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Why is there so much moss on my roof?

All that green looking stuff on your roof needs ample moisture.  Every roof gets wet — the idea is for rain and snow to shed from the shingles, never reaching the plywood.

But if water doesn’t shed enough, or if the only source of moisture isn’t from the weather, then you may find your roof builds up plant life (and fungus).

Most of the time, roofs shed water from the outside well enough that moss buildup isn’t caused by weathering.  The typical cause is twofold: lack of sunlight heat and lack of air venting underneath the roof deck.

Sunlight reheats the roof, evaporating moisture.  Air passing underneath the roof deck normalizes the temperature to the outside, thereby preventing some condensation buildup below the shingles.

When moss builds up in areas that get little sunlight, there’s not a whole lot that can be done to prevent it.  Instead you’ll want regular cleanings (no pressure washers), otherwise your roof’s life can be greatly diminished.

When moss builds up all over your roof, it’s usually a sign that ventilation is poor.  Your attic will more closely represent the temperature inside your house then.  You’ll probably also notice deforming shingles.

Can I leave moss on my roof?


You can, but it will shorten the lifespan and make replacement more expensive.  Once you get a new roof, you’ll probably find that the areas with moss also have rotted plywood that you need replaced.

If you already get a lot of moss on your roof, your options are not amazing.  Removing the moss will help, but your roof also probably will age poorly because of the same thing that’s causing the moss buildup.

In that case, you’ll want to be sure to get a well-ventilated roof when you get it replaced.  That means a lot of intake ventilation and enough exhaust.

Is it time for you to get a new roof and you know you have too much moss, algae, fungi buildup?  Give us a call or feel out our free estimate form (if you live in the South Puget Sound area).  We know how to make sure your roof is ventilated properly and your moss issues don’t return.

Check out the  transformation of this beach house in Shelton, WA!

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