How do I get moss off my roof?

Summary:

Jeremiah opens by warning against pressure washing. He recounts replacing a roof in Snohomish that was only six years old, where an evaluation prompted by leaking on a front patio cover revealed scars in the shingle where pressure washing had blown through the granules, the asphalt, and into the fiberglass mat. His method instead is a soft wash system with no high pressure nozzles, using a chemical treatment that kills both algae and moss. He explains that algae is the food source for moss, and that the coastal climate combined with tree pollen drives moss growth, so any treatment must address both. He emphasizes preserving granules over time rather than knocking them off, which rules out raking moss with a heavy brush. He also stresses killing moss before removing it, because moss removed while still alive and attached takes portions of the shingle with it, which is why previously cleaned roofs often show extra granule loss at the bottom edge of the shingle.

Answer:

Well, don't get moss off your roof by pressure washing. I'll tell you that first and foremost. I have replaced one roof in Snohomish that was only six years old. The saddest thing, and when I went out to do the original evaluation, it was because they were experiencing leaking. Fortunately it wasn't in the main living space, it was actually on a front patio cover. But when I got onto the front patio cover, I noticed these huge scars in the shingle where it literally blew through the granule, it blew through the asphalt and some of the fiberglass mat of the material. And it was due to pressure washing. So never, never, never use a high pressure system to clean off your roof. When you do that, it's going to knock the granules off, which is the number one reason that a roof will last. And two, it's so invasive and it can cause a lot more damage than good. So how I choose to pursue a roof cleaning is with a soft wash system, so no high pressure nozzles are being applied to the roof. The goal is to use a chemical treatment that actually kills both the algae and the moss. The reason that is important is because algae is the food for moss. We're a coastal climate, so all the algae coming in off the coast, mixed with the pollen from the trees, boom, moss growth. So you want to use some sort of a treatment that both affects the algae and the moss growth from returning. And the last thing I'll say is the number one thing when cleaning a roof is you want to think of overall roof health. And a big key factor to that is not knocking off the granules, but preserving the granules over time. So no taking a heavy brush and trying to rake all that moss off, because again that'll knock off the granules. The best approach that I've found is using some sort of a chemical treatment to kill the moss first, because if you're trying to remove the moss while it's still live and attached to the shingles, it's going to remove portions of the shingles with it. That's why sometimes when I look at a roof and I see that it's been cleaned before, right at the very bottom of the shingle you'll see that it has more granule loss than the rest of the shingle itself, because they've removed that moss while it was still alive and attached to the shingles.