5 Signs Your Roof Needs a Professional Cleaning

Most homeowners don't think about their roof until something goes wrong — but the surface of your roof tells you a lot before that happens, if you know what to look for. Here are the five most common signs it's time for a professional cleaning.

1. Dark streaks running down the roof

This is the big one. Those black or dark gray streaks aren't soot or dirt — they're almost always a type of algae (Gloeocapsa magma) that feeds on the limestone filler in asphalt shingles. It spreads over time and can eventually affect the whole roof if left alone.

2. Green or dark patches, especially on shaded sides

Moss and algae both thrive in areas that stay damp longer, like the north-facing side of a roof or sections shaded by trees. A patchy, uneven color across your roof is a strong sign moisture is sitting somewhere it shouldn't.

3. Visible moss growth between shingles or tiles

Moss doesn't just look bad — it holds moisture directly against the roofing material, which can lead to premature wear and, in some cases, water intrusion underneath shingles or tiles.

4. Your roof looks noticeably older than your neighbors' similar roofs

If homes around you with roofs of a similar age and material still look clean while yours looks dull and discolored, that's usually a maintenance gap, not an actual difference in roof quality.

5. It's been more than 2–3 years since the last cleaning

Even if none of the above are obvious yet, algae growth is often gradual before it becomes visible. A roof that hasn't been cleaned in a few years is worth a look, especially before it becomes a bigger, more visible problem.

Why we don't recommend DIY roof cleaning

A quick warning: pressure washing a roof yourself is one of the most common ways homeowners accidentally damage shingles or tiles, void warranties, or create leaks. Roofing material needs a low-pressure, roof-safe approach — never a standard pressure washer nozzle. If you're seeing any of the signs above, it's worth having it looked at by someone who does this daily.