A roof mounting system for installing a plurality of photovoltaic modules (170, 172) on a roof surface, the roof mounting system comprising: a. a base mount assembly for attaching to a roof surface, the base mount assembly comprising: i. a base member having a top surface comprising a waterproofing means consisting of an upstanding portion that extends away from the roof surface, the upstanding portion defining a distal end aperture; ii. a block member comprising: 1. an elevated seal portion configured to fit over the base member; 2. a through hole configured to fit over the upstanding portion; and 3. a vertically extending engaging portion; iii. a tightening means for attaching the base mount assembly to the roof surface by insertion through said through hole and said distal end aperture; and iv. a sealing washer for fitting on the tightening means and adapted to seal the through hole in the elevated seal portion to prevent seepage of water, wherein the sealing washer comprises two parts, that is a disk of rigid material and an outer layer of deformable material; b. a clamp assembly for connecting a frame member of at least one PV module to the base mount assembly; and c. a structural member having a top portion for connecting to the clamp assembly and a bottom portion for connecting to the vertically extending engaging portion of the base mount assembly. a. a base mount assembly for attaching to a roof surface, the base mount assembly comprising: i. a base member having a top surface comprising a waterproofing means consisting of an upstanding portion that extends away from the roof surface, the upstanding portion defining a distal end aperture; ii. a block member comprising: 1. an elevated seal portion configured to fit over the base member; 2. a through hole configured to fit over the upstanding portion; and 3. a vertically extending engaging portion; iii. a tightening means for attaching the base mount assembly to the roof surface by insertion through said through hole and said distal end aperture; and iv. a sealing washer for fitting on the tightening means and adapted to seal the through hole in the elevated seal portion to prevent seepage of water, wherein the sealing washer comprises two parts, that is a disk of rigid material and an outer layer of deformable material; i. a base member having a top surface comprising a waterproofing means consisting of an upstanding portion that extends away from the roof surface, the upstanding portion defining a distal end aperture; ii. a block member comprising: 1. an elevated seal portion configured to fit over the base member; 2. a through hole configured to fit over the upstanding portion; and 3. a vertically extending engaging portion; 1. an elevated seal portion configured to fit over the base member; 2. a through hole configured to fit over the upstanding portion; and 3. a vertically extending engaging portion; iii. a tightening means for attaching the base mount assembly to the roof surface by insertion through said through hole and said distal end aperture; and iv. a sealing washer for fitting on the tightening means and adapted to seal the through hole in the elevated seal portion to prevent seepage of water, wherein the sealing washer comprises two parts, that is a disk of rigid material and an outer layer of deformable material; b. a clamp assembly for connecting a frame member of at least one PV module to the base mount assembly; and c. a structural member having a top portion for connecting to the clamp assembly and a bottom portion for connecting to the vertically extending engaging portion of the base mount assembly.