Dhaka, the capital of Bangladesh, is a megacity that over the last few years has undergone an exponential population growth. Consequently, several slums have emerged and grown to an extent difficult to quantify. Our case study case study - Karail Slum - focuses on the largest slum in Bangladesh. Understanding its operation for a subsequent intervention requires first an awareness of the phenomenon and the reasons for the development of megacities, particularly in the case of Dhaka, and finally, understanding of their slums. It is therefore challenging to design a dwelling unit that is sustainable, economical and environmentally-friendly. When replicated in the informal city grid, the proposed dwelling would respond to the local high density conditions, and hold as a fundamental goal an improvement to the well-being of its residents.