A panel configured for attachment to a mounting surface includes raised faces extending between upper and lower edges thereof. The raised faces define a face plane. A shoulder is defined on the raised faces adjacent the upper edge and is spaced from the mounting surface by a shoulder offset. The face plane is also spaced from the mounting surface by the shoulder offset. Keyways are defined between the raised faces and recessed from the face plane. The keyways are spaced from the mounting surface by a bottom keyway offset adjacent the lower edge. The bottom keyway offset is substantially equal to the shoulder offset. Therefore, the face plane of the raised faces at the upper edge of the panel is spaced from the mounting surface by substantially the same distance as the keyways are spaced from the mounting surface at the lower edge of the panel.