Attic Sheathing Black

The other two possibilities for the stains.

Attic sheathing black. Condensation determining the cause of attic mold. White and green fuzzy growth on osb sheathing. This can be caused by the action of fungal growth and molds and the affect they have on the tannins in the wood. I m aware of the cause poorly vented bathroom fans and not well sealed fan fixtures lights wires etc.

If the wood is soft if it s easily imprinted when you push on it it s probably rotten. In our roof interior attic photo at left you can see antique roof framing along with black stains and probably some mold growth from a long history of roof leaks. If the dark surface of the wood smudges it could be mold. Despite what your roofer would like you to believe roof leaks rarely cause significant mold problems.

Uniform black mold growth on attic sheathing. The following picture is of a long standing moisture condition in an attic where much of the roof sheathing has turned black. When moisture condenses on plywood roof sheathing repeatedly or continuously the wood will turn black. Even in this case in our opinion the reasons to remove and replace roof sheathing and framing would normally be based on the condition of the roof framing and sheathing not on the presence of mold or stains.

I have surface mold on the sheathing in my 1982 vintage 12 6 pitched attic. This occurs when the temperature of the sheathing drops below the dew point creating a thin layer of moisture on the substrate. The mold itself may have a cottony texture but can also be velvety leathery or. In the vast majority of cases the mold growth is caused by condensation.

In many cases the continued wetting of the sheathing will cause it to rot but that may take several years or decades depending on the attic ventilation. Mold growth on attic roof sheathing is a common issue in cool climates such as the pacific northwest.