If you live in Western Washington, specifically in Seattle, Bellevue, Tacoma, or anywhere in the Snohomish area, you are likely familiar with this problem. Your roof is green. Or it has black streaks. Or it looks like it is wearing a shaggy green coat!
That green stuff is moss, and it loves our mild, wet climate.
Moss can look unappealing, but it is much more than just an unappealing appearance. It is a serious threat to the life of your roof. For homeowners with asphalt shingles, moss is enemy number one.
If you have any moss on your roof this guide is for you. We will show you the safest, proven ways to get rid of moss and keep it from coming back. We will talk about what works in the Puget Sound area and what you should never do.
Why Moss is the Enemy of Your Western Washington Roof
In the Pacific Northwest (PNW), moss grows fast. Here is how it slowly destroys your roof:
- It Traps Water: Moss acts like a wet sponge. It holds water right against the surface of your shingle. The shingle is never allowed to dry out.
- It Lifts Shingles: As the moss grows and expands, its tiny roots push up the edges of your asphalt shingles. This lets water get underneath the shingle.
- It Causes Cracking: When the weather gets cold, the trapped water can freeze. When water freezes, it expands. This pressure can crack your shingles and make them buckle.
- It Eats Your Protection: Asphalt shingles have small, protective stones called granules on top. These granules stop the sun from damaging the asphalt. Moss causes these granules to come loose and wash away. When the granules are gone, your roof ages very fast!
Simply put, a moss-covered roof will not last as long as a clean one. You need a good PNW roof maintenance plan.
Step 1: Fix the Root Cause (The Air and Sun Solution)
Moss loves shade and moisture. If you want a good moss prevention asphalt shingles plan, you have to cut off its food source: dark, wet conditions.
Our region is heavily treed. This is great for shade in the summer, but bad for roofs in the fall and winter.
- Tree Pruning is Key: Look at your roof, especially the north-facing side. Trim any tree branches that hang over your roof. You do not need a lot of sunlight, but you need some sunlight and air flow to dry out the shingles quickly after it rains.
- Clear the Debris: Leaves, pine needles, and sticks are not just messy. They hold moisture and dirt, which moss uses to start growing. Make sure to clear all debris from your roof valleys and behind chimneys at least once a year.
Step 2: Safe Moss Removal (The MUST-DO Techniques)
Your asphalt shingle roof is tough, but it is also delicate. Its surface is covered in those important granules. You must use soft, gentle cleaning methods.
1. The Soft Brush Method (For Dead Moss)
If you have large, dried clumps of moss, you can remove them, but be careful.
- Wait for Dry Weather: Only clean when the moss is completely dry. Wet moss sticks tightly to the shingles, and scrubbing it will pull off those protective granules.
- Use a Soft Brush or Blower: Use a soft-bristled brush or a leaf blower to gently sweep the dead clumps off the roof. Do not scrape or scrub hard. Your goal is simply to knock off the loose pieces.
2. Chemical Application (The Killer)
The best way to kill moss and black algae streaks is with a chemical treatment. This is called soft wash cleaning.
- The Best Killers: The most popular DIY killer is zinc sulfate powder. You can buy this at hardware stores. It is spread lightly over the roof. The rain slowly washes it down, killing the moss as it goes.
- Eco-Friendly Options: Because we live near sensitive PNW waterways (the Puget Sound, lakes, and rivers), many people prefer safer options. Some companies use a mix of oxygen bleach or other cleaners. These work well and are safer for plants and the environment.
- The Method: Never spray the cleaner with high pressure. It should be applied with a simple garden sprayer, like a heavy rain. The idea is to soak the moss and let the rain do the rest of the work.
DIY Mistakes (The NEVER-DOs for PNW Roofs)
If you want your roof to last, you must avoid these common mistakes that many homeowners make:
NEVER, EVER Pressure Wash Your Roof!
This is the number one mistake people make when trying to remove roof moss in the Western Washington style.
A pressure washer will blast the protective granules right off your asphalt shingles. Once those granules are gone, your warranty is void, and your roof will lose years of life in a single summer. Only use a garden hose to rinse, never a pressure washer.
NEVER Use Harsh Household Cleaners
Do not use chlorine bleach or other harsh household cleaners. These can hurt the asphalt and ruin the color of your shingles. They also create a lot of runoff that is bad for the environment. Stick to the approved zinc or specialized soft-wash cleaners.
NEVER Walk on a Wet Roof
This is a safety warning. Moss is slippery, and the Pacific Northwest roof slopes can be steep. Wet asphalt shingles are very dangerous. It is not worth risking a fall.
Step 3: Long-Term Prevention (Stop it from Coming Back)
Killing the moss is only half the job. You need a long-term asphalt shingle care plan in Seattle to prevent regrowth.
1. Zinc or Copper Strips
This is a very common method in the PNW.
- How They Work: Thin strips of zinc or copper metal are placed along the peak of your roof. When it rains, small amounts of the metal are washed (leached) down the roof. This metal is toxic to moss and algae, which prevents them from growing.
- The Catch: These strips are only effective for a limited distance. Usually, only 10 to 15 feet down the roof. If you have a large roof, you may need multiple strips of shingles.
- Environmental Note: Be mindful of the runoff from these metals, especially copper, if you have sensitive gardens or rain catchment systems.
2. Algae-Resistant Shingles (The Ultimate Solution)
If your roof is old and you know you need a replacement soon, consider this option.
- What They Are: These are new asphalt shingles that have copper granules mixed into the surface. The copper granules prevent the growth of moss and the ugly black streaks of algae for the lifetime of the shingle.
- Why It Works: It is the best long-term moss prevention asphalt shingles solution because the moss killer is built right in.
Your PNW Roof Maintenance Schedule
To keep a moss-free roof in Western Washington, you must do maintenance twice a year.
- Late Fall (After Leaf Drop): Clear all debris off the roof. Apply your chosen moss killer (like zinc sulfate) to kill anything that started growing in the fall rain.
- Early Spring (March/April): Clear any debris left over from winter. Inspect the roof and apply a new preventative treatment to stop spring growth before the heavy rains start.
Do Not Risk Your Roof. Or Your Safety!
Moss removal is tricky. It needs to be done gently to save your granules, and it needs to be done safely to save your body.
If you are unsure how to get on your steep, slippery roof, do not try it!
We offer Professional Moss Removal and Preventative Treatment services designed for Western Washington homes. We use only the manufacturer-approved, soft-wash techniques. Our team is licensed and insured, which means we risk our neck, not yours, to get the job done right.Contact us today for a free roof inspection! Protect your investment and give your asphalt shingles the long life they deserve.