What’s the Best Time of Year to Clean Your Roof in Western Washington?

Here’s why: the drier months give us the best chance to clean your roof safely and effectively. The roof dries faster, the cleaning solution works better, and there’s less slipping around. Plus, no one wants their roof cleaned while it’s pouring outside.

Why dry weather helps

A roof cleaning solution needs time on the shingles to do its job. The Asphalt Roofing Manufacturers Association’s cleaning guidance calls for letting it sit for 15 to 20 minutes before a low-pressure rinse. Heavy rain cuts that short by washing it off early. So the best day is dry and mild. Not a downpour, and not a 90-degree afternoon that bakes everything dry in five minutes.

But moss doesn’t wait

That said, moss doesn’t really care what month it is. We’ve done roof cleaning in January in Spanaway and June in Kent. If moss is growing fast, it’s better to get it taken care of than wait for the "perfect" season.

Here’s something most people don’t expect. Moss does most of its growing in the cool, wet months. In August it dries out, turns brown, and looks dead. It isn’t. The first good rain in fall and it’s green again, a little bigger than last year.

We use a soft washing method that works even when the weather’s not perfect. As long as it’s above freezing and not raining sideways, we can usually clean safely.

A rough calendar for Western Washington

• Late spring through early fall. The easy window. Dry roof, long days, and the solution gets its full time to work.
• Fall. Rain is back and fir needles are piling up in the valleys of the roof. A good time to clear debris and look at the gutters, even if the wash itself happened in summer.
• Winter. Peak growing season for moss. Cleaning still happens on dry days above freezing. Ice on a roof is where we draw the line.

Signs it shouldn’t wait for summer

Some roofs can sit until June. Some can’t. Don’t put it off if:

• The moss is thick enough to lift the edges of the shingles
• Clumps of it keep ending up in your gutters or on the driveway
• You’re planning to sell, or a home inspection is coming

Here’s a tip: walk around your home and look at the roof after a few rainy days. Are there black streaks, mossy patches, or shady spots that stay wet? If yes, it might be time.

If you’re not sure, just send us a photo. We’ll tell you if it needs cleaning now or if it can wait. It’s all about keeping your roof in shape for the long haul.