Fire resistant building board

A building board, comprising:

• a first cover sheet;
• a second cover sheet;
• a first layer comprising gypsum disposed between the first and second cover sheets;
• a second layer comprising gypsum disposed between the first cover sheet and the first layer;
• and
• an interlayer between the first cover sheet and the second cover sheet, wherein the building board has one or more of the following:
• a TC4 failure time of greater than 73 minutes, wherein the TC4 failure time is the amount of time it took to reach 140° plus room temperature on the cold face (TC4) of the building board;
• a TC4 failure improvement time of at least about 3 minutes, wherein the TC4 failure improvement time is equal to the amount of time longer that the building board lasted in a TC4 failure time test as compared to the amount of time that a standard board without an intumescent layer lasted;
• a TC4 failure improvement percentage time of at least 1.5%, wherein the TC4 failure improvement percentage time is equal to the percentage of time longer that the building board lasted in a TC4 failure time test as compared to the percentage of time that a standard board without an intumescent layer lasted;
• or
• at least a 15% expansion improvement over a standard board, wherein the expansion improvement is equal to the percentage the building board expanded over an amount of expansion of the standard board tested during the TC4 failure test.