Bricks, Masonry, Asphalt and Concrete - Fire rated CMU assembly

I have a specification calling for a 3 hour rated wall, per UL U904, using CMU. My problem is the lead time on the UL certified 4-hour units. The architect is willing to change the specification to an equivalent thickness rating (Table 43-B, UBC), so long as I can show a congruence with the IBC. So far, I have found the name of the section of the IBC that deals with it (Table 719.1(2)), but I have no books or knowledge of the IBC. Anyone out there able to help me? OK, OK, ConcreteMasonry, can you help me.

It is a good thing your architect is referring to the UL standards since that means he does not understand code fire ratings (don't tell him that). You will have to go many miles and pay a big premium for the UL listing, which I had a previous employer drop 20 years ago.

It is also good that he will accept equivalent thickness instead of the old "boilerplate" spec he inherited. this is much more realistic and easy to document.

You have to meet a 3 hour (somewhat unusual) rating. This can be accomplished by using block with different aggregate (usually block density in pcf) or by using a block with more material in it (% solids).

For an 8" wall, your choices are probably an 8" lightweight block with a thicker face shell. These should be available from inventory at one of the plant's yards. A 8" lightweight block is 2+ hour rating. If you have a thicker wall, you probably have a 3 hour rating no matter what aggregate you use.

You are probably considering Eagle or Valley Builders as a supplier and their internet pages are not very detailed, although I found they did copy some of my old drawings.

If you can get the information on the possible suppliers products (block density & % solids) to me via PM, I should be able come up with a solution. If there are other materials (gypsum, brick or core fill insulation) these can be added to the rating of the basic block in most cases.

just waiting for info.

Dick

All the thick web units at the plant are gone. The Eqiv. Thickness of the available units test at 2.79", so my suggestion was solid grout (spec. is 32" OC for vertical reinforcing). Per my calc, this gives plenty to meet UBC, considering the block-web/grout aggregates (expanded shale/pea gravel grout). I am not sure of the IBC requirements at all, though.

Is is a residential firewall between a parking garage and the units. All of the rest of the project, retail, was spec'd 3-hour as well, but no UL certification of the CMU required. All of the manufacturers's 4 hour (and UL 4-hour, when they ran out of non-rated units) on-hand went to that aspect of the project, via a different masonry contractor, so it is a 4-6 week lead time.

Just to be clear, ConcreteMasonry, I am the supplier on this project.

Tscarborough -

The first thing is get the specifier off the out-dated, impractical and unrealistic UL standard. It is rarely used for masonry. There are other more current national standards with better documentation and testing back-up.

Are you the supplier of the masonry materials or the masonry contractor?

What is the wall thickness? - 6"? 8"? 10"?

The equivalent thickness you mentioned does not sound correct. An 8" unit meeting minimum ASTM requirements would have an equivalent thickness of about 3.85 to 4.00 and not 2.79. Usually, fire rated units have a thicker face shell than normal since it is more effective to acheive a fire rating. - It all boils down to how much material is in the block and what the material is.

Grout, sand or vermiculite in the cores will all increase the fire rating. Vermiculite fill is well documented to increase a 2 hour unit to a 4 hour wall. Surface treatments such a sheet rock and plaster also increase the fire rating of a wall assembly.

You may not find true lightweight block (less than 105 pcf) in your part of the world. Many people recognize the benefits of mass as opposed the phoney pink fluff numbers made for TV.

Dick

Thanks for your help, ConcreteMasonry; it is in their hands now and I think they understand and will change the spec.

We ship regular lightweights on Tuesday. Not only did it save the contractor about 45% of the block cost, the architect and GC are now cognizant of the issue and it's proper application. Thanks to ConcreteMasonry for technical assistance.

"You are probably considering Eagle or Valley Builders as a supplier and their internet pages are not very detailed, although I found they did copy some of my old drawings."

I worked for Eagle for 10 years, and Valley block makes good 6" regulars for fences, to be generous.

Please provide if you have same
David A. lamb