A method for the continuous production of boards of a ligno-cellulosic fiber material wherein the material is broken up into particles and/or fibers. These are dried, glued and formed to a mat. The mat is compressed to a finished board while steam is introduced. According to the present invention, the compression is performed as a single step and the steam is introduced through one or many compression rollers. By injecting steam in this way a sufficient cure is obtained to withstand the spring back characteristics inherent of the fibers so that it is possible to obtain a finished thickness of the board with one single compression step.