic inspections above.
Special screening tests may assist in evaluating the condition in inaccessible crawl spaces.
Prevent mold movement into the living area: As with a moldy basement, keep openings between the crawl space and living space closed as much as possible.
Remove wet or mold-suspect insulation.
Test representative samples of mold before going to a major expense to be sure you're not just looking at cosmetic mold on framing lumber,
or at something else that is not even mold.
If a large area of visibly moldy material is present (more than 30 sq .ft.) professional cleaning and remediation are probably in order. In
that case, a building inspection and preparation of a mold remediation plan is a good idea - that work should be performed by someone who has
no conflicts of interest - in other words, not by the mold cleanup company or their agent.
Follow any costly mold remediation job
with a clearance inspection and test before you make final payment.
Review MOLD PREVENTION GUIDE
Correct the Causes of Mold and Prevent Indoor Mold or other indoor environment problems
Mold in fiberglass insulation in a crawl space
These photos show crawl space fiberglass which had fallen onto the dirt crawl space floor.
We can pretty much count on this material to be mold contaminated unless the building was in an arid climate.
You can expect to find rodent contamination as well in insulation in this condition.
This photo shows crawl space fiberglass which the installer supported by chicken wire. The crawl space was pretty drafty which we might hope would keep it dry and less moldy.
However we might expect to find a nice mouse colony here, and depending on
weather variations and crawl space flooding, this insulation too is at risk of becoming a mold reservoir.
We'd have preferred to use a solid foam insulation in conditions like this.
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.
Recognizing Mold: What mold looks like mold identification photos to help identify mold - choosing what to sample in buildings
Recognizing Allergens: What various indoor allergens look like - identification photos to help identify pollen, dust mites, animal dander, toxic or allergenic mold - Common Mold and other Allergens, Irritants, Remedies & Advice
Stuff that is not mold but is often mistaken for it - things you may not want to test. Also, not all "black mold" is toxic - here are examples of harmless black mold.
Mold Action Guide: an easy step by step outline of what to do about mold
Mold Investigation Tips for Home Inspectors how to find mold, where to look, what is likely to be important. Advice to building inspectors intending to inspect or test for toxic or problematic mold indoors, mold inspection methods, and mold test methods which are valid or invalid
Contact Us to arrange mold/IAQ building on site inspection and testing.
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
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.