The purpose of this study is to evaluate the potential of bio-sourced material based on cereal straw for an efficient insulation. Decreasing significantly energy consumption of buildings requires not only the very best insulation material for heat loss reduction through the wall but also the reduction of air permeability which can affect automatically the comfort in the building. This is why, propose an insulation material with low thermal conductivity remains insufficient and the evaluation of the performance of the new insulation material in situ in real conditions is an essential step. The experimental building ( PROMETHE demonstrator) is set up with wood frame and multilayered walls composed with cinder blocks and insulation bio-composite based on cereal straw in order to simulate the thermal rehabilitation conditions according the External thermal insulation principle. Each façade is divided in four part with three different insulation bio-composites and naked part for comparison reasons. Hygrothermal sensors are used both inside and outside of the demonstrator, and heat-flux sensor is placed at the cinder blocks biocomposite interface. These in situ measurements are used to compare the efficiency of three bi-sourced materials and for the modeling the hygrothermal behavior of the multilayer wall by using the set of identified parameters in laboratory.