An original model describing non-equilibrium heat transfer in ablative composite layers has been studied. The model is obtained as an extension of previous work involving the use of the volume averaging method to upscale the micro-scale equations. Using this methodology, it is shown that non-equilibrium models existing in the literature may lead to equilibrium conditions for typical aerospace applications. The new model presented in this paper takes into account two separate macro-scale "phases", but, contrary to previous models, they are constituted of the inert part of the material, on one side, and the mixture of gas and pyrolysable part of the material on the other side. The theoretical development allows to estimate the transport properties in the macro-scale model from micro-scale unit cell characteristics. They are obtained for different types of unit cells: simple stratifed unit cells, and unit cells characteristic of woven composites. Quantitative indications are given for the estimates of the macro-scale thermal diffusivity tensors, and for the volume heat exchange coefficient.