Chhaya 2.0© is an Excel based design tool that helps designers optimize glazing size and orientation, shading and natural ventilation to extend the period that the building can run passively. It used TMY2 weather data and a series of interactive matrices to help the user come up with optimal design solutions. The use of slider bars to allow the user to increase window sizes as well as shades in each direction and ventilation rates allows the architect to enter the world of the engineer with instantaneous interactive feedback to building shell decisions.