Radiant floor vapor barrier and placement of PEX tubing

Tom Manton

Staple down systems are ok, what I don't like about them are staples don't get a good purchase in foam and a worse one in an insultarp. I don't want the tubing getting loose during a pour because is will invariably float and come to the surface, one nick fron the trowel, you can guess the rest.

If the tubing does get loose you'd have better have one person stand there and make sure it stays in the pour, not worth it in my opinion. There are many ways to approach building, after hundreds of flatwork pours I'm telling you what works best for me. We rarly do any flatwork anymore without tubing.

As for fibermesh, I personally don't care for it, we've done lots of it. I feel it's a down and dirty way to save some labor for the most part, my septic tank supplier uses it in his tanks but he also pours high strength mixes. It can sometimes make polishing a slab a challenge.

I use steel, I like to tie my tubing to it, I know it's not going anywhere in the middle of a pour, it makes for easy tubing layouts. Maybe I'm strange but I don't look for the fastest or easiest ways to build, I look for what works for me on a consistent basis to give me a quality product.

Adam Greisz

Radiant floor vapor barrier and placement of PEX tubing

I am installing a radiant heating system in a concrete slab for the first floor of a two story house. I am trying to understand where to place the vapor barrier. In the past (before I became the decision maker) I have placed the vapor barrier on top of the cappillary break backfill. We then installed 2" of R-10 insulation and wire mesh as structural reinforcement (local building standards). We tied our PEX tubing to the wire mesh. My problem with this method is the 6 mil visqueen is on the the cool side of the insulation.

Now, my heating contractor tells me that he prefers to use staples to hold the PEX to the 2" insulation. Then we put the wire mesh (or rebar) over the top. This elimates the issue of the mesh curling and bringing the PEX to the surface of the concrete.

My questions are;
1. Where is the proper placement of the vapor barrier? The JLC Guide to Moisture Control discusses the controversy between builders who resist using any vapor barrier and the ones who claim it is necessary. The Guide does not discuss sub slab vapor barriers in a heated floor application.
2. Is it OK to place the PEX tubing directly on the insulation board? It makes sense that it will not get too close to the surface and it holds the slab reinforcement at the proper elevation.

I appreciate any insight that you might pass on.

ScottRW

Adam, I thought I replied once but didn't see my message , so I'll try again.
Assuming your pouring a 3-1/2" to 4" slab: Stay away from the wire mesh. Too difficult to deal with. Staple the tubing to the insulation. Install rebar over the tubing. The rebar will help hold everything down until your concrete crew arrives. In our area, (North Idaho) our inspectors allow us to use Tyvek Tape, or some type of plastic tape on the seams of the 2" rigid insulation. This meets the requirement for the vapor barrier. Cheaper and probably lasts as long as 4 mill plastic under the slab. Check with your code officials before trying this.

singh

a slight

boost in fluid temps and/or closer tubing on center spacing may be needed when tubing is on bottom.( 9".o.c instead of 12" o.c) And slightly longer recovery.
However, I've notice more even surface temps, with no stripping effect, which you may have when tubing is closer to top.
Not so important in a garage, but a finsish floor with foot traffic , even surface temps is nice. You may also want to try counter flow pattern with tubing layout.

As far as the insulation, the taping of the seams, and tight cuts around penetrations will act as a vapor barrier, but it won't hurt to put 6 mil plastic under insulation.
You could also do two layers of insulation 1" o.k and stagger the joints, if you want two layers of 2" for a R-20 sure is nice!

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Chris S

reinforcing wire (WWM)

If the crew is not good at straightening out the rolled type wire mesh, you will have problems. Tell the contractor to order 5 x 10 WWM sheets. They are slightly more expensive than the rolls, but go down very fast with no bumps and curls. I've never had a tube pop up.
Then of course sombody has to be in the pour with boots on to lift everything as you go. Or... just leave it on the bottom as suggested here
Chris

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Maine Ken

I use Crete Heat for all my slab work now. Sooooo much faster.

http://www.crete-heat.com/



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DEREK_12

Radiant Panels


Ken, I went to the crete-heat web site just now. Very cool. I've never even heard of these panels before. Install is pretty quick I see. Whats the price per panel? Thanks for the link. I'm calling my rep to see if he will carry them.
Scott

Jim_65

We

use/order 8' x 20' FLAT welded wire mesh. Doesn't roll up on us The KEY is that it is FLAT to begin with.

I also agree with Singh...the bottom of the pour is going to change the game.

Tom Manton

Jim French got it right

6"x6" mesh comes in flat sheets, we haven't used rolls in years. Pouring 3.5" to 4" slabs with mesh is no problem.
Zip tie .5" tubing to the mesh, I use home made dobies to hold the mesh up 1.5" so I don't have to pull it into the crete. Take a 2"x8"x16" patio block and break it with a hammer to make dobies.

As to the vapor barrier on the cold side, Technically in this application it is a moisture barrier, not a vapor barrier, and needs to be on the side with the highest vapor pressure (the ground). Vapor barriers in a cold climate go on the warm side because warm air can carry more moisture than cold air, thus the vapor pressure is higher on the warm side. Vapor barriers are to protect vapor permeable insulations from picking up and holding moisture thus rendering them a less efficient insulator and a wick for moisture and its related damage within a wall cavity.

Closed cell foam is immune to this, thus no vapor barrier is requierd only vapor sealing as a previous poster stated (although in my experience tape and concrete don't get along very well).

Around here we typically run .5" tubing 4 rows at 4" spacing around the perimeter the 8" spacing in the field, and about 110 F water depending on heat load.

Sorry for the long post, but hope it helps

Adam Greisz

Thanks

for the great information. Adam

kpc_16

ken..where

are you getting it from? no one here in NH has it...kpc

Don Regan

Crete-Heat

If you can not find Crete-Heat in your area. Please contact me for help.

Maine Ken

Redlon & Johnson stocks it, Portland Winnelson has it, Bell/ Simons also. RST reps it.

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Adam Greisz

I am North of Seattle

who is my local supplier?

Rich Devens

Radiant in slab

If you use a 2 inch foam board under the slab and staple the pex down you can use fibermesh in the pour. The wire serves no purpose if its not in the bottom third of the pour. I would recomend using insultarp instead of the foam. It is a great vapor barrior has a higher r value than foam and won't settle causing the floor to crack.

kpc_16

insultarp...

has a higher r- value than foam? I Don't think so....kpc

http://healthyheating.com/Page 55/Page_55_o_bldg_sys.htm

Rich Devens

R value

I don't know what foam you use but all I can get out of a 2inch foam board is R5 and the insultarp is r7.5

Ron Gillen

R-Value

Extruded foam is R-5 per inch. Expanded foam is R-4.5 per inch

Adam Greisz

Foam insulation value

Code requirements here in Snohomish County are R-10 of underslab insulation. Adam

Tom Manton

mesh

1.5" dobies put the mesh near .333 of a 4" slab, if we are going to argue over .1666 of an inch in a concrete pour I'm not playing.

Fibermesh ok but not on my jobs. Insultarp, no thanks

Don Regan

Fibermesh...

Just out of curiosity, what don't you like about fibermesh?

Why would you want to zip tie the tubes to wire if there's a better way?

Don fron Crete-Heat

ScottRW

Bluestone

I've stapled down many jobs and never had one pop loose on me. As I stated a few days ago, I always use 1/2" rebar on 2' centers both directions. This holds the tubing in place until the pour occurs. I usually set my pex the day before the pour. I have used the same concrete guy since 1985, and he knows what I'm expecting. His crew is very diligent (read that as really flippin' careful) about the pex, and they lift the rebar as they go. To date the only time I have EVER had a problem, is when an architect specified that the tubing be tied to wire mesh. About a week after the pour, the concrete cutting crew started to make some shallow decorative cuts and made it about 8" before they hit the tubing. I'll never tie to mesh again. I'll decline the job rather than go through that again. Just another perspective. To each his own,right?? Scott

Tom Manton

System

Sounds like a good system to me Scott, rebar on top to protect the tubing from lifting. Lots of money and work though to tie the mat.

About the tubing being cut, thats why I use the homade dobies so I know where the mesh mat is, we used to pull our our mesh up into the pour but lately I've found it to be more work to do that than making a few dobies and placing the mat on them, a lot less work on pour days.

Good tip though and I might use it where we find staple down tubing. Another thing I like about tying to mesh is the tubing is fully envelopedin the concrete, just seems to me to be better for conductance