Keeping your house trim clean is good preventive maintenance. Cleaning the underside of your eaves where the soffit panels cover the bottom of your rafter tails, and the edge of the roof, where your fascia runs horizontally along the ends of the rafter tails, not only keeps your house looking fresh, it allows you to see early signs of damage or needed repairs. Water pressure is the best tool for cleaning fascia and soffit, but keep the pressure to what will come out of your hose to minimize damage.
Mix 4 ounces, or 1/2 cup, of dish washing or laundry detergent to 2 gallons of warm water in a bucket. Add two tablespoons of bleach to kill mildew and mix thoroughly.
Set your ladder in a stable position where you can reach one end of your soffit easily. If possible, position it so that you can clean both fascia and soffit at the same time.
Soak a large sponge in the warm water solution and scrub it over the fascia and soffit working back toward the house. Concentrate on indented or textured areas that typically hold more dirt trapped in their indentations. Work on a section as large as you can reach from the ladder.
Fit a squeeze trigger nozzle onto the end of your garden hose, turning it clockwise to tighten, and turn the pressure on high. Rinse the section of the soffit you just scrubbed, washing away all of the dirt and rinsing enough to clear the surface of detergent and bleach.
Move the ladder and scrub the next section in the same way, rinsing it with the hose when scrubbing is complete. Use a stiff nylon brush on stubborn stains and in the louvers of soffit vent grills. Angle the water horizontally when spraying grills to minimize the moisture that goes up through the vent.
Use a thin paint scraper or razor scraper to remove sticky spots left by insects or adhesives. Remove especially stubborn stains with nail polish remover applied with a cotton ball.