Is there such an animal as "Fire Rate...

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Author Message Jerome J. Lazar, RA, CCS, CSI, SCIP Senior Member Username: lazarcitec Post Number: 1099 Registered: 05-2003 Posted on Thursday, May 22, 2014 - 04:36 pm:    I thought I'd better start a new thread on this question... So when a client calls out for fire rated gypsum board on a drawing is this correct? ken hercenberg Senior Member Username: khercenberg Post Number: 759 Registered: 12-2006 Posted on Thursday, May 22, 2014 - 04:54 pm:    They're actually requesting Type X board which, when used in a tested assembly, provides a fire-resistance rating. Many manufacturers make a "Type C" board which is meant to out-perform the Type X. To my knowledge, Type C board is considered by both Code and testing agencies as a variation of the Type X board and is not listed as a separate designation. As Lynn pointed out in the previous post, sticking a sheet of Type X gyp board in the middle of the room will not provide a rated assembly. As an aside, if you are using foam insulation the IBC does recognize a layer of gypsum board (does not need to be Type C) as a 15 minute fire barrier. No independent test report is required to comply which is interesting since, from my understanding, some of the new lightweight boards won't provide 15 minutes of protection. Oh well. Hope that never becomes a lawsuit. George A. Everding, AIA, CSI, CCS, CCCA Senior Member Username: geverding Post Number: 746 Registered: 11-2004 Posted on Thursday, May 22, 2014 - 04:58 pm:    Here's my understanding of how gypsum board works: All GB prevents the spread of flame by its chemical composition. H2O is bound into the material in the manufacturing process, and when fire hits the product, the H2O converts from a part of the solid to a water vapor. The energy to make this change in state has to come from somewhere, and that somewhere is the heat of the flame. So it takes longer for the fire to penetrate any GB than a comparable thickness of something else with a chemical composition lacking the H2O. Now, obviously when the H and O molecules leave the GB, the mass of the material is less, and it tends to crumble. So fire-rated (type X) GB has small fibers added to it to help hold it together longer. And fire-rated (type C) GB has an expansive material (perlite? vermiculite?) added in addition to the fibers to help hold it together even longer. That's why 5/8" type X is roughly equivalent to 1/2" type C. Of course, this is all assembly based and tested under ASTM E119. But you can see the fibers of fire-rated GB exposed along a cut edge next time you are on a jobsite. Used to be that you could get various thicknesses of regular and fire-rated pretty easily. For years now, the manufacturers make "all" 1/2" board regular, and "all" 5/8" board as type X. Type C is generally special order. At least that WAS my understanding from 5 or so years ago. Anyone in the GB industry that can offer corrections or additions, please do so. George A. Everding AIA CSI CCS CCCA Allegion PLC (formerly Ingersoll Rand) St. Louis, MO Ronald L. Geren, FCSI, AIA, CCS, CCCA, SCIP Senior Member Username: specman Post Number: 1219 Registered: 03-2003 Posted on Thursday, May 22, 2014 - 06:45 pm:    George covered the science of it very well. Gypsum board technically does not have a rating, but the IBC does allow the building of assemblies using times assigned to certain materials (See IBC Section 722 "Calucalted Fire Resistance"; 2012 edition). Gypsum board has different times assigned to it based on thickness and type from 10 to 40 minutes. Ron Geren, FCSI, AIA, CCS, CCCA, SCIP www.specsandcodes.com