Roof Moss vs. Roof Algae: What's Growing on Your Shingles?
Homeowners in Rock Hill often call us about “moss on the roof” when what they actually have is algae — or vice versa. They look different, grow differently, and cause different types of damage. Here's how to tell them apart and why both need attention.
Quick visual guide
Roof algae (Gloeocapsa magma)
- • Looks like: Dark black or dark green streaks running down the roof
- • Texture: Flat, smooth — no raised growth
- • Location: Usually starts on north-facing or shaded slopes
- • Spread: Airborne spores — spreads to neighboring roofs
- • Common in: All of Rock Hill, Fort Mill, Tega Cay, Lake Wylie
Roof moss
- • Looks like: Thick, green, fuzzy growth — raised off the surface
- • Texture: Spongy, carpet-like — you can see individual plants
- • Location: Shaded areas, between shingles, in valleys
- • Spread: Grows slowly but bonds deeply to shingle surface
- • Common in: Heavily shaded roofs near trees
How algae damages your roof
Algae is the more common issue in Rock Hill. Gloeocapsa magma feeds on the limestone filler in asphalt shingles, gradually degrading the protective granule layer. The dark color it produces absorbs more heat, raising your attic temperature and energy bills.
Left untreated, algae can shorten your roof's lifespan by 5–10 years. It also spreads through airborne spores, which is why you often see entire neighborhoods with the same black streaks.
How moss damages your roof
Moss is less common than algae in our area but more destructive when it does appear. Unlike algae, moss is a plant with roots that grow into and under shingles. This causes several problems:
- •Lifts shingles: Moss roots grow under shingle edges, lifting them and creating gaps where water enters
- •Traps moisture: Moss acts like a sponge, holding water against the roof surface for extended periods
- •Causes rot: Trapped moisture leads to wood rot in the decking underneath
- •Creates leaks: Lifted shingles and rotted decking eventually lead to interior water damage
What about lichen?
Lichen is a third type of growth you might see — it's actually a combination of algae and fungus living together. It looks like small, crusty, light-colored patches on shingles. Lichen bonds very tightly to the surface and is the hardest of the three to remove. It requires proper soft washing with adequate dwell time.
How soft washing treats both
The good news: our roof soft wash process kills algae, moss, and lichen effectively. The sodium hypochlorite solution penetrates the root system of all three organisms, killing them at the cellular level.
Our roof soft wash process
- 1.Protect landscaping and pre-wet plants
- 2.Apply sodium hypochlorite + surfactant at low pressure
- 3.Extended dwell time for moss and lichen (longer than algae-only treatments)
- 4.Rain naturally rinses dead growth over the following days and weeks
For heavy moss, results improve over 2–4 weeks as rain washes away the dead growth. Algae results are more immediate.
Prevention tips
- ✓Trim tree branches that overhang the roof to increase sunlight and airflow
- ✓Keep gutters clean so water doesn't back up under shingles
- ✓Schedule a roof soft wash every 2–3 years before growth gets established
- ✓Consider zinc or copper strips along the ridge line for long-term prevention
Send us your address and we'll take a look. Roof soft wash starts at $399.
Roof Washing Details →