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Why is it Bad to Have Moss Growing on Your Roof?

June 26, 2019 by ROTban Services Corp.

Why is it Bad to Have Moss Growing on Your Roof?

Answer: Moss can cause many types of damage.

You may not have noticed it, but many roofs have some level of moss growing on the shingles. While moss may seem harmless, it can cause a lot of damage to the roof and should not be left there.

First let’s talk about the bulk of the flowering moss.  It can cause dams and leaks on sloped roofs.  When moss grows in moist areas where water is restricted by nooks and corners, rainwater will back up behind it. Sloped roofs are not built like swimming pools.  They aren’t completely sealed! The design of the roof underlay and covering depends on gravity to pull water downhill.  If the water pools up too much, it’ll get behind flashings and underlay overlaps and into the home, causing expensive damage.  This is also true of debris in those tight corners around dormers and fancy, restrictive designs.  Flowering moss falls into gutters and also grows in them, causing overflowing gutters, with misery and possible structural rot.

Some say that moss gets between the shingles and weakens the system that way, but in my 35 plus years of working on roofs, I’ve never seen that happening.  The roofing is normally too strong for that.  What we do see happening constantly on asphalt roofs is degranulation and weakening of the surface.

Asphalt roofs are the most abundant type in our area, so I’ll talk about the effects on them.  Moss moves as it grows and feeds.  If you were to see a time lapse video clip, you would see that it’s shaking over time and the roots are moving.  That wearing action is a significant problem, because it loosens the protective sand-like protection which is put on top of the asphalt part of the shingle to protect it from weather and especially the sun’s damaging rays.  The rays quickly break down the asphalt material under the grains of coloured sand or ceramic.

That’s not all.  As the moss feeds, it’s extruding acid, which breaks down the material the moss is growing on.  It feeds on impurities of any sort and loves the oily asphalt.  Roofing is expensive, and moss is designed to biodegrade it.  Huh!

Moss is bad for your roof and your economic health.  So, what can be done?

Do it yourself projects for this have a few problems.  Firstly, the products sold in stores and recipes available on the net almost always depend on bleach.  This common cleaning solution sterilizes quickly but has no staying power.  There are many other disadvantages to it.  Secondly, they promote putting whatever product into a hand pumped sprayer or backpack sprayer and going onto a sloped roof with this offsetting weight, which is a serious safety hazard.  Much damage is done to the roof by walking on it.  Also, the hand pump or hand application of powder isn’t thorough enough.  If you want economical results, all areas must be thoroughly treated.  Trying to pressure wash or scrub mossy shingles can damage the cedar, asphalt or concrete shingles.

When you put all the negatives together, it’s not advisable to do this job yourself.  There are many risks, and then in a year or two the same problem arises. Thankfully, ROTban has studied and resolved these issues over a long period of time and provides a safe and effective method of moss removal that’s gentle and long lasting.  Monitored!  Having this home maintenance task done professionally can not only keep your roof functioning for years to come, but make it look cleaner and more beautiful, while you stay safe.