subject invention is generally designated as 20 with reference to its orientation in fig1 the upper side of a modular ceiling insert 22 is shown the ceiling insert 22 projects above a ceiling 24 having a plurality of parallel extending joists 26 a 26 b 26 c 26 d 26 e 26 f 26 g 26 h 26 i 26 j 26 k further structural support is provided by assembled groups of parallel extending joists 28 a 28 b which extend perpendicular to joists 26 as shown in fig2 a particular configuration of ceiling structural supports is defined by a plurality of joists forming an octagon configuration the sides of the ceiling structural supports are formed by joists 30 a 30 b 30 c 30 d 30 e 30 f 30 g 30 h secured to the ceiling structural supports 30 a 30 h are four support collar sections 40 as shown in fig4 each support collar section 40 includes a curved support portion 42 for supporting a peripheral edge of a modular ceiling insert 22 opposed end edges 44 46 cooperate with adjacent support collar sections to interconnect adjacent support collar sections together and thereby define an opening to be filled by the modular ceiling insert 22 end portion 46 includes a support flange 48 and a projection 50 for inter engaging and supporting end 44 of an adjacent support collar section with the projection 50 fitting into a corresponding recess 52 of end.