Hot Tub vs. Concrete over Corrugated

[JohnnyMX]

Looking at a 6-8 person hot tub and a potential placement on our front porch. The total weight with water and people is in the roughly 5K lb range. The porch is an elevated concrete over corrugated steel and spans about 12' out from the house. The side of the slab where it adjoins to the house is sitting on a 12" (1/2") I beam. The slab is roughly 6" thick and the steel webbing height is in the 2 1/2" range. Everyone has said this place is built like a brick shiznit house, but I don't want the hot tub in my basement either and don't have the construction or engineering background to know for sure. I feel like it would be ok..... but there are smarter people on here. Good idea or bad idea?

 

[4570Man]

Obviously the correct answer is consult an engineer but given the size of that beam, the slab thickness and the fairly large footprint of the hot tube it will be fine IMO. Do you know how much rebar is in the slab?

 

[JohnnyMX]

I do not know, but when the original owner/builder met with me after purchasing he said the house itself is rated to be hit by a Cessna-sized plane given the amount of rebar in the exterior walls (poured/insulated/rebar). Even if that is tongue in cheek, I would assume he didn't skimp on the porch. It is hard to get answers because most of the people that look at the house just shake their head and wonder what the guy was thinking. I know that isn't an accurate answer. Prior owner was an engineer by the way.

 

[PILOON]

I'm not an engineer but have seen a few odd ones.

Like hard wood flooring on double layers of 3/4 ply glued/screwed on pre fab floor joists that were 12 inches apart. (that is, like 9/10 inch gap between joist tops)
(I asked the 'architect' if he wanted to park a buss on the flooring.)
Owner asked what was the difference, my reply was about $3000. of plywood!
(We did single ply.)

Another that was supposedly 'engineered' ---double hot tub over a kitchen with no load bearing transfer, all was cantilevered--we added a new load bearing post.

New house with multi sloped/faced roofing all converging in a central area (and in heavy snow zone) BUT no proper load transfer---again cantilevered---under no load I used a 12 ft straight edge t demonstrate that there already was a 1,5" dip in the floor.
LOL, a quick load bearing post found its way into being.
(However there was no 'load pad' even poured for a such post)

Same project as above, while I was not involved with flooring but since the floor guy walked off* I was asked if I could finish it up B4 Xmas.
Sure, about a mere 3-4 hrs will do it I said.
Well, we had to evacuate the house as the staples penetrated the propane line that was attached to underside of the subfloor.

*actually could barely walk as he was so 'high' on something!

That last job was such a disaster that I wonder if it is still standing.
I could almost write a book on that one. My take is they always went to the lowest bidder and never checked references. Builder/owners were both accountants and certainly not manual.
Furring was all wrong and the plasterers scrapped a dump truck load of gyprock cut offs.
Furring for siding was oriented the wrong way at all corners, foundation was multi stepped so we had to create a a reference in order to have the multiple surfaces of siding align properly.
Chimney so high that they installed the structure with a noticeable twist in it.

Nope, not everybody should DIY such projects.

 

[4570Man]

I'm not an engineer but have seen a few odd ones.

Like hard wood flooring on double layers of 3/4 ply glued/screwed on pre fab floor joists that were 12 inches apart. (that is, like 9/10 inch gap between joist tops)
(I asked the 'architect' if he wanted to park a buss on the flooring.)
Owner asked what was the difference, my reply was about $3000. of plywood!
(We did single ply.)

Another that was supposedly 'engineered' ---double hot tub over a kitchen with no load bearing transfer, all was cantilevered--we added a new load bearing post.

New house with multi sloped/faced roofing all converging in a central area (and in heavy snow zone) BUT no proper load transfer---again cantilevered---under no load I used a 12 ft straight edge t demonstrate that there already was a 1,5" dip in the floor.
LOL, a quick load bearing post found its way into being.
(However there was no 'load pad' even poured for a such post)

Same project as above, while I was not involved with flooring but since the floor guy walked off* I was asked if I could finish it up B4 Xmas.
Sure, about a mere 3-4 hrs will do it I said.
Well, we had to evacuate the house as the staples penetrated the propane line that was attached to underside of the subfloor.

*actually could barely walk as he was so 'high' on something!

That last job was such a disaster that I wonder if it is still standing.
I could almost write a book on that one. My take is they always went to the lowest bidder and never checked references. Builder/owners were both accountants and certainly not manual.
Furring was all wrong and the plasterers scrapped a dump truck load of gyprock cut offs.
Furring for siding was oriented the wrong way at all corners, foundation was multi stepped so we had to create a a reference in order to have the multiple surfaces of siding align properly.
Chimney so high that they installed the structure with a noticeable twist in it.

Nope, not everybody should DIY such projects.

I drove my 10,000 pound excavator on house floor that wasn’t designed for such. It held it surprisingly well.

 

[PILOON]

I drove my 10,000 pound excavator on house floor that wasn’t designed for such. It held it surprisingly well.

An excavator on tracks is kind of like a man walking on snowshoes, low PSI's.
I have even seen extra wide tracks for swamp usage.

 

[Streetcar]

Looking at a 6-8 person hot tub and a potential placement on our front porch. The total weight with water and people is in the roughly 5K lb range. The porch is an elevated concrete over corrugated steel and spans about 12' out from the house. The side of the slab where it adjoins to the house is sitting on a 12" (1/2") I beam. The slab is roughly 6" thick and the steel webbing height is in the 2 1/2" range. Everyone has said this place is built like a brick shiznit house, but I don't want the hot tub in my basement either and don't have the construction or engineering background to know for sure. I feel like it would be ok..... but there are smarter people on here. Good idea or bad idea?

What is the span of the steel beam
is steel beam also supporting your walls and house floor

 

[o2batsea]

My question is why you want 6-8 naked people on your front porch?

 

[MikeFarm]

Well your Honour "Everyone has said this place is built like a brick shiznit house"
That won't go down well in a court of law

Well your Honour "Here is an Engineers report authorising the installation of the hot tub"
That is your get out of jail free card

Mike

 

[riptides]

Spring for a structural engineering report.

 

[Streetcar]

Will your house be damaged if the beam deflects from the heavy load?
What is under the porch, can supports be easily added for the hot tub?
No easy way to determine strength of slab
Porch can be reinforced with carbon fiber if the beam is adequate.

 

[dodge man]

My degree is in civil engineering and I had both structural analysis and structural design classes. That said I was a land surveyor and never did any structural design but what that background did do was give me the knowledge to know that no one on this board can answer your question.

If I understand the situation you have a 12 foot span of a 6” slab. It sounds like one side sits on a steel beam. What does the other side sit on? Sounds like it was poured over corrugated steel which wouldn’t add much strength. If I’m reading this correctly a 6“ slab spanning that much doesn’t sound very strong. Probably fine for foot traffic. The question is how strong is the concrete and what if any reinforcing is in that slab? Takes a structural engineer to figure it out.

 

[Streetcar]

You are looking at $2000 minimum for engineer to review and rate your slab.
Corrugation is form work not structural.
If properly installed and reinforced the slab is strong enough for your hot tub.
I just installed similar slab rated for truck loading

 

[riptides]

You are looking at $2000 minimum for engineer to review and rate your slab.
Corrugation is form work not structural.
If properly installed and reinforced the slab is strong enough for your hot tub.
I just installed similar slab rated for truck loading

Seems awful high.

But insurance, repairs or bodily injury.....

 

[Streetcar]

The price for structural review is based that somebody will require to spend several hours measuring and testing concrete for strength and rebar.measuring beam and span. Then engineer can take that information and run calculations. I am guessing slab will not be adequate for that hot tub. Failure mode would probably be excessive deflection. The free engineer analysis is worth what you paid for it

 

[dodge man]

On a flat slab, you can take pavement cores. I’ve done this hundreds of times on asphalt and concrete pavement. The problem is in this case you take a core you are damaging the slab and any reinforcement.

They make devices, such as a Swiss Hammer that can give an estimate of the concrete strength. It’s a non destructive test. The problem is what is the reinforcement? I’m not sure there is a way to figure that out. Maybe some kind of x ray machine?

Add in the fact I’m not sure what a hourly charge is for a structural engineer is. Probably at least $150 an hour, maybe more. It’s easy to get $2000 wrapped up in this.

The best thing to do is put the hot tub somewhere else.

 

[Egon]

There are corrugated steel forms that are part of a concrete floor design.

 

[mkendrix]

If the hot tub must be on the porch, then a few hundred dollars for a concrete pad under each corner and a stack of blocks with HARDWOOD shims to hold floor up is cheaper than a structural engineer. Last engineer I used was $180/hour to rate a load bearing beam. 2 hour drive round trip from office to job site is more than material.

 

[JohnnyMX]

Found the engineer plans for the house and specifically the porch. The concrete was to be 3,000psi with #4 rebar laid 12" center running both ways. The corrugated steel is 3" deep 18gauge under the 6" slab. The beam is under a 9' wall on the exterior + the truss. The rest of the foundation is on 12" eReward ICF walls.

 

[dodge man]

Nice looking porch, looks like a great place for a hot tub. If I recall a number 4 bar is 1/2” diameter, sounds well built but I still can’t tell you if it will hold a hot tub.