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Declaring War on Roof Moss – Tips for Removal and Prevention

It’s a problem brought to thousands of home owners every year. Maybe your insurance company tells you to get the roof cleaned or no renewal. Maybe you got a letter from your HOA. Maybe you are a savvy home owner, who likes to stay on top of maintenance. Maybe you just noticed that there is moss on your roof and want to know if it’s OK.

Part of every roof spends most of its time in the shade, especially on the north side of the house, leading inevitably to the growth of moss and algae. Which in turn prompts a series of questions: Is it causing damage to the roof? Does it really need to be removed? What’s the best way of going about roof moss cleaning? Is it safe to use bleach as so many seem to suggest? How about ensuring it doesn’t come back? Should I call in the pros?

A Nationwide Nuisance–Especially in Portland

In truth, moss isn’t particularly picky when it comes to setting up home. Roofs made of wood, asphalt, metal, concrete tile, clay tiles – all fair game when it comes to moss growth. All it takes is plenty of moisture and a shady environment to transform a once-clean surface into a thriving mass of moss. As such, homes and properties of all types throughout the Portland Metro area could be affected by moss at any time.

Unfortunately, while there’s often something quite charming and rustic about the appearance of moss, it’s also a costly nuisance if left unchecked. By accumulating water and maintaining the ideal damp environment it needs, moss can significantly increase the risk of rot, erosion and leaks. Left untreated, moss has the potential to reduce the lifespan of almost any roofing material. It can actually lift shingles and make them more susceptible to wind or storm damage.

Trouble Spots

Where conditions favor growth, it usually tends to be more pronounced on parts of the roof that face north. These are generally the areas that stay wetter for longer, increasing the likelihood of moss growth. In addition, homes that sit in the shadows of large trees and protruding branches may have a particularly high risk of roof moss development.  Quite simply, anywhere on your roof where rainfall and morning dew are likely to evaporate more slowly, you’re looking at prime territory for a moss move-in.

If you look carefully, you’ll see that right at the top of the vertical slots between the shingles is precisely where moss first starts to appear. Which is because this is also the very last place from which roof moisture evaporates. As such, it’s the ideal place to monitor for signs of moss growth, allowing for action to be taken as soon as possible. Basically, if you see green on your roof, it is actually past time to take action!

Removal of Roof Moss

Before we go further, anything described herein should only be done by licensed professionals. Anyone can remove moss from your roof. It requires an Oregon Department of Agriculture Commercial Pesticide Operator’s license to treat your roof for moss. If you are thinking about doing it yourself, our advice is don’t. Unless you are experienced in roofing and walking on roofs, you are exposing yourself to tremendous risk. Anyone on your roof should be protected by safety-rated and secured ladders for access, and by roof anchors, harness, rope and lanyard for the individual. OSHA research indicates that any fall over 6 feet is likely to result in serious injury or death.

If nipped in the bud, roof moss cleaning can be a relatively simple job. Application of an EPA approved moss killer will kill the moss, and wind and rain will remove almost all of it over time. This is the best approach, get it early, and take it easy on your roof. No scraping or sweeping should be necessary, which is always better for your roof.

If the moss has been let go, and is entrenched, then removal is necessary, especially if your insurance company or HOA has called it to your attention. Removal is done with brushes, and complete removal, due to potential damage to the roof is not necessary. Professionals go for between 75% and 95% removal, and then treat the roof to kill the rest of the moss and the roots. If the moss has to be removed, the gutters should be cleaned at that time to make sure no moss is left in the gutters. When you have your roof cleaned and treated, it is also a great opportunity to take a look at the condition of your roof and your gutters in general. Be sure to check for any signs of damage to the roof or gutters, as well as shingles in need of replacement.

Reaching for the Bleach and Other Myths

While you are entitled to put anything you want on your roof to kill moss, if you pay someone else to do it, they must be ODA licensed, as mentioned above, and may only use products which have been approved for use on roofs, and it has to say so on the label. Bleach is not one of those products. Neither is laundry soap. These are 2 oft mentioned ideas for treating moss.

There are commercially available approved products that are very effective in treating moss. The most common and best products contain zinc sulfate. Also available are organic-type, bio-degradable moss killers that are appropriately labeled. Our experience is that the trade-off for the bio-degradable is that it kills the moss just fine, but it doesn’t seem to work to prevent future moss growth.

Future Prevention

So people sell and customers ask about zinc strips to get a “permanent” solution. The short answer is that the test literature says that at best, the strips can be effective for about 10 feet of roof run below the strip. They really don’t work because the surface area of the zinc strip is too small to have enough zinc leach off of it to do much to the moss. The best long (one to three year) term preventative is a properly applied solution of a zinc sulfate product. And if you see a roof with big, thick piles of white powder on them along the ridges, you know that you are looking at an “amateur hour” production.

If in doubt, contact us and see how we can help you get your roof back in tiptop shape.