Another nice article I found online.   This one pertains to roof cleaning.   While it was obviously written with a perspective for the type of roof cleaning done in another part of the country, it is still relevant to the Portland Oregon market.   The principles of hiring a good roof cleaning contractor apply regardless of where you live. – Tom Roof cleaning contractors and services are springing up all across the eastern and southern United States to address the growing problem of roof algae stains, but you should know that not all of them are executing their service with the proper methods. Here’s a rundown of what qualities you should look for.

1. First and foremost, be sure to find a roof cleaning company that uses non-pressure methods for roof stain removal.

In most situations a roof should not require high-pressure washing or a power washer of any kind. The rare exception could be very old roofs that have a thick mat of green moss. In the vast majority of cases all that is required is the non-pressure application of a bleach or chlorine-based solution, followed by a gentle non-pressure rinse. This is the recommended method for roof cleaning by ARMA (the Asphalt Roofing Manufacturers Association) and GAF (North America’s largest shingle manufacturer), and is simply the safest and most effective method for removing unsightly black algae stains.

2. Make sure that your roof cleaning contractor has liability insurance.

Of course you should double check a contractor’s liability coverage no matter what his or her service is, but as you can imagine it is very important for roof cleaning. This is an especially important step if you decide to foolishly hire a roof cleaning service that wants to pressure wash your roof!

3. Find a cleaning professional who knows that your whole roof should be cleaned, even though you might only see black stains in certain areas.

You should be aware that the presence of visible stains ANYWHERE on your roof is actually an indicator that the algae is already widespread across your shingles, and will only require a little more time to thicken to the point of visibility in other areas. Make the mistake of just doing a spot-clean and you should be prepared to see black stains all around those areas in a short amount of time.

4. Ideally you’ll hire a roof cleaning company that works in teams of two,

so that one man can work at the roof level while the other can stay on the ground to rinse the perimeter and to act as a safety measure just in case the roof-man should fall or require assistance.

5. Check the company’s reliability report with your local BBB.

If they are a member, even better. BBB accredited businesses usually have been around for awhile and demonstrate a record of excellent customer service. When entrusting the cleaning of your expensive roof to a contractor, you’ll want to make sure that they are qualified and take their business seriously. Those are just a few pointers for hiring the right person to clean your roof. If done correctly and professionally, stain removal can be achieved without any roof damage whatsoever, and should provide you with years of a clean, beautiful-looking roof.

Neo Johnson is an author for the Roof Cleaning Products Guide.

I think if you replace the focus on stains with a focus on moss and UV damage, this article make some good points about contractor selection for roof cleaning and treating for a homeowner in Portland.   Additionally, these days, the BBB is taking a backseat to more content rich sources such as Angie’s List and ServiceMagic that allow to read reviews, good and bad, of a contractor – Tom