# RADIANT FLOOR JOIST INSULATION



## 91LMS (Oct 29, 2012)

has anyone used this product to insulate between floor joists with radiant heat?  or have anything that they suggest that has worked well for them?

http://www.reflectixinc.com/images/...ion pdf files/diy rad fl wood joists 0411.pdf


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## Fred61 (Oct 29, 2012)

I guess it works well for the reflection qualities and I believe in the need for a reflective surface but I've heard that it doesn't measure up to fiberglass blanket insulation.


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## 91LMS (Oct 29, 2012)

they claim its r21 if its doubled up.  wonder if i would see a differance with how much heat is driven up through the floor with fiberglass as apposed to the refectix?


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## peakbagger (Oct 29, 2012)

It may work fro your purposes but their R value claims have been debunked numerous times


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## DaveBP (Oct 29, 2012)

And remember that reflective surfaces only work as long as they remain dust free. I don't see many horizontal surfaces that remain dust free for long. Anywhere.

I hate installing fiberglass overhead but at least fiberglass (and foam) don't rely on miracle effects.


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## maple1 (Oct 29, 2012)

Hmm, I got some of this stuff this weekend to try covering the Roxul tied around my storage tanks. I wasn't counting on it for a lot of insulating value though.


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## charly (Oct 29, 2012)

91LMS said:


> has anyone used this product to insulate between floor joists with radiant heat? or have anything that they suggest that has worked well for them?
> 
> http://www.reflectixinc.com/images/uploads/diy application instruction pdf files/diy rad fl wood joists 0411.pdf


I used the foil bubble sheets on our radiant install as well. Had it at the bottom of the joists. Worked fine for us , but was told a better install would be to keep it an inch or so away from the tubes instead of heating the whole joist area. We had 12 inch wide knotty pine floors , Advantec sub-flooring and it worked fine. I thought this was a pretty straight forward site to answer some radiant questions. *radiantdesigninstitute.com*


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## Hollow Pine (Oct 30, 2012)

My heat guy had me lay radiant foil shiny side up on top of the 3.5" fiberglass that we stapled to the bottom of the floor joists, We used the ultrafin system so my tubing hangs about 3' below the subfloor in what is essentially a dead air space. The foil and insulation is another 3 or so inches below that.

Jeff_L


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## 91LMS (Oct 30, 2012)

interesting jeff l.  my system is of the same design with 12" joists.  i am just concerned trying to push heat through my advantec and 3/4 oak floor.  hoping that 3.5" of insulation is sufficient and thinking that a reflective layer should be there to help my cause.  i agree with the dust thing but the pockets should be sealed so hoping the dust will be minimized.


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## JP11 (Oct 30, 2012)

91LMS said:


> interesting jeff l. my system is of the same design with 12" joists. i am just concerned trying to push heat through my advantec and 3/4 oak floor. hoping that 3.5" of insulation is sufficient and thinking that a reflective layer should be there to help my cause. i agree with the dust thing but the pockets should be sealed so hoping the dust will be minimized.


 
I used the foil faced hard foam.  2" 

I left one inch of air space between the pipes and the foam.  I'm going thru advantek, mortar, ditra, mortar and tile.

No reflector plates, tubes just stapled to subfloor.  Works good.


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## 91LMS (Oct 30, 2012)

is that foam foil faced on both sides jp?  that was my first thought but at 40 bucks a sheet i was doing more research


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## JP11 (Oct 30, 2012)

91LMS said:


> is that foam foil faced on both sides jp? that was my first thought but at 40 bucks a sheet i was doing more research


yes.  I don't remember it being that pricey.  I was slicing roughly 22" x 8' sheets.. and sticking them up in floor trusses.  a few toe nails to hold them.  If you cut them right.. they pretty much just stick in from pushing them in.


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## 91LMS (Oct 30, 2012)

even easier in my case jp where i have engineered joists.  depot was the cheapest so far on the foamular.  the reflectix with fiberglass is less money than foam.  mainly want functionability over price, should be forever if its right.


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## davidsutton (Oct 31, 2012)

I put 1/4" foil faced foam (cut to fit fan/fold) from menards foil side up towards screwed up pex tubing (pex spaced off bottom of floor 1.5") and then r13 under that. It is working like charm through a sand which of flooring ( 3/4" tongue and groove sub-floor, 1" hardwood original floors and on top of all that the new 1/2" floating wood floors). Also working great upstairs through 2 layers of sub-floor and then stain-masters rubber carpet pad for radiant and new plush carpet. It is cheap and works well. I did every floor in my house is this way. Just my 2 cents.


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