I would use JOMAX to clean the siding as this product is applied with a pump up sprayer and washed off with a garden hose. It should not bother your shingles but it will clean them up if they are really dirty.

I just did my niece's house that had mold & all I used was a power washer with power wash soap then rinse If you are able to climb a ladder the hose should reach the top

Thanks for the reply's...I've got myself a new powerwasher and a friend that's willing to hold the phone and call for help if I fall off the roof while scrubbing off the mold and dirt!

Also, FYI...I contacted Zinsser, the company that manufactures JOMAX...here's what they said when I asked them my question:

"JOMAX House Cleaner and Mildew Killer is recommended for non-porous surfaces such as vinyl and aluminum siding or other painted or sealed surfaces. Because asphalt shingles are generally, porous we would not recommend using JOMAX. You might want to check with your local home improvement center for other mildew killing products."