In this paper, we study the influence of two types of starch on earth hemp or flax straw mixtures at fresh and hardened states. The main goal is to propose new non-load bearing earthen for indoor. The mass percentage of starch/binder (S/B) in mixtures was fixed at 1% of mass. The VEBE consistometer test has been used to fix a similar consistency between mixtures. The targeted workability has to allow an easy introduction of materials in the moulds. Adding both of starch has shown a positive effect on mixtures workability at the fresh state and mechanical resistances at the hardened state. At hardened state, mechanical and thermal-acoustic performances have been measured on laboratory samples and blocks at real scale. Results have shown a significant effect of starch on mechanical strengths.