Black Markings On Attic Sheathing

Inspected a house today built in 1991.

Black markings on attic sheathing.

The roof had ridge vents as well as soffit vents and. The variety i see most often is fuzzy green when active and goes black like that when dormant or dead. Attic moisture and poor ventilation are the causes. Mold growth on attic roof sheathing is a common issue in cool climates such as the pacific northwest.

When this humid relatively warm air cannot escape the attic space before the temperature drops condensation can occur. In this photo of very dark mold in an attic in a wet attic mold which we found to be brown in the microscope looked black on the plywood. Black mold in attics. If the wood is soft if it s easily imprinted when you push on it it s probably rotten.

That is a stain caused by mold mould. This can be caused by the action of fungal growth and molds and the affect they have on the tannins in the wood. In old houses you ll usually see some spots that are stained dark or black where there was a roof leak at some point in time which was repaired but the stain remains. Mold on attic sheathing.

In the vast majority of cases the mold growth is caused by condensation. In addition to dark spots at the drywall nails and or screws in the ceiling there were also dark outlines of the ceiling joists in many areas of the house. The new roof doesn t help much most of the moist air is likely coming up from below. 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. This occurs when the temperature of the sheathing drops below the dew point creating a thin layer of moisture on the substrate. The black attic mold shown here confirms that this attic had a serious venting and moisture problem including moisture from sources lower in the building.