Hard-Lid Ceiling

HI Omar, without knowing the full details of your construction, it's not safe to assume so. The requirement is to prevent fumes or gasses from penetrating an adjacent space. Steel would be fine provided you could show the sealing/gasketing around it, or better yet, welding, was airtight. If you are designing to an accepted construction standard that demonstrates this criteria is being met, then your unique assembly will have a much better chance of being accepted, in my opinion.

Good luck to you! David

Omar – LEED Interpretation #5677 describes the hard-cap ceiling requirement that “construction method and details demonstrate that the assembly is adequate at containing and isolating pollutants/chemicals”:
http://www.usgbc.org/leed-interpretations?keys=5677.
This is an old, LEEDv2.1 Interpretation, but it is consistent with language in the LEED-2009-BD+C Reference Guide:
“These rooms must be physically separated from adjacent spaces via installation of deck-to-deck partitions or sealed gypsum board enclosures….Drywall ceilings may be used in place of full-height partitions, but acoustical lay-in ceilings are not adequate."

The current LEEDonline IEQc5 form does not appear to require an upload of enclosure details, but you would be wise to prepare such detail in case of question. Reviewers once asked us for details. We also provided written specifications showing that the ceilings were taped, finished, and sealed, providing separation equal to what the gypsum board partitions provided. The reviewers accepted this.

If standard gypsum ceiling construction meets the Credit requirement, a single gypsum ceiling should suffice. Two ceilings (a steel plate above a suspended ceiling) should be unnecessary.

What kind of room are you working so hard to get qualified? What activity is taking place in that room? A drywall ceiling construction, exhaust fan are likely required. Any borrowed light or interior glass window would need to be sealed to prevent air migration between spaces. This is going to depend on your glass mounting details.

Yes, everything depends on your glazing details. USGBC based IEQc5 requirements upon standard construction methods. The use of standard glazing systems, proven to provide an effective seal, should not compromise the enclosure, but special, untested glazing methods could be a problem. The further you stray from standard, the harder it becomes to prove that your approach works.

Remember that you must isolate the pollutant source AND provide the required exhaust to achieve a 7-Pa negative pressure differential. As noted in LI#5677, leaks in the enclosure can undermine the exhaust system.

If your enclosure differs significantly from what IEQc5 prescribes, reviewers might ask for testing and commissioning (similar to IEQp2 smoking rooms) to show whether your alternative construction methods meet credit requirements. See LI#5890 for an example of the kind of testing reviewers might require. (http://www.usgbc.org/leed-interpretations?keys=5890)

If this is too much, your design team might wish to rethink their approach to these enclosures.

Omar—I apologize for misleading you. The LEED Interpretations that I posted are very old. They contained outdated information. Under LEEDv2.1, EQc5 required a minimum negative pressure differential of 7-Pa at rooms housing pollutant sources. This requirement no longer applies. Under LEED-2009, the minimum differential is only 5 Pa.

To clarify, for rooms where hazardous gases or chemicals may be present or used, LEED-2009 EQc5 requires the following:
.. 1) Provide continuous mechanical exhaust of at least 2.5 L/s/m2 (0.50 cfm/sf) with no air recirculation.
.. 2) Maintain minimum 5 Pa (0.02 inH2O) average pressure differential with adjacent spaces.
.. 3) Maintain minimum 1 Pa (0.004 inH2O) pressure differential when door to room is closed.
.. 4) Doors to such rooms must be self-closing.
.. 5) The walls around such rooms must extend deck-to-deck or the room must be capped with a sealed gypsum board ceiling.

The point behind both LEED Interpretations is that leaks in the enclosure can undermine the exhaust system’s effectiveness. For example, LI#5677 states that lay-in acoustical ceilings are not acceptable. They do not provide a sufficient seal, making it difficult or impossible to maintain the required pressure differential. Likewise, LI#5890 prescribed a rigorous regimen of tests to justify an enclosure that was not airtight.

You have proposed a room enclosure that differs significantly from that prescribed in Item 5 above. If you pursue this alternative compliance path, the LEED Reviewers may require you to provide commissioning and test reports proving that your enclosure is sufficiently air-tight to maintain the exhaust rates and pressure differentials required in Items 1, 2, & 3 above. To avoid costly tests, it might be wise to alter your design.

? My "mental Arithmetic" is still trying to figure out why the physical build characteristics are important if the pressure differential is held.

How do you document that? 2 options: 1) tests, post build 2) design documentation

Re: 2)
Providing design documentation that "proves" that the required pressure differential "will be held" should in my opinion show a crackflow calculation (better yet simulation), which is highly dependant on the build characteristics. But you could achieve the dP with a hole in the wall if you "do it right".

What I'm saying is that the requirement of the build characteristic "hard lid" is superfluous, if the specification is "actually" for a pressure differential.

Aggreed. However, EnergyEfficiency would be traded off in EAp2 where it belongs. That is saying it is still accounted for. Generally LEED is an super system because it does not shrink the abillity for ingenuity in design. You can still have curtain glazing, if you make up for it elsewhere. Plus, we don't need extra complications in this system. I've previously also made the point of how this ties in with ASHRAE 62.1.

Re: testing...this has been accepted on our projects to prove compliance with the credit. IMO this is the best way, because it is real and not based on "theory".

Jean & Omar—I agree that, theoretically, if you “do it right” and size the exhaust system appropriately, you should be able to achieve the required pressure differential, even in a leaky room. However, the LEEDonline template only offers the two prescribed separation options, “deck-to-deck partitions” or “hard-lid ceiling” (both with a self-closing door). If you select “Other,” you must document your “Alternative Compliance Path.” This shifts the burden of proof to your project team, and, possibly, leaves them at the mercy of Reviewers.

I also agree that exhaust systems should be commissioned and tested to show compliance. However, I believe that IEQc5 is still typically a “Design Phase” submittal, made as construction begins, long before it is possible to test as-built conditions to “prove” compliance if required to do so by the Reviewers.

Finally, this whole issue may be immaterial.

Are the copiers and printers in these rooms “high-volume” machines? Remember that small, convenience copiers and printers are exempt from IEQc5 requirements. See LI#1938 and the “Bird’s Eye View” comments at the top of this webpage (LEEDuser members only).