Municipal waste as a renewable resource has been processed into biocomposite boards as a substitute for wood to reduce environmental pollution. The biocomposite performance is governed through the interface between the fibers and the polymer matrix. However, the manufacture of biocomposites is often limited to the use of homogeneous types and sizes of fibers, with complex chemical or biological treatment of fibers to improve interfacial compatibility. Herewith, we report success in increasing compatibility through simple mechanical and physical treatment. The increase in the mechanical properties of biocomposites is influenced by variations in filler fiber sizes, the maximum polymer coating on the filler surface, and the addition of reinforcing elements to the biocomposite board structure. Variations in size of plant fiber can be obtained through mechanical treatment with single milling process, while physical treatment of repeated hot-press processes ensure that polymer coats the entire fiber surface. Furthermore, glass fiber laminate is added to the middle of the board as a structural reinforcement. Our result shows that the properties of the simple processed biocomposite have strength equivalent to commercial particle board and Albasia wood, as well as better fire resistance properties than Albasia wood. This makes waste composite boards suitable as a new substitutes for wood boards.