What is the best pressure washing detergent for washing homes with mold and mildew? The best detergent for pressure washing houses is a custom mixture of a soap surfactant to help the mixture "stick" on vertical surfaces and Sodium Hypochlorite to dissolve mold and mildew. Sodium Hypochlorite (SH) is very common chemical in today's world. It is used to clean clothes, purify water, clean pools, and found in numerous household cleaners. Sodium Hypochlorite is also best chemical to kill mold & mildew found on the exterior of homes. Sodium Hypochlorite is produced by electrifying salt water and is very inexpensive. Since it is so inexpensive and effective companies can't brand and market it effectively for pressure washing use. They create proprietary detergents with brand names and do everything possible to disparage Sodium Hypochlorite by saying it is "dangerous, ineffective, and bad for the environment." None of these things are true but are just marketing ploys so you will use their $20/gallon soap instead of $1.50/gallon SH. Sodium Hypochlorite is commonly marketed as bleach, and is best found in a more concentrated form at chemical or pool supply companies. However you can still use store bought bleach, it's just weaker and much more expensive. You can find SH at Walmart for about $3.00/gallon at about 8% strength. This means we will have to use it without watering it down otherwise it will be ineffective. For pros it is recommended to find a local supplier of 12% SH which gives more flexibility in mix ratios and can be bought more cheaply at greater quantities. In this area a 55 gallon of 12% SH costs just over $100.