It depends a lot on the weather, the area around your house, and the building materials of its exterior. A little dirt isn’t a big deal, but mold and algae can damage the structure of your home. A good rule of thumb is to wash all exterior surfaces at least once a year.

• Pressure washing can prevent costly repairs. It reduces damage caused by mold, mildew, and algae. It can also help avoid rot caused by moisture buildup under caked-on sap, soil, and bird droppings.
• Pressure washing can help you save money on your power bill. If the outside structure of your home is compromised, it will reduce the effectiveness of your insulation, which will force your HVAC system to work harder to keep your home at a comfortable temperature.
• Pressure washing is a great way to prep surfaces for painting, refinishing, or resurfacing. It is always best to start with a clean slate before changing or repairing your home, and pressure washing is an easy way to accomplish that task with very little effort.
• Pressure washing is a fast, inexpensive way to improve the curb appeal and value of your home. If you are considering selling or renting your home, it is highly recommended to start with a good exterior wash.

While pressure washing can help preserve your home, if it is done improperly it can cause significant harm. If the water pressure is too high it can strip layers off softer materials, like older bricks or paint. There is also a risk of damaging siding or even knocking it off the house. The biggest danger is forcing water inside cracks around eaves, windows, and doors which will damage the wood framing.