daestrom wrote:
"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.
Well that puts an interesting spin on my underfloor, staple up, unheated
basement app.
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)
I think the radiant barrier is essential due to the higher temp of the
radiant to ambient.
Originally I had only thought of method 1.
But radiant barrier batts are hard to find. Adding a radiant barrier
to an existing is awkward.
So 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.
Have I missed something, or is this really the best app for radiant
bubble? Perhaps the only time it should be used.
Jeff
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