Traditional architecture remains alive in Bhutan. All buildings are constructed with multi-coloured wood frontages, small arched windows, and sloping roofs. Walls of homes in western Bhutan are most frequently rammed earthen walls, pounded into wooden frames and rendered with lime. Completed mud walls may be left naturally colored or whitewashed. In the wetter eastern valleys of Bhutan where settlements are dug directly into mountainsides, the walls are more often made of stone. No plans are drawn up, nor are nails or iron bars used in the construction.