# Single Family Home Precast Floors



## jar546 (Jul 8, 2020)

The slab is poured but for the 2nd and 3rd floor they will be using these for this SFR to increase the speed of construction.  Anyone else use these?


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## Msradell (Jul 8, 2020)

I've seen them used a lot in commercial buildings, especially hotels, but never in a residential setting.  They certainly would make a good solid floor for residential and would greatly reduce noise transmission from floor to floor.


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## tmurray (Jul 9, 2020)

We see them occasionally for garages in SFR to create a basement for the garage. Most of the time it is for houses on the river to give them a place to lug in their canoes, kayaks, etc.


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## jar546 (Jul 9, 2020)

Msradell said:


> I've seen them used a lot in commercial buildings, especially hotels, but never in a residential setting.  They certainly would make a good solid floor for residential and would greatly reduce noise transmission from floor to floor.


If you use sound attenuation below your tile and hardwood.


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## steveray (Jul 9, 2020)

I've seen them in a hotel....


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## Pcinspector1 (Jul 9, 2020)

Do they have some camber built into them? They don't appear to have a T&G connection?


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## e hilton (Jul 9, 2020)

Pcinspector1 said:


> They don't appear to have a T&G connection?


If you look closely you can see a bit of a rounded recess in the edge of the precast.  They probably set them in place, caulk the bottom of the joint, and fill the gap with high strength grout.  If there was a traditional t&g on the edges, the installers would have to be sure not to get two T’s or two G’s together ... this way the precast is omnidirectional.


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## ADAguy (Jul 9, 2020)

e hilton said:


> If you look closely you can see a bit of a rounded recess in the edge of the precast.  They probably set them in place, caulk the bottom of the joint, and fill the gap with high strength grout.  If there was a traditional t&g on the edges, the installers would have to be sure not to get two T’s or two G’s together ... this way the precast is omnidirectional.



Careful with longer spans as they can bounce depending on weight applied.


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## Mark K (Jul 9, 2020)

I do not see where the IRC provides for this type of construction which suggests that the IBC governs.


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## jar546 (Jul 9, 2020)

Mark K said:


> I do not see where the IRC provides for this type of construction which suggests that the IBC governs.



Agree 100%.  Then again, there is nothing in my wind zone that is structurally prescriptive in the IRC either.


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## Paul Sweet (Jul 9, 2020)

We used them once many moons ago in a house for a German doctor who wanted it built SOLID the way they do in Germany.  The main problem we ran into was that some of the strands got cut when they core drilled for plumbing.  I'm guessing there were a couple extra strands because we didn't notice any structural distress afterwards.


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## e hilton (Jul 9, 2020)

Paul Sweet said:


> I'm guessing there were a couple extra strands because we didn't notice any structural distress afterwards.


Looking at the picture, i only see a strand at the bottom of the webs.  So if you located the hollows and drilled there it shouldnt be a problem.  
The plumber is going to need something stronger than a sawzall.


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## e hilton (Jul 9, 2020)

Paul Sweet said:


> I'm guessing there were a couple extra strands because we didn't notice any structural distress afterwards.


Sorry ... don’t know how to edit a reply after it is posted. 
The concrete units might not have prestressing tendons.  Not all precast concrete is prestressed, or post-stressed.


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## tmurray (Jul 9, 2020)

In my limited experience,

These are pre-stressed. They are cast with a bow in the center to allow them to settle level, the space between the panels is stuffed with a backing material and a top coat of concrete applied over top, because the people who can afford this type of thing in their garage/house will not accept having those beveled edges. If there is coring or drilling, they should be factory installed (precast). site modification of the panel is a huge no-no. An engineer is required on each project not just for the panel, but the wall supporting it as well.


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## Rick18071 (Jul 9, 2020)

So what are the supporting walls?


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## Pcinspector1 (Jul 9, 2020)

tmurray said:


> These are pre-stressed. They are cast with a bow in the center to allow them to settle level, the space between the panels is stuffed with a backing material and a top coat of concrete applied over top, because the people who can afford this type of thing in their garage/house will not accept having those beveled edges. If there is coring or drilling, they should be factory installed (precast). site modification of the panel is a huge no-no. An engineer is required on each project not just for the panel, but the wall supporting it as well.



Now we're cooking, so there's an engineer involved, I thought so. 

So there should be an arrow saying this side up ^. Probably some paperwork for Jar to read...I would think..


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## jar546 (Jul 9, 2020)

Rick18071 said:


> So what are the supporting walls?



CMU with lots of rebar & tie beams.


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## tmurray (Jul 10, 2020)

Pcinspector1 said:


> Now we're cooking, so there's an engineer involved, I thought so.
> 
> So there should be an arrow saying this side up ^. Probably some paperwork for Jar to read...I would think..


We get stamped plans and the factory turning these out sends a crew to do the installation. Our subdivision inspector actually used to do this. He is an invaluable source of information on these.

Walls here are a reinforced concrete wall (CMU is not typical for residential construction in Canada). Typical reinforcement is 2 rebar mats 15M at 12" vertical and horizontal.


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## e hilton (Jul 10, 2020)

tmurray said:


> Typical reinforcement is 2 rebar mats 15M at 12" vertical and horizontal.


Don’t understand 15M.


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## tmurray (Jul 10, 2020)

e hilton said:


> Don’t understand 15M.


Metric rebar size. 

Apparently this is somewhere between a #4 and #5 for you folks.


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## jar546 (Jul 10, 2020)

tmurray said:


> Metric rebar size.
> 
> Apparently this is somewhere between a #4 and #5 for you folks.



You guys use the system we should be.  #gometric


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## Pcinspector1 (Jul 10, 2020)

tmurray,

I clicked on your like button, cuz you explained what 15M means, but that does not mean I like the metric system!


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## e hilton (Jul 10, 2020)

Right ... 15 mm = 0.59” ... #5.5 rebar.  So how does that work?   The rebar i see has the size molded in with the ribs ... whole numbers ... surely there isn't a separate rebar mill for metric sizes.


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## tmurray (Jul 10, 2020)

e hilton said:


> Right ... 15 mm = 0.59” ... #5.5 rebar.  So how does that work?   The rebar i see has the size molded in with the ribs ... whole numbers ... surely there isn't a separate rebar mill for metric sizes.


I got a shocker for you. There is also European sizes that is different than both of ours.


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## MACV (Jul 13, 2020)

These are prestressed "hollow core precast concrete" panels formed by an extrusion process with edges shaped to form a recessed "keyway" for field grouting. I've used them in parking garages.  I only saw them used in a house in a side-by-side duplex in France where you could stand in the garage at one end and hear someone speaking in the garage at the other end as if they were standing next to you. 
They're formed, cables pre-tensioned and poured in very long beds and then a giant extruding machine runs along them forming cores in the concrete with pontoon-like tubes on fins. When they've cured they're cut to the required lengths.
Here's a video, hope it works. 



  If not, you can google to find one.
Any residential structural element not addressed by the IRC is required to be designed by a licensed design professional. Normally that's an engineer.
These slabs are inexpensive compared to poured in place concrete that requires forming and shoring in the field. 
All field penetrations must be evaluated by the manufacturer and the engineer. In general it's good to locate them at the panel joints and/or align them parallel to the span.


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## TheCommish (Jul 13, 2020)

The extruding method is interesting


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## ADAguy (Jul 15, 2020)

Damn! Love this forum, great technical topics.


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## jar546 (Jul 24, 2020)

For the record, 2 inches of concrete is poured over the top of these precast floors


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