The aim of a passive cooling system is to minimize or eliminate the high costs of the air conditioning system, as well as reduce carbon emissions. This research explores an integrated thermal chimney and roof gap design with an underground air intake as a non-mechanical method of cooling. Specific focus is on optimizing the roof gap and thermal chimney design through CFD analysis. An underground air inlet system cools the air to ground temperature by convection before it is drawn into the interior of the structure eliminating the need for a mechanical cooling system. The air gap integrated under the copper roof in the rafters creates a pocket of hot air under high heat gains which causes a pressure differential in the interior of the home and draws the cool air entering the living space upwards through air vents on the ceiling of the room, and this air is then drawn out the thermal chimney. As a method of validation, numerical solutions were compared to analytical solutions for individual geometric shapes in the home. Extensive comparisons of results generated in ANSYS CFX software to Ostrach’s Similarity Solutions for an isothermal vertical flat plate, Sparrow’s solutions for a vertical flat plate under constant heat flux, and Bejan’s discussion on vertical parallel plates (a 2Dvertical duct) were performed. Once CFD solutions proved valid, simulations were performed to optimize the integrated natural cooling system. In the final design of this research, the interior air achieves the temperature of the the cooled air intake, thus achieving a predetermined comfortable steady state temperature for building inhabitants. The heated thermal chimney exit draws the cool air upward to the chimney exit. Mixing occurs throughout the interior of the structure as the air rises until it reaches fully mixed steady state. This research explores cases of an integrated air gap to chimney approach, including iterations of chimney shapes and locations of vents from the room to the roof gap. With this foundational research, the concept can be implemented and further optimized with materials that improve practicality and reduce construction costs.