The turbine housing assembly includes a housing surrounding a plurality of turbine shroud segments mounted to support members of the housing. Impingement holes extend through the housing and have outlet openings communicating with a cavity between the shroud segments and the support. A deflector rail protrudes axially away from the support members into the cavity. The deflector rail defines a flow-redirecting surface to redirect the cooling air flow from the impingement holes radially outwardly, away from the turbine shroud segments.