How does the roof insulation framing factor affect total Rvalue in BeOpt?

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We have been trying to model a flat reinforced concrete roof in BeOpt. We initially assumed that the framing factor to be very small or zero since concrete roofs tend to not have additional external supports. After doing some sensitivity analysis, we found the framing factor % to have a direct correlation to reductions in energy consumption due to cooling. We have not been able to find more information on how the framing factor is being incorporate in the BeOpt documentation or code. Any suggestions or explanations would be appreciated.

Thank you