insulation for under radiant heat

[wayoff]

I don't know if this belongs in Heating or flooring, but since I am preparing to pour my floor, I'll start here.

The one thing I have noticed about radiant heat is that everyone says it's really simple and you can set it up yourself, but nobody knows anything about it and if you ask six people about it, you get six different answers. Case in point, insulation. I have contacted Six companies who do floors exclusively and got quotes to have my floor poured that were surprisingly close in price. I figured I would pick a contractor and go with whatever type of insulation they prefer/recommend for radiant heating. But every one has a different opinion and for very different reasons. The way I see it, I have three very different choices.
One is two inch foam board. Two is R-13 insulating blankets. Three is bubble pack with no R-value but a silver heat reflective surface. Everybody likes and dislikes these three products for drastically different reasons.

The pros as I see it is that they are all being used every day and are supposed to work.

The cons as I have been told are as follows.

Two inch foam adds 2" to the floor thickness without adding to the strength and may not contact the sand under it 100% and may form air gaps that take away from the structural integrity of the floor over the long term.

Insulating blankets may become saturated and compressed during the concrete process and loose most of their R-value.

bubble pack has no R-value and seems like a silly way to insulate anything. It also gets misplaced and popped while being stepped on during the concrete process.

Help me choose the right insulation so I can get my floor poured!

 

[hemi]

wayoff,
I used a product called "The Barrier" on my 32 x 72 polebarn. It is a 3/8" thick
extruded poly W/vapor barrier on both sides. It does not compress like the 2"
foam board which I used around the perimeter. The product "the Barrier" is made by a company Northwest Ohio Foam Packaging.
Try http:/ww.nofp.com/barrier.html for more info. good luck!
hemi

 

[RickP330]

Wayoff,
I'm sure this will be of no help LOL, but my house was built in the '50's on a slab with radiant heating with no insulation at all. I just upgraded to a condensing gas boiler and am amazed at the efficciency of the system. with my set up, sure I would have to heat up the ground (if starting from ice cold) but once the ground is warm it always stays warm. So why insulate at all? The ground is a natural heat sink. Sure, I probably loose a ton from the sides. I can see melted snow against the footing all the time. Should probably do something there....
RickP

 

[wayoff]

Wayoff,
I'm sure this will be of no help LOL, but my house was built in the '50's on a slab with radiant heating with no insulation at all. I just upgraded to a condensing gas boiler and am amazed at the efficciency of the system. with my set up, sure I would have to heat up the ground (if starting from ice cold) but once the ground is warm it always stays warm. So why insulate at all? The ground is a natural heat sink. Sure, I probably loose a ton from the sides. I can see melted snow against the footing all the time. Should probably do something there....
RickP

Well, insulation is going to cost me just shy of $1000 which ever path I choose, and I wondered if it is just wasted money. I have been told that a large percentage of floors are done with blankets that when wet with concrete have no more insulating properties than concrete does.

 

[PAToyota]

One is two inch foam board. Two is R-13 insulating blankets. Three is bubble pack with no R-value but a silver heat reflective surface. Everybody likes and dislikes these three products for drastically different reasons.

On the commercial side of it, I've only ever seen the foam board used and that is all that we spec. If you mean blankets as in fiberglass batts - that will do absolutely no good. If some other product, I'd be interested in more information. Never seen it done that way. And typically, the only way a reflective surface does any good is if you have an airspace...

As for your concerns about the foam, the 2" should not replace any of the concrete thickness. If you are doing a 4" slab (or whatever) it is still a 4" slab with 2" foam below that. If they are making the slab thinner for the thickness of the foam, they are doing it wrong... Also, the sand bed should be relatively flat and smooth. If it is within a 1/4" to 3/8" the foam will compress enough under the weight of the concrete to conform to the sand bed - probably up to half an inch... But it should be flat and smooth.

I did mine with a geotextile fabric (so the stone won't compact into the clay over time), compacted stone base, geotextile fabric (so the sand wouldn't filter into the stone over time), 2" foam board, and four inch concrete with 4ga. x 6" welded wire mesh. Ten years later no problems...

 

[toms73novass]

If doing vapor barrier it should go just above the sand correct?

 

[PAToyota]

Yep! You are correct.

 

[toms73novass]

thanks,

One more question where is the best place to get the geotextile fabric, for this application?

 

[PAToyota]

When I did mine, I was using it under the floor of the garage and under the stone in my driveway. So I went to a builder's supply and got a roll - 100 yds or 150 yds... Can probably get smaller amounts elsewhere... But I'd start by looking under building supply in the phonebook.