Thanks Nick,

That was an old draft and I didn't mean to send it, you had answered
this days ago...

Cheers,
Jeff


Table 2 on page 22.2 of the 1993 ASHRAE HOF covers air gaps down to 0.5",
with a footnote a: ... Thermal resistance R = 1/C, where C = Hc + EeffHr,

From your calculations of a typical EeffHr (radiation coefficient) of

.04555 this would give a maximum effective R value of 22 no matter how
thick the insulation. Thicker would get you closer to it but there are
diminishing returns.


No. Add Hc to EeffHr and take the reciprocal to find the R above, for
the foil only. THEN ADD THAT TO THE R-VALUE OF THE INSULATION ITSELF.

Nick