A method for manufacturing a compound construction element, in an
extrusion process wherein a composite material is pressed through an
extrusion die, which composite material includes a matrix of
thermoplastic synthetic material including wood particles or other,
cellulose containing particles in a content on the order of 50% by weight
or more, wherein also one or more elongated additional elements are
passed through the extrusion die, which additional elements are brought
into tight engagement with the composite material, after which the
compound element is shaped and preferably cooled in a die.