The continued growth of the high-rise residential building market in conjunction with the latest releases of energy codes demonstrates the importance ofconsidering the design of mechanical and building enclosure systems on a holistic basis. Modern energy codes require airtight construction which can leadto problems with the ventilation strategies that mechanical system designers have historically used, specifically reliance on natural ventilation through eitheroperable windows or “incidental air leakage.” This paper will discuss the areas where building enclosure and mechanical systems have an important effecton one another including air quality, air pressure control, condensation, and energy. The paper will also discuss how traditional ventilation strategies,including operable vents in fixed fenestration systems, can have unintended consequences.