5/8" Type X Gypsum Board Standards,
Testing and Certification
Type X gypsum board, 5/8" in thickness (5/8" Type X board), is manufactured for use as one component of an assembly/system (such as a wall) where a fire-resistance rating is required in a residential, commercial or other structure by an applicable building code.
5/8" Type X board is required to be manufactured in accordance with established ASTM standards defining Type X gypsum board as that which provides not less than one-hour fire resistance when tested in specified building assemblies/systems in a laboratory setting under certain controlled conditions and pursuant to certain ASTM procedures.
Because ASTM procedures require that fire tests be conducted on complete building assemblies/systems and not just on the board itself, the ability of any particular 5/8" Type X gypsum board product to pass a specific ASTM fire test may well depend on factors other than the fire resistance of the board being tested. These factors include the other components used to construct the building system being tested, the manner in which the system is constructed and the inherent variability of ASTM fire tests.
Independent third-party organizations, such as Underwriters Laboratories, Inc. (UL), may authorize manufacturers to certify or label their 5/8" Type X gypsum board as acceptable for use in one, two, or three-hour fire-rated systems based on criteria established by the third-party organizations. The third-party organizations may approve changes to certified formulations using criteria they believe appropriate, such as new full-scale ASTM fire tests, small-scale fire tests, or engineering studies and evaluations, and without requiring a full-scale ASTM one, two, or three-hour fire test. Accordingly, the fact that a particular 5/8" Type X board product has been certified as acceptable for use in one, two, or three-hour fire-rated systems by a third-party organization does not necessarily mean that board made according to that specific formulation has been subjected to a full-scale ASTM one, two, or three-hour fire test.
Given the very different circumstances that may exist from one fire to another, the differences between conditions in an actual fire and the laboratory conditions in which a test is conducted, and the inherent variability of ASTM fire tests, passing an ASTM fire test in a controlled laboratory setting or certifying or labeling of 5/8" Type X gypsum board as acceptable for use in one, two, or three-hour fire-rated assemblies/systems under third-party certification or labeling procedures does not mean that either a particular assembly/system incorporating 5/8" Type X board or any given piece of 5/8" Type X board will necessarily provide “one, two, or three-hour fire protection” in an actual fire or last for one, two, or three hours in a new laboratory fire test.
Even if 5/8" Type X gypsum board is referred to by using terms like “one-hour board” or “has a one-hour fire rating,” this does not mean that either a particular assembly/system incorporating 5/8" Type X board or any given piece of 5/8" Type X board will necessarily last for an hour in a new laboratory fire test or provide “one-hour fire protection” in an actual fire.
Once a 5/8" Type X gypsum board formula has been certified by a third-party organization, the company using that formula to manufacture 5/8" Type X board does not have to conduct periodic fire tests on that board as long as the company follows the procedures established by that third-party organization to ensure that the gypsum board is manufactured in compliance with the certified formula.