Leaking Heating Duct
This crawl spaces located in a cold climate, where
condensation is a big problem. When there is hot and cold air within a
confined area, the moisture in the air will start to turn into water and
now we could have a problem if there isn't enough ventilation to remove
The incorrect installation or repair of this heating duct has created a financial problem for the current homeowner. In the picture below you can see the damage caused from the hot air escaping from the heating duct system and mix in with the cold air in the crawl space to create excess moisture on the floor framing.
The excess of moisture has created excellent living conditions for this fungus that is growing underneath the plywood sub flooring. This fungus will eventually weaken the subfloor sheathing.
Someone could actually fall through the floor as the fungus weaken it. All of this was caused from the improper installation or repair of a heating duct. As part of the home repair in this house, the entire floor needed to be replaced.
Don't forget to repair the original culprit to your problems. When repairing the flooring, make sure that you fix any water leaks or moisture creating conditions.