Prescribed R-values for air films shall be as follows:
|0.17||All exterior surfaces|
|0.46||All semi-exterior surfaces|
|0.61||Interior horizontal surfaces, heat flow up|
|0.92||Interior horizontal surfaces, heat flow down|
|0.68||Interior vertical surfaces|
Exterior surfaces are areas exposed to the wind.
Semi-exterior surfaces are protected surfaces that face attics, crawl spaces, and parking garages with natural or mechanical ventilation.
Interior surfaces are surfaces within enclosed spaces.
The R-value for cavity airspaces shall be taken from ASHRAE 90.1 Normative Appendix A. No credit shall be given for airspaces in cavities that contain any insulation or less than 0.5 inch (12.7 mm). The values for 3.5 inch (84 mm) cavities shall be used for cavities of that width and greater.