"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.
I always thought the shiny side reflects, so needs to be facing where heat
needs to be reflected back and there needs to be a 1" gap between that and
any other surface. Having it under floors facing down should not be
effective. Yet I have read that some makers say it does not matter which way
it goes, I find that hard to believe.