A rail-less roof mounting system for installing a plurality of photovoltaic modules (170, 172) on a roof structure, the rail-less roof mounting system comprising: a base mount assembly attached to the roof structure comprising: a base member having a top surface and a bottom surface, the bottom surface being engaged with the roof structure, the base member includes a waterproof means on the top surface thereof; a block slider having an elevated seal portion and a vertical engaging portion, the elevated seal portion having a borehole formed therethrough to receive the waterproof means, and a top slider attached with the block slider having a top portion and a bottom portion, the top slider having a track with a horizontal groove at the top portion, and a sliding seal member with a sliding groove and a slot at the bottom portion; a clamp assembly for attachment to the base mount assembly, the clamp assembly having a clamp member comprising at least one aperture on an inner surface; and, at least one cap screw for attaching the clamp assembly to the base mount assembly; characterized in that the clamp assembly further comprises a plate member with at least one slot, the clamp member interconnecting a frame member of a PV module to a frame member of an adjacent PV module, wherein the clamp member, the plate member and the track on the top slider are adapted to be secured to each other by: sliding the at least one cap screw into the horizontal groove on the track; by receiving the at least one cap screw through the at least one slot provided on the plate member; by receiving the at least one cap screw through the at least one aperture provided on the clamp member; and, by securely tightening a lock nut to the at least one cap screw; whereby the plurality of PV modules (170, 172) are interlocked in a way to provide a corner-to-corner coupling arrangement which enables the connection of PV module corners to adjacent PV module corners by sandwiching above and beneath the frame members (164, 166) of the plurality of PV modules (170, 172). a base mount assembly attached to the roof structure comprising: a base member having a top surface and a bottom surface, the bottom surface being engaged with the roof structure, the base member includes a waterproof means on the top surface thereof; a block slider having an elevated seal portion and a vertical engaging portion, the elevated seal portion having a borehole formed therethrough to receive the waterproof means, and a top slider attached with the block slider having a top portion and a bottom portion, the top slider having a track with a horizontal groove at the top portion, and a sliding seal member with a sliding groove and a slot at the bottom portion; a base member having a top surface and a bottom surface, the bottom surface being engaged with the roof structure, the base member includes a waterproof means on the top surface thereof; a block slider having an elevated seal portion and a vertical engaging portion, the elevated seal portion having a borehole formed therethrough to receive the waterproof means, and a top slider attached with the block slider having a top portion and a bottom portion, the top slider having a track with a horizontal groove at the top portion, and a sliding seal member with a sliding groove and a slot at the bottom portion; a clamp assembly for attachment to the base mount assembly, the clamp assembly having a clamp member comprising at least one aperture on an inner surface; and, at least one cap screw for attaching the clamp assembly to the base mount assembly; characterized in that the clamp assembly further comprises a plate member with at least one slot, the clamp member interconnecting a frame member of a PV module to a frame member of an adjacent PV module, wherein the clamp member, the plate member and the track on the top slider are adapted to be secured to each other by: sliding the at least one cap screw into the horizontal groove on the track; by receiving the at least one cap screw through the at least one slot provided on the plate member; by receiving the at least one cap screw through the at least one aperture provided on the clamp member; and, by securely tightening a lock nut to the at least one cap screw; whereby the plurality of PV modules (170, 172) are interlocked in a way to provide a corner-to-corner coupling arrangement which enables the connection of PV module corners to adjacent PV module corners by sandwiching above and beneath the frame members (164, 166) of the plurality of PV modules (170, 172).