Insulation Under Concrete pad

[wmonroe]

After reading all the threads that came up in my search I still didn't find a definate answer. Do I need styrofoam insulation under my concrete pad? I will be using radiant floor heat. I don't like the idea of the concrete sitting on the styrofoam instead of the gravel. In my mind it doesn't seem as solid of a base. Can the styrofoam compress allowing the concrete to crack.
I will be putting 2" styrofoam around the outside perimeter but would prefer to not put it under the concrete.
Sorry for the confusing post , I can try and reword it if no one understands.
Thanks
Will

 

[PAToyota]

If you don't insulate under the slab, the floor heat will also heat a large chunk of earth under the structure as well.

Don't use styrofoam. You want the extruded polystyrene. Styrofoam will compress.

 

[HoosierBuddy]

"Styroafoam" is sort of a generic term that can mean a lot of things to different people. What you want to use is 2" High Density polystyrene. You have compacted stone, then a plastic vapor barrier, then the HD polystyrene, then the steel grid to tie your PEX lines to.

You don't have to use fiber in the concrete since the steel grid serves as reinforcement wire too, but I did. It was only $7 more per yard for the fiber reinforcement.

Here's the thing nobody is talking about...and I think they should be. I think EVERYONE should use polystyrene under ever slab in slab on grade construction regardless of whether they are going to use hydronic heating. My garage stayed 65 degrees even during a recent cold snap when it got down to 20 outside. That was with the hydronic loop set to 55, so it was off. Just having the polystyrene under the slab makes a HUGE difference in energy loss in the structure.

I understand your fear about putting big heavy concrete on light foam...but this is a standard building practice...and in my opinion a VERY GOOD one.

It cost me right at $1.00 per square foot for the 2" polystyrene. WELL WORTH IT!

Phil

 

[wmonroe]

Is the 4'x8' sheets of blue "foam" they sell at lowes polystyrene? And yes I do plan on putting a 6 mil plastic vapor barrier on top of the stone.
Will

 

[BowtieNut]

I put the 2" type 250 under my entire slab. From what I've been told, type 250 is rated for under a slab, type 150 is not. It all looks about the same to me, but the 250 is supposedly denser. When I got mine last year it was right about $20 per 4x8 sheet at the local building supply. Around here the type 250 is pink or yellow, and the type 150 is blue, but I don't know if that really means anything or not.

Also, I didn't put any vapor barrier down under the slab either. I was told that I didn't need to because the soil is so sandy. This was all just information given to me by the local radiant "experts" where I got all my stuff (except the 2" insulation), so if everyone else says you need the vapor barrier, then take my experience with a grain of salt.

 

[HoosierBuddy]

Is the 4'x8' sheets of blue "foam" they sell at lowes polystyrene? And yes I do plan on putting a 6 mil plastic vapor barrier on top of the stone.
Will

Probably normal polystyrene. You want the high density. Lowes might sell it. I got mine from the concrete company. They sold me the special PEX reinforcing wire too. The color is more an indication of the manufacturer I think. All owenscorning is pink. I think all dow is blue. Mine was blue in any case.

Phil

 

[wmonroe]

Probably normal polystyrene. You want the high density. Lowes might sell it. I got mine from the concrete company. They sold me the special PEX reinforcing wire too. The color is more an indication of the manufacturer I think. All owenscorning is pink. I think all dow is blue. Mine was blue in any case.

Phil

By "special pex reinforcing wire" do you mean remesh or is there something else needed with the pex?
Thanks for all the replies
Will

 

[HoosierBuddy]

By "special pex reinforcing wire" do you mean remesh or is there something else needed with the pex?
Thanks for all the replies
Will

What they sold me was a heavy wire mesh that was supposedly designed for installing pex. It came in flat 4 X 10 sheets rather than rolls. It was pretty heavy gauge. Again, the concrete company supplied that. Now that I think about it, they did have to special order both the HD polystyrene and the mesh.

 

[BowtieNut]

It seems like everyone always recommends the wire mesh, but when I did mine, I just stapled the pex to the 2" insulation. I haven't heard of anyone else doing this, but that's what was told to me by the place that sold me all of my radiant hydronic stuff. They are just plastic U-shaped staples that look like they were made for this. It seemed like it worked pretty good for me. I'm not saying it's better, we definitely had to be careful when we were doing the cement so we didn't rip the tubing out of the foam/staples. Just another option I thought I'd throw out there.

 

[wmonroe]

I've also been thinking about putting the pex below the remesh instead of on top of it. Just to give me a little more room when making the control cuts.
Will

 

[FarmerSid]

I agree 100% with HoosierBuddy. What I did was use discarded exterior door cutouts. The piece that is cut out when installing a window in. A picture is attached. It cost me $350 cash CDN to cover my floor cpmpared to $2100 taxes included to use styrofoam SM. SM is R10 where the door panels are R15. I would use vapour barrier to prevent the floor from sweating in the summer. It will be damp if you don't. I would also use the mesh for a couple reasons. On the mesh I used, the squares were 6" square and came in 4'X8' sheets. It was recommended to me to come in 12" from the outside walls with the PEX then separate the PEX by 6" and then go back to the 12" spacing through out the floor. The 6" spacing was to get a little more heat to the colder area's of the floor. WIth that said, the mesh made laying out the PEX MUCH easier. Just follow the mesh. The other reason is since the PEX is tied to the mesh, you can just lift the mesh with the PEX attached to it to the center of the pad when pouring the concrete floor. JMO

Cheers!

Sid

 

[FarmerSid]

Here's a pic of the door panels that are cut out of the type of door that is seem in the pic.

Cheers!

Sid

 

[GreenInsulation]

The superior way to insulate under concrete is with the BARRIER. It is a product made for this application. It comes in a roll with patented self sealing tape on both sides for 99% moisture control, vapor control, radon resistor, thermal control all in one product that will not break under concrete allowing for moisture to crack your slab. Excellent for radiant slabs and also for a underlayment for floors also. It is available in 3/8", 3/4" and heavy duty 1 1/4" thickness. Factory direct shipped. The Barrier is made with recycled material so is a GreenInsulation Product. for more info see it on www.barrett-inc.com or call 877 904 8424

 

[69Cat]

I'm prepping for my heated floor and have a couple of questions:
1. Is it common to glue the seams of your poly when overlapping it like when doing walls?
2. Is there any point to glue the seams of the insulation boards?
3. What would the befit be of lifting the PEX to the center of the concrete when being poured? Why not just leave it lay on the insulation at the bottom of the slab? I am going to use rebar midway through the slab so won't need to lift a layer of wire mesh/tubing to provide the reinforcing.

Seems to me that leaving the PEX at the bottom of the slab would be better since you have the thickest layer of concrete possible rather than having tubing crossing mid way through the depth of slab.

 

[5wndwcpe]

I just did my floor two months ago and I didn't glue the overlapping edges of the poly but I did tape them. I used Stego wrap which is a 15mil. vapor barrier, very tuff stuff.

I thought about gluing the seams of the EPS but decided against it as the weight of the concrete is just going to push down on it anyway. If the vapor barrier is doing it's job, the glued joints really offer no advantage.

I stapled my PEX directly to the EPS, then used 1.5" slab bolsters, criss crossed re-bar on those and topped it off with wwr. This put the tubing at the very bottom of the slab and the bolsters kept the re-bar from laying on it and the welded wire allowed the concrete finishers to walk all over it without damaging the tubing. Overkill? Yeah, probably, but I slept well that night.

Here's the thread of my build, check pages 7 & 8
http://www.garagejournal.com/forum/showthread.php?t=13286&page=7

 

[ScaldedDog]

5wndwcpe, how much are those slab bolsters? I looked at the link, but surely they aren't $300 for five feet, are they?

NICE work, BTW.

Mark

 

[Ford GP]

I used the bubble foil product sold at lowes to do our basement. I can't say for sure how well it actually insulates. It is generally pretty tough and even where it was stepped on by the concrete guys, it still provided an air gap, and the weight of the concrete is probably not as concentrated as the foot of one of the workers. What are your thoughts on this product?

As for the walls, we installed corrugated plastic sign material around the whole edge of the floor/wall joint with the corrugations running vertically. The thought was that if there is any water coming in through the walls, it would have a clear path to flow through the corrugations to the drain pipe set below. As it turned out, the concrete shrunk enough that there is even a gap between the concrete and the sign material so now I have to caulk it. I suppose the 1/4" air gap of the signage will provide the insulation from the wall.

 

[5wndwcpe]

5wndwcpe, how much are those slab bolsters? I looked at the link, but surely they aren't $300 for five feet, are they?

NICE work, BTW.

Mark

Thanks ! The slab bolsters were .40 per foot. It did add to the overall cost, but IMHO was well worth it. The kept the re-bar up and protected the tubing. What I did was run them end to end (wire tied to each other) and cut them with a pair of bolt cutters where the tubing crossed under them ( as in the turns) If the cut end of the bolster was a little too close for comfort, I cut a piece of 3/4" PEX about 1.5" long and slit down one side. I wrapped this around the 1/2" PEX to protect it should the slab bolster shift at all.

 

[5wndwcpe]

I used the bubble foil product sold at lowes to do our basement. I can't say for sure how well it actually insulates. It is generally pretty tough and even where it was stepped on by the concrete guys, it still provided an air gap, and the weight of the concrete is probably not as concentrated as the foot of one of the workers. What are your thoughts on this product?

As for the walls, we installed corrugated plastic sign material around the whole edge of the floor/wall joint with the corrugations running vertically. The thought was that if there is any water coming in through the walls, it would have a clear path to flow through the corrugations to the drain pipe set below. As it turned out, the concrete shrunk enough that there is even a gap between the concrete and the sign material so now I have to caulk it. I suppose the 1/4" air gap of the signage will provide the insulation from the wall.

Well Ford, I hate to break it to you, but I haven't heard anything good about that stuff except from the guys who are selling it. I don't think it will hurt you though. Some internet radiant sites even recommend you don't insulate the center of the floor, under the slab at all. The theory here is the earth will act as a heat sink. And I'm sure it will. Why you would want to contribute to the global warming of China is beyond me.

Far more important is that you insulate the edges of the slab as well as the outside of the foundation, down to the footer if possible.

 

[69Cat]

Geez, that is a lot of steel in there 5window! In my mind that would be the right way to do it. I like the idea of slab bolsters (haven't seen them before) as that is a problem I still have to solve but they seem kind of pricey. Normally I would just drive in rebar pegs and tie the bar to the pegs but the insulation prevents me from doing that. Maybe some 2 inch angle iron cut into 1 inch long pieces and laid with the V upside down and a lot of stick welding to hold them under the rebar - hmmm.

 

[5wndwcpe]

Geez, that is a lot of steel in there 5window! In my mind that would be the right way to do it. I like the idea of slab bolsters (haven't seen them before) as that is a problem I still have to solve but they seem kind of pricey. Normally I would just drive in rebar pegs and tie the bar to the pegs but the insulation prevents me from doing that. Maybe some 2 inch angle iron cut into 1 inch long pieces and laid with the V upside down and a lot of stick welding to hold them under the rebar - hmmm.

You could do that but my concern would be that the angle iron, only being 1" long, would tend to sink into the EPS. Yes, I probably spent about $2k on the steel in my slab, but I figure it like this:

A. I only have one shot at this.
B. More steel can't hurt anything but my wallet.
C. If the floor develops a problem, such as the PEX is
damaged or a severe crack surfaces, I'll have to live
with it and I've spent far too much money on this
project to be unhappy with it.

 

[69Cat]

Yup, I know what you are saying - there never is a good place to cut corners. I figure that the slab bolsters would only cost me a couple hundred bucks on a floor that will run quite a few thousands of dollars. They do have a number of design advantages over what I could fab up at home. I'll give them some more thought.

 

[GreenInsulation]

The Barrier, extruded expanded polystyrene is 100% waterproof and vapor proof, seamless and specifically designed for under concrete and radiant heating applications. It does not break when walked on, cost effective and is shipped direct to job site. can be seen on www.GreenInsulationProducts.com

 

[tdkkart]

The Barrier, extruded expanded polystyrene is 100% waterproof and vapor proof, seamless and specifically designed for under concrete and radiant heating applications. It does not break when walked on, cost effective and is shipped direct to job site. can be seen on www.GreenInsulationProducts.com

GO AWAY SPAMMER!!!!

 

[Ezzie]

I was just at a hydronics product fair this morning and was speaking with a company that sells under slab insulation products. Couple of things they said that I was unaware of were:

6" of crushed stone has an R value of 3.5 - usually taken into consideration when doing the heat load calculations.
Using a foil radiant heat reflective type of product is useless if the foil is placed directly against the concrete.

Apparently there are no industry standards in place yet to help the construction industry specify or set standards for radiant in-slab design - this is why there are so many different theories and products that are currently being peddled - some effective and some not so good.

 

[GreenInsulation]

Kuddos Ezzie for helping to set the record straight on reflective foil under concrete! AS a major distributor of reflective foil we always are trying to educate people about NOT using foil underground and using the Barrier instead (see above) . We have studies to back this up if people are interested.

 

[ScaldedDog]

Contractor Magazine ran a test of various products for use under slabs in snowmelt systems. A description of the test can be found here, and the results are here. For those who don't care to read, 1" of XPS foam won, and Barrier, Insultarp, bubble foil and all that other stuff wasn't close.

Unless one of these vendors hawking their junk on here cares to refute this with a documented, third-party funded and performed study, I don't believe a word they say.

I'll be using 2" of Owens Corning 250 under my slab and driveway.

Mark

 

[5wndwcpe]

...

I'll be using 2" of Owens Corning 250 under my slab and driveway.

Mark

That's the ticket.

 

[GreenInsulation]

Mark, as you are aware temp differencial is not only vital element to look at. Having a product that resists moisture, is radon resistant ,as well as thermal barrier all in one . If you want equal temp differencial please try the Barrier X5 which is 1 1/4 thick.

 

[DIY Man]

I have used 2" XPS many times but if you want to get a thermal seal as well as a condensation and radon barrier, you must also install plastic sheeting befor the 2" XPS. I recently started using a product by Ecofoil.com called Ultra Under Concrete Barrier. It is a new version of the Foil/Bubble insulation that has foil in between the bubbles. We di a test between 2 of our spec houses and it performed very well considering how thin and light weight it is. The 2" XPS held in only a few degrees of heat loss to the ground below. Considering the ease of installation and great cost savings, the Ecofoil Ultra Under Concrete Barrier is our new insulation of choice.

 

[walrus]

I have used 2" XPS many times but if you want to get a thermal seal as well as a condensation and radon barrier, you must also install plastic sheeting befor the 2" XPS. I recently started using a product by Ecofoil.com called Ultra Under Concrete Barrier. It is a new version of the Foil/Bubble insulation that has foil in between the bubbles. We di a test between 2 of our spec houses and it performed very well considering how thin and light weight it is. The 2" XPS held in only a few degrees of heat loss to the ground below. Considering the ease of installation and great cost savings, the Ecofoil Ultra Under Concrete Barrier is our new insulation of choice.

That stuff is joke

 

[bimmer1980]

a few people have asked what the benefit is to having the pex tubes in the middle of the slab. the answer is simple heat transfer. The part of the tube that is laying right on the insulation is attempting to trasfer heat to the insulation. THerefore, it is not as efficient at transferring the heat from the fluid, thru the tube and into the concrete.

By having the tube in the middle of the slab, it will evenly transfer heat to the concrete and the warm concrete will radiate the heat into the air of the space (garage, etc).

For the record, heat does not rise!!! heat merely moves from a hotter area to a colder area. now, air on the other hand, will rise when it is warmer than its surrounding due to it being less dense.

As far as insulation properties go, it all comes back to the thermal properties of the material. Fiberglass is only good if there is no air movement. that's why the foams are much better--they are solid and do not allow heat transfer by moving air. THe bubble product is only going to add minimal insulation value. the air will move around in each bubble and transfer heat from one side to another. Granted, it might be minimally better than no insulation at all, but it can't compare to true insulating materials.

 

[Racecarl]

I am also in the throws of prepping for a shop floor (24X30). I started with a fairly level compacted subgrade. I then added 6" of pea gravel, which I compacted with a plate ******** in 3" lifts. The floor perimeter got 2" of gravel, followed with 2" of high density extruded polystyrene (the 250 stuff, 4X8 sheels laid lenthwise), and topped off with 2" of pea gravel. After compacting the entire floor with the plate ********, I intalled a 10 mil reinforced plastic vapor barrier.

The next layer is 6X6 #10 re-mesh. The mesh is tied to a grid of 1/2" rebars on 4' centers. I didn't like how the mesh sagged between the 1/2" rebar grid, so I added 3/8" rebars between the 1/2" bars. I used what seemed like a million wire rebar ties, tying the mesh to the rebar at least every foot and every place where the rebars cross. I have the rebar grid sitting on old bricks, which places the highest point of the grid 3.5" below the finish level of the floor.

I will be using 1/2" PEX in three 'zones'. The PEX tubes will run mainly lenthwise (30') with bends of a radius of no less then one foot. I experimented with several configurations on the computer and decided to make 8 runs, which will result in the 1' spacing that seems to be recommended most.

I finished with the concrete reinforcement tonight and will begin laying the PEX soon. I have done all the work myself so far, but I will hire a contractor buddy to pour the floor for me. He has a crew and they know what they are doing. They also have a power trowel. I want this floor smooth and level.

I'll try to borrow the wife's digital camera and post some pics.

 

[GreenInsulation]

Insulation under the slab should be about keeping the heat in the slab, keeping the moisture out of the slab, the radon out of the slab, and preventing cracks in the slab. Having a product that will help with all aspects is adventageous and one that also is a radiant tube grid holder is an additonal plus. Crete-Heat is a modular panel that is 2 inch EPS foam so it does not loose R value as it ages like XPS foam does, has a shiplap panel design for moisture control and saves up to 2/3 of the labor time. Don't let the heat slip thru the cracks! if you want to see a pic of it look at www.GreenCoolingAndHeatingStore.com

 

[Bigrhamr]

Insulation under the slab should be about keeping the heat in the slab, keeping the moisture out of the slab, the radon out of the slab, and preventing cracks in the slab. Having a product that will help with all aspects is adventageous and one that also is a radiant tube grid holder is an additonal plus. Crete-Heat is a modular panel that is 2 inch EPS foam so it does not loose R value as it ages like XPS foam does, has a shiplap panel design for moisture control and saves up to 2/3 of the labor time. Don't let the heat slip thru the cracks! if you want to see a pic of it look at www.GreenCoolingAndHeatingStore.com

Can you provide facts on how XPS under concrete ages and loses R value?

 

[Dragster Racer]

Can you provide facts on how XPS under concrete ages and loses R value?

I thought I read that it will stay in a landfill for something like 5000 years.
I will say that the roll out stuff will avoid the voids under it. But my pex manufacturer didn't recommend it. They still say 2" foam.
I stapled to it, and layed mesh over it. I don't think the roll out mesh is a good idea since you have to be so careful to flatten it out.

 

[GearBeer]

I used the rolled mesh and it worked out fine. I definitely had to spend some time flattening it out but I'm willing to do that to save a few bucks. It also fit more conveniently in my Caravan.

 

[DIY Man]

Sounds like someone doesn't fully understand the different modes of heat transfer.

 

[DIY Man]

That stuff is joke

Sounds like someone doesnt understand the different modes of heat transfer.

 

[Bigrhamr]

Sounds like someone doesnt understand the different modes of heat transfer.

Why don't you explain them? Are you by any chance a shill for one of the companies hawking the bubble wrap?

I did my own informal test of bubble wrap vs. 2" foam last winter. Laid a 4'x8' sheet of owens corning 25psi on the ground and a 4'x8' piece of double bubble wrap insulation next to it, piled a little dirt on top of both to hold them down flat. After a week of temps on the teens I pulled them both up. Under the bubble stuff the ground was frozen solid just as the surrounding dirt was. Under the 2" foam it was only frozen around the perimeter with decreasing frost towards the center which was frost free. Seems pretty clear to me.