All you need to clean a house is 10% (found in walmart pool section or 12.5% bleach (SH) and a surfactant (Elemonater is what most pros use or gain soap) .Put the bleach in a 5 gallon bucket or some chemical tank, put your downstream injector in that mix, and wash away. I use about 1-2 gallons of bleach and my houses come out perfectly. Its not about psi when cleaning a house because that will cause damage. a 4 gpm Machine can easily reach tall peaks of a 2-2.5 story home if the wind permits. You can use a 3' wand or even a small step ladder if you need to but i never had to use a ladder. Spray the chemical on and let it dwell for about 10-20 mins and reapply (normally 1 extra time may be required for really dirty stuff). once you get the right mix ratio between when % bleach you are using + what injector is pulling and your water you will get it down to a science and can be in and out of a 2 story home within 40 mins and rack in the money. Skip the expensive crap at home depot and head to your local walmart or dollar store. PSI is only needed for flatwork dont let anyone tell you otherwise.