Stains on a roof happen for many reasons. Some are only cosmetic. Others point to a problem that can shorten the life of your roof. Roof stain colors, and where the stain sits, usually tell you which.
What roof stain colors usually mean
Black or green streaks
Algae grows on shingles and on concrete and clay tile. Green stains are usually green algae. Dark streaks are often a type of bacteria called Gloeocapsa magma. The dark color is a coating it makes to protect itself from the sun. On shingles, it’s mostly a cosmetic problem.
Black streaks from one spot
If black streaks run down from a single point on a shingle roof, it may be “extractive bleeding.” It’s a product issue in the asphalt that shingle makers describe as cosmetic. It’s easy to mistake for algae or soot. A roofer can tell the difference during an inspection.
Brown, gray or black stains from debris
Leaves and twigs left on the roof break down and stain it. They also hold moisture, which helps moss and algae grow and keeps the roof from drying out.
Black stains below a chimney or flue
Dark stains in a line below a chimney often come from soot washing down. Soot below a flue from a gas appliance is different. It can mean the appliance isn’t burning right, which raises the risk of carbon monoxide in the home. Have that appliance checked right away.
Red or rust-colored stains
Red stains often come from rusting metal, like flashing, chimney caps or vents.
White stains on masonry
White or yellowish-white stains on a brick or stone chimney are called efflorescence. Water soaks in, then leaves mineral salts behind when it dries. It’s usually cosmetic, but it means water is getting into the masonry. It’s worth checking that water isn’t getting inside the chimney.
Stains on tile roofs
Stains on tile are often harmless. But stains near valleys and drainage channels can mean debris is blocking the water path. On a tile roof, clogged drainage channels are one of the main ways water gets under the tile to the underlayment. See tile roof repair.
Stains inside your home
A brown stain on a ceiling or wall is a different story. That usually means a leak. Read about roof leak repair.
Cleaning and preventing roof stains
- If you clean the roof, follow the shingle or tile maker’s instructions and the cleaner’s label.
- Walking on a roof is dangerous, especially when it’s wet. Tile can also break underfoot. If in doubt, call a pro.
- Clear leaves and debris off the roof and out of gutters.
- Trim branches back so the roof gets more sun and dries faster.
- If you’re replacing a shingle roof, ask about algae-resistant shingles.
Related: Shingle roof repair · Roof inspection · Roof repair
Not sure what a stain on your roof means? Roof Recovery is licensed and insured, with women owner-operators. We’ll inspect your roof for free, take photos, and give you a written quote the same day if it needs work. Call (916) 678-9786 or request a free inspection.
