Home Improvement: Roof Stains
Our Home Improvement columnist gets to the root of the issue with roof stains and talks about why pressure washing is the last thing you want to do to remove these unsightly eyesores.

We have all seen the unsightly dark streaks and stains on roof shingles. You may even have them on your own home. What causes them, and better yet, how do you get rid of them short of replacing your roof?

Over the years, I have heard of a variety of sources for the streaks and stains with the most common cause being the acid from the leaves of overhanging oak trees. They have also been linked to jet fuel, acid rain or other emissions.

The real story is the stains are a form of algae called gloeocapsa magma. It feeds on the limestone filler that is used as a binder in asphalt and fiberglass shingles. It is spread to roofs through wind, birds and small animals. It first appears as black spots and grows to get worse. Many people mistake the black appearance initially for soot or dirt.

Other growths that are much more easily identified are moss and lichen. Lichen, which is moss in its early stages, appears as tiny white strands. More developed moss is green, thick and spongy with roots penetrating into the shingles to stay firmly attached.

So, what kind of damage can these growths cause to your roof? Developed moss is probably the most damaging because the deep-penetrating roots dislodge the granules from your shingles. Significant loss of granules can reduce your shingles life span by 40 to 50 percent. So, a roof with 25- to 30-year rated shingles may need to be replaced after 10 to 15 years with thousands of dollars cost.

The algae stains cause UV rays to penetrate the shingle granules increasing your attic temperatures driving up your utility bills and possibly decreasing the life of your shingles as well. Since this is more than a cosmetic issue with bacteria spores feeding on your shingles, the staining will only get worse. It will not go away unless treated or the roof replaced.

Now for solving the problem. Many companies advertise roof cleaning with a wide variety of cost options. A lot of window washers and even roofing companies have gotten into the business with only a few specialized companies out there. There are a couple very important points to note if you are looking for someone to clean your roof stains. First, clearly understand which method they will use. If they even mention pressure-washing, get away from them as fast as you can. This will be the least expensive option and may give a temporary look of improvement, but the problem is not solved.

Mostly they washed away a lot of granules from your shingles, giving the appearance of a clean roof. What they really did is decrease the life of your roof, and the stains will be back in a matter of months. They should not use a pressure washer or brushes to clean your roof. You probably will not get more than a one-year warranty from them, and all the stain will not be gone.

The other point is that cleaning small sections doesn't cure the problem either because the bacteria will spread just through the cleaning process to other parts of the roof.

I have only come across one company in the area so far that uses a biocide-type cleaner with surfactants similar to ones in hair conditioner that causes the material to hold on to your roof and kill the bacteria. The stains will disappear after a couple good rains. They do not rinse the chemical off your roof, so it is there to continue working, which allows them to offer a two-year warranty.

Believe me, a good, proper cleaning is a lot less expensive than replacing your roof. If your roof is showing these unsightly stains and you want it cleaned properly, let us know, and we can put you in touch with a reputable company that will do the job correctly. You can reach HomeServicesLink at This e-mail address is being protected from spambots. You need JavaScript enabled to view it or 513-271-1888. I hope you found this information helpful. Let me know if you have any questions or subjects you would like me to address in the future.