Apparatus and methods for spacing, securing, and stabilizing I-joists at their ends, and insulating and structural enhancing I-joist assemblies, are provided around the perimeter, or in the interior, of a floor or ceiling where ends of I-joists are located. Insulated blocking panels may comprise an insulating portion that provides a high-R-value and a structural portion which may comprise vertical panel(s) and optional integral support blocks that provide a profiled end surface for extending to the web of the I-joists. Alternatively, insulated blocking panels with flat, vertical end surfaces may be used with field-installed support blocks, or insulated blocking panels with profiled end surfaces may be used without any support blocks. The support blocks or profiled end surfaces of the insulated blocking panels extend to the web of each I-joist, to fill in the space between the I-joists near the I-joist ends, including a substantial amount of the space immediately adjacent the web of each I-joist. The preferred insulated blocking panels, therefore, insulated the outer perimeter of a floor or ceiling and also contribute vertical load carrying capability, and lateral shear and roll-over resistance.