Jeff wrote:
daestrom wrote:

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.

With how many foils and what temp? What's the significance of "W" and "S"
with downward heatflow? A winter floor and a summer ceiling?

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.

So up-facing foils may not help much, unless they are well-sealed above.

It looks to me that I have two ways to go:

1) 3 1/2" (R 11 + R 6 or so for the radiant) fiberglass batts with a
radiant barrier wired up with wire hangers or
something similar. An airspace of an 1 1/2" or so.
2) double bubble (triple radiant)

It seems that Reflectix makes a product with no radiant effect for use
under concrete, and another with 2 foils (not "triple radiant") on the
outside. The inner layers have no foil. Other options are double-foil
polyiso board and double-sided "builders foil" in 4' rolls at 10-20
cents/ft^2 from companies like Innovative Insulation, and more costly
adhesive-backed foil, and OSB with one foil face, which might be found
on the underside of a roof.

... method two, which is what at least some staple up suppliers
provide, seems plausible. It would be easier to dust seal this and it
certainly would be easier to install.

Dust sealing the exposed upper foil would be difficult.

Have I missed something, or is this really the best app for radiant
bubble? Perhaps the only time it should be used.

Radiant barriers are good for downward heatflow (including a fridge roof),
OK for horizontal heatflow, and poorish for upward heatflow.

Nick