Quick question before the slab pour....

[Randy in Maine]

40' x 28' garage/woodshop. Radiant floor heat. Slab will be 5" thick of 4000 psi fiber concrete.

I was planning to use a 6 mil poly vapor barrier under the slab with 2" of Dow scoreboard foam on top of it. Wire mesh to attach the 3/4 PEX.

I ran into this Slabshield stuff the other day. They claim it takes the place of the vapor barrier and the 2" foam.

http://www.low-e.com/products/products_view.php?Product=SlabShield

Thoughts?

Thanks!

 

[tdkkart]

Use the foam........

 

[Dave28]

What is the R value of the Slabshield? I used 6mil vapor barrier, 2" Owens Foam, wire mesh and attached tubing to the mesh. Someone recommended using the aluminum bubble wrap instead and when I checked the R value is was only R1.1. With the foam I have R10. I just finished my pour Friday and have not finished hooking up the water to it yet. I got the Viper vapor barrier and clips from http://www.insulationsolutions.com/products.html

 

[CARS]

I didn't use a separate vapor barrier. I just taped the 2" foam with that red, very sticky, house wrap tape.

 

[Randy in Maine]

Thanks for the replies.

I just got off the phone with my concrete guy and he told me to use the Slab Shield. He tells me that it provides the needed thermal break between the slab and the ground just fine, that it "reflects" the heat back into the slab better, and provides the needed vapor barrier all in one. Also important to him, is that because there is less compression of the foam (from 2" to 1/2"), so that it will be easier to control "concrete cracking" over time even with the "cut slots" he is going to be cutting in + the fiber in the concrete. He still wants the 2" foam (cut at a 45º angle) at the intersection of the load bearing wall footings to the slab floor.

I guess I will give it a try and see how it holds up. I will post pictures of the intstall.

I did spin over to "insulation solutions" and bought 500 of the little clips that hold the 3/4" PEX to the 10x6x6 wire though for about $50. They look like money well spent.

 

[Charles (in GA)]

Do a rebar grid on "chairs" you will get a much better reinforcement, fiber is a joke (or a scam, not sure which).

Charles

 

[stingry]

Thanks for the replies.

I just got off the phone with my concrete guy and he told me to use the Slab Shield. He tells me that it provides the needed thermal break between the slab and the ground just fine, that it "reflects" the heat back into the slab better, and provides the needed vapor barrier all in one. Also important to him, is that because there is less compression of the foam (from 2" to 1/2"), so that it will be easier to control "concrete cracking" over time even with the "cut slots" he is going to be cutting in + the fiber in the concrete. He still wants the 2" foam (cut at a 45º angle) at the intersection of the load bearing wall footings to the slab floor.

I guess I will give it a try and see how it holds up. I will post pictures of the intstall.

I did spin over to "insulation solutions" and bought 500 of the little clips that hold the 3/4" PEX to the 10x6x6 wire though for about $50. They look like money well spent.

Bad advice in my opinion. First of all, the slab does not radiate heat into the ground, it travels by conduction. Secondly, the foam does not compress into a 1/2 inch thickness, it compresses very little if any at all!! Personally, I would use the foam, it is the standard for radiant heat floors and you ONLY GET ONE CHANCE to do it right. Do your own reaearch and do not rely on the advice of your "concrete guy", he is just that, a concrete guy not a radiant floor heat expert.


Cheers
Steve

 

[rburke65]

I think this guy is selling.......sold......you a large smelly load. Been on this site and countless others reading on radiant heat, insulation, vapor barriers, thermal breaks...on and on. NEVER have I read anyone recommending a product such as this......unless it's the guy selling it, or the "concrete guy" that doesn't want to fool with this the foam board and the wire. Me? I'd vote "No". IMO. Good luck.

 

[tdkkart]

I can tell you, from my personal experience, that you definitely want insulation under your slab, at least a single layer of R10, and maybe more if you can swing it. A 1/2" layer of bubble wrap with tinfoil or any other coating on it IS NOT the same thing, period.

I need to do some calcs and figure out just exactly what my system is doing, but I have a side-by-side example of what with/without insulation will do for you. Basically I have 1/3 of a 30x40 pole building without insulation under the floor(done by the previous owner), and 2/3 with insulation that I did. It cost me as much to heat 1/3 the first year as it does to heat the whole building now. This year I'm running an experiment, I think I can cut my bill by 50% without losing much comfort at all, we'll see, so far it's working fine.

 

[queenbee]

I just did my floor this summer and used a product called crete-heat, i used the 2 inch stuff, it comes with a built in vapor barrier and you don't need wire mesh or staples, my concrete guy said he's never seen the stuff and when he was done pooring the floor he's going to reconmend it to people who want to use radiant floor heating, he loved how he didn't have to worry about the concrete getting in between the normal foam sheets.
It seem expensive when you price it out until you add the wire mesh, staples, and tie wraps to a normal instilation

 

[jtshusker]

lol right

 

[walrus]

I'm in Maine, if you want your slab to be insulated you best use 2" of foam under it and not some scam bubblewrap ****. I have 2 inches under my slab, been there for 3 years now, guess what, no cracks

 

[Randy in Maine]

Thanks for the comments!

I think I will go back to "Plan A" (the poly and the 2" foam) since it is tried and true. I have not bought anything yet.

My goal here is to keep the yearly heating costs (running propane and a condensing boiler) to about what I am paying now (500 gallons of propane @ $3 a gallon). The plan is to keep the new garage at about 50º or so from December till March.

This project really has three phases to it...

1. The new garage/workshop that uses the 6 1/2" SIP panels.
2. Running radiant heat to the existing 24' x 32' existing single story house in the unheated crawl space and attaching it to my 2x 6 floor joists. I heat this house with a fake woodstove 28K BTU that runs on propane + my on demand propane hot water Rinnai.
3. Running radiant floor to the existing 14' x 22' 1 car garage (to make it sort of a "bonus room" for my wife to do her stained glass in).

That #3 phase may be a better use for this sort of stuff as I will be installing the heat/new floor over the existing concrete floor.

I will post some pictures when it all happens.

 

[Randy in Maine]

I will just continue this thread to keep it all together.

The footings are ready to go in and the stem walls will happen shortly. The guy actually doing the concrete work wants to delay pouring the garage floor until the SIP garage goes up...roofed, doors and windows...to avoid the potential for frost damage to the floor. Should be about Jan 25 or so. I don't have a problem with that.

My plan is to use 2" thick foam between the stem walls and the 5" of floor to give me a thermal break between the two. I could run them the whole 4' to the footings or just a foot or so. Got any thoughts on that? It will get backfilled a few days after the stemwalls and I want to deal with that while it is all open.


I was planning on cutting them at a 45º where it meets the stemwalls. Sound reasonable?

 

[SportFury59]

Regarding what to put under the concrete and how thick, wouldn't the building inspector tell you what you have to do? I know when I started my garage a few years ago the guy told me exactly what the requirements were. (I decided against the floor heat). When it comes to energy use they're touchy on that. Some areas may differ.

 

[rkstr]

I didn't use a separate vapor barrier. I just taped the 2" foam with that red, very sticky, house wrap tape.

Where do you get that House Wrap Tape? Any specific brand name?

thanks

 

[Highbeam]

Right next to the rolls of hosue wrap you will find rolls of house wrap tape.

The concrete will not compress the foam as even a 6" lift of concrete only weighs 0.5 psi and the foam is rated at 25psi.

The yahoo need not worry about blowing concrete under the foam. The mesh does a nice job of holding it down and proper concrete placing techniques do not BLAST the subgrade. This is probably why he wanted you to use the scam rolled insulation. He was imagining the foam pieces floating away.

 

[dirttracker18]

I didn't use a separate vapor barrier. I just taped the 2" foam with that red, very sticky, house wrap tape.

Same, I often see claims on here to use poly first but taped foam board is a VB so I dont see the need.

That being said, 6 mil poly is cheap so if it makes you feel better . . .

 

[dirttracker18]

Where do you get that House Wrap Tape? Any specific brand name?

thanks

Commonly called Tuk tape around here but that is a brand name.

What you are looking for is sheathing tape, usually red and semi transparent and damn sticky so put it on right the first time.