Pressure washing is the preferred method. And you don't need any chemicals. As you get closer to the house, wet the siding and start cleaning the deck. This way, if the walls are already wet BEFORE you get over there, the 'stuff' won't stick if it 'splashes' up. Then, you can rinse the walls as you go. Plus, if you angle your nozzle AWAY from the house a little, you should do even better.
My best to ya and hope this helps.
Jay J -Moderator
PS: IF you've never used a pressure washer in this scenario, it would pay to do some reading. There are a few 'things' to be mindful of ...