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Community and Q&A

Wood Mositure Content – Mold and/or Decay

Joe_Adams | Posted in General Questions on

Hi everyone !

I am passing by to ask a question that has generated some confusion during my research. 

The question is related to the necessary Wood Moisture Contents to generate Mold and/ or Decay. 

I have read that although many factors such as temperature affect the water activity at the surface of wood, moisture content above 20 percent for approximately a week is required for significant mold growth to occur on wood.

However, wood decay fungi that can actually destroy wood require much wetter conditions and start growing when the moisture content by weight is greater than 28 percent (which corresponds to saturated wood).

I have notice that many authors point the 10-16% Moisture Content as desirable values.

However, these values vary a lot from author to author. I am seeking to valuable help trying to understand these values.

What is the healthy Moisture Content?

What is the dangerous Moisture Content for mold?

What is the dangerous Moisture Content for decay?

A complementary question is: Why people talk so much in indoor relative humidity to adress mold problems in brick walls and Moisture Content to adress mold in wood ? 


Thank you in advance


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  1. PAUL KUENN | | #1

    Joe, the whole idea behind our building practices is to keep any water (vapor or otherwise) out of the wall assembly. The biggest reason following your last question is that brick is very conductive and cold in cold climates. Any water will follow temps from hot to cold. So, if you have any moisture that can make contact with the brick it will condense and thus the wood or plaster wall next to it in the interior will suffer with damage from the moisture.

  2. walta100 | | #2

    At 10-16% sound like the wood has reached equilibrium with the air inside most home so that it will not dry anymore given the humidity in the local air.

    In my opinion moisture meter are mostly useless in that you get different reading from one species to the next and heart wood and sap wood.

    Relative humidity is important because generally when wood is wet it is often because the wood absorbed the water from the air. More water in the air equals more water in the wood.


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