Stop!!! ... Never Pressure Wash Your House
Your home or property was not built to withstand the forces of washing with high pressure water ranging from 1,500 ~ 4,000 psi.
Unfortunately, the vast majority of people, believe that you need to use high pressure water blasting away merely inches from the surface in order to get the exterior of a home clean (hence the term "Pressure Washed" or "Power Washed").
Also, to be able to maintain enough force to blast the dirt, grime and mold off of the surface they are attempting to clean once they get higher than they can reach from the ground, they will attempt to work off of ladders. This is an extremely dangerous practice and one that need not be done if when the cleaning is done properly.
The inexperience may spray bleach directly to the home's siding with a pump-up sprayer pump then attempt blast the dirt off with high pressure in an effort to clean it. However, this is a poor, ineffective and dangerous cleaning technique.