Surface covering comprising laminate panels and an extraneous locking element

A surface covering comprising panels and at least one extraneous locking element, each panel provided with parallel, opposing longitudinal edges and parallel, opposing transverse edges, these edges being provided with respective longitudinal and transverse coupling means which are adapted to connect similar panels at corresponding adjacent edges, whereby the transverse coupling means are adapted to lock panels perpendicular to adjacent transverse panel edges and parallel to the panel plane, the transverse coupling means in coupled condition forming a channel which is adapted to receive the extraneous locking element, the longitudinal coupling means comprise a tongue on one edge and a corresponding groove on the opposing edge, the longitudinal coupling means being adapted to lock similar panels perpendicular to adjacent longitudinal edges and perpendicular to the plane of the panels as well as parallel to the plane of the panels, whereby the longitudinal coupling means are adapted to be locked with angling and the transverse coupling means are adapted to be locked with vertical folding,

• wherein a lower lip of the groove is provided with a lower lip contact portion positioned at a lower lip contact portion height hlower—lip, and an upper lip of the groove is provided with an upper lip contact portion positioned at an upper lip contact portion height hupper—lip, whereby the difference between these heights hupper—lip−hlower—lip is equal to an effective thickness deff of the extraneous locking element, such that when two parallel rows of panels are assembled, the extraneous locking element, when inserted into the channel formed by the transverse coupling means of panels in the first row, is adapted to extend at least partially into the groove of an adjacent parallel panel in the second row, such that a lower surface of the extraneous locking element is in contact with the lower lip contact portion, and the upper surface of the extraneous locking element is in contact with the upper lip contact portion.