with all the necessary protective gear, (goggles, rubber suit, gloves, etc) you can apply whichever bleach is the cheapest (like butter, there really isn't a difference between one and the next as far as I know) to the side of your house. If you use a long handled brush, and scrub lightly, you should have good results. Spray lightly with water so as not to strip the paint off the boards, and hose the general area down real good too so as not to kill any plants.
Bleach breaks down to essential elements that are environmentally safe. Smells good too, in my opinion.
Do take care of your hands and skin, bleach burns are subtle when you get them, but very nasty later.
Don't wear ANYTHING you like or care about.
(Did I put enough safety disclaimers on this?) FOLLOW LABEL INSTRUCTIONS AND ANY MSDS!!!!