Why Is My Roof Stained?

Dark stains on roof shingles are unsightly and don’t help your home’s resale value. They can also indicate underlying issues.

These dark stains are most often caused by algae (gloeocapsa magma) spread through airborne spores. This is particularly common in humid areas. It tends to grow on shaded sections of the roof such as those along a north facing slope.


Roof stains are not just unsightly, they can be signs of serious damage that can shorten your roofing system’s lifespan. It’s important to understand what the different stain colors indicate, so you can diagnose the problem and prevent future occurrences.

Black stains are caused by algae spores growing on your shingles. This type of roof algae, referred to as Gloeocapsa magma, thrives in warm and humid environments. It typically begins as small spots, and can quickly develop into visible streaks. According to Family Handyman, if the problem isn’t addressed promptly, the spores will absorb moisture and cause the shingles to deteriorate. This process can leave the shingle susceptible to fungus and mold growth, which will further damage the shingles.

Algae stains are most often seen on shady areas of a house’s roof. The shady area prevents the sun from drying the surface, which encourages algae to grow. This type of roof algae can be easily removed with a simple power-washing, but the stain may return if the root cause is not addressed.

Using copper or zinc-coated sheet metal, like those used on chimneys, along the ridge of your roof is a good solution to prevent re-occurrences of algae stains. These metal strips are toxic to algae and can keep them from growing. They also help deter birds, ants, squirrels and other pests from nesting on your roof.

Another way to keep algae at bay is to trim nearby trees. A trimmed tree will allow the sun to reach your roof surface more directly, which can help reduce algae growth. Lastly, investing in asphalt shingles that incorporate algae-resistant granules is one preventative measure that can keep your home’s roof free of unsightly stains for years to come.


Moss grows in cool, moist environments, and it is a common cause of roof staining. It often forms a thin layer on top of shingles, where it eats away at the outer protective layer and allows moisture to seep into the house. Moss also holds water, which makes the shingles more likely to rot and leave your home vulnerable to leaks. If moss is growing on your roof, it may indicate that it's time for a new roof.

Black or red stains hugging a chimney can be caused by rust accumulating on the metal surface of the chimney and other metal components on your roof. These stains can be removed with a special cleaning product that contains oxalic acid, which removes rust and prevents further corrosion.

Brown stains on a roof can be caused by organic tree debris such as leaves, animal droppings, sticks and rotting vegetation that falls on the roof. These stains can be washed off with a power cleaner. If the stains occur only on a specific area of a roof, look for a relationship between the stained section and a proximate cause, such as a tree that shades the roof or drops organic debris on it.

White stains on a roof may be calcium salt deposits left by roof-mounted swamp coolers or evaporative cooling equipment. These stains can be easily removed with a commercial or homemade mineral cleaner, but it is important to clean up the deposits immediately and not let them build up on shingle surfaces.

Using a high-pressure hose, start by spraying all of the mossy sections of your roof. Work the spray in a downward direction so that the force of the water doesn't lift up or damage your shingles. Next, use a scrub brush or a long-handled soft-bristle brush to gently scrape or scrub the moss away from the shingles. Work in one small area at a time, to avoid lifting or breaking the shingles.

It's important to remember that a roof isn't designed to support the weight of human beings. Walking on a roof can cause it to warp and break, and can also lead to injury if you fall off the side of your roof. If you find that your roof is covered in moss, it's best to hire Roofers In South Jersey roofing company to do the job safely and properly.


Rust stains are usually reddish brown and appear at nicks in the roof surface. They are the result of iron atoms reacting with oxygen in moisture to produce iron oxides (also known as ferric oxide or Fe2O3). These oxides weaken the bonds between metal surfaces, causing the material to flake off and rust.

Rust staining may occur on any type of roofing material, including shingles. However, it is less common for rust to form on shingle roofing than on other types of roofing materials. Rust on a shingle roof is normally confined to the edges of the roof and under flashings.

The rusty appearance of a shingle roof may also be the result of an algae, moss, or hard water buildup. In these cases, the stains should be removed with a power-washer or scrubber to prevent damage and further decay of the roofing materials.

If a stain pattern develops only in limited areas of a single roof slope, look for a relation between the stain color and a proximate cause such as a sooty chimney top or a tree that shades that part of the roof. Stains arising from these proximate causes are typically easier to treat than stains caused by the underlying roofing material or by the overall environment of the building site.

In some cases, a stain pattern is independent of proximate causes and is instead a characteristic of the underlying roofing materials or its installation. These conditions are typically more difficult to treat, and they tend to shorten the life of the roofing system.

Black stains on asphalt shingle roofs that appear to emanate from a single spot are sometimes traced back to extractive bleeding, a product defect of the shingle manufacturers. These stains are not easily treated by power-washing or scrubbing because they can weaken the shingles and may expose them to further damage from freeze-thaw cycles. For this reason, it is best to contact a professional roofer and ask about solutions that will adhere to shingle manufacturer specifications.

Water Damage

A well-raked yard, meticulously trimmed hedges and flawless seasonal displays don’t mean much when dark discolorations are creeping up your roof. Those ugly black streaks are more than an eyesore; they’re usually a sign of roofing problems that can lead to water damage inside your home.

Algae stains on shingles are the most common cause of unsightly roof streaks. The algae, called Gloeocapsa magma, feed on the limestone in asphalt shingles and spread as they grow, leaving behind those dreaded dark greenish or black streaks. Algae is especially prevalent in warm, coastal climates and can also be found in areas of a roof that don’t receive a lot of sunlight (such as a north-facing roof section). The good news is, this type of stain can be removed with bleach or other commercial algae-fighting chemicals.

If the stains are caused by a roof leak, however, the problem is more complicated. The water can seep through the shingles, and then drip down onto ceilings, walls and floors. If the leak is not stopped quickly, it can cause significant and costly damage to furnishings, carpeting, drapes and other belongings inside a home.

Leaking water can also cause drywall to become wet, which in turn can lead to a mold or mildew problem and bubbling paint. The best course of action is to call a local professional as soon as possible to stop the leak and prevent further damage.

Once the leak is stopped, the next step is to make a plan for repairing the damaged area of the ceiling. This may require placing a new piece of drywall, adding insulation and repainting. If the drywall is severely damaged, it may be necessary to replace it entirely. A qualified roofer can assess the severity of your leaking ceiling and recommend the best course of action for a repair.

Dark stains on roof shingles are unsightly and don’t help your home’s resale value. They can also indicate underlying issues. These dark stains are most often caused by algae (gloeocapsa magma) spread through airborne spores. This is particularly common in humid areas. It tends to grow on shaded sections of the roof such as those…