# Corrugated Metal Concrete Porch Over Basement



## 3onthetree (Dec 7, 2018)

I think . . . you are describing a composite steel deck slab system covering a 6'x44' cold room. Is this being designed by an architect or DIY? There should be bearing details about where it connects at the house, the front edge of porch, and wherever interfering porch roof columns drop down. These construction details may handle some water infiltration issues and could eliminate the foam closure. Are you using DIY "metal corrugated panels", or the proper "composite corrugated metal decking panels?" There will be a set thickness of concrete and gauge of steel for your span and loads. The proper decking will also have a method of attaching to the concrete, like indentations or louvers. And depending on product you may have to have supports along each long edge overlap (the 6' length). Also with 44' long, you may want WWF in there to hold shrinkage cracking and hairlines caused by the deck.

The concrete will hold moisture. Regardless of a sealer on top of the concrete, water will infiltrate and sit on the metal deck. They do make perforated deck, however, since the top side is exposed to the elements there will be lots of moisture. That is why you don't see composite deck slabs left as exposed concrete to the exterior. You add a membrane under a topcoat or pavers or something.

For residential, just a 6' span, you would just frame up some plywood forms and pour a reinforced slab.


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## Nealtw (Jun 22, 2017)

Here they are doing concrete deck over a wood frame, they cover the deck with a peel and stick and where it meets the house it extends up the wall 6 to 8". This is a roof but it looks the same.


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## 3onthetree (Dec 7, 2018)

There are some fluid applied, and some specific sheet membranes, but you are relying on no application error too.


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## markhaire (Feb 18, 2019)

3onthetree said:


> I think . . . you are describing a composite steel deck slab system covering a 6'x44' cold room. Is this being designed by an architect or DIY? There should be bearing details about where it connects at the house, the front edge of porch, and wherever interfering porch roof columns drop down. These construction details may handle some water infiltration issues and could eliminate the foam closure. Are you using DIY "metal corrugated panels", or the proper "composite corrugated metal decking panels?" There will be a set thickness of concrete and gauge of steel for your span and loads. The proper decking will also have a method of attaching to the concrete, like indentations or louvers. And depending on product you may have to have supports along each long edge overlap (the 6' length). Also with 44' long, you may want WWF in there to hold shrinkage cracking and hairlines caused by the deck.
> 
> The concrete will hold moisture. Regardless of a sealer on top of the concrete, water will infiltrate and sit on the metal deck. They do make perforated deck, however, since the top side is exposed to the elements there will be lots of moisture. That is why you don't see composite deck slabs left as exposed concrete to the exterior. You add a membrane under a topcoat or pavers or something.
> 
> For residential, just a 6' span, you would just frame up some plywood forms and pour a reinforced slab.


No it's an architect design and it is a steel decking/ slab system. These are decking panels made for the application. The roof is an engineered truss system that ties back into the house. The weight that the columns are holding is the beam across the front span - 8 columns. I can't remember now how they are securing the decking. The decking is overlapped by at least 6". I think a fewof them had to go one more ridge. It was cold and dark when I set them out and it was a temporary placement. Ignorant question - WWF? I know you're not referring to Hulk Hogan. 

Here they require the use of the metal...so I was told...The panels are designed for the 6' span and up to 3 inches of concrete above the top ridge. 

Yeah the membrane or topcoat is really what I was getting at and should have articulated better. Would it be better to use a vapor barrier type plastic or rubber membrane or a painted on cool-seal type product? They used these same type of panels on my last house only it wasn't done as well. They used a rowlock of brick that the panels sat down in so moisture was always a real fight. No sealing WHAT SO EVER to the concrete. No matter what I did, it got through the brick. I know concrete is a hard sponge, but I have seen that it can be stopped to an extent.


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## 3onthetree (Dec 7, 2018)

WWF = Welded Wire Fabric (I try not to say "Mesh" as that confuses people with "fibermesh").

The example that Neal shows has the wood framing as the structure. The concrete is just the topping. So that's what you need to find out about yours.

If the metal deck is just a set-in-place form to remain, then have at it. It probably isn't fastened down by any means nor panels aren't attached to each other. Put a waterproof membrane or bituminous roll-on product over it and extend it up the sidewalls and stick it out the edge like a flashing. The concrete spec should be similar to what would be in your driveway, thickness/rebar/WWF.

But, if it's a structural component of the floor, then there is nothing to put on the deck. There is a limit on the products that can be applied to the top of the deck and underneath the concrete, because the concrete has to adhere and it's structural capability is dependent on the deck and concrete together and its connection to the shear tabs. The galvanization will have to suffice as a rust inhibitor and the topping sealant will have to prevent water infiltration. Also any sealants used under the laps are prohibited. The metal deck will be a sort of a vapor retarder for the storage room, but be careful applying anything to the inside as it will trap moisture in the concrete between the deck and the topping sealant.


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## Old Thomas (Nov 28, 2019)

My uncle did the same thing you want to do. He painted the bottom of the steel and it made a nice ceiling.


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## stadry (Jun 20, 2009)

*have 2 more of these coming up - we're using westcoat alx system but there are others,,, slope is critical*


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## stadry (Jun 20, 2009)

*never saw a conc deck (hi-rise OR bdge ) built w/stay-in-place metal forms that had sand thrown in before the conc was placed,,, we do see many porches w/them that are 50% rusted thru due to improper lwater management
we use 2'x8' expanded wire mesh straight outta the apron/vest stores for alx,,, deck system averages 3/8" thick*


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## Nealtw (Jun 22, 2017)

I think the choice is where you put waterproofing, under the concrete with a path out
or water proof the top surface of the concrete. 

This is much like we do on a wood deck.


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## 3onthetree (Dec 7, 2018)

Nealtw said:


> I think the choice is where you put waterproofing, under the concrete with a path out
> or water proof the top surface of the concrete.


That was the point in my wordy responses. He can not waterproof with membrane, silicone or anything under the concrete if the metal deck is part of a structural system. Only if the deck is formwork to remain can he put something there.


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