Below Concrete Insulation

[LifeLongWNYer]

Hi all. I'm planning a garage and post some in other sections on this forum, but think this is the place for this question. It is spring in WNY and the season for home shows. At a recent one, a exhibit of the 84 Lumber chain was showing a foam board to be placed on a garage floor subgrade, before concrete is poured. It comes in 4'x4' sheets and the top surface has raised, circular, "nubs" on an approximate 1 1/2" grid pattern. You are supposed to be able to lay PEX tubing between the nubs, which hold the tubing in a pattern and where you want it to stay.

The salesman "said" that the subgrade is prepared, and leveled, then this stuff is laid down on top of the base. After laying in the PEX, concrete is poured for the floor. "Supposedly" no mesh, rebar or fiber is required. All of this sounds too good to be true.

The material is called "Hydrofoam" and it is made by a firm called "Nudura". Has anybody heard of it, or tried it, and how did it work?


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[joe--h]

How much a sheet? Just curious on that one.

EPS aka beadboard in 4x8 sheets is probably cheaper and stapling it to the foam works the same.

"Supposedly" no mesh, rebar or fiber is required. All of this sounds too good to be true.

Nothing this foam does will negate the need for mesh, rebar or fiber, all it does is hold the PEX in place which can also be done with staples or tiewraps to the rebar or whatever.

So, the salesman is full of ****, surprise surprise! This magic foam will eliminate the cost of rebar?

You need to do some research on radiant floors.

How big a shop? You can buy direct from foam manufactures if you need enough.

Joe H

 

[LifeLongWNYer]

Well, it was a home show.... the salesman, a typical salesman, wouldn't tell me a price until he came to my house to "look the site over". Well, this building hasn't been built yet, so there is nothing to see, but he still wanted to stop by.

I never have shopped at 84 Lumber, and darn sure won't now, but I was asking about the stuff because if it is any good, I thought that I should be able to get it some place else.

I have been researching radiant floors, and have a lot to learn still, but was in awe of that product, and was wondering if it is any good. I guess the saying "if it sounds too good to be true, it isn't true" applies in this case. By the way, garage will be 40'x40' with concrete in 2/3 of it.

Finally, last summer I was in a new housing tract where high end homes ( $ 800K - 1 mil ) were going up. I watched a crew laying, then tieing PEX tube to the rebar AND mesh ( were using both ) in a 6 car garage. I guess if this foam stuff was any good, they would have been using it.

Thanks, Joe, I appreciate the response.


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[matt_i]

Sounds like it would speed the PEX layout at the expense of the concrete's integrity.

Many labor-saving products claim to take the place of rebar...but do they??

 

[yeldogt]

I would like to know how many garage and basement floors have been installed without any rebar or mesh ... a lot. In fact .. in all my years of rebuilding old houses I have never run into mesh in a slab. When did it start to be commonly used?

It's common to staple tubing directly to the insulation .... there are companies making plastic grids that sit on top of the insulation. Some fully cover the insulation board others are strips that hold the tubing. What you found combines the two ... making it easier for a DIY ..or anyone else not familiar. It's a question adding up the various parts and seeing if this makes sense in both time and money. It looks like a good idea ... someone else makes a red plastic version. I would still do the VB under it

I typically have used the 2" foam and the 6" mesh for tube attachment -- in reality the mesh gets push to the lower part of the slab .... not sure it does anything for the slab ..... it makes placing the tubing 6" on center easy .... I do more tubing in my radiant.

Around me the staple method is used often followed with fiber in the slab

 

[like2wheel]

Hi all. I'm planning a garage and post some in other sections on this forum, but think this is the place for this question. It is spring in WNY and the season for home shows. At a recent one, a exhibit of the 84 Lumber chain was showing a foam board to be placed on a garage floor subgrade, before concrete is poured. It comes in 4'x4' sheets and the top surface has raised, circular, "nubs" on an approximate 1 1/2" grid pattern. You are supposed to be able to lay PEX tubing between the nubs, which hold the tubing in a pattern and where you want it to stay.


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There is a guy on this forum that posted he used something like that stuff approx 1 year ago. He posted a reply in a thread with pictures of the tubing snapped into the foam.

Edit;
Found it.
https://www.garagejournal.com/forum/showthread.php?t=366323

 

[LifeLongWNYer]

At the risk of stealing my own thread.... I think I understand about the underfloor insulation, BUT need to know more about the insulation treatment at the edges of the slab. Bear in mind, that I am talking about a pole barn construction building.

As I understand it, the underfloor insulation should run to the edge of the slab, which would be at the perimeter poles. Then, I think the foam should run vertically, down, at the outside edge of the slab, to prevent heat from leaking down from the slab, and then out, to the ground outside the perimeter of the building. So, how deep should this extend?

Now I am seeing some descriptions on GJ that indicate I need a piece of foam laid horizontally, outside the perimeter of the building, and extending away from the building, but parallel to the wall. How deep should this be, and how far should it extend away from the wall?


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[OzarkMan]

I don't know about winter/cold areas, but in Phoenix, mesh isn't normally used in concrete slab pours. I have never had cracks in any of my houses.

 

[LifeLongWNYer]

Thanks, Mesa, I WISH I was in AZ, but unfortunately.... Here, the program is both mesh and rebar. I am not a mason, but each add something, and in this area, both are needed. As I recall, it isn't so much the cracking, but what happens AFTER the crack forms. Hopefully a mason will weigh in on this. If one does, I'll make a note so I remember the next time someone asks.

Last time I was there I visited the hot sauce firm in Goodyear.... Had a ball.


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[Mancino]

Never heard of the product "Hydrofoam" you mentioned, but I used a similar product on my floor before I poured...made installing the pex super easy. It's called Crete-heat. Basically, it's 2 1/2" EPS foam with a vapor barrier on top. These sheets were 2'x4' sheets and interlocked together. I had never heard it could replace mesh or rebar, but I put mesh in anyways. My thought was it cost me $300 more to put it in. Cheap insurance for spending $4k on concrete...I can't post a picture at the moment, but check out my build thread. I have pictures there.

https://www.garagejournal.com/forum/showthread.php?t=373162

I also built a pole barn and worried about the sidewall insulation...I went down 1ft with XPS foam around the skirtboards. I should've went deeper, but $ and time prohibited me...from what I read, going to the frost line is the best depth.

 

[LifeLongWNYer]

Hi Mancino. I looked at your thread, nice building and, by the way, congrats on the baby.

Where did you place the vertical foam; inside the poles, or outside them? After you dug down and placed the foam, how much backfill did you place before you poured the concrete?

I am finding that the various contractors only want to talk about their part of the job, the framer only talks about framing, the mason only talks about concrete, and it is hard to make the parts fit together. I have talked with a general contractor, but he won't say much until I give him a deposit, I guess he doesn't want me to take his ideas to another GC.


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[Mancino]

Thanks! Quite the experience...At first I was scared to have one, but it's been great so far.

I put the foam inside the building, up against the skirtboards. Then I took the Crete-heat panels and butted them up against the vertical insulation. You'll want some backfill against the vertical insulation from outside, but you'll also have the skirtboard as your "form" so to speak. That's what the concrete guys would do if you weren't using foam there anyways. I also took small pieces of foam and wrapped it around the poles...

For the door openings, do the same thing. Then just put your form in front of that to hold it all. I put 45* cuts in my foam so the concrete would cover the top of the foam. Just make sure when you do your pex loops to stay at least 1-2' from the door opening. Concentrate your hot water loop where it's needed most.

I'm definitely no expert, but these were things I read and was told by radiant guys.

 

[Randy in Maine]

If it were me, I would stay with the standard 2" insulation under the slab and providing a thermal break to the foundation stem walls. My concrete was a 6000 PSI with fiber to minimize cracking. My slab was pretty much at grade so they did not use rebar and the purpose of the 6"x6" wire mesh was just to attach the pex tubing for the heat.

I ran several PVC conduits under the stem walls as my 1) heating hot/cold run in there, 2) one for hot& cold "drinking water" for my sillcocks, and 3) one 2" schedule 80 for the electrical feed. I have an interior wall for plumbing & electrical and they all run to there.

I will I had put some winch hooks into the floor so I could pull a dead car into the shop with winch. Might be handy someday.

 

[LifeLongWNYer]

Thanks, Randy, I am getting the idea that 2" of foam under a concrete floor is the way to go. I also like the idea of a couple of hooks in the floor, I've noted that in my list.

6K concrete is pretty strong stuff. My idea is to use 5K.


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[850xpeps]

We’ve used the foam that locks the pex in and I won’t use it again on a customers build or my own. It was a hassle to snap in and also forces you to order more cement based on the fact that Get a true 4” slab you’d be buying essentially 7” of cement plus or minus. I’ll stick to securing it to the rebar. I also think it’s a better option to actual have it encased in cement.

 

[Randy in Maine]

In the interest of full disclosure, I must admit that I was fully committed to reducing the total amount of money to keeping my home hobby shop warm and comfy during the winter here at the coast of maine. I am going to retire in a couple of years and money to keep it useable will be important down the road. My shop is only 40x28x12 (includes a 12x 28 "woodshop") but I used good Murus R-40 SIPs to make it tight and radiant floor heat to keep it comfortable even for a old fart like me. My heat source is piped in from my house boiler all of 20 feet away. Everything is nice and tight inside with serious tunes. My 6" slab is more than adequate for a lift or whatever. I prewired for a serious meat air compressor I just installed and will be adding a nice TP Tool blast cabinet because I wanted one. Figure out what YOU want and make that happen.

 

[LifeLongWNYer]

Thank you, 850Xpeps, THAT is very valuable information.



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[PWC Repair]

I did plastic vapor barrier, then foil faced foam(foil down), then 2" rebar chairs with 3/8" rebar in a 12" grid, then pex zip tied right to the rebar, then 6" of 4000psi concrete. I also suffered through lots of confusion and people giving different answers and internet searching and basically took all of it with a grain of salt and did what I thought was best.

 

[LifeLongWNYer]

Thanks, PWC, that is sounding better all the time. It appears this is an "art" and not a "science."



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[yeldogt]

The foam insulation under the slab is so you don't drive the heat into the ground -- heat flows from warm to cold. The hotter the water -- the more it wants to flow into the ground. You don't want to be heating the ground .. insulation under the slab improves slab response. The delta is greater as you move to the permitter of the slab .. so insulation becomes more important at the edges.

Water is your enemy -- must have good drainage under the slab. The basic layout has been proper stone base w/drainage if necessary -- heavy continuous plastic VB and foam. Tubing above. Any water that gets above the foam will take heat from the slab.

Proper soil conditions are very important.

Not that I think it will amount to much -- but the foil (it on the rigid foam) should go towards the heated part of the building .. reflecting up into the dwelling.

Building Science recommends the VB on top of the foam ... never understood this and never do it. I have seen it done -- VB always gets holes in it. You can't use stable method or tube holders.

Also -- having seen ants in rigid foam ... I like the idea of the plastic under the foam.

 

[climb.on]

Not that I think it will amount to much -- but the foil (it on the rigid foam) should go towards the heated part of the building .. reflecting up into the dwelling.

Radiant Barrier requires an airspace on the reflective side. Without the airspace it's worthless. A good application would be the attic side of a knee-wall in a bonus room. When you sandwich a radiant barrier between 2 things, it loses all effectiveness.