Historically, geographers, anthropologists and colonial British administrators (1860–1947) frequently mentioned two ethno-geographical categories – khoungtha and toungtha – when referring to the tribal groups in the Chittagong Hills of Bangladesh. Some of these early works considered the livelihood patterns of these groups and the nature of their social and economic interactions. However, a discussion of the changes to their vernacular built environment has escaped any serious investigation. Using empirical findings, this article examines the changes to architectural practices of lowland and highland groups in the socially and ethnically complex region of the Chittagong Hills. Narrowing the discussion to the toungtha Mru ethnic group, this article also examines religious patterns, building techniques and spatial changes in a remotely placed, relatively inaccessible part of the hills where the built environment is still a strong cultural priority.