Is cement slab insulation worth it in Florida?

[driver50x]

I am building a 22x24 shop in St. Petersburg, FL. It will have a split AC unit, but only turned on when I am working out there, maybe two days a week. Is floor insulation a worthwhile investment? How about moisture barrier? I’m also wondering about the type and thickness of the base to use in this area, and if I should use rebar.

If it matters, I live about a mile from the Tampa Bay, 18 feet above sea level.

 

[theoldwizard1]

At least do the vapor barrier.

 

[Dagny]

If I lived there I wouldnt do it .

 

[mm08822]

I would also add welded wire fabric. Rebar could be overkill. I doubt you need insulation. I'd say it has most value in freezing winter locations.

 

[driver50x]

Thanks guys. I forgot to add that I plan on installing a four post lift. That requires at least 3000 psi cement. I’m not sure if rebar or wire fabric makes the most sense with that.

 

[ConCretin]

Given your circumstances, underslab insulation won't pay for itself in your lifetime if ever. The need for a vapor barrier depends on your soil conditions and whether you intend to apply an adhered floor covering such as epoxy. With that said, you only have one chance to do it and it's relatively inexpensive so it probably makes sense to do it.

Rebar and mesh perform the same function, which is to restrain cracks whether they are random cracks or those that occur at the bottom of control joints. Neither makes a slab stronger or prevents cracks. The necessity and value of reinforcing depends on the type of slab you are building.

Have a look at my Guide to Floor Slabs in the link below for some additional thoughts on the process of constructing a slab. Good luck with your project.

 

[428PI]

Make the foam thick enough and your shop can float when the hurricanes start flooding everything.

 

[Spider Curry]

What do you mean by "floor insulation"?

If you're in St. Pete I would say a monolith pour with a thickened edge. And yes, do a 6mil vapor barrier under the whole thing.

Use a poured footer about 16 inches wide and 8 inches deep, with two runs of #5 rod through the entire perimeter, and a #5 rod as a "J-dowel" standing up every 2' on center, with the bottom of the J wire-tied to one of the #5 runs in the footer. Add block courses on top of the footer, enough to get your slab up to grade. The top course will be a 'u-block'. One more run of #5 in a continuous path around the entire perimeter, wire-tied to the top of the J. Pour that sucker solid. Fill the inside of the foundation and compact it. Do a 4 inch slab on top, and you can use fibermesh but old-fashioned 6x6 welded-wire mesh is just fine.

I've seen a lot of slabs in Florida, this will work. But really, I think you'd be best served by finding an engineer and asking him to design a slab and seal some drawings for you.

 

[driver50x]

Thanks. That’s just the kind of info I was looking for. I know nothing about this stuff. Lol

 

[cliffcharb]

Moisture barrier is required in Florida. I’m in south Sarasota county built at 20’ elevation.
I went 4” thick 3500psi fiber mesh, no rebar or steel mat.
As our soil is basically sand, for my base I went with 5-6” of a dot base material. It compacted nicely and passed the soil compaction test.

 

[Spider Curry]

Thanks. That’s just the kind of info I was looking for. I know nothing about this stuff. Lol

You're welcome. If you're in St. Pete proper I hope you have a fence and/or hedges around your yard before you start on this, because what the code enforcement people can't find on their own, your neighbors will make sure they find it.

Moisture barrier is required in Florida. I’m in south Sarasota county built at 20’ elevation.
I went 4” thick 3500psi fiber mesh, no rebar or steel mat.
As our soil is basically sand, for my base I went with 5-6” of a dot base material. It compacted nicely and passed the soil compaction test.

One advantage to fiber mesh is you won't get the rust punch-through that can occur with WWM. My most recent slab is three years old and I already have a couple rust dots that I'll need to take care of before it leads to something worse, like spalling.

Despite this, I still stick with WWM. It's what I'm used to seeing. It meets code and does the job. A rust point here and there isn't too much to deal with.

 

[ConCretin]

If the WWF is properly supported in the middle of your slab, you won't have any issues with rust.

 

[driver50x]

You're welcome. If you're in St. Pete proper I hope you have a fence and/or hedges around your yard before you start on this, because what the code enforcement people can't find on their own, your neighbors will make sure they find it.



One advantage to fiber mesh is you won't get the rust punch-through that can occur with WWM. My most recent slab is three years old and I already have a couple rust dots that I'll need to take care of before it leads to something worse, like spalling.

Despite this, I still stick with WWM. It's what I'm used to seeing. It meets code and does the job. A rust point here and there isn't too much to deal with.

I definitely know what you mean. I happen to live in one of the few spots in St. Pete where the neighbors are all cool and code enforcement seems almost non existent. Lol. I wish I could build a much bigger shop, but that is not possible here.

 

[Spider Curry]

If the WWF is properly supported in the middle of your slab, you won't have any issues with rust.

You might think so, but thats not how it works here in Florida. My most recent slab here was done by a very careful contractor, probably one of the best you'd ever find. I watched the entire job since it was next to my house, everything was done perfectly. Yet I have a couple of rust spots. Most likely because this slab has a broom finish instead of smooth. That presents more opportunity for water to get in. I'll fix that before I finish the slab, probably 5 years from now at the rate I'm going.

 

[ConCretin]

You might think so, but thats not how it works here in Florida. My most recent slab here was done by a very careful contractor, probably one of the best you'd ever find. I watched the entire job since it was next to my house, everything was done perfectly. Yet I have a couple of rust spots. Most likely because this slab has a broom finish instead of smooth. That presents more opportunity for water to get in. I'll fix that before I finish the slab, probably 5 years from now at the rate I'm going.

With all due respect, you are incorrect. Steel imbedded in concrete with adequate cover is not subject to corrosion. There is nothing special about Florida that defies the laws of physics. Steel reinforced concrete bridge decks here in Maine endure far worse conditions than your garage slab including freeze/thaw, heavy traffic and deicing salts. They somehow last for decades. If your reinforcing truly is rusting, which I doubt, it's because it's too close to the surface. Period. If that's the case, maybe your contractor isn't as perfect as you think he is.

By the way, I'm interested in how you intend to 'fix' your rusty reinforcing.

 

[nadogail]

Should you not build your shop on a Hull, so it can float when the floods come?

 

[Spider Curry]

With all due respect, you are incorrect. Steel imbedded in concrete with adequate cover is not subject to corrosion. There is nothing special about Florida that defies the laws of physics. Steel reinforced concrete bridge decks here in Maine endure far worse conditions than your garage slab including freeze/thaw, heavy traffic and deicing salts. They somehow last for decades. If your reinforcing truly is rusting, which I doubt, it's because it's too close to the surface. Period. If that's the case, maybe your contractor isn't as perfect as you think he is.

By the way, I'm interested in how you intend to 'fix' your rusty reinforcing.

We can get into all that after you tell me what "laws of physics" that you think I'm saying Florida "defies".

 

[ConCretin]

We can get into all that after you tell me what "laws of physics" that you think I'm saying Florida "defies".

I was responding to your assertion that somehow concrete and reinforcing behave differently in Florida than they do everywhere else when you said;

You might think so, but thats not how it works here in Florida

I'm not trying to be a **** here but I try to correct erroneous information when I see it and it is incorrect to say that properly installed wire mesh will rust and "punch through" the surface of the concrete.

 

[Spider Curry]

I was responding to your assertion that somehow concrete and reinforcing behave differently in Florida than they do everywhere else when you said;



I'm not trying to be a **** here but I try to correct erroneous information when I see it and it is incorrect to say that properly installed wire mesh will rust and "punch through" the surface of the concrete.

Nevertheless, this slab was done properly. I watched, and I'm no novice to this.

 

[FJ4FUN]

At least do the vapor barrier.

A properly spec'd and installed vapor barrier at that.