Prefabricated staircase and finishing arrangement and installation method therefor

A method for installing a prefabricated staircase, the method comprising the steps of:

• connecting generally opposed frame ends of a prefabricated staircase frame to first and second floor structures of a building with the frame extending between the first and second floor structures, the frame having at least one vertical riser, at least one horizontal tread, and at least one stringer board to which each said at least one vertical riser and each said at least one horizontal tread are connected, the frame connected at said opposed frame ends to the first and second floor structures;
• preassembling at least one preassembled finishing plate arrangement by connecting at least one prefabricated finished stringer plate to at least one prefabricated finished riser plate and to at least one prefabricated finished tread plate, the at least one prefabricated finished riser plate connecting to the at least one prefabricated finished tread plate;
• and
• after the steps of connecting the generally opposed frame ends and preassembling at least one preassembled finishing plate arrangement, connecting the at least one preassembled finishing plate arrangement to at least a portion of the prefabricated staircase frame;
• wherein the at least one preassembled finishing plate arrangement includes lower and upper preassembled finishing plate sections connecting to an adjacent one said at least a portion of the prefabricated staircase frame, each said lower and upper preassembled finishing plate section including at least one prefabricated finished stringer plate, at least one prefabricated finished riser plate and at least one prefabricated finished tread plate, the step of connecting the at least one preassembled finishing plate arrangement including:
• for each said lower and upper preassembled finishing plate section, connecting, said at least one prefabricated finished tread plate onto and covering the at least one horizontal tread with said at least one prefabricated finished riser plate in covering alignment with an adjacent said at least one vertical riser and with said at least one prefabricated finished stringer plate in covering alignment with an adjacent said at least one stringer board;
• and
• connecting a lowermost of said at east one prefabricated finished riser plate or of said at least one prefabricated finished tread plate of said upper preassembled finishing plate section in alignment with, respectively, and adjacent uppermost of said at least one refabricated finished tread plate or of said at least one prefabricated finished riser plate of said lower reassembled finishing plate section;
• wherein the upper preassembled finishing plate section is a corner section connecting to a corner portion of the prefabricated staircase frame and includes an inner corner finished stringer plate, said inner corner finished stringer plate having a protrusion downwardly extending therefrom, the step of connecting the at least one preassembled finishing plate arrangement further including connecting said protrusion of said inner corner finished stringer plate of said upper preassembled finishing plate section into a recess extending into an adjacent one said at least one said at least one prefabricated finished stringer plate of said lower preassembled finishing plate section.