News wrote:

"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.


We're talking about the FOIL side. Its going to be shiny regardless.

With a crawl space underneath, IT MAKES LOADS of sense. But the
direction it faces is CLIMATE dependent. Cold climates, foil side
faces towards the house to radiate heat back to the floors. Hot
climates, it faces down to reflect back heat from the crawl space.

Foil, insulation, paper, or foil insulation foil are available

In new construction, you can get foam boards for sheathing that have the
radiant barrier foil attached, in some cases to BOTH sides.
www.atlasroofing.com for an example of such. A 2" board will add about
$1.15 sq ft to materials cost of the house and adds R12 to the walls.
Similar boards are available for roofs, in areas that will see water
freeze on the roof.