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Rebar in slab on grade code requirement

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redcoat

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Discussion starter · #1 ·
I'm looking in the IRC 2021 and can't find any requirement for rebar or welded wire mesh being placed in the flat work of a monolithic slab. I understand the footing rebar requirements and they are apparent in the book but I don't see anything regarding the slab itself. I know architects spec a grid pattern with varied spacing but apparently there is no minimum standard of spacing or even placement of it.

Does anyone have a reference they can post that calls out a standard practice or minimum? thanks
 
#4 ·
Thom Paine said:
What does engineering say?

In order to better communicate,
What is your field of construction?
Click to expand...
Engineering and code have little to do with each other. Engineering must follow code, but can go beyond code or make stuff up if code doesn't exist.
 
Discussion starter · #6 ·
Thom Paine said:
What does engineering say?

In order to better communicate,
What is your field of construction?
Click to expand...
Thom Paine said:
What does engineering say?

In order to better communicate,
What is your field of construction?
Click to expand...
Homebuilding, carpentry

i dont have a set of plans in front of me. I just know ive seen it detailed in plans before. I assumed it was in the code book but it isnt. After a great deal of research i found an engineering discussion that said there is no standard. And many builders place a 48” oc spacing just because and it is a waste of time and material. If it is going to be done at all it should be 16” oc with #3. Wwm. Or none at all. This is for residential only
Pounder said:
I've never looked at IRC requirements, but to me it would be insane not to place rebar in a slab.
Click to expand...
I want to be clear im not talking about the turned down footings or the gradebeams. But just the 4 inch slab. According to what i could find in some engineer duscussions the rebar serves little purpose if the slab substrate is properly compacted and control joints cut
 
#7 ·
redcoat said:
Homebuilding, carpentry

i dont have a set of plans in front of me. I just know ive seen it detailed in plans before. I assumed it was in the code book but it isnt. After a great deal of research i found an engineering discussion that said there is no standard. And many builders place a 48” oc spacing just because and it is a waste of time and material. If it is going to be done at all it should be 16” oc with #3. Wwm. Or none at all. This is for residential only

I want to be clear im not talking about the turned down footings or the gradebeams. But just the 4 inch slab. According to what i could find in some engineer duscussions the rebar serves little purpose if the slab substrate is properly compacted and control joints cut
Click to expand...
I'd still never do it. On a properly prepared patio it might be alright, but for a slab floor it's just not worth the risk. If the client didn't want to pay for it I'd walk away from the job.
There are two kinds of concrete, concrete that's cracked, and concrete that's going to crack. Adding rebar controls the amount of movement after the crack occurs.
All my building was done in California, and we put a grid in everything, it was never even a question. Driveway, patio, pad to set the trash cans on, even the bottom step of an outside deck had steel in it. If it was structural, the engineer always inspected it before the pour. In 37 years as a general contractor in CA I only ran across one engineer who would even consider wire mesh in concrete.
 
Discussion starter · #9 ·
I was able to find a reference in the IRC section regarding concrete floors to ACI 332, if you review that reference you will see they refer slabs on ground to be non-structural and specifically state they can be unreinforced or reinforced to resist the effects of temperature or shrinkage. In ACI 332, 5.1.6.1 states rebar may be used in applications where the number of control joints is to be minimized.

The irc also states that for expansive soils, the standards would be set by the IBC, which would then trigger a number of other requirements including rebar for structural slabs.

It isnt straight forward at all
 
#10 ·
redcoat said:
Homebuilding, carpentry

i dont have a set of plans in front of me. I just know ive seen it detailed in plans before. I assumed it was in the code book but it isnt. After a great deal of research i found an engineering discussion that said there is no standard. And many builders place a 48” oc spacing just because and it is a waste of time and material. If it is going to be done at all it should be 16” oc with #3. Wwm. Or none at all. This is for residential only

I want to be clear im not talking about the turned down footings or the gradebeams. But just the 4 inch slab. According to what i could find in some engineer duscussions the rebar serves little purpose if the slab substrate is properly compacted and control joints cut
Click to expand...
I'm a GC; over 50 years in business.

Soil engineering, compaction testing, and concrete specs enter into the equation.

I've never professionally allowed a 4" residential slab. Too often that equals 3.5" actual.
Full 5" plus minimal thickness with poured piers and bar.

For what it's worth:

Personal anecdote: I live on a twenty year old finished, sans expansion joint or cuts, pour with zero cracks.

When in question, build stronger, build better.

(y):)
 
#11 ·
redcoat said:
I'm looking in the IRC 2021 and can't find any requirement for rebar or welded wire mesh being placed in the flat work of a monolithic slab.
Click to expand...
Rebar is required by code in footings and foundations while there is no code requirement for rebar in a slab.
An engineer may include rebar in a slab if the slab is for special use.
 
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#12 ·
Thom Paine said:
I'm a GC; over 50 years in business.

Soil engineering, compaction testing, and concrete specs enter into the equation.

I've never professionally allowed a 4" residential slab. Too often that equals 3.5" actual.
Full 5" plus minimal thickness with poured piers and bar.

For what it's worth:

Personal anecdote: I live on a twenty year old finished, sans expansion joint or cuts, pour with zero cracks.

When in question, build stronger, build better.

(y):)
Click to expand...
R506.1 requires a 3.5" minimum concrete slab.
Standard pour is 4".
Garages typically are 6".
 
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#13 ·
On sand or clay, like around Houston, ALL the slabs were waffle style with grade beams/footings on a 10’x10’ grid pattern.
Many were also post tensioned.

if you’re planning on building your own house and you’re here looking for input in order to save a few dollars, by not putting in additional metal, that’s on you.

I’ve never seen someone pour a house slab without reinforcement in the slab part. It’s the same for driveways. We would always add 20 foot panels of hog wire in the concrete. Seems like common sense.

I did work on one project where they used fiber mesh instead of metal in the garage slab, since we do crawlspaces mostly. Talk about ugly when you can go into the garage and see little furry pieces of fiberglass sticking up. That was the one and only time I’ve seen anyone use fiber mash.
 
Discussion starter · #14 ·
Im not. I wanted to know if anyone had a standard or reference for the building code. I realize people have done it their way forever. But i found it interesting and figured id put it out there. Ive built several houses in florida with no rebar in the slab but we did place wwm. I always believed it was in the code to do so but i was wrong
 
#15 ·
redcoat said:
Im not. I wanted to know if anyone had a standard or reference for the building code. I realize people have done it their way forever. But i found it interesting and figured id put it out there. Ive built several houses in florida with no rebar in the slab but we did place wwm. I always believed it was in the code to do so but i was wrong
Click to expand...
Many, mistakenly, believe structural codes are the "be all, end all" of the best
means and methods. They are only minimum established structural and functional standards.

It's okay to exceed them.
 
Discussion starter · #16 ·
Thom Paine said:
Many, mistakenly, believe structural codes are the "be all, end all" of the best
means and methods. They are only minimum established structural and functional standards.

It's okay to exceed them.
Click to expand...
Im aware its ok to exceed them. But the code seems to specify damn near everything else. Have you seen the latest year’s section on brace wall lines? Its 50 pages of specs.
 
#17 ·
People build differently around the country.
There are no code requirements for how to reinforce a slab here, it's up to your designer (engineer or architect) to design a floor system for the intended loads. Residential and AG stuff around here does not require an engineer or architect to sign off on plans.

We must have pretty good soils compared to other parts of the nation because we rarely used rebar in slabs unless they were going to be heavily loaded. Offices, Residences, garages, driveways, light to medium duty warehouse floors, etc. were almost always just reinforced with wire mesh. Having said that, we always built a good base to pour on and followed ACI American Concrete Institute standards regarding joint spacing, joint details, reinforcement placement, etc.
 
#18 ·
redcoat said:
Im aware its ok to exceed them. But the code seems to specify damn near everything else. Have you seen the latest year’s section on brace wall lines? Its 50 pages of specs.
Click to expand...

Hey! Don't complain about the sometimes complex confusion of some regs.

It's why we're in demand as interpreters bridging the gap between engineers, architects, inspectors, and the folk who only want a safe, functional, and nicely built structure.

I s'pect any Pro has nightmare stories to share. :)

All should keep a favorite Engineer or two on speed dial! :LOL:
 
#19 ·
Fishindude said:
People build differently around the country.
There are no code requirements for how to reinforce a slab here, it's up to your designer (engineer or architect) to design a floor system for the intended loads. Residential and AG stuff around here does not require an engineer or architect to sign off on plans.

We must have pretty good soils compared to other parts of the nation because we rarely used rebar in slabs unless they were going to be heavily loaded. Offices, Residences, garages, driveways, light to medium duty warehouse floors, etc. were almost always just reinforced with wire mesh. Having said that, we always built a good base to pour on and followed ACI American Concrete Institute standards regarding joint spacing, joint details, reinforcement placement, etc.
Click to expand...
There are many areas of the country with no code compliance restrictions or inspections.

If I build something, you can "bet your Bippy" there's at least one Engineering Stamp on the plans.

WAIT! I take that back! I've built a few 'outhouses' and trash containers without engineering! :LOL:
 
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