Systems and methods for retrofitting an existing troffer light fixture, or for a new installation application, comprising a housing and a door assembly, wherein the door assembly comprises four side walls, a recessed cavity, a light source, one or more lens, and at least one support extension supporting the assembly are disclosed. The support extension may be a fixed horizontal protrusion of the frame of the retrofit assembly and configured to engage a T-bar of a ceiling system. The protrusion may rest on a horizontal portion of the T-bar to thereby support the assembly. Existing troffer light fixtures can be retrofitted to include a more efficient light source, replace components of a damaged troffer style light fixture, and/or otherwise upgrade or replace an existing fixture. The retrofit assembly may enable existing fixtures to be modified from a number of different fixture types without the need to remove and replace components of the existing fixture.