Green streaks, fuzzy moss, and piles of leaves on a roof worry many homeowners. Some of it is cosmetic. Some of it can lead to leaks over time. Knowing the difference helps you decide what to do.
Algae
Dark streaks on shingles are usually algae. They tend to show up on shady, damp roofs. Algae is mostly a cosmetic problem, but it can make a roof look worn, and some roofs hold heat differently with dark streaks. It is not usually a direct cause of leaks. See our asphalt shingle roof care guide for safe cleaning options.
Moss
Moss grows in shady, damp spots, and it can hold moisture against the shingles. As it spreads, its roots can work under the edges and lift them, which can let water in. On a heavily covered roof, that can add up over time.
Leaves and debris
Leaves, seeds, and twigs collect in valleys, behind chimneys, and against walls. They hold water against the roof and block drainage, which can send water under shingles or over the gutters. Debris on a flat roof can clog drains.
What to do
- Trim trees that shade the roof and drop debris. More sun and airflow slow growth.
- Clear debris from valleys, flat sections, and gutters. Hire someone if you would need to climb up.
- Do not pressure wash shingles. It can strip granules and force water under the edges.
- Do not scrape or pry moss off. That can tear shingles.
- Ask a roofer about gentle cleaning treatments and what is safe for your roof. Some treatments can harm plants or stain surfaces, and some shingles have specific care requirements.
- Zinc or copper strips near the ridge are sometimes used to slow growth, and a roofer can tell you whether they make sense for your roof.
When it signals a bigger problem
Heavy moss growth can mean the roof stays damp, which can point to poor drainage, shade, or ventilation. If shingles under the moss are curled, cracked, or bare, the moss may be a symptom of a roof that is nearing the end of its life.
Check for damage
After the roof is cleaned, look for damaged shingles and flashing, and for stains in the attic and ceilings. A roof that stays wet may have damage that is easy to miss until a leak shows. For more, see our guide to preventing roof leaks.
Do not ignore a stain
A stain inside the house is a stronger sign than anything on the roof surface. If you have a stain, get the cause found, whether or not you see moss.
Get the roof looked at
For roof leak repair in Carol Stream, call Roof Leak Repair Carol Stream IL at (630) 866-1445. Tell us what is growing on the roof and whether you have any stains inside.
Carol Stream Leak & Restoration is a free referral service. We connect Carol Stream homeowners with independent local roofing contractors — no fees to you, ever. Call (630) 866-1445 for fast help with a roof leak.