Dec 16, · Insulating exposed rim joists. what can I use on the rim joists that is fire resistant when left exposed. would mineral wool qualify as a "thermal barrier"? FIRE PERFORMANCE OF TRUSSES FIRE to resist penetration by fire or by heat protection barrier between occupancy spaces if a fire starts in. Nov 03, · The building is Type III Non-rated construction with a 2-Hour Fire Barrier Wall seperating the The fire barrier wall extends above this penetration to the.