How to (properly) remove roof moss

Virtually every house I inspect has one defect in common: moss growth on the roof. The persistent rain and gray days in the Northwest create a perfect environment for moss to grow and often make it hard to find the right time to climb up onto a roof. But, now that’s it’s summer, it’s time to start thinking about getting some of those house maintenance projects done. Removing and preventing roof moss is one of the easiest ways to extend the life of your roof.

Roof Moss

When moss grows on the roof it damages the shingles, especially wood and asphalt, but others as well, and can dramatically shorten the lifespan of a roof. As the moss continues to grow, it works itself underneath the shingles, lifts them up, and creates space for rain to sneak into the underlayment, which can lead to leaks. This can happen relatively quickly and it’s often hard to catch because most of the time you can’t see it. That’s why seasonal maintenance on your roof is important. If you’re selling your house, do the work preemptively and save yourself, and the home inspector, some time.

Removing and preventing moss

One of the most common methods of removing roof moss is with a pressure washer. This is usually a bad idea. Although pressure washing is effective at removing moss, it will also remove the granules on your shingles and significantly shorten the life span of your roof.

Moss Out!

Moss Out! (follow link for dosage guidelines) is the product I generally recommend because it’s easy to use, readily available, and it works. You can sprinkle it on dry straight out of the container or create a solution to spray on. You’ll want to apply this on the peak of the roof and then again about halfway down the roof to ensure full coverage. After you have applied a product to kill the moss, you still need to scrape off the dead moss. The easiest way to do this is with a push broom or a large handle scrub brush. This can be a little tricky — trying to balance on a steep roof while using a broom — so if you’re not comfortable, hire it out. Make sure to clean out the gutters after you’re done, too, or you’ll end up with clogged gutters, which can result in a whole host of other issues.

The best times to apply moss killing products for preventative maintenance is in the spring or early fall, generally. Basically, you want to apply it when it’s dry and have the rain wash it down the roof. Luckily, even in the summer, we get plenty of rain around here to help you with that.