O.K. before you guys start w/ all bullwinkle jokes lets answer the question first.
I was going to put a poly/bubblewrap/foil sheeting under my radiant slab but I mistakenly ordered foil/foam/foil sheeting. Somebody told me that the concrete would eat the foil off the sheeting eliminating any radiant benifits. True? Could I put 6mil plastic over the fFMf sheeting or would this cause moisture/mold problems in the basement? I don’t have time to reorder and time is short– they pore on monday.
Replies
there is NO SUCH THING as "radiant benefit" under the slab.
Your mistake is a good one. the concrete may eat the aluminum, but then at least you'll still have foam which is providing a real insulation benefit, not a nearly worthless bubblewrap layer.
"Radiant" heat transfer is the transfer of heat through space. Objects touching each other do not count. That's conduction, and that requires good old fashioned R-value.
Smile! You made a better choice than you intended to ;)
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
Radiant foil under slab is worse than worthless. If it wasn't for the bubbles or foam between layers it increase heat flow downward.
SamT
Praise the Corporation, for the Corporations' highest concern is the well being of the public.
So it sounds like I would be better off removing a couple inches of gravel and putting down foam and a plastic barrier.
The literature that I've read gave the fFMf a r-14 I figured that was comparable to 2 inch foam. Sounds like this a clash of old vs new tech
I am a firm believer in radiant barriors. I saw it in use before it was invented. Well before it was commecialized any way. Back in the 50's and it's use spread because of empirical observations. It works.
Radiant material in contact with conductive material on both sides improves heat transfer. IOW it lowers R.
Foil faced bubble wrap under slabs is a scam.
SamT
Praise the Corporation, for the Corporations' highest concern is the well being of the public.
Thanks for the info---P.S. People are not the main concern of corporations; shareholders are! But when the shareholders make money they spend money AND THAT is good for the people.
PS: That's irony below.
Praise the Corporation, for the Corporations' highest concern is the well being of the public.
I agree with your sentiments samT, but I have to challenge some of your statements here.Aluminum has an R value.. just like everything else. It has some measurable resistance to heat transfer. It just happens to be very low.Adding layers in anything, IF IT DOES NOT CHANGE CONTACT AREA, will not increase heat transfer between two objects that would be in conduction in the first place. There is no such thing as a substances with a negative resistance to heat transfer, as far as I know.Now, it won't slow it down much either. But it wouldn't increase heat transfer to the ground below to have a layer of aluminum, unless the aluminum layer is larger than the slab to ground natural contact area... then, it could conduct more heat from the slab to more area of ground. Or maybe be a radiation fin above ground or something ;)-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
Ok, I shoud have said "it increases heat flow downward over any other material you can put under the slab."
Even that is not strictly trrue, 'cuz if you used gold, silver, or diamond,, those would be worse.
Thermal Coefficient of Conductivity, Thermal Expansion, Material Watt/cm .multidot. .degree.C. 10.sup.-6 /.degree.C. ______________________________________ Semiconductors InP 0.80 4.75 GaP 1.1 5.91 GaAs 0.37 6.63 Ge 0.64 5.75 AlAs -- 5.20 InAs 0.29 5.16 Si 1.24 2.5 Metals Cu 4.0 16.6 Ag 4.3 19 Au 3.2 14.2 Al 2.4 25 Diamond Type Ia 9.9 0.8.sup.a Type IIa 23.2 0.8.sup.a Type IIb 13.6 0.8.sup.a ______________________________________ Note: .sup.a This value is reported for diamond at 20.degree.
Worst of all: helium II (< 2.2 K)~100,000
SamT
Praise the Corporation, for the Corporations' highest concern is the well being of the public.
Edited 4/27/2007 11:00 pm by SamT
No one else addressed this, but I would think that a vapor barrier (polyethylene film sheeting) would be a good thing right under the slab--prevent water vapor from getting the slab wet. Concrete is hydroscopic, so I would think your slab would always be damp if you didn't use a VB under it. But, I am not a concrete finisher.
Over the Foam or under? I was planning gravel,plastic.foil foam barrier,then concrete.
The plastic will eithier be glued or taped to the wall about 4" up the wall.
I think what you propose would be fine--and less likely to put holes in the vapor barrier that way. Mainly want the VB somewhere between the wet ground or gravel and the slab.