Yes, they can. A Passive House by definition doesn't really require windows that open, as there is a fresh air system in the home that is constantly bringing fresh filtered air in, often at a rate of three volume changes of the house per hour. This allows the fresh air that does come into the home to be filtered and regulated, versus an open window that is unregulated in terms of both airflow and contaminants in the air, such as allergens. For code compliance, certain rooms do require operable windows in order to escape if there were a fire, for example. Most operable windows in a PH home open using a European tilt and turn method versus a traditional up down opening for a window from the U.S. Moreover, these windows utilize three pieces of glass, special gases between the panes, and improved glazing to provide the ultimate in performance and comfort. In addition, in terms of cost, PH operable windows are typically more expensive than their fixed-glass alternatives.