Ecomaterials used in traditional construction are experiencing renewed interest for their low environmental impact. However, the lack of reference values for the hygrothermal behaviour of some composite ecomaterials with a low carbon footprint prevents the overall analysis of the structures of buildings designed with these materials. The wood-clay construction system is an ecological and sustainable building system. These materials have great potential for applications in places where housing needs are high, in rural areas of Africa, and have been used for hundreds of years in Europe. The plant fibres improves the hygrothermal, mechanical and weather resistance performance of clay materials. This study determines the water content absorbed by the wheat and corn stalk fibres that will allow the water/clay ratio to be adjusted. For the characterization of red and white clay, the results obtained by the pycnometer method show that the bulk density of the clay is 2.80 and 2.73 with an absolute density of 2.79 g/ml and 2.72 g/ml. The results of the characterization of wheat and corn fibres show that they have the capacity to absorb more than 200% and 120% water by weight in only 25 minutes respectively at 23℃. The water absorption of fibres increases with increasing temperature. This increase contributes to the improvement of the hygrothermal performance of the materials by the restitution of the absorbed humidity, providing a very good feeling of comfort. Samples formulated with 0% to 3% wheat fibre have shown that the addition of fibre reduces the shrinkage of clay materials by 6.35 to 1.53%.