How exactly do Natural Buildings Breathe? 

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Many of us talk about how Natural Buildings "breathe" and have "life". On a large scale, a building has thermal regulations and air ventilations as its life system, but more importantly, a building inhales and exhales on a micro-material level. Mainly, mud and lime are the two main materials which causes buildings to breathe.

Usually the comfortable temperature of mud houses are because of their width of the walls that takes long time to allow heat to conduct inside (called heat lag). But there is also another less mentioned reason -

Mud and lime are porous materials and they can cause evaporative cooling effect. Whenever a liquid becomes vapour, it takes with it a certain amount of heat which causes the cooling. Mud absorbs moisture from the air, evaporates it and causes cooling, thereby regulating temperature and humidity. That is why doing a cement-based plaster or paint on mud walls gets mud rid of this property to interact with the external environment.

Most modern paints and emulsions has lower permeability than the wall behind it. But, Lime is material that soaks well into the underlying wall and has a good vapour permeability. While in cement structures, the Trapped moisture in walls causes damp problems, cracking and flaking of walls, Lime is porous enough to let the moisture from the building to evaporate.

This life-like properties of Mud and Lime is what causes Buildings to respire, recover and strengthen.

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