Insulated slab on metal deck 2

[Struct1206]

I have an architect that wants to use a concrete slab on metal deck but he wants to put several inches of rigid insulation between the concrete and deck. Has anyone ever seen or done this? Any input would be appreciated.

Thanks in advance!

 

[phamENG]

I'm going to assume that it isn't going to be composite deck as that would be out of the question for obvious reasons.

So that leaves us with non-composite form deck. I don't think I'd want to do it, but that doesn't mean you can't. Do you have mechanical properties for the insulation? Particularly its strength in compression, maximum bearing stress, etc.? Is this a roof slab or a floor slab? You'd have to be cautious about crushing the insulation at the ribs in the form deck.

 

[structSU10]

As Pham states, crushing of the insulation would be a big question. It also forces a less than optimal steel layout as you will be limited by the deck span capabilities as just a form deck.

The other question is if the dew point will be forced between the insulation and metal deck, increasing the potential for it to corrode from trapped moisture.

 

[SlideRuleEra]

High compression rigid foam insulation is manufactured for use under concrete slabs. See:
"Owens Corning Formula" products

You may want to talk to a company representative to pick the best for your application.

http://www.SlideRuleEra.net

 

[dauwerda]

The other question is if the dew point will be forced between the insulation and metal deck, increasing the potential for it to corrode from trapped moisture.

I think this is a very valid concern, perhaps one option would be to use closed cell spray foam insulation instead of rigid foam? I have heard of this being done for slabs on grade, but I have never personally been involved.

 

[RPMG]

I see no issues with this. Rigid board insulation is a structural material with a compressive stress rating. We pour footings on rigid board insulation.

 

[Gerber_EIT]

Perhaps I'm not experienced enough to grasp this situation, but what exactly does placing the insulation between the concrete and the metal deck achieve? What prevents you from placing insulation on the underside of the metal deck? As the others have said above, I think crushing may be an issue for the insulation. I'd also be pretty wary about localized compression of the insulation (i.e. insulation compressing over time below common traffic areas), which could cause issues for the concrete above.

 

[Boiler106]

could you architect be looking for a "sandwich slab?" that's pretty common construction in the US that consists of conventional slab on metal deck, waterproofing, a layer of rigid insulation and another topping slab.

 

[RPMG]

Sorry. I didn't understand that you were asking if concrete could be poured on insulation place on a bare metal deck. In my head, I thought "roof", but the detail as you describe it is no good. Boiler106 describes it well. I have seen that detail used for hollow core precast.

 

[Struct1206]

Ok, thanks everyone for the input, sorry for waiting so long to respond. What we have is an elevated floor over a crawl space and the architect needs to insulate the floor. He wants to put rigid insulation on metal deck and then pour a slab over the insulation.

phamENG - You are correct, this would obviously not be a composite deck situation. One of my concerns was how this would effect my diaphragm but I can't think of a good reason why it couldn't be made to work.

In general, I just don't like it. At the very least, it seems like an idea someone had and went with, rather than thinking it through and likely coming up with something that makes more sense overall.

 

[BridgeSmith]

It seems like it could work. We use metal deck forms for highway bridges which often have rigid foam in some of the flutes, so a similar configuration, except ours is out in the weather and exposed to deicing salts. Granted, in our case once the concrete hardens it's self-supporting and the metal deck isn't counted on to support anything except it's own selfweight.

That said, it would seem that insulating below the deck would be the simpler and better solution, especially if the concrete topping is relatively thin. If there are gaps between the foam and the deck when the concrete is poured, the concrete could end up spanning across whatever areas that the foam is not supported by the deck.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[phamENG]

mwhite - using it as a diaphragm limits your options based on availability of information. You can't use the concrete filled values, so the smaller (i.e. 0.6C deck) probably wouldn't work for you. Vulcraft's 1.5C is essentially the 1.5B flipped over, so you can probably get some information from that. Otherwise, you may need to get the SDI Diaphragm Manual out and run a bunch of manual calculations to estimate capacity, stiffness, etc.