Isn't the reflective surface only effective if there is an air gap
next to it?

I have read some testing reports that show those 3/8" doubvle radiant
barriers under slabs to have a non-measureable difference to no
insultaion at all. ****ed off my concrete guy but I gave him a print
out of the report and now I can't find it again.



"daestrom" wrote in message
...

"Jeff" wrote in message
k.net...
wrote:
snip


From The Passive Solar Energy Handbook, Edward Mazria 1979 we have
this in Appendix E.6 Resistance values of airspaces

Horizontal, Heatflow Down
NR=Non Reflective

Thickness | Season | NR/NR | NR/Aluminum Coated | NR/Foil
3/4 W 1.02 2.39 3.55
1 1/2 W 1.14 3.21 5.74
4 W 1.23 4.02 8.94
3/4 S 0.84 2.08 3.25
1 1/2 S 0.93 2.76 5.24
4 S 0.99 3.38 8.03


Obviously that's all from observations.

What strikes me for my application at hand, insulating under staple
up radiant, is that 8.94 for a single radiant barrier. It sure
makes foil double bubble look good.


One thing though about radiant barriers. It's well settled that the
upper surface of horizontal installations will not retain its low
emissivity. Unless you fancy wiping and cleaning off the dust every
year or so, it will accumulate and lose its effectiveness.

In attics, it's advised to put the radiant barrier on the rafters
overhead so the radiant surface is on the underside. For underfloor
installations, the same thing. The foil goes on the underside to
limit the accumulation of dust that will ruin its effectiveness.

daestrom