This was an unusually dirty house that was covered with algae and some lichen. This typically occurs when surface areas are shaded for long periods of time, over a year and in this case 2+ years. I had to decide to either downstream it with pressure washer (downstream allows pressure washer to be used as low pressure) or use a separate system, in this case I used a 12V system, also referred to as softwash system. I have both on my truck(s). Each system has its pros and cons. Houses like this take longer to clean and cost more due to the amount of chemicals needed to achieve desired results. The time of the year also impacts amount of time and chemical cost due to outdoor temperatures which impacts chemical reactions. All the above is considered when providing estimates and doing the work.