Why Is Moss Growing on My Roof?

If you’ve ever looked up at your roof after a few weeks of rain and noticed a soft green fuzz creeping across the shingles — welcome to life in Tacoma. Around here, moss is just part of the scenery. It grows on fences, driveways, trees… and, unfortunately, roofs too.

At Robb’s Roofing, we see this all the time. Moss might look harmless — even kind of pretty in the right light — but it’s tough on a roof. Once it settles in, it traps water, lifts shingles, and slowly eats away at the surface. And in our damp, shaded Northwest climate, it spreads faster than most people expect.

Why Moss Loves Tacoma Roofs

Moss is a quiet problem. It doesn’t show up overnight — it builds, little by little, in the corners where sunlight never reaches. Here’s what gets it started:

• Constant dampness: Rain, drizzle, fog — Tacoma’s weather keeps roofs wet most of the year. Moss loves that.
• Shady spots: Overhanging trees and north-facing slopes stay cool and dark, giving moss a perfect home.
• Leaves and debris: They pile up, hold moisture, and create a soft base for spores to grow.

By the time you notice that green layer, moss has already started to root into the shingles. Those roots — called rhizoids — pull up the edges just enough to let rain sneak underneath. Over time, that trapped moisture can rot decking or even lead to leaks.

Quick Guide

Quick answer: Moss grows fast in Tacoma because our shade and moisture feed it.

Try this: Gently brush it off and use a zinc or moss-killing treatment.

Stop signs: Never pressure wash — it grinds off protective granules.

Typical cost: Moss treatment $250–$600; full roof cleaning $500–$1,200 depending on roof size.

Why It’s a Bigger Deal Than It Looks

A little patch of moss might not seem worth worrying about, but it’s like rust — once it starts, it keeps spreading. The more it grows, the longer your roof stays wet. Over time, that can lead to soft decking, leaks in the attic, or mold in insulation.

We’ve replaced plenty of roofs around Tacoma where moss was the main culprit, not wind or age. Keeping it under control isn’t just about looks — it’s about protecting your home from slow, hidden damage.

How to Get Rid of Moss Safely

If you spot moss early, you can stop it before it spreads:

• Brush it gently. Use a soft brush, not a power washer — those just strip the shingles.
• Use a moss treatment. Zinc or specialized roof products stop new growth.
• Keep the roof clean. Clear off pine needles and branches after storms.
• Trim trees back. More sunlight helps the roof stay dry.

Schedule a roof cleaning once a year. A professional can clean and treat the roof without damaging it.

Taking care of it now means you’ll avoid paying thousands later for repairs.

Final Thoughts

In Tacoma, moss is almost guaranteed but roof damage doesn’t have to be. A little prevention goes a long way. If you’ve spotted moss starting to grow, give Robb’s Roofing a call at (253) 820-2163. Because here in Washington, a clean roof isn’t just about looks — it’s about keeping your home dry, healthy, and ready for whatever weather comes next.