Abstract: A modular building panel is provided having interlocking bead and groove conformations formed in mating interfitting tongue and socket structures and provided with sealing strips for forming a fluid seal between adjacent assembled panels. The modular building panel is fabricated with longitudinally extending marginal edge portions of mating tongue and socket configurations for enabling interfitting assembly of adjacently disposed panels. The tongue and socket edge portions of each panel are provided with respective interlocking bead and groove conformations for cooperative interlocking engagement for securing adjacently disposed panels in assembled relationship. A sealing strip formed from an elastomeric material is attached to at least one of the socket or tongue marginal edge portions in longitudinally extending relationship thereto and at a location for contacting interengagement with surfaces of the adjacently assembled panel in forming a fluid impervious seal therewith.