Well out here in Chicago, we usually back fill, compact, pin with rebar to foundation, and pour. But we have done suspended pours at the H/O request without an engineer and 1/2 inch rebar every 6" each way. :thumbsup:

 

:thumbup: Same here in cleveland ohio.

 

I'm also interested in what can be done in the way of a "suspended" floor. What can I span with 4" of 4000 psi concrete, and what can I do with different sizes of rebar at different spacing? There should be something like a span chart. Of course the thickness of the concrete is another possible variable.

Around here it is common to backfill a stoop or small porch, then pour. Sometimes people figure out that the space below will make a nice storage area, so they will put up a temporary support and pour a porch, etc. over the area.

Naturally one concern is rain coming through. Another is condensation.

I poured one that spanned about 6' and I don't remember what we had for rebar in it. I remember the truck dumped quite a load in one area right in front of the front door and it was piled up quite high and I was worried about the whole thing collapsing.

Of course you've got your preformed prestressed panels that they put in, then pour on top.

I'm with you, I think there should be some way to figure these without an engineer the same way we figure lumber spans, based on what has worked over the years.

 

Porches here (regardless of size) are poured integral to the rest of a slab foundation.

 

How do you pour it integral if you are building it with block and brick face?

 

Are you thinking of using pan decking? Most of the porches I have ben involved with have been mono poured.

 

i was thinking about doing a suspended floor, but i wasn't quite sure what I would've used for the pan.... I've seen floors done with both the corregated steel and with plywood.... honestly I don't know enough about it say what i would use, i doubt i would use plywood, i would probably use some sort of engineered system, but i willl most likely backfill with 3/4 gravel and pour on top

 

I'm still waiting for someone to chime in and tell you what you can span with different thicknesses and re-bar reinforcement.

 

Most here are backfilled. However, depending upon how deep the porch is makes a difference on the aggregate size. Deeper porches need to have larger aggregate towards the bottom and middle. Also, compaction needs to be done.

 

I am not an engineer nor do I pour concrete. We have done many here over the years with 2x framing, plywood, and then concrete over that. Most times now they backfill and then pour. I had a self contracted homeowner this year do the frame and pour over. He was concerned about water so he had a piece of the rubber roofing membrane made up and he installed it over the framing first. Seemed like a good idea.

 

I just order what I need the local concrete place makes them to what ever I want. Just have to dig and pour a footing then they set the pre cast steps and landing in with a crane. Allready has tread on the stairs and reinforced hand rail mounts.

Cole

 

I've seen guys fill the space with hollow block with semis on top. The slab is poured over everything, with bars into the foundation or by corbeling a few blocks to support the slab. There is no settlement, no moisture buildup in the fill and if weeps/drains are used, no hydraulic pressure from water infiltration.