Fire Resistant Drywall: Type X and Type C
All gypsum based drywall is fire resistant. It will actually slow the progress of a fire because most of the materials of which it is made up are not flammable. In fact, some moisture is always trapped within the gypsum, and the drywall will actually steam when heated to high temperatures. This steaming actually slows heat transfer through the wall. This is not to say that drywall provides an absolute firebreak. When a fire rages within a structure it is so hot that drywall will not stop it forever. However, it does give extra time to people escaping from the conflagration.
Thickness of the drywall is obviously a factor. Thicker drywall will provide more fire protection. There is also another type of drywall, sometimes called firewall, which will provide even greater fire resistance. Type X firewall has fiberglass added and increases the fire rating per thickness of the sheet. It actually helps maintain the structural integrity of the firewall when it is exposed to high temperatures. Type X firewall 5/8-inch thick on both sides of a 2X4 studded wall should provide about 1 hour of fire protection. Type C firewall has even better fire protection.
Both Type X and C drywall will be specially labeled. Local building codes vary on the level of fire-resistance required. Here is a directory of local codes.
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