How to Safely Clean a Cedar Shake Roof

Cedar shake roofs need cleaning, but never with a pressure washer. In the Pacific Northwest, the safe method is a gentle low-pressure rinse paired with a specialized, wood-friendly cleaner that kills moss and algae without splintering or eroding the shakes. Done correctly, it can add years to a cedar roof's life.

Why cedar shake needs special care in the Pacific Northwest

Cedar shake is beautiful, but it's also a natural wood product — porous, soft, and far more delicate than asphalt or composite shingles. In the damp Pacific Northwest, cedar stays wet for long stretches, and that lingering moisture invites moss, algae, lichen and mildew to settle into the grain. Around West Linn and the wider Portland metro, shaded and north-facing cedar roofs are especially prone to growth. The real challenge is removing that organic buildup without harming the wood itself — which rules out the aggressive methods homeowners often reach for.

How to safely clean a cedar shake roof

1. Skip the pressure washer entirely

A pressure washer is the fastest way to ruin a cedar roof. High-pressure water tears at the soft wood fibers, gouges the surface, strips the weathered protective layer, and drives moisture deep into the shakes where it causes rot. It can also blast shakes loose and void whatever warranty remains. If a cleaning company arrives ready to pressure wash your cedar, send them home.

2. Clear the debris first

Before any cleaning solution goes on, the roof needs to be cleared of loose debris — pine needles, leaves, twigs and the built-up "duff" that collects in the keyways between shakes. This is done by hand or with a gentle blower, working down-slope so nothing jams under the shakes. Clearing debris also helps the roof dry properly afterward, which slows how fast moss returns.

3. Use a wood-safe cleaning solution

The correct way to clean cedar is soft washing: applying a specialized, wood-friendly cleaning solution at very low pressure. The solution — not the pressure — does the work, breaking down moss, algae and lichen at the root and lifting stains from the grain. A quality cleaner is formulated to be gentle on cedar and safe for the plants and soil around your home, which matters in the landscaped yards common across the PNW.

4. Rinse gently and let it dry

Once the solution has had time to work, the roof gets a low-pressure rinse — think garden-hose pressure, not a machine. The goal is to carry away the loosened growth without disturbing the wood. Cedar should then be allowed to dry fully. Rushing the job or over-saturating the roof traps moisture, which is exactly what you don't want on a wood surface.

5. Add moss prevention

Because our climate keeps feeding moss, prevention is what makes a cedar cleaning last. Installing zinc or copper strips near the ridge lets rain carry trace metals down the roof, creating conditions moss and algae dislike. A periodic maintenance wash and trimming overhanging branches for more sunlight also go a long way. For more on why our region grows moss so aggressively, see our guide on why PNW roofs grow moss.

Cedar dos and don'ts

When it comes to cedar shake, a handful of rules keep your roof safe:

• Never use a pressure washer or stiff wire brush
• Avoid harsh chlorine bleach, which dries out and greys the wood
• Don't walk on cedar when it's wet — it's slippery and shakes crack easily
• Don't ignore growth; moss traps moisture and shortens roof life
• Do use low-pressure soft washing with a wood-safe cleaner

Should you DIY or hire a pro?

You can handle light surface cleaning yourself if you're comfortable and safe on a ladder, but cedar is unforgiving of mistakes, and roof work carries real fall risk. For most homeowners in West Linn and across the Portland metro, hiring a pro who specializes in soft washing cedar is the safer, longer-lasting choice — and it protects the considerable investment a cedar roof represents. If you're weighing costs, our breakdown of roof cleaning prices in Portland can help you budget.

Want your cedar roof cleaned the safe way? Get a free, no-obligation quote — and take 30% off your first service right now.