Roof cleaning that makes a difference.

What those black streaks actually are

Almost always, the dark stripes running down a shingle roof in South Carolina are Gloeocapsa magma — a blue-green algae that travels by air and settles on roofs. It feeds on the limestone filler used in asphalt shingles and protects itself with a dark pigment, which is why the growth reads as black from the driveway.

It starts on the shaded north side, spreads downhill with rain, and doesn't stop on its own. Our climate is close to ideal for it: humid summers, mild winters and a lot of tree cover.

Algae, moss and lichen are three different problems

• Algae — flat black streaks. Surface level and the most common thing we clean.
• Moss — green clumps, usually along shingle edges and in valleys. It holds water against the roof and can lift shingle edges over time.
• Lichen — crusty gray-green spots that grip the shingle surface. The most stubborn of the three, and it may take longer to fully release after treatment.

All three are living organisms, which is why cleaning them is a chemistry problem more than a pressure problem.

Why we don't pressure wash roofs

A pressure washer can absolutely take the black off a shingle. It can also take the granules off with it. Those granules are the shingle's UV protection and a big part of its rated life. Once they're in the gutter, they aren't coming back.

High pressure can also drive water up under shingle courses and into places water isn't supposed to go. Most asphalt shingle manufacturers direct homeowners toward low-pressure cleaning for exactly these reasons.

If a company shows up to your roof with a surface cleaner and a 4000 PSI wand, ask questions.

How soft washing works

Soft washing uses low pressure — roughly what comes out of a garden hose — and a cleaning solution that kills the organic growth. The pressure is only there to carry the solution and rinse it. The chemistry does the cleaning.

1. We look at the roof, the pitch, the gutters, the landscaping and the water source.
2. Plants, shrubs and anything else sensitive around the house get covered or pre-wet, and get rinsed again during and after the job.
3. The solution is applied evenly from a ladder or from the roof, working in sections.
4. We let it dwell, then rinse as needed.
5. We walk the property with you before we pack up.

Streaks lift during the wash on most roofs. Heavier moss and lichen can keep releasing over the following weeks as the dead growth breaks down and rain carries it off.

What to expect on the day

• We'll confirm a window ahead of time and let you know when we're on the way.
• We need access to a water spigot and room to set up. Cars out of the driveway helps.
• Windows and doors closed, and pets inside while we work.
• You don't have to be home — plenty of our customers aren't.
• We rinse landscaping before, during and after.