While most professionals agree that your home should get at least one pressure washing a year to stay on top of grime buildup, how often you should pressure wash your house depends on multiple factors, such as your home's location. Another factor is the number of trees surrounding your home, as they can cause sap buildup on your exteriors. The best way to determine whether it's time for a house washing is to closely monitor the state of your exteriors and watch for the development of grime, stains, and organic growths. If there is visible evidence of dirt buildup or if dirt comes off on your hand when you touch your siding, then it's likely time to call your local pressure washing contractor.