Black Staining On Roof Sheathing

Green or black algae stains.

Black staining on roof sheathing.

After several years of this there may be dark rings around protruding roofing nails and larger dark spots or areas on the roof sheathing and or exterior gable walls. If your roof is older or in bad shape and needs replaced anyway you may want to invest in these copper infused shingles. If these isolated spots are seen away from these roof penetrations then the roof may be damaged and leaking. The following picture is of a long standing moisture condition in an attic where much of the roof sheathing has turned black.

Note the heavy staining and growth on the plywood. Mold usually causes a musty odor and may cause staining that may be black brown gray white yellow or green. Builders forever looking to save a few bucks began turning toward plywood roof sheathing. Roof algae rarely poses a threat to the health of the roof.

Natural wood is expensive. The original skip sheathing has much less growth. The leak was fixed. I had a roof leak a year or more ago.

Replacing the shingles on your roof just because you have black stains is not necessary however and you should be suspicious of any roofer that suggests roof shingle replacement as the only solution to your algae problem. However i was in the attic the other day and noticed the underside of the roof sheathing plywood at the old leak area has some black staining where the plywood got wet from the leak. It s been over a year since the leak was fixed and the stain is not going away on it s own. It may be difficult to remove the mold stains from sheathing but you can kill.

Across the entire eastern half of the country roof shingles tend to grow a species of algae called gloeocapsa magma. This can be caused by the action of fungal growth and molds and the affect they have on the tannins in the wood. It appears in streaks or patches of slime that can be anywhere from blue green to dark black. It was a result of bad flashing at the chimney pentration.

Mold can form but often it. When moisture condenses on plywood roof sheathing repeatedly or continuously the wood will turn black. These are commonly seen underneath roof vents plumbing stacks vent hoods and around chimneys.