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Table 4. R-values of air films and air spaces

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MIL-HDBK-1003/19
TABLE IV.  R-values of air films and air spaces.
R-value for Air Film on:
Type and
 Direction  
Non-
Fairly
Highly
Orientation
of
reflective    reflective  
reflective
of Air Film
 Heat Flow    surface
surface
surface
Still air:
Horizontal
up
0.61
1.10
1.32
Horizontal
down
0.92
2.70
4.55
45deg. slope
up
0.62
1.14
1.37
45deg. slope
down
0.76
1.67
2.22
Vertical
across
0.68
1.35
1.70
Moving air:
15 mph wind
any[*]
0.17
--
--
7.5 mph wind
any[**]
0.25
--
--
R-value for Air Space Facing:
Orientation
 Direction  
Non-
Fairly
Highly
& Thickness
of
reflective    reflective    reflective
of Air Space
 Heat Flow    surface
surface
surface
Horizontal
1/4"
up[*]
0.87
1.71
2.23
4"
0.94
1.99
2.73
3/4"
up[**]
0.76
1.63
2.26
4"
0.80
1.87
2.75
3/4"
down[*]
1.02
2.39
3.55
1-1/2"
1.14
3.21
5.74
4"
1.23
4.02
8.94
3/4"
down[**]  
0.84
2.08
3.25
1-1/2"
0.93
2.76
5.24
4"
0.99
3.38
8.03
45deg. slope  3/4"
up[*]
0.94
2.02
2.78
4"
0.96
2.13
3.00
3/4"
up[**]
0.81
1.90
2.81
4"
0.82
1.98
3.00
3/4"
down[*]
1.02
2.40
3.57
4"
1.08
2.75
4.41
3/4"
down[**]  
0.84
2.09
3.34
4"
0.90
2.50
4.36
Vertical
3/4"
across[*]
1.01
2.36
3.48
4"
1.01
2.34
3.45
3/4"
across[**]
0.84
2.10
3.28
4"
0.91
2.16
3.44
One side of the air space is a non-reflective surface.
[*]Winter conditions.
[**]Summer conditions.
A more accurate and general approach for multi-zone structures involves
calculating the NLC separately for each control zone in the structure.  In
order to implement this approach, the user must apply Worksheet 2 for each
control zone, bearing in mind the following differences in interpretation:
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