Black Stains On Plywood In Attic

Black mold in attics.

Black stains on plywood in attic.

Last winter i took a look into the attic and noticed black stains and water marks on a portion of the sheathing material. In winter moist air is transported from the heated area of the home into the unheated attic space where it not only settles on the wooden rafters and plywood roof sheathing but also melts the snow on the roof leading to ice dams. 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. If the wood is soft if it s easily imprinted when you push on it it s probably rotten.

If the dark surface of the wood smudges it could be mold. 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 can be caused by the action of fungal growth and molds and the affect they have on the tannins in the wood.

While the black stains are either mould or just black dust from attic insulation settled on the. This summer i cleaned the portion of the black stain with a dry mop as much as i could reach from the hatch opening. First let s look at the source.