The Hidden Dangers of Moss Growth on Roofs in Seattle’s Summer Sun

Seattle summers are known for their warm, sometimes dry days and a temporary reprieve from constantly grey skies. But even in this sunny season, one of the biggest threats to your roof doesn’t go away. In fact, it gets worse. We’re talking about moss. While moss is often seen as a cosmetic nuisance, it can cause serious damage to your roof, especially when combined with the heat of the summer sun.

Most homeowners understand the risks moss poses during rainy seasons, including excess moisture, slippery shingles and mold. But few realize how the summer sun can bake moss into your roofing materials, making it harder to remove and compounding the damage already being done underneath.

How Moss Takes Root on Seattle Roofs

Moss thrives in the damp, shaded conditions typical of Seattle’s long rainy season. Roofs that don’t get enough sunlight due to tree coverage, northern exposure or cloudy weather are especially vulnerable to moss growth and damage. Even after spring passes, moss continues to grow quietly, often unnoticed until it forms thick, green clumps across shingles and in between tiles.

By the time summer arrives, much of the moss has already attached itself firmly to the roofing surface. That’s when the real danger begins.

The Summer Sun Doesn’t Kill Moss—It Bakes It In

Contrary to popular belief, the summer sun doesn’t dry out and kill moss.

Instead, it bakes moss into the shingles, causing:

• Root penetration – Moss anchors itself deep into asphalt shingles, lifting them and allowing water to seep beneath.
• Moisture retention – Even on hot days, moss holds moisture like a sponge, keeping parts of your roof damp and weakening the materials.
• Accelerated granule loss – The trapped moisture and heat cause protective granules on asphalt shingles to deteriorate faster.
• Warping and rot – Wood decking underneath can begin to rot as moisture becomes trapped below raised or cracked shingles.
• Discoloration and stains – The longer moss stays, the more it stains and degrades the roofing surface.

So instead of the sun helping your roof recover after a wet spring, it may actually cement the damage in place. That makes removal much harder and raises the cost of eventual repairs.

Moss Can Shorten Your Roof’s Lifespan

A typical asphalt shingle roof in Seattle should last 20-30 years if properly maintained. But when moss is allowed to grow unchecked, it can shorten that lifespan dramatically. Some homeowners have had to replace roofs after just 10-15 years due to structural deterioration caused by untreated moss infiltration.

This is especially frustrating because moss damage is preventable with routine maintenance and timely intervention.

The Financial Toll of Ignoring Moss

Let’s say moss has started growing on your roof this past winter and spring. If you don’t address it now, during the summer, the cost of future repairs could include:

• Shingle replacement from cracking or curling
• Plywood replacement from underlying rot
• Mold remediation if water penetrates into the attic or walls
• Full roof replacement if the damage spreads unchecked

Compare that to the much smaller cost of having moss safely removed and a protective treatment applied.

DIY Moss Removal vs. Professional Help

While there are DIY methods for moss removal, like using a long-handled brush or zinc-based products, doing it wrong can do more harm than good. Using too much pressure or the wrong cleaning agents can strip shingles, void your warranty or lead to injuries from slips and falls.

Professional roofers, like the team at Chet’s Roofing & Construction Inc., have the tools and experience to:

• Safely remove moss without damaging shingles
• Apply eco-friendly moss inhibitors to prevent regrowth
• Inspect your roof for underlying issues (like rot or cracked shingles)
• Look for problems with gutters that might contribute to moss growth

When done professionally, moss removal isn’t just a cleanup; it’s a smart investment in the longevity and safety of your roof.

Preventing Moss Growth Going Forward

Once your roof is clean, it’s important to stay proactive with moss prevention and roof upkeep. Here are some tips to keep moss from coming back:

• Trim back overhanging trees to let in more sunlight
• Clean your gutters regularly so water drains properly
• Ask your roofer about installing zinc or copper strips near the roof ridge to inhibit moss growth as rainwater runs off
• Schedule annual roof inspections, ideally in spring or early summer

These small steps can go a long way in protecting your roof and avoiding expensive repairs down the line.

Don’t Let Moss Ruin Your Seattle or Puget Sound Roof

Seattle’s summer sun can do a lot of good for people living in the Puget Sound region, but when it comes to moss, the weather may be working against your roof. If you’ve noticed green patches on your shingles, curling edges or signs of water damage, don’t wait until fall to take action.

Give us a call today at (877) 611-1514 or fill out the form on our website to schedule your roof inspection and protect your home from the hidden dangers of moss this summer.