Plant & fibre
Thatch & reed
Grasses, palm, and water reed bundled and layered into roofs and even whole halls; harvested from the landscape the building stands in.
How it behaves
Trapped air makes thatch a genuine insulator (unlike most vernacular mass materials); steep pitches shed heavy rain fast. It wants ventilation and periodic renewal, and it composts when done.
Where it belongs
Kerala and Bengal · Mesopotamian marshes · Northern Europe
In a modern project
Thatch over waterproof membranes as living insulation; reed boards as breathable internal insulation.