radiant floor insulation

Harvey_5

I read in a slant/fin manual about the stress cracks,

but I think our ideas
differ a little being from different states, in a normal
basement here in wisconsin concrete is poured up to the
outside wall, I have never seen a builder let a slab float
in a basement. We also do not put the tubing under the
mesh, or at least I don't, we strap it to the top of the
mesh so it can be picked up and placed near the center of
the floor. Like I said, we obviously have different
ideas, both seem to work well, I simply questioned the
floating slab idea.

smoore

insulation

THE BUILDER THAT I'M DOING A RADIANT JOB FOR WANTS THE BASEMENT SLAB TO SIT ON THE FOOTING SO HE WANTS ME TO STOP MY INSULATION ABOUT A FOOT BACK FROM THE FOOTING SO THIS LEAVES ABOUT 2 FOOT NOT INSULATED. IS THIS THE NORM AND WITH OUT A THERMAL BREAK HOW WILL THE HEAT NOT GO STRAIGHT TO THE GROUND? I'M USING 2 INCH POLY AND THOUGHT ABOUT INSTALLING R-FOIL OVER THE FOOTINGS.

THANKS FOR ANY HELP

John Felciano

Insulation

without some kind of thermal break between the floor and the footings there will be high heatloss.Any thermal break is better than none so sometimes we use thin foam simular to what the fraimers use bewteen the sill plate and the foundation (sill seal).

With insulation the more you put in the less the heatloss.Two inches is prefered but sometimes you just can't get it in.

One other thing,Turn off your caps lock key when making posts.It makes it much easier to read and when we do write in all caps,here in cyber space,it's equivilent to YELLING.



To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"

Al Letellier

radiant insulation

I agree about the need for insulation at the footing. We general have the contractor grade 2" below the top of the footing and use 2" foam board butted to the footer, even with the top. We then use 1" board and overlap the top of the footer. Don't forget sideways heat migration as well. We install 1" up to the floor level against the wall. Taper the insulation so the concrete slab actually touches the wall at the very top surface. The point is that the entire slab should sit in a "bowl" of insulation. Keep the heat in the slab, not the foundation.

To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"

Harvey_4

Bowl of crete

I understand your reasoning on running the 1" foam up the
wall, but aren't you creating a floating slab that way?
Most of the articles I read warn of concrete shifting and
causing stress cracks in the pex tubing. I am in no means
doubting your installation, I'm just curious what happens
when the concrete shifts

Rock Solid Restoration_3

basement slab

Slab shifting where? Down relative to the footing causing a shear fracture? Shrinkage cracks? I've never heard of the pex cracking. I can't even imagine it cracking.

Anyway, the entire radiator (the slab) should be surrounded in insulation. If the concrete is properly reinforced, cracking (other than hairline shrinkage cracks) should not be an issue.

Rock Solid Restoration_3

I've never heard of pex cracking from shifting concrete. Where did you read these articles?

I can't even imagine pex cracking due to anything other than a severe structural crack in the concrete. Copper yes, pex no.

I think the entire slab should be surrounded in insulation. If it is properly reinforced, there shouldn't be any cracks other than hairline shrinkage cracks.

hot_rod

If the

foam you are using is rated for the proper psi loading, then I would at least run it up to the footing. Going over the footing will lift the slab an inch or whatever the foam thickness. This may be upsetting the builders elevations?

Actually in a basement wall application, 8 feet under ground I wouldn't worry about that much loss at the bare footing detail.

Slab on grade is the one to really watch edge and footing loss.

Maybe compromise at a 1/2" foam layer over the footer, 1" elesewhere. Again make sure it is at least 25 psi rated underslab approved foam. This will address the loading issues from a code standpoint anyways.

hot rod

Jim_19

RADIATION vs. CONDUCTION

"in a normal basement here in wisconsin concrete is poured up to the outside wall, I have never seen a builder let a slab float in a basement."

Yes, that is fairly universally true.

"We also do not put the tubing under the mesh, or at least I don't, we strap it to the top of the mesh so it can be picked up and placed near the center of the floor."

The tubing needs to be in the center of the slab. Your method works as long as the crew is careful about always picking it up as the concrete is poured. There are also cradles or supports that can be placed under the mesh. Your concrete supplier can show you what I mean. They tend to be more reliable because no one needs to pick up the mesh, it's already where it belongs.

The important part is that once the slab has been heated, you want the heat RADIATED from it upwards, not CONDUCTED downwards or sideways into the ground or the foundation wall. The insulation serves as a thermal break. Since the slab weighs many tons, it's not really "floating". It's just not CONDUCTING heat away.

Rock Solid Restoration_3

Harvey:

What do you mean by letting a slab "float"?

Can you tell me what manual you read that in because that is causing me some concern. After all, all concrete WILL crack, it is a matter of physics. But to think that this could cause pex to crack makes me wonder why I am using pex at all.

As far as putting the tube down, and then the wire. Usually, I will set my wire or rebar on top of wire supports to keep it off the ground and then tie my tubing to the wire like you said.

In this case, I didn't have any supports, so I thought I would be real slick and use my tubing as the support.

I know a lot of guys will pull the wire up as they pour. To me, that is a joke. To think that you will remember to pull up all the wire as it is being walked on during the chaos of a pour AND getting it where it is supposed to go does not happen in reality. Use supports first, like Jim said.

By the way, the picture is from my basement. I poured it flush with the top of the footing, to give me a little more head room.

Jim:

Why does the tubing have to be in the center of the slab? I don't see how that could make any difference except possibly affect the responsiveness of the slab.



Thanks,

Craig

Mark Eatherton1

Tube in the middle of the slab...

is a dream unless you have chairs 12" OC.

They have yet to come out with a concrete placer/finisher that can flap his arms hard enough to keep his clod hoppers from stepping on the tube/steel which generally puts it on the bottom of the slab.

In every case I've had the opportunity to see the tube after the fact, it is ALWAYS on the bottom. The best we can hope for is complete encapsulation.

And yes Craig, it affects response time...

ME

Rock Solid Restoration_3

Pardon my ignorance but what is the big deal about response time. Do you really have the need to change the temperature that quickly and frequently?

Also, isn't it more a function of how close the tubing is to the top of the slab and not how close it is to the middle of the slab.

i.e. The tubing at the bottom of a 4" slab is basically the same distance from the top of the slab as the tubing in the middle of an 8" slab.

Rock Solid Restoration_3

Pardon my ignorance but what is the big deal about response time. Do you really have the need to change the temperature that quickly and frequently?

At least when you put it at the bottom of the slab, it is the same distance from the top of the slab everywhere. When it is pulled up during a pour, the guy is not measuring where the tube is. It could end up near the top in some places, the middle in other places, and the bottom in other places.

Also, isn't it more a function of how close the tubing is to the top of the slab and not how close it is to the middle of the slab.

i.e. The tubing at the bottom of a 4" slab is basically the same distance from the top of the slab as the tubing in the middle of an 8" slab.

Rock Solid Restoration_3

Pardon my ignorance but what is the big deal about response time. Do you really have the need to change the temperature that quickly and frequently?

At least when you put the tubing at the bottom of the slab, it is the same distance from the top of the slab everywhere. When it is pulled up during a pour, the guy is not measuring where the tube is. It could end up near the top in some places, the middle in other places, and the bottom in other places.

Also, isn't it more a function of how close the tubing is to the top of the slab and not how close it is to the middle of the slab.

i.e. The tubing at the bottom of a 4" slab is basically the same distance from the top of the slab as the tubing in the middle of an 8" slab.

When I use chairs(actually the ones I use are called slab bolsters with runners)I put them about 2' apart and I use heavy 4 guage wire mesh and when tied to the chairs becomes very rigid but still we are very careful to step just where the chairs are when we pour.

Rock Solid Restoration_3

I just had another thought regarding slab cracking.

You are way less likely to have a crack in the slab if it is totally separated from the wall and footing with insulation than if it is sitting on the footing and therefore bonded to the footing so that when it shrinks the edges can't move.

hot_rod

step on a crack, break your mothers back

I agree with Craig on lifting wire and tube to the middle of a pour. Ever try that! Any yes the risk of lifting too much far out weighs leaving it where it lies, near the bottom.

As you lift mesh and tube as the mud flies down the chute the force of that concrete will keep lifting till the tube ends up near the surface, way too risky, in my opinion.

The only sure way is lots of chairs, or tying to rebar every foot to foot and a half. Then place the rebar on chairs. This is fairly common in commercial work where thew slab is structal for heavy equipment loading. As rebar at the bottom of the pour is also useless

Siggy did some modeling of tube depth, try this link.http://www.pmmag.com/CDA/ArticleInformation/features/BNP__Features__Item/0,2379,3185,00.html

I also like the idea of the slab disconnected from both the walls and footers. The edge band insulation allows some expansion movement and helps prevent what the industry calls external restraint cracking. This happens when the slab is contained inside 4 concrete walls, and has no place to move when the radiant warms the mass. This is also why expansion joints were used. Rarely see them in residential work anymore, however. Not even driveways or sidewalks.

Most concrete guys just saw cut for "crack control" Yet another tricky practice with tube in the slab that has been pulled up!

hot rod