Why Is My Shingle Roof Discolored?

(From the team at Zenith Roofing – Serving Marietta, East Cobb & Northeast Atlanta)

One day your roof looks normal… and the next time you pull into the driveway you notice dark streaks, black patches, or strange discoloration spreading across your shingles. It’s one of the most common questions we get from homeowners in Marietta, Lawrenceville, Roswell, and Cumming
“Why is my shingle roof discolored?”

The good news? Not all discoloration is bad.
The better news? If it is a problem, catching it early can save you from leaks and costly repairs.

Let’s break down the real reasons your roof may be changing color — and what to do about it.

1️⃣ Black Streaks: Algae (Gloeocapsa Magma)

If you’re seeing long, dark streaks running down the shingles, that’s almost always algae.

This type of algae thrives in humid areas like North Georgia and feeds on the limestone filler in asphalt shingles. It spreads fast, especially in shaded areas or under tree cover.

Is it dangerous?
Not immediately — but it does trap moisture, which can shorten the life of your shingles over time.

Solution:
A professional roof cleaning using safe, non-pressure methods. (Never let anyone pressure-wash an asphalt roof — it destroys the granules.)

2️⃣ Green Patches: Moss or Lichen

If your roof looks fuzzy or has raised green/white patches, you’re likely dealing with moss or lichen.

These organisms root into the shingle surface and hold moisture like a sponge — a bad combination for roof longevity.

Common in:
East Cobb, Roswell, and wooded neighborhoods with lots of shade.

Why it matters:
Moss can lift shingles, trap water, and lead to rot or leaks.

3️⃣ Rust Stains From Metal Fixtures

Orange or brown streaks often come from:

• Chimney caps

• Flashing

• HVAC mounting brackets

• Metal vents

If the metal is rusting, the runoff will discolor shingles below it.

Fix:
Replace the corroded flashing or cap and clean the shingles.

4️⃣ Granule Loss

If parts of the roof look lighter or “bald,” the granules may be wearing off.

This is a major aging sign, especially on roofs 15–20+ years old or roofs that took hail damage.

What causes it:

• Hail

• Heavy tree branches brushing the roof

• Old shingles

• Poor ventilation cooking the shingles from underneath

Check your gutters — if they’re full of granules, your roof may be nearing the end of its life.

5️⃣ Wet or Dark Spots After Rain

If your roof stays darker long after the rest has dried, it may indicate:

• Areas where water is pooling beneath the shingles

• Compromised underlayment

• Ventilation problems causing moisture buildup

• Hidden leaks

These spots deserve attention ASAP — especially before winter.

6️⃣ Sun Fading

Over time, UV exposure lightens the color of your shingles.
This is normal aging and purely cosmetic — not a structural issue.

However, uneven fading can signal previous repairs or mismatched replacement shingles.

⚠️ When Roof Discoloration Becomes a Bigger Issue

Cosmetic discoloration is common…
but if you’re seeing:

• Soft spots

• Curling shingles

• Mold in the attic

• Water stains on ceilings

• Moss lifting shingles

• Large areas of granule loss

…it’s time for a professional evaluation.

🧰 What Zenith Roofing Can Do

We offer:

• Free roof inspections

• Safe roof cleaning recommendations

• Moss and algae mitigation

• Shingle repair/replacement

• Storm damage documentation

• Insurance guidance when discoloration points to hail or wind damage

Our inspections are honest and pressure-free — we simply show you what’s happening and what your options are.

📞 Worried About Roof Discoloration?

Let us take a look before it turns into something bigger.
We’ll inspect your roof, document everything, and help you understand what’s normal and what needs attention.

👉 Schedule your free inspection today.
Proudly serving Marietta, East Cobb, Roswell, Woodstock, Sandy Springs, Milton & North Atlanta.