In many parts of the Pacific Northwest, you can frequently encounter issues with algae, mold, moss or lichen growing on your roof. These types of roof growth are especially common on houses with asphalt shingles. Many people think that this is only a concern because it negatively impacts the appearance of the roof and takes away from the house’s curb appeal. The reality is that the growth can cause significant damage and shorten the life of the roof if left unchecked.
Causes of Roof Growth
Algae, mold and moss all thrive in damp environments, which is the main reason why they are commonly found growing on roofs in rainy, humid climates like we have in our part of the country. Lichen also requires moisture, as it is a composite organism that forms from a symbiotic relationship between algae and fungi. Even though sloped roofs are designed so that water quickly drains off into the gutters, some areas can still remain damp for quite some time for various reasons. Prolonged periods of rain and heavy cloud cover that block out the sunlight can create the potential for algae, mold or moss to start growing. Nearby trees or buildings that shade the roof for much of the day also commonly result in growth starting to form. North- and east-facing roof slopes are the most prone to growth since they receive less direct sunlight and tend to stay damper.
Why Roof Growth Is a Concern
All types of roof growth retain moisture, which is partly why the growth can spread so quickly and be difficult to control. Over time, moisture retention can lead to the wooden roof deck rotting. Wood rot is a serious issue, as it greatly shortens the life of the roof and can lead to it leaking.
Lichens and moss often loosen and strip off the granules that coat shingles. The granules are not only what gives shingles their color. They also increase the amount of sunlight the shingles reflect, helping to protect against UV damage and slowing the rate of deterioration. If there are bare patches where the granules are missing, the shingles absorb more heat and quickly start becoming brittle. This increases the chances of them getting damaged by hail or flying debris or getting torn off the roof by strong winds.
Moss growth on a roof can be extremely damaging. Not only does moss retain moisture, but it can also penetrate into shingles and cause them to deteriorate more quickly. Another concern with moss is that it often starts growing under shingles, causing them to lift and curl. This allows water to seep underneath them, creating the potential for roof leaks.
Algae growth on a shingle roof creates several issues. One is that it usually results in unsightly black streaks on the roof. The type of algae that grows on asphalt shingles does so because it feeds on the limestone in the shingles, causing them to deteriorate and become more susceptible to impact and wind damage.
Mold growth on a roof is less common. However, when it’s present, it can penetrate the shingles and spread incredibly quickly. Once it starts growing underneath the shingles, it can infest the roof deck and potentially infiltrate the attic.
Tips for Preventing Issues With Roof Growth
There are a few basic maintenance steps you can take to lessen the chances of algae, moss, mold and lichen growing on your roof. If there are any large trees on your property that shade part of your roof, you should keep their branches trimmed to minimize the shadow they cast. Instead of doing major pruning and risking damaging the tree or ruining its shape, the better solution is to have an arborist thin out the branches to allow more sunlight to shine through.
Keeping your gutters clean is important for avoiding moss growth. Gutters that are full of leaves and organic debris provide an ideal environment for moss due to how much moisture the debris retains. Once moss starts growing in a gutter, it can quickly spread out and grow upward onto the roof. If you have an upper roof and a lower section below it, it’s especially important that you have the gutter on the upper roof cleaned regularly so that it doesn’t overflow and dump additional water on the lower roof.
How Roofing Professionals Overcome and Prevent Roof Growth
If there is visible growth on your roof or you start seeing the tell-tale black streaks that indicate algae is present, the first step is to have a professional clean your roof. We don’t recommend trying to clean the roof yourself due to the risk of injury or roof damage. If you do attempt it, you need to make sure to take the appropriate safety precautions. You should also only wash the roof with a low-pressure sprayer. Using a pressure washer can cause significant shingle damage and blast off many of the protective granules.
Roofing professionals have different products that they can use to clean the roof and kill the growth, depending on what type of organism is present. There are even broad-spectrum treatments that will kill algae, mold and moss. After they’ve cleaned the roof, it’s a good idea to have the roofers apply a roof coating. The coating works to inhibit future growth to protect the roof from damage.
Applying a coating like ShingleArmor is a great investment. This coating is a clear-coat adhesive that bonds the granules to the shingles to prevent them from getting washed off by rain or blown off by the wind. This ensures that the roof is less susceptible to UV damage and doesn’t get as hot. By applying the coating to an older roof, you can extend its lifespan for at least a few years to put off the high cost of replacing your roof. However, you must act before the roof is in poor condition. If there is already a large amount of granule loss across much of the roof, the coating won’t be effective. Before applying the coating, you also need to take care of any repairs, such as replacing any cracked, broken or missing shingles.
When you replace your roof, it’s worth investing in algae-resistant shingles. These shingles have copper or zinc granules mixed in with the normal granules that inhibit algae, moss and mold growth. Another option is to have a roofing company install copper or zinc strips on the ridge of your roof. Whenever it rains, some of the metal gets washed over the roof to kill any growth that’s present and prevent it from returning.
If you’re searching for a reliable, trustworthy roofer, Jimmy's Roofing is who to call. We offer the full range of residential and commercial roofing services, including repair, replacement, maintenance, cleaning and roof coatings. We work with shingles, tiles and flat roofs, and we’re a certified installer of roofing products from leading manufacturers such as GAF, Owens Corning, John Mansville, Duro-Last, GenFlex and Versico.
If you live in the Seattle area and are dealing with any type of growth on your roof, Jimmy's Roofing has the expert solutions to properly overcome the problem. For more information or to schedule an inspection and get help with your roof growth issues, contact us today.
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