Soft washing is a cleaning method using low pressure water. It was originally coined by companies selling biocide solution that was mixed with the water. More recently, the term "softwashing" has been used to describe any form of spraying chemicals at buildings where harmful solutions (typically bleach) are used to remove mildew, bacteria, algae and other organic stains from roofs and other building exteriors.
It is so named to differentiate the method from power washing. The Asphalt Roofing Manufacturers Association recommends low-pressure bleach or detergent assisted washing as the preferred method for cleaning asphalt roofs in order to prevent damage to the shingles.
Soft washing is using an electric agricultural sprayer to apply a water-based, biodegradable disinfecting cleaning solution to kill the mold, mildew, bacteria, algae, fungus, moss and more on exterior home and building surfaces.
Soft washing Equipment is distinctly different than power and pressure washing equipment. The electric diaphragm pump applies the cleaning solution at 40-80 PSI. The equipment used for soft washing may also have telescoping handles so that the cleaning solution can easily reach roof eaves, upper story windows, and other such areas, without this added pressure. 
- "ARMA - Asphalt Roofing Manufacturers Association | Algae & Moss Prevention and Cleaning for Asphalt Roofing Systems". www.asphaltroofing.org. 2016-09-23. Retrieved 2017-06-29.
- "What is Soft Washing". Ann Arbor Power Washing Pros. Retrieved 2018-08-23.