Can you build a block wall on bare slab?

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Old 09-08-19, 06:21 PM
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Question Can you build a block wall on bare slab?

I have a one story slab on grade 62 year old home in Florida with an enclosed single carport. There are a couple 8' segments of 24" high block on the side. Those were framed in, above the short walls, with 2x4s and plywood probably decades ago. The front of the carport was also framed in all the way to the slab. The edge of the slab is at least 6" on the side.

The framed walls are starting to get rotten. Especially the one holding a window A/C unit. I'm trying to figure out if there is a way to replace the framing with fully grouted block, without creating new footings, and still meet code. CH04 TABLE R403.1(3) of the 2017 Florida Building Code seems to suggest that 6" footing thickness is sufficient for a fully grouted masonry wall. However, I can't seem to find any evidence to suggest a method of adding block to a slab that does not have rebar dowels embedded into the concrete in preparation. There certainly aren't any at the front of the carport, and given that the short walls were not intended to be load bearing, I doubt I will find slab embedded rebar if I break them apart.

The edges of each new block wall could have horizontal rebar reinforcements drilled into the existing adjacent block.

I was considering using long 1/2" wedge anchors into the slab with 2" plates and a nut atop a couple horizontal rebar reinforcements on the first course. However, I readily admit that is significantly weaker than slab embedded rebar.

Anybody know if it is even possible to add a concrete wall to and existing slab? Or does this always require a new slab and footer?

Thanks,
Steve
Titusville, FL
 
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Old 09-09-19, 02:32 AM
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Welcome to the forums!

While I don't know about houses built when yours was, those built 20 yrs or more later should have rebar in the concrete slab along the perimeter. I would think the main thing is whether or not the edge of the slab is thick enough extending wide enough into the slab. If the inspector or permit office signs off on what you have, you are good to go. Worst case scenario would be to remove the outer 16", excavate and repour it. If I'm not mistaken fla requires lintel block, steel and concrete on the top layer of block.
 
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Old 09-09-19, 04:47 AM
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I would talk with your local building inspections dept. as they are the ones that will have to approve whatever you do. They may want to see a couple test digs along the wall to verify the slab thickness but then might approve you to block the wall.
 
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Old 09-09-19, 09:07 AM
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Up here in the tundra, most everything has a thickened slab at the perimeter. Like Pilot Dane said, do a little digging in one or two spots, then talk to the building official. Grouted block is a fairly heavy dead load. You may also want to do some research on underpinning in case you have to reinforce the slab where the block wall will be.
 
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Old 09-09-19, 09:55 AM
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I spoke with somebody from my local building permit office. He said that as long as I don't attempt to replace the load-bearing truss support beam, and make the block wall load-bearing, that it is permissible to be constructed, even fully grouted, with vertical dowels epoxied into the slab and horizontal dowels epoxied into the adjacent block, as required. Woohoo!
 
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