A turbine blade assembly for a gas turbine includes a spar with raised ribs, a spacer with a plurality of protrusions mounted around the spar, and an outer shell mounted around the spacer. The protruding portions on the spacer surround the raised ribs on the spar. The protruding portions of the spacer act to space the interior surfaces of the outer shell away from the spar to provide a thermal insulation layer of cooling air.