Burned wood acts as insulation for the unburned core so large timbers can have long fire ratings. The rule of thumb is 1.5" per hour. [0] I can’t comment on re

Burned wood acts as insulation for the unburned core so large timbers can have long fire ratings. The rule of thumb is 1.5" per hour. [0] I can’t comment on reinforced concrete, but structural steel requires protection to meet 1+ hour fire ratings. [0] https://www.nishkian.com/fire-rated-wood-construction/ https://www.nishkian.com/fire-rated-wood-construction/