if its plain old mud, dirt, dust, etc. it has to be pressure washed and/or scrubbed by hand. if it is mildew or algae (the green stuff) you can get a pump sprayer from wal mart, buy a gal. of bleach, mix bleach and water together in the sprayer, (one third bleach and the rest water) and spray the house--it will look fabulous when you finish, its easy as hell. rinse the bleach solution off with a hose when the sprayed area looks clean.