Abstract: A joint support is adapted to be disposed beneath a joint at adjacent ends of horizontally disposed overlapping siding panels to support same and to assist in preventing the formation of a gap at said joint by virtue of inward buckling or deflection of one of the panels relative to the other. The joint support, as seen in a cross-section view taken at right angles to the longitudinal dimension of the panels in the installed condition has a wedge taper and has minimum thickness adjacent a first end which, in use, is uppermost. The opposite end of the joint support is contoured or shaped to overlie and accommodate the panel holding lip of a preceding lower panel. The first end of the joint support has an outwardly and downwardly turned portion adapted to fit over the panel holding lip or lips of the panels which the joint support, in use, underlies and the opposite end of the joint support includes shallow hook means thereon for snap fitting engagement over the holding lip of the preceding lower panel.