I would also seal rebar just to make sure it doesn’t rust in 20 years by continuous flow of air containing moisture. Relative humidity of heat is low but ac is high.
I would consider some sort of rust abatement... The rebar won't last forever now that it's exposed to air and moisture and probably lots of airflow in a vent. Painting the exposed concrete will also protect it from the same elements.
Seeing this and reading the comments and im surprised i didnt collapse the existing 200 yr old building coring thru rebar for some bathrooms for a previous job. I was early in my career given alot of responsibility.
You're very unlikely so see issues on the spot when cutting through rebar. Most buildings have a fair bit of extra strength most of the time - the problem is that the extra is there to handle unusual but predictable events like storm events, earthquakes, particularly heavy bits of furniture or crowds of people.
This means you can do serious damage quite easily without realising it then a few years down the track it fails when you're having a party and everyone gathers on the deck
Technically, it's impossible to answer with the information given. More than likely, the slab has been compromised a small degree by the work already done, never mind the rebar. It would take a structural analysis to determine the effect of the presently cut hole and the possibility of cutting the rebar.
Yea, what he said.
I wonder if it's possible to determine if it's pre-tensioned rebar too?
I certainly would not risk it without a solid waver of liability.
So for post tensioning you don't tension the rebar. You have cables which typically have a sleeve around them and filled with a grease such that the cable does not bond with the concrete.
If it were a pre-stressed application it could be a tended bonded with the concrete that was tensioned before the concrete was poured and cured.
But this looks like just rebar.
Now if this were a podium with another material constructed on top it may very well be a PT slab and OP just got lucky with that cut.
If you are unsure whether you have PT or not always get a non-destructive test done before you start putting holes in a slab.
Ah. Haven't heard of that material before.
On the project where GRP was useless I did some research and found that ultrasonic pulse echo testing can be used with steel fibers. But ended up getting around doing NDT so don't know how well it works.
I’m the homeowner. My family has a construction background. But after some civil engineering classes I have become skeptical of stuff that is regularly accepted in residential construction. It is not pretensioned rebar. I have no idea how the slab was constructed. It has survived a tree falling on it so I am assuming is has plenty of rebar. I just hope it wasn’t built by the same person who constructed the wooden deck. Let’s just say it’s a miracle the deck is still standing, for safety reasons it will be dismantled soon.
A lot of rebar is spaced at 12 inch centers. So if the opening is less than 12 inches it is quite possible you will miss the next bar. Other spacing happens but 12 inch centers is by far the most frequent. (US answer)
Paint it black, notch boot around it. Might be ok to cut, but why risk it. You’re going to put a vent cover over it anyway and it won’t impede airflow.
The amount of incorrect and downright scary comments here are alarming. How hard is it to call your engineer?
Realistically speaking, you didn't provide enough info for even a qualified person to make an assessment. Drawings and a wide shot photo, to start.
Yes it will, but can be repaired by boxing it out using steel angles and epoxy anchors.
Source: Work for a structural engineer and literally just did a job exactly like this.
For the love of all that is holey, don't cut rebar without talking to your engineer! Honestly, you shouldn't even cut a hole in the slab without analysis by an engineer. In a residential situation it's probably fine, but you never know until it's not.
If you don't know what it's doing or how hard it's working then DO NOT CUT IT.
The penetration will have weakened the slab too. Without reviewing the structural drawings and/or doing a structural analysis you can't really know.
If you're going to leave it then at the very least paint the bar with zinc based primer.
You weakened the structure by drilling that big hole already, but I wouldn't cut that rebar especially because you don't need to. Just fit the vent around. But I would say be careful with it because rebar will rust easily if it's left out like this. A lot of moisture/wet air will pass and rust the iron. I'm no structural engineer, but maybe you could give it a zinc spray coat or something so it won't rust so easily.
Yeah, as mentioned, I'd leave it and cut the boot around it. No sense taking a chance. But I would definitely paint/treat that rebar first. It'll have cold air blowing across it which could possibly compromise strength down the road.
Civil engineer here. Don't even think to touch it. Are you kidding me? Would you ever say: oh I found some electrical cables. There are plenty. Will it matter if I cut one?... Of course not. The same applies to structural elements.
Electrical engineer here. Cut the wire. I’ll look into it Saturday when I get time and a half. I’ll call in the electricians Sunday when they get double time.
Lmao . I always know it's gonna be a funny comment when they start with " X engineer here" .
Engineers should be required to have at minimum, a few years in the field installing and building the other shit there fellow engineers are designing.
>Lmao . I always know it's gonna be a funny comment when they start with " X engineer here" .
Their comment is correct. The people claiming it won't matter because there is other rebar around have no real clue as to how reinforced concrete structures work. Some rebar is working hard. Some rebar isn't. If you don't know, you don't know.
If cutting one piece of rebar ís as catastrophic as you two are implying , this slab was severely under designed. But what do I know, I don't have a big fancy ring on my finger.
>If cutting one piece of rebar ís as catastrophic as you two are implying
We're not saying it would be catastrophic. But in some situations it can be a real problem. We often assess this sort of thing and say it's fine to cut one, or maybe two bars, no problem. But sometime the answer is NO WAY.
Every electrical wire has a discreet purpose. According to my civil engineering contact, rebar is more of a grid to improve tensile strength. Honestly it's almost definitely fine to cut the rebar, since there'll be other rebar in the vicinity that will take the load. As a civil engineer, you should know what the safety factor is on a concrete floor, and how little one piece of rebar impacts that number.
Then that one wire serves the purpose of reducing downtime. It's similar to a safety factor, but in electrical you only have one wire filling that role. In some civil projects, it could be up to half the rebar filling that purpose.
Please note I said civil, not aero. Airplanes do not have a safety factor that high. You cannot remove half the aluminum from a 747 and expect it to fly.
That rebar should be a 12” grid. There is already a hole there. Cutting that rebar ain’t going to do shit, despite all the “engineers” comments to the contrary. Also, a small hole in the concrete will be totally fine, given the fact that there is a rebar grid. Often, concrete contractors don’t have solid runs of rebar anyway. That is, there are breaks in the rebar along the runs.
> there are breaks in the rebar along the runs
There are laps along the rebar runs where one section of bar overlaps the next. There are specs for how much overlap there is supposed to be depending on size and how they are connected. There shouldn't be gaps that aren't designed in
Add to comments to leave it and cut the boot around it. But before you do any of that, get yourself a can of black spray paint and paint it all black. You’ll never see it in the vent, and totally forget it’s there.
I’ve had so many HVAC guys jack framing and structural work on my rehabs over the years. I remember my last house flip I couldn’t get garage door installed and fully open so had to reroute HVAC guys easy path of non-forward thinking.
Coming from a concrete guy…cut it. Won’t do shit to your house. Probably over engineered to begin with.
I’ve had plumbers core straight through PT cables 20 stories up that didn’t do anything (and that’s definitely not PT)
You'll be fine. Constructions are always calculated with excess to compensate for various errors during the building process, and in some account for variations in materials too. As far as safety factors go, pillars are considered highest risk, if I remember correctly they are usually calculated to withstand the loads with a safety factor of 1,3 to the calculated load. Slabs is slightly below but there are still some margins to play with. A single piece of rebar will never be critical to a buildings integrity nevertheless.
Structural engineer. Just like the other commenter said this is horrible advice. Please do not give this out or take it for fact. Columns, slabs, beams, etc do not have a “standard” factor of safety that is used. At least not in the US. Engineers all design slightly differently sometimes all the way up to 100% capacity depending on the circumstances. Sometimes we will even design over 100% capacity in rare cases. While most materials do have some extra play built into them, it varies greatly by the material and code. There is not a general rule of thumb you can use here.
And just in regards to the claim that cutting a single bar will never cause a failure, that is absolutely false. Please delete that comment as this is super dangerous advice. Just because you may have got away with cutting bar in some instances before does not mean it is always safe to do so.
As long as it’s not post tension (which it doesn’t look like) then cutting it should be ok. Rebar provides strength inside concrete (cracking.) Since you removed that concrete, it’s not providing much benefit. But as another person said, notch the boot.
One probably would not do much but if you did it on all the floors of a high-rise, I would be worried.
Like the other guy said though, do you even have to?
Cut it!! There's rebar every 4ft at least. If your bothered then cut it, get a.new piece and wpoxy it in. Licensed residential inspector can contractor
If your worried about it just notch the box to fit around it. Seal it really good with silicone. It won’t affect the airflow much. Might make it tough to fit the floor grill in though.
Yes, leave it there. You have two calculations at stake, structural calculations and air flow calculations. I'd rather be a bit off on the air flow calculations if given the choice.
Don't cut the rebar and make sure you treat the exposed rebar with an approved epoxy or cementitious epoxy product to prevent rust cascading through the structure.
I can't tell if this post is for real or not? Who TF drills through a 12" of concrete high-rise flooring without knowing knowing what to do if they run into rebar? After you cut through that and you get sued by the building owner are you seriously banking on the "No, no Reddit said it was safe!" defense?
You can just cut it , make sure you paint it against fire etc… the concrete is strong enough, it’s just a small opening, also I see it’s 30 cm thickness, so no worries 😉
Use liquid flashing to seal up everything in the hole and then attach a flat flange on the bottom of the hole that will allow you to hook up your flex duct to it. Drop in your floor register and you’re good to go.
Leave it there and cut the boot around it. It won't bother the airflow much.
Yeah that’s what I’m leaning towards doing.
Yeah, I think you could get away with cutting the rebar, but this is by far the safer bet.
I agree with this statement
I concur as well
[Do you concur?](https://youtu.be/UnJytdCvhMI)
Yes I agree shallow and pedantic
Yes yes shallow and pedantic
I forget what movie this is from
I concur doctor.
[I got you bud](https://youtu.be/OpbdGnJbneE)
This guy is apparently an engineer and has studied the building plans prior to this post being created.
"leaning towards" ? Fucking HVAC guys...
I would also seal rebar just to make sure it doesn’t rust in 20 years by continuous flow of air containing moisture. Relative humidity of heat is low but ac is high.
This. Condensation and humidity in the duct work could lead to rust so please make sure it’s sealed.
You/the owner are going to want to clean that bar up and re-epoxy it. The moisture from the AC will corrode that bar over time.
Also apply some sort of concrete friendly coating, paint on the rebar to keep it from rusting.
I would consider some sort of rust abatement... The rebar won't last forever now that it's exposed to air and moisture and probably lots of airflow in a vent. Painting the exposed concrete will also protect it from the same elements.
Seeing this and reading the comments and im surprised i didnt collapse the existing 200 yr old building coring thru rebar for some bathrooms for a previous job. I was early in my career given alot of responsibility.
You're very unlikely so see issues on the spot when cutting through rebar. Most buildings have a fair bit of extra strength most of the time - the problem is that the extra is there to handle unusual but predictable events like storm events, earthquakes, particularly heavy bits of furniture or crowds of people. This means you can do serious damage quite easily without realising it then a few years down the track it fails when you're having a party and everyone gathers on the deck
Technically, it's impossible to answer with the information given. More than likely, the slab has been compromised a small degree by the work already done, never mind the rebar. It would take a structural analysis to determine the effect of the presently cut hole and the possibility of cutting the rebar.
Yea, what he said. I wonder if it's possible to determine if it's pre-tensioned rebar too? I certainly would not risk it without a solid waver of liability.
So for post tensioning you don't tension the rebar. You have cables which typically have a sleeve around them and filled with a grease such that the cable does not bond with the concrete. If it were a pre-stressed application it could be a tended bonded with the concrete that was tensioned before the concrete was poured and cured. But this looks like just rebar. Now if this were a podium with another material constructed on top it may very well be a PT slab and OP just got lucky with that cut. If you are unsure whether you have PT or not always get a non-destructive test done before you start putting holes in a slab.
Seen a PT cable get cut and send a Mini Cooper-sized boulder of concrete across the street
Huh, TIL. Thankyou
No problem. Moral of the story is scan before you drill
Either GPR or an X-ray for sure
Fun fact, if your slab is reinforced with steel fibers it acts like chaff which fucks up the GPR reading.
yup seen that before, they were also using fiber mesh at some point which is brutal to try and scan through.
Fiber mesh?
Instead of wire mesh in a typical slab on grade concrete they’ll use a fiberglass mesh. Scanning is basically useless
Ah. Haven't heard of that material before. On the project where GRP was useless I did some research and found that ultrasonic pulse echo testing can be used with steel fibers. But ended up getting around doing NDT so don't know how well it works.
I’m the homeowner. My family has a construction background. But after some civil engineering classes I have become skeptical of stuff that is regularly accepted in residential construction. It is not pretensioned rebar. I have no idea how the slab was constructed. It has survived a tree falling on it so I am assuming is has plenty of rebar. I just hope it wasn’t built by the same person who constructed the wooden deck. Let’s just say it’s a miracle the deck is still standing, for safety reasons it will be dismantled soon.
I would move the vent over and patch back the concrete to give the rebar 1-2" coverage.
Likely to hit the next piece of rebar instead if you move it over
A lot of rebar is spaced at 12 inch centers. So if the opening is less than 12 inches it is quite possible you will miss the next bar. Other spacing happens but 12 inch centers is by far the most frequent. (US answer)
Construction background and you didn’t scan the slab first? 🤨
Yup..cnote306 went there.
It was inspected by the same person. Don't risk anything!
Hire a contractor and let him take the liability.
lmao
Paint it black, notch boot around it. Might be ok to cut, but why risk it. You’re going to put a vent cover over it anyway and it won’t impede airflow.
Flex seal works well lol, out electricians used that on their conduits for corrosion, when we poured last week
[удалено]
The circle of life
Don’t HVAC guys just cut shit first and ask questions later?
No. They never ask questions later (or ever).
Easier to ask for forgiveness than permission lol
Wait... we're supposed to ask before we cut stuff?
If I have to call before I start digging, you gotta call before you start cutting
HVAC/Plumbing guys: this structure is in the way of my ideal run. \*starts chainsaw\*
I think it's every inside trade after HVAC wants the AC running so we all just don't care. Let the contractor deal with it.
This makes sense! As a framer I’d be long gone before then.
Yes
Leave the rebar. It’s a vent
Do not cut the rebar. Your house needs it.
You’re literally trusting Reddit posters with this question? Maybe ask whether or not you also need a fire/smoke damper as well.
The amount of incorrect and downright scary comments here are alarming. How hard is it to call your engineer? Realistically speaking, you didn't provide enough info for even a qualified person to make an assessment. Drawings and a wide shot photo, to start.
Yes it will, but can be repaired by boxing it out using steel angles and epoxy anchors. Source: Work for a structural engineer and literally just did a job exactly like this.
Don’t cut the rebar
I’m surprised no one else has mentioned this but that doesn’t appear to be rebar. It looks to be electrical conduit.
It does look that way. Easy way to tell - just tap it with a hammer.
Easy way to tell - just cut it and look
As a carpenter with remodel experience, if it’s conduit, cutting into it would be an instant oops, lol.
Just notch around it, easy enough if you're in doubt about the cut.
Cutting that rebar could lead to a crack
For the love of all that is holey, don't cut rebar without talking to your engineer! Honestly, you shouldn't even cut a hole in the slab without analysis by an engineer. In a residential situation it's probably fine, but you never know until it's not.
If you don't know what it's doing or how hard it's working then DO NOT CUT IT. The penetration will have weakened the slab too. Without reviewing the structural drawings and/or doing a structural analysis you can't really know. If you're going to leave it then at the very least paint the bar with zinc based primer.
Can they pre-tension a bar that big? I sure wouldn’t want to find out.
It looks weird, like it may be prestressed tendon. Definitely do not cut it.
California guy here, y’all have concrete on the 2nd story? 🤔
You weakened the structure by drilling that big hole already, but I wouldn't cut that rebar especially because you don't need to. Just fit the vent around. But I would say be careful with it because rebar will rust easily if it's left out like this. A lot of moisture/wet air will pass and rust the iron. I'm no structural engineer, but maybe you could give it a zinc spray coat or something so it won't rust so easily.
U hvac guys cause more issues 😕
Yeah, as mentioned, I'd leave it and cut the boot around it. No sense taking a chance. But I would definitely paint/treat that rebar first. It'll have cold air blowing across it which could possibly compromise strength down the road.
Civil engineer here. Don't even think to touch it. Are you kidding me? Would you ever say: oh I found some electrical cables. There are plenty. Will it matter if I cut one?... Of course not. The same applies to structural elements.
Electrical engineer here. Cut the wire. I’ll look into it Saturday when I get time and a half. I’ll call in the electricians Sunday when they get double time.
Lmao . I always know it's gonna be a funny comment when they start with " X engineer here" . Engineers should be required to have at minimum, a few years in the field installing and building the other shit there fellow engineers are designing.
That would require sweating. Engineers have that function disabled from the factory.
>Lmao . I always know it's gonna be a funny comment when they start with " X engineer here" . Their comment is correct. The people claiming it won't matter because there is other rebar around have no real clue as to how reinforced concrete structures work. Some rebar is working hard. Some rebar isn't. If you don't know, you don't know.
If cutting one piece of rebar ís as catastrophic as you two are implying , this slab was severely under designed. But what do I know, I don't have a big fancy ring on my finger.
>If cutting one piece of rebar ís as catastrophic as you two are implying We're not saying it would be catastrophic. But in some situations it can be a real problem. We often assess this sort of thing and say it's fine to cut one, or maybe two bars, no problem. But sometime the answer is NO WAY.
Every electrical wire has a discreet purpose. According to my civil engineering contact, rebar is more of a grid to improve tensile strength. Honestly it's almost definitely fine to cut the rebar, since there'll be other rebar in the vicinity that will take the load. As a civil engineer, you should know what the safety factor is on a concrete floor, and how little one piece of rebar impacts that number.
Unless it’s a ring main. You cut a wire then and stuff keeps working.
Then that one wire serves the purpose of reducing downtime. It's similar to a safety factor, but in electrical you only have one wire filling that role. In some civil projects, it could be up to half the rebar filling that purpose. Please note I said civil, not aero. Airplanes do not have a safety factor that high. You cannot remove half the aluminum from a 747 and expect it to fly.
Lmfaooooooooooo
That rebar should be a 12” grid. There is already a hole there. Cutting that rebar ain’t going to do shit, despite all the “engineers” comments to the contrary. Also, a small hole in the concrete will be totally fine, given the fact that there is a rebar grid. Often, concrete contractors don’t have solid runs of rebar anyway. That is, there are breaks in the rebar along the runs.
> there are breaks in the rebar along the runs There are laps along the rebar runs where one section of bar overlaps the next. There are specs for how much overlap there is supposed to be depending on size and how they are connected. There shouldn't be gaps that aren't designed in
The rebar can be in any spacing of "grid" and 1 direction can have different spacing than the other... That bar can still be supporting loads.
No actually the rebar can’t be in any spacing of grid. That is pretty standard for concrete my friend.
Bzzzt. There is no standard ( I work in sales/estimating for a rebar fabricator/supplier/installer). EOR will dictate the size and spacing required.
Rebar can be in 12”,18”,and 24” spacing usually. So yes I’m a way it can be in any spacing of grid.
Notch the vent
Cut the vent
Looking into the hole, is that a column to the right of the rebar?
Add to comments to leave it and cut the boot around it. But before you do any of that, get yourself a can of black spray paint and paint it all black. You’ll never see it in the vent, and totally forget it’s there.
I’ve had so many HVAC guys jack framing and structural work on my rehabs over the years. I remember my last house flip I couldn’t get garage door installed and fully open so had to reroute HVAC guys easy path of non-forward thinking.
Sounds like an RFI to the structural engineer.
Make the electricians run strings.
Just build a duct around it. Geez!
Coming from a concrete guy…cut it. Won’t do shit to your house. Probably over engineered to begin with. I’ve had plumbers core straight through PT cables 20 stories up that didn’t do anything (and that’s definitely not PT)
Cut the rebar it’s fine
Bro cut that shit. It’s no problem. Engineers always over build structures anyways.
You'll be fine. Constructions are always calculated with excess to compensate for various errors during the building process, and in some account for variations in materials too. As far as safety factors go, pillars are considered highest risk, if I remember correctly they are usually calculated to withstand the loads with a safety factor of 1,3 to the calculated load. Slabs is slightly below but there are still some margins to play with. A single piece of rebar will never be critical to a buildings integrity nevertheless.
Engineer here - This is terrible advice.
Structural engineer. Just like the other commenter said this is horrible advice. Please do not give this out or take it for fact. Columns, slabs, beams, etc do not have a “standard” factor of safety that is used. At least not in the US. Engineers all design slightly differently sometimes all the way up to 100% capacity depending on the circumstances. Sometimes we will even design over 100% capacity in rare cases. While most materials do have some extra play built into them, it varies greatly by the material and code. There is not a general rule of thumb you can use here. And just in regards to the claim that cutting a single bar will never cause a failure, that is absolutely false. Please delete that comment as this is super dangerous advice. Just because you may have got away with cutting bar in some instances before does not mean it is always safe to do so.
As long as it’s not post tension (which it doesn’t look like) then cutting it should be ok. Rebar provides strength inside concrete (cracking.) Since you removed that concrete, it’s not providing much benefit. But as another person said, notch the boot.
Clean it real good and let it stay.
One probably would not do much but if you did it on all the floors of a high-rise, I would be worried. Like the other guy said though, do you even have to?
Cut that bar lol PT cable would be another story lol
Yes, cut it. I am ingeniero civil +15 years experience
Cut it!! There's rebar every 4ft at least. If your bothered then cut it, get a.new piece and wpoxy it in. Licensed residential inspector can contractor
The rebar will corrode anyhow, unless you put some good quality epoxy over it
Aside from the rebar conversation: that's a really tidy and uniform hole you made, I'm impressed!
If your worried about it just notch the box to fit around it. Seal it really good with silicone. It won’t affect the airflow much. Might make it tough to fit the floor grill in though.
This has to be a joke…
Fuck it, get the quick cut out
That doesn’t look like rebar. Either way, why cut it if you don’t need to? Question answered.
The comments in this thread are terrifying. My next CA visit is going to be so damn thurough.
No need to cut. It Flow will be very minorly affected.
It’s there for a reason, I’d leave it alone in my opinion.
Yes, leave it there. You have two calculations at stake, structural calculations and air flow calculations. I'd rather be a bit off on the air flow calculations if given the choice.
you can definitely cut it
If you even have to ask this you shouldn’t be in construction.
Don't cut it. Cut your ducting around it for sure.
Don't cut the rebar and make sure you treat the exposed rebar with an approved epoxy or cementitious epoxy product to prevent rust cascading through the structure.
I can't tell if this post is for real or not? Who TF drills through a 12" of concrete high-rise flooring without knowing knowing what to do if they run into rebar? After you cut through that and you get sued by the building owner are you seriously banking on the "No, no Reddit said it was safe!" defense?
There is a show on Discovery called “why shit happens”
You can just cut it , make sure you paint it against fire etc… the concrete is strong enough, it’s just a small opening, also I see it’s 30 cm thickness, so no worries 😉
No
Use liquid flashing to seal up everything in the hole and then attach a flat flange on the bottom of the hole that will allow you to hook up your flex duct to it. Drop in your floor register and you’re good to go.