Slotted metal deck

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Author Message David Axt, AIA, CCS, CSI Senior Member Username: david_axt Post Number: 829 Registered: 03-2002 Posted on Tuesday, March 13, 2007 - 07:52 pm:    Our building envelope consultant claims that slotted metal deck helps the concrete dry out faster. The concrete supposedly dries from top AND bottom. Can anyone here back up this claim? Richard L Matteo, AIA, CSI, CCS Senior Member Username: rlmat Post Number: 203 Registered: 10-2003 Posted on Tuesday, March 13, 2007 - 08:07 pm:    Don't you just love "consultants" like this? That may be true, but generally, the only time "slotted" or "vented" metal deck is used is with the Lightweight Concrete Roof Insulation systems like Zonolite or Elastizell. Even then I try to avoid it as it can present a problem when the wet concrete oozes thru the slots - and it will! Creates somewhat of a mess below I've never used it with standard concrete decks. David Axt, AIA, CCS, CSI Senior Member Username: david_axt Post Number: 830 Registered: 03-2002 Posted on Tuesday, March 13, 2007 - 08:17 pm:    Richard, Don't get me started on building envelope consultants! We are just using regular weight concrete composite type decking. Nothing fancy. We are NOT using light weight gypsum concrete products. Steven Bruneel, AIA, CSI-CDT, LEED-AP Senior Member Username: redseca2 Post Number: 33 Registered: 12-2006 Posted on Tuesday, March 13, 2007 - 09:38 pm:    There is no difference from a structural viewpoint, as in concrete curing. But I have had consultants say vented decking improves slabs for vapor emmission issues relating to floor adhesion failures. A highly impermeable floor product, like a roll goods rubber sheet flooring over a non-vented deck may leave no way for the slab to breath out moisture, now or in the future, with potential bubbling and adhesion problems. Mark Gilligan SE, CSI Senior Member Username: markgilligan Post Number: 143 Registered: 05-2005 Posted on Wednesday, March 14, 2007 - 03:40 am:    I regularly use vented deck. As I understand it, the requirement typically comes from roofing manufacurers and manufacturers of flooring materials. We typically use structural light weight concrete for the deck fill to minimize seismic loads but I understand that vents are still needed under floor products. While there might be some extreme events where this makes a difference, I suspect that in most cases this requirement is the result of manufacturers who do not understand their product. The common slab moisture test is junk science and does not measure what they claim it measures. But unless I want to take the fall for any roofing or floor failures I had better comply with the manufacturers recommendations. John Bunzick, CCS, CCCA Senior Member Username: bunzick Post Number: 674 Registered: 03-2002 Posted on Wednesday, March 14, 2007 - 08:32 am:    Mark, From a structural perspective, is there a difference in either performance or cost between vented and non-vented deck? (I assume you're probably specifying composite deck.) Have you observed the problems described with concrete oozing through? Mark Gilligan SE, CSI Senior Member Username: markgilligan Post Number: 145 Registered: 05-2005 Posted on Wednesday, March 14, 2007 - 12:06 pm:    There is no difference in performance of vented versus non-vented deck. I am not aware of a cost premium for factory vented deck. If there is one it has never come up. If there is an added cost for vented deck is should be seen as part of the cost of the flooring or roofing product selected. When the area of venting required exceeds the deck manufacturer's standard then there is a cost to add additional venting in the field. The two options, proposed by the deck manufacturer, were to use a pointed steel rod to poke holes in the bottom of the deck or use a welding electrode to burn holes in the bottom of the deck. I have had no problems with leaking concrete. Remember that in most cases there is a ceiling below the deck. I would not recommend the field fixes noted above if the bottom of the deck was visible. Note that you would have the same issues with pre-punched hanger tabs that comes standard with some decks. Wayne Yancey Senior Member Username: wyancey Post Number: 316 Registered: 05-2005 Posted on Wednesday, March 14, 2007 - 12:15 pm:    David, It is not a big deal. Take a valium. Your BE consultant is most likey restricting their comments to the building enclosure (read roofing). They do not concern themselves with the conditioned space, with the exception of assemblies separating conditioned and nonconditioned spaces. Steve states the case for interior floor slabs but by the time the interior floor coverings are installed the point may be moot. I agree with the use of a vented metal roof deck, and have done so long before I wore the dreaded "building enclosure consultants" hat. This practice is preached by vapor impermeable roof/waterproofing membrane manufacturers to allow hydration of vapors to diffuse in both directions. Most recent project had a protected roof membrane (split slab) for roof top terrace. Wayne Jerome J. Lazar, RA, CCS, CSI, SCIP Senior Member Username: lazarcitec Post Number: 334 Registered: 05-2003 Posted on Wednesday, March 14, 2007 - 12:54 pm:    Wayne, I find Xanax much better for dealing with stress from BE Consultants. Steven Bruneel, AIA, CSI-CDT, LEED-AP Senior Member Username: redseca2 Post Number: 35 Registered: 12-2006 Posted on Wednesday, March 14, 2007 - 01:34 pm:    Wayne and Jerome, For purposes of a competitive bid, would you consider Valium and Xanax equals? Would a "slow cure time" product such as Prozac be an acceptable substitution? After life cycle cost analysis, for our LEED projects, we tend to go with renewable resource products like Jagermeister. David Axt, AIA, CCS, CSI Senior Member Username: david_axt Post Number: 831 Registered: 03-2002 Posted on Wednesday, March 14, 2007 - 01:50 pm:    I find that any blunt object works really well. Just a few dull blows to the base of the skull makes those building envelope consultants start making sense. I contacted my local Verco Decking rep and found out that vented deck is only $.01 /SF more. Yes, one penny a square foot more that conventional deck! I wonder how much cleanup of the cement paste on the floor below costs? The Verco rep also said that there is no structural difference between the conventional and vented metal deck. BTW, Our building envelope consultants also want an FM rated (FM 4450 & 4451) roof deck. Specifying this FM rating severely limits the maximum span of the deck.