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Old 07-25-2007, 04:40 PM   #1
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radiant vapor barrier


I am installed DIY radiant heating before the basement slab is poured and I think I may have made a mistake. We first graded the sand so it is level, then we installed R10 insulation and stapled the PEX on top of the insulation for all 7 runs. Lastly we a vapor barrier down. I figured out afterwords that the vapor barrier should be under the foam. We haven't poured yet, but the contractors want to do the pour ASAP. Here are the three choices I see

1) leave it as is and pour
2) eliminate the vapor barrier and pour
3) completley remove all of the radiant tubing and insulation and start over.

I supposed they are listed in my order of preference, but I am wondering what impact each option would have on the efficiency and overall reliability of the system

Thanks,
Brian

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Old 07-25-2007, 04:49 PM   #2
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radiant vapor barrier


What did the installation instructions for the in-floor system say? - or were you just winging it?

By the seat of my pants, I think the vapor barrier should have gone in first so it was continuous, protected and effective. I hope you used extruded polystene at least.

Is the concrete contractor dictating how the heating system should be installed?

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Old 07-25-2007, 07:05 PM   #3
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You only have one chance to do it right the first time.

With the vapor barrier on top, where do you think any condensation will occur? Yep, between the foam and around your pex. Plus you just put a small thermal barrier between the pex and your slab (plastic is an insulator). The pex is supposed to be in the concrete, not under it, at least in all the "in slab" systems that I've seen. This is what creates your thermal mass. Option #2 IMO isn't an option unless you want to risk having potential seepage problems like this person in this thread. There's no way I could sleep soundly at night knowing that this wasn't done right. I vote for option #3.
  1. sub material is usually stone (capillary break)
  2. vapor barrier (6 mil poly)
  3. foam insulation (Styrofoam)
  4. wire mesh or rebar grid raised slightly off of foam
  5. pex strapped to grid
  6. concrete
Of course the manufacturer of your radiant product could have a different configuration.

Last edited by SecretSquirrel; 07-25-2007 at 08:53 PM. Reason: additional web links
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Old 07-25-2007, 09:03 PM   #4
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radiant vapor barrier


my radiant guy said #1 would be OK, and the concrete contractor said he had seen it before.

If #3 is the best option, I can do it. I have sand as a base, but it's clean fill that we had to bring in to stabilize the foundation (2300 tons). Do I need anything (like geotextile mat) between the sand and vapor barier to help with radon?

Thanks,
Brian
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Old 07-25-2007, 09:30 PM   #5
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radiant vapor barrier


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Originally Posted by bjherron View Post
my radiant guy said #1 would be OK, and the concrete contractor said he had seen it before.

If #3 is the best option, I can do it. I have sand as a base, but it's clean fill that we had to bring in to stabilize the foundation (2300 tons). Do I need anything (like geotextile mat) between the sand and vapor barier to help with radon?

Thanks,
Brian
Well??? What can I say? If the radiant guy says it's ok to isolate the pex between the concrete with a vapor barrier then who am I to argue? From a physics point of view I can state that your heating efficiency would be greatly increased if the radiant tubing were embedded in the concrete. Now you have half your tubing faced against the concrete separated by poly and half faced against the insulation. But you did state you were going to move the vapor barrier between the sand and insulation, so I believe you're on the right track. Enough said!

Radon remediation??? It's too late for that. The conventional method for that is installing 4" perforated pvc piping, in a loop, beneath the slab, encased in gravel, and having a vertical riser extend beyond the roof line to vent the gases.

Addendum: I stand corrected on Radon prevention. The EPA has modified the recommendations since the last time I researched this. See http://www.epa.gov/radon/construc.html

Last edited by SecretSquirrel; 07-25-2007 at 09:48 PM. Reason: Addendum.
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Old 07-26-2007, 06:42 AM   #6
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radiant vapor barrier


It might better to not have any vapor barrier. IF you have a well drained sub floor and your insulation seams are tight, I would think you would have a decent barrier. You didn't indicate which kind of insulation you have, but Owens Corning and off hand I can't find the Dow literature, but Owens Corning claims to be a barrier. I think in the this specific application, the vapor barrier is a bonus, and not a minimum requirement. I don't think stopping the migration of moisture at the pipe level would be the way to go, but that's just my thought. Good luck.
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Old 07-26-2007, 07:05 AM   #7
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radiant vapor barrier


Quote:
Originally Posted by RippySkippy View Post
I can't find the Dow literature, but Owens Corning claims to be a barrier. I think in the this specific application, the vapor barrier is a bonus, and not a minimum requirement.
Here's the Dow Styrofoam Document

Quote:
I don't think stopping the migration of moisture at the pipe level would be the way to go, but that's just my thought.
Rippy, I believe he's looking for a way to vent Radon gas... which is a separate issue with respect to the vapor barrier.

Last edited by SecretSquirrel; 07-26-2007 at 07:30 AM.
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Old 07-26-2007, 08:14 AM   #8
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radiant vapor barrier


I agree that it makes sense to have the PEX inside of the concrete, even though I was told otherwise. I came here hoping to get a second opinion to either agree with me, offer alternatives, or tell me that they are right and to stop worrying about it. I am the homeowner, but I am also the general contractor so the responsibility ultimatly lies with me. The person designing the radiant system is someone I found on the internet, he is just giving me materials and instructions but I am the actual installer. This is my first time doing this, so I don't have the experience to know everything.

I am using the owens corning insulation. If that is an acceptable vapor barrier, maybe I could just tape up the gaps? I noticed on their site that they recommended putting a vapor barrier down first. I don't want to cut corners, but I am not building a million dollar house either. Any advice would be appreciated.

here's a pic of the insulation

Last edited by bjherron; 07-26-2007 at 08:23 AM. Reason: add image
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Old 07-26-2007, 08:51 AM   #9
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radiant vapor barrier


I didn't want to step on any toes as far as asking about the credentials of the 'radiant guy' as I suspected he was more of a salesman than an Engineer.

Anyway... I believe it's a move in a positive direction that you took the poly off the top of the pex. As far as the suitability of Styrofoam or rigid foam as a vapor barrier, I think the confusion lies where the product specs state that the material is moisture resistant or impermeable. This doesn't necessarily imply that the product will provide a vapor barrier when butted together. If you take a peak at the Dow Styrofoam Document you'll see where they advocate the usage of a vapor barrier beneath the Styrofoam. I couldn't find any relative material at the OC site about the application of the product in an in-slab radiant system. None the less, I understand your dilemma and totally sympathize with you as I'm sure there is a lot of angst at looking at the prospect of a "do over". I have found a couple of installations where the vapor barrier is on top of the foam. You may have a workable solution by applying the tape to the junctions between foam pieces... at least that is better than nothing. I hope that I didn't appear that I was coming at you like a Rotweiller... it's just that I'm very passionate about getting things done right.
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Old 07-26-2007, 09:06 AM   #10
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radiant vapor barrier


With-in the last year, I wore your shoes...and believe me...they cause lots of blisters. We just moved in last weekend.

Everyone will have a list of what's right and what you should do. I firmly believe that for many things there's a wide margin of error. Case in point your last post about having the pipe in the crete...both sides will beat there chest and say "my way is best" when in reality there's thousands of installs done each way (in crete on chairs, and stapled). How many continue the discussion talking about efficient heat sources? I've not run into many.

It looks to me like you may have another issue on your hands, the insulation you've installed isn't rate for under slab. Is that going to cause issues? I don't have a clue. It might be worth calling OC and checking it out before pouring. Find out what your risks are and go from there.

WRT to the vapor barrier -- at this stage I'd skip it.

I see you have one pipe running around a 3" riser...is that for a stool? If it is, you might want to either keep all heating pipe away a foot or so, or plan on using the plastic push in toilet ring not the wax type. I've been told (not from personal experience) that the heat will soften the wax rings to the point they will fail.

Hang in there....it really is a fun process! Hard at times...but fun!
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Old 07-26-2007, 09:08 AM   #11
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radiant vapor barrier


Quote:
Originally Posted by SecretSquirrel View Post
... OC site about the application of the product in an in-slab radiant system.
Check this out: http://www.owenscorning.com/around/i.../underslab.asp
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Old 07-26-2007, 09:43 AM   #12
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radiant vapor barrier


Quote:
Originally Posted by RippySkippy View Post
I was searching for an in-slab radiant heating application document. Thanks for the link.

Oh, by the way.. the OC installation instructions state:

Quote:
Installation:
1. Install moisture vapor retarder sheet after gravel fill has been built up to grade and thoroughly tamped.
2. Lay FOAMULAR insulation in place with edges pressed together and butting foundation wall or adjacent vertical insulation.
3. Pour concrete slab to cover all FOAMULAR insulation.

Last edited by SecretSquirrel; 07-26-2007 at 11:26 AM. Reason: Quoted installation instructions
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Old 07-27-2007, 11:39 PM   #13
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radiant vapor barrier


I started pulling it up tonight. It seems like the radiant tubing is going to be easier to reinstall the second time around.

Any particular wire mesh I should get? How do I raise it off the foam? Also, how much does it typically cost? Now that I tore the radiant clips out, it would be a good time to add wire mesh if I am going to.

Thanks!
Brian
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Old 07-28-2007, 07:54 AM   #14
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radiant vapor barrier


Quote:
Originally Posted by bjherron View Post
Any particular wire mesh I should get? How do I raise it off the foam? Also, how much does it typically cost? Now that I tore the radiant clips out, it would be a good time to add wire mesh if I am going to.

Thanks!
Brian
There's 2 options; you can use that 6x6 roll mesh that can obtained from most building supply houses and the big box stores. I don't know the cost right off hand but it's chump change compared to the other components in your install. You can lay it flat on the foam and get the concrete guys to pull it up into the pour as they progress from one end of the building to the other... or you can prop it up with some chunks of cinderblock. There's also some little wire supports that can be used and the mesh strapped to them but I don't have any info on those. The cons of using mesh is that it tends to have a little memory as far as curling is concerned and unless the concrete guys are careful it'll get stepped on and pushed to the bottom.

My personal preference is for rebar using Hercules Rebar Chairs to keep it up off the foam. The last time I bought #4 rebar, it was $.38/ft and comes in 20' lengths ($7.60/a stick), but that was a year or so ago. The rebar chairs can be found at Guaranteed Supply Company or perhaps at some local supply house.

I don't want to start a war over mesh vs rebar, but here's an excerpt from an article titled "Avoiding Common Mistakes in Concrete and Masonry". The author; Thor Matteson is a civil engineer in San Luis Obispo, CA.

Rebar performs better than wire mesh in
slabs—Steel rebar and wire mesh both serve

the same function: They add structural rein
forcement

to the concrete. Rebar is only slightly
more expensive than mesh but easier to keep
centered in the slab. If mesh is properly placed,
it should do just as good a job of strengthening
the concrete as rebar.

I'm attaching a picture of a small pumphouse that I did using the rebar chairs. Anyway... glad to hear that you've decided to do this properly. I know it has created a little heartburn but I truly believe you'll walk away with a feeling of satisfaction knowing that it was done right and that your heating system will perform to it's maximum potential.



Attached Thumbnails
radiant vapor barrier-dsc00412.jpg  

Last edited by SecretSquirrel; 07-28-2007 at 08:12 AM. Reason: spelling
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Old 07-28-2007, 12:41 PM   #15
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Go for the second option.Third is too $$$ wasting and tedious


Last edited by HiFi; 07-28-2007 at 12:44 PM.
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