By Matt Baggett 

photo credit to nachi.org

I recently met Dave Gilday from L&L Contractors at a realtor open house and I found out that he did exterior contracting work: roofing, gutters, siding and windows. Our conversation turned to the stains you see on asphalt shingle roofs. Dave told me that it is basically a kind of algae. His advice is that when you see it–you can assume that the roof is probably 10 years or older.

I asked him what were some misconceptions about algae on the roof. He really didn’t consider it a cause for big concern as it is basically a discoloration. However, it is unsightly and one thing he doesn’t recommend is pressure washing your roof. That high pressure will just dislodge the tiny granules from the shingle and lessen the life of your roof. One difference though is if you see moss on your shingles it means that you are getting moisture penetration and it is stuck under the shingle and not drying properly.

Even though the algae isn’t a major concern, it can be unsightly and many people want to have their roofs treated so that their house looks better. Dave’s company can do this. Individual houses vary but this can usually be done for a few hundred dollars. Additionally his company wants to earn your business and they will do lower dollar volume repairs that other exterior contractors may not want to do. They will come out and walk your roof and do a “tune-up” that can extend the life of your roof (things like nail pops, cracked shingles, or shingles blown off in storms, replace vent caps, etc…)

Back to the algae, I did some additional research online and the type of algae making these discolorations is Gloeocapsa magma or blue green algae. Other sources online tended to think that the algae can lessen the life of your roof. So the jury is out.

But why do we see it more these days? Apparently the materials for the granules on the shingle tabs has changed. I don’t know what they used to be, but now they are tiny limestone granules. Limestone tends to  be porous and likely is easily invaded by the algae–which other sources online say can break the granule down over time. Dave did tell me that Atlas Brand shingles have a built in feature that combats algal growth. Also, any brand that has the trademarked “Scotchgard” logo is anti-algal as well. What is built in to those shingles? A low dosage of copper is blended into the materials at manufacture. Copper inhibits the growth of the algae. Also the treatment that they put on the roof to take the stains out is made of copper in a diluted solution. I wonder if that is harmful to my health–but then remember that my drinking water is delivered in copper pipes and I don’t worry as much.

If you have any questions about this or any other housing matter–give me a call….I speak “house”.