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Removing Moss from Lower Mainland Roofs
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Article on Cedar Roofs
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DARK STAINS ON ROOFS AND EXTERIORS

Those streaks on your roof – what are they? Some people think it might mean the roof is getting near its end, but is that true? The dark stains that show up, often in streaks, are algae. It’s a strain of blue-green algae which has adapted itself to a dark color, to avoid UV ray damage. This little plague is growing in proliferation all around North America. In addition to being an eyesore, it is harmful.

Algae, mold, mildew, moss, fungus, lichen and many other varieties of simple plant life are carried in the air in invisible spores, which grow, under favorable conditions, into what you can see and touch. If they have moisture, warmth, shade and slight impurities on any surface for a couple of hours a day, they can grow, sometimes very fast.

They grow fastest on organic surfaces like unfinished wood fences, siding and cedar roofs. But they also grow on unfavorable surfaces like a parked car! Ever seen moss growing in the cracks and crevices of an abandoned vehicle? It’s likely got a coating of algae over some areas, and where the water pools and remains, the moss will gain a foothold. We instinctively know this is harmful! It’s not just ugly; it’s breaking down the soft parts, and will gradually eat into and permanently damage the oven baked, super hard, shiny paint surface on smooth metal.

Since it’s relentlessly eroding abandoned cars, it’s clear that organic surfaces are affected too! If you stay with me and read this article, you’ll see why that’s hitting you in the pocket book.

Home exteriors, are made with a variety of materials – wood, vinyl, aluminum, stucco, brick and asphalt, for example. All are prepared and used with a watchful eye on their ability to withstand the weather. As a general rule, the harder the surface is, the less it is damaged by algae and its friends. Vinyl siding will get green streaks, for example, but due to the fact that the color is the same throughout the material, it won’t be noticeably damaged when you clean it off.

On the other extreme, wood siding which has not been pressure treated, stained or painted will break down under the various environmental pressures. You don’t see unprotected siding generally. Cedar roofing is beautiful and popular, but most of these homes have untreated shingles or shakes, and obviously, they are not painted.

Our roofing service in Metropolitan Vancouver has to charge an average of about $20,000 now to re-roof a nice home in cedar. That means the roof is costing over $1,000 per year! These roofs need help to reduce that expense! If you have a cedar roof I urge you to look into algaecide before the roof reaches 10 years of age. You’ll save so much money!

algae and mold growing in a 10 yr old cedar shake

Algae and mold growing in a 10 year old cedar shake.

If cedar roofs are the most vulnerable, what about the other materials? I’d put vinyl roofing on the other end of the scale. Like a car, the surface is hard, and like siding, the color is deep into the material. They’ll grow ugly stains and that can be dealt with. The damage itself will be minimal. Metal roofs are much the same, except that discoloration can occur. Asphalt roofing is damaged by algae.

When we use hearty building materials and keep them resilient, we’re preserving them against the onslaught. Look at how disease attacks a live tree. A tree is very resilient because of its bark and the life and nutrient carrying sap that moves about within the growing wood. But when bark is damaged and cell walls are ripped apart, let’s say by an axe blow, which leaves a place of bare cut wood, or a branch breaking off in nature, the tree has a problem. It goes to work protecting the area with sap. Microbes in the air, the foot soldiers in nature’s army, land and try to live in that vulnerable spot. As they establish a small colony, they secrete by-products, which provide a more favorable environment for other microbe strain, and as each wave of life form establishes itself, the environment gets progressively more inviting for the real damaging strains. They can even kill a tree.

Asphalt shingles, which have improved greatly in the past few years, are based on an oil by-product, called bitumen, which is a tar. Recently, a layer of fiberglass is being added and sheets are being laminated together, but the base of bitumen is the same. It is a hardy waterproof protection that works well. However, the bitumen will break down in the UV rays of the sun, which are more and more damaging in modern times. These harsh light waves weaken the asphalt, and eventually the oils will dry out, the shingles will become brittle and fragile. This effect is greatly reduced by the protective granules on the surface. The granules give us the color and protect the bitumen. On Tar and Gravel roof, the protection is afforded by pebbles. It’s all based on the same rules.

They act a little like the ceramic shields on a space shuttle, which ward off re-entry heat. If one of those amour pieces comes off, the re-entry can be a disaster, because the intense heat gets through and begins a melt-down.

Lichen proliferating on an unkept cedar shake

Maybe your roof isn’t that high tech, but with granule loss, you still have to fork over for a new roof on the early side of its life expectancy rather than the late side. So you might say that roof granules rock! Now, remembering what happens to the live tree, you can picture what’s happening.

What this does to the granules in the first phases, before moss even shows up, is to disturb and dislodge the protective granules, which wash off in the weather, allowing the sun to bake the bitumen. In the case of moss and larger plant life, the roots, along with constant moisture retention, do the work. It’s nature’s way, and it’s costing you money. You may have a 30 year manufacturer’s warrantee, but reading it you will likely find that in the last 10 years the benefits are not very strong.

Cedar roofs are made of shingles and shakes, cut or split from dead trees. Cedar has a lot of resin, but a weak cell wall. Pine, on the other extreme, has a minimum of resin and a strong cell wall. The resin in cedar is its big plus. It’s got its own preservative built in! However, over time, the dead wood experiences a depletion in resin. The natural preservative goes, the wood softens, and the simple life forms attack, if the factors of moisture, warmth and shade are there.

sphagnum moss in a cedar shake

Sphagnum moss on cedar roof

The best shakes are split along the grain. When wood is sawed, cell walls are cut through, leaving them weakened. Splitting wood leaves the cell walls intact, affording the wood much better protection, to hold in the resin. Remember the tree diseases, and this makes perfect sense.

Don’t let nature take your investment down. Guard against microbial growth. See your professional algaecide applicators and learn how to keep your building exteriors resilient on an ongoing basis. Keep building exteriors healthy, year after year.

Gregg McBurnie,
Hay’s Roof Management Ltd.