If you’ve noticed dark streaks spreading across your roof, you’re looking at one of the most common sights on Baton Rouge homes — and it’s not just dirt.
What Those Black Streaks Actually Are
The streaks are a type of algae called Gloeocapsa magma. It feeds on the limestone filler that manufacturers put in asphalt shingles, and it spreads across the roof as dark, ugly streaks — usually starting on the north-facing slopes and shaded sections that stay damp the longest.
Baton Rouge is practically built for it. Our heat, humidity, frequent rain, and heavy tree cover keep roofs damp enough for algae to thrive year-round. Once it takes hold, it spreads a little more every rainy season.
It’s More Than Ugly
Algae holds moisture against your shingles. Over time that constant dampness can shorten the life of your roof and lead to premature aging. It also tanks your curb appeal — a streaked roof can make a well-kept home look neglected, which matters if you’re thinking about selling.
What About Moss and Lichen?
Algae shows up as streaks, but you might also see green moss patches or crusty white-green lichen spots — especially on shaded or older roofs. Moss is worse than algae: it grows roots into the shingle and can lift edges, letting water underneath. Lichen bonds to the granules and is stubborn. Soft washing handles all three, but moss sometimes needs a follow-up treatment after the first wash kills it.
Why You Should Never Pressure Wash Your Roof
This is the big one. Blasting shingles with high pressure strips the protective granules right off them. Those granules are what protect the shingle from the sun — lose them and you lose years of roof life. It’s also why every major shingle manufacturer requires soft washing, not pressure washing, for cleaning. Pressure wash your roof and you can void your warranty.
Can I Just Use Bleach Myself?
You’ll see this advice online. Straight bleach can kill the algae, but it also kills your landscaping, can corrode your gutters and flashing, and without the right additives it runs right off the roof before it finishes the job. Pros use a measured mix with additives that help it cling and dwell — and they protect your plants first. The DIY savings usually aren’t worth the dead flower beds.
How Soft Washing Fixes It
Roof cleaning in Baton Rouge should always be done with a soft wash: low pressure plus a cleaning solution that kills the algae at the root instead of just blasting the surface. The streaks rinse away, and because the growth itself is dead, they stay gone far longer than any surface-level cleaning.
A professional soft wash also treats the whole roof evenly — spot-cleaning just the streaks leaves you with a patchy, two-tone roof.
Keeping It Clean Longer
Once your roof is clean, a few things slow the algae down: trimming back tree branches that shade the roof, keeping gutters clear so water doesn’t back up, and in some cases zinc or copper strips near the ridge (rainwater picks up metal ions that discourage regrowth). Nothing stops it forever in Louisiana — but a clean roof with good sun exposure stays clean years longer than a shaded, neglected one.
When to Call a Professional
If you can see the streaks from the street, it’s time. Don’t climb up there yourself — steep, algae-slicked shingles are dangerous, and store-bought chemicals rarely reach the root of the problem.
Tiger Pressure Wash has been soft washing roofs in Baton Rouge since 2012. Get a free quote and we’ll take a look at what your roof needs — no pressure, just an honest assessment.