Abstract: A siding panel formed from a body of hardboard material is formed with a locking tongue at or adjacent its upper edge and a locking seat at its lower edge. The locking tongue of one panel is arranged to be seated in the locking seat of another panel when adjacent panels are arranged with their marginal edge portions overlapping one another in use. The locking seat is in the form of a notch which is formed in the back face of the body of the panel. The notch extends upwardly from the lower edge and underlies the lower marginal edge portion of the panel.