Rated CMU

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Author Message Ralph Liebing, RA, CSI Senior Member Username: rliebing Post Number: 839 Registered: 02-2003 Posted on Friday, May 09, 2008 - 11:29 am:    Frustrated and scouring around for location of UL Design numbers for 12" CMU- 4 hour 12" and 8" CMU- 2 hour Asking help-- and many thanks Marc C Chavez Senior Member Username: mchavez Post Number: 304 Registered: 07-2002 Posted on Friday, May 09, 2008 - 11:42 am:    2006 IBC Table 720.1(2) This table calls out min thickness of unit for rating required e.g. CMU Expanded slag or pumice 4.7 inches = 4hr and if it's in t he code book you dont need a UL test cause it's already been acceped as part of the code. or am I missing something. Ronald L. Geren, AIA, CSI, CCS, CCCA, SCIP Senior Member Username: specman Post Number: 647 Registered: 03-2003 Posted on Friday, May 09, 2008 - 11:48 am:    The fire-resistance of masonry is heavily dependent on a term called "equivalent thickness." Therefore, each manufacturer might have a varying rated products because of their unique shapes. Equivalent thickness is calculated by dividing the net volume of the block by the product of the length and width. Most manufacturers can provide you the equivalent thickness for their block. Once that is determined, and you know the material make-up of the block, you can use the prescriptive requirements in the IBC in Table 720.1(2), Items 3-1.1 through 3-1.4. Wayne Yancey Senior Member Username: wayne_yancey Post Number: 48 Registered: 01-2008 Posted on Friday, May 09, 2008 - 12:02 pm:    UL Design No. U901 - Bearing Wall Rating - 4 hours; non-bearing wall rating - 4 hours: 8" nominal CMU UL DESIGN No's. U904, U905, U906, U907 for other ratings 2 - 3 hour. All based in 8" nominal with the exception of U906 which is 6" nominal. Some are generic, others proeuct specific. Manufactures are listed starting page 1270, Volume 1, 2008. Ralph Liebing, RA, CSI Senior Member Username: rliebing Post Number: 840 Registered: 02-2003 Posted on Friday, May 09, 2008 - 12:22 pm:    Thanks all-- the old head finally flashed "Equivalent thickness" and I found my references from the mid-80s [when a code guy!] Wayne, I think the U900 series really are assemblies with CMU and not just the CMUs themselves. Should mention the unusual circumstances here-- the contractor asked for the UL Design number! George A. Everding, AIA, CSI, CCS, CCCA Senior Member Username: geverding Post Number: 426 Registered: 11-2004 Posted on Friday, May 09, 2008 - 12:50 pm:    Ralph- There is a NCMA technote that explains eq. thickness and probably can be used as a reference standard. If you need it, I can dig it up for you. Code officials here accept the NCMA equivalent thickness, and block manufacturers can provide for each unit they make. Wayne Yancey Senior Member Username: wayne_yancey Post Number: 49 Registered: 01-2008 Posted on Friday, May 09, 2008 - 01:20 pm:    Ralph, Our local AHJ wants UL Design Numbers included with the partition wall types. Are the assemblies not the important thing versus a single CMU unit and it's equivalent thickness? There isn't a UL Design number for a single unit. George A. Everding, AIA, CSI, CCS, CCCA Senior Member Username: geverding Post Number: 427 Registered: 11-2004 Posted on Friday, May 09, 2008 - 01:44 pm:    The issue as it was explained to me: block manufacturers do not do testing on each and every unit they manufacture, so getting a "block with a UL-label", "2-hr block", or "block that works in a 2-hr assembly" is impossible, at least in this market. What the AHJ does is accept an equivalent thickness from NCMA or as defined in IBC in lieu of a UL tested assembly. True, assemblies usually are the important thing, but typically the rating on a CMU wall comes from the CMU portion and not from any furring or finish added to the CMU. BTW, the same equivalent thickness techniques can be applied to clay masonry. NCMA tek mentioned above deals with both concrete and clay masonry and the number is TEK 7-1B.