Mold in OSB sub-flooring is commonly found in Florida homes, even when there is no known leak or water damage.

Mold Inspection Services Jacksonville, FL

Most homeowners panic when they find “mold” in the sub-flooring and often their first call is to their insurance carrier, a mold remediation company, or a water damage restoration company. It’s understandable, but neither of these companies should be your first call for help, and let me explain why…

First Things First

The first thing we need to know is why the mold is present and we will determine that by determining the level of moisture present in the OSB. By knowing the amount of specific moisture, we will know the type of mold which can exist in that level of moisture. Further, we will know how we may be able to treat the material based on the moisture content. OSB which is saturated (wet) will require removal and will always be associated with a water leak or flooding. Surface molds or opportunistic molds like aspergillus, penicillium, or Cladosporium do not require active moisture from a leak to colonize but rather can thrive on condensation or elevated humidity. We typically find these initial colonizer molds with slightly elevated moisture readings and this mold can be treated easily with drying and disinfecting.

Aspergillus/penicillium mold is the most common mold found in OSB sub-flooring as well as behind baseboards or wallpaper in our homes. It is rarely a cause for alarm and without an active leak does not present an elevated health threat. It is an opportunistic, initial colonizer mold meaning it is a common surface mold. We find it in homes with elevated humidity, dampness, or as a surface mold beneath vinyl flooring products or vapor barriers that trap condensation.

You Have a Condensation Problem

Homeowners should be careful in choosing floor covering materials, especially when using vapor barriers with the products. Our humid climate creates condensation in surfaces where hot air meets cold air such as our floors, walls, windows, and ceilings. When hot air meets cold/conditioned air, it creates condensation and unless we have planned how we will dissipate that condensation, we will always find dampness and opportunistic molds.

When you find mold in OSB sub-flooring, you need to know why the mold is present so that you can resolve the dampness issue. You don’t really have a “mold” problem, you have a problem with condensation, and you may need to hire a Licensed Mold Assessor who understands building science. You most likely will not need expensive mold remediation and you will never need “encapsulation”. You need someone who can advise you on how to stop the condition from creating condensation.


William Chandler is a Licensed Mold Assessor and a Certified General Contractor with Property360. He is also a Council Certified Indoor Environmental Consultant with over 40 years of indoor air quality experience.

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