What is a reasonable range of values for resistance to heat flux?
Alec Bennett calculates resistance to heat flux values in an urban canyon as part of his MSc in meteorology dissertation: Heat Fluxes from Street Canyons.

The calculated values range from 76.6 to 84.2 and are based on measurements taken on May 18th and 19th 2004 from 08:00 to 17:00 (both days).

See the two tables in the Appendix on page 68 for the full range of values.

I have not read the entire thesis.  It's unclear to me what confidence I should place in these values.