Babcock-Davis BU-Series: BUT fire-rated, uninsulated access doors provide access through openings in fire rated vertical surfaces and have a minimal sight line for a concealed appearance. UL Listed "B" label for 1-1/2 hours in vertical surfaces (maximum temperature rise to 250F in 30 minutes). BUT fire rated access doors provide access through fire rated vertical surfaces, in any material including drywall, plaster, and CMU.