R- value of different assemblies in building (conditioned) cannot be averaged. Why?? Only U-value, C-Factors can averaged.again Why??
LEEDuser Basic Member
7 thumbs up
CEO & Founder
The Green Engineer
LEEDuser Expert
630 thumbs up
Physics & Math. R-values don't work that way.
The average of 1/x & 1/y is not the same as 1/(the average of x&y)
The equation for conductive heat transfer is:
Q= U x A x TD
U= 1/R
where Q=rate of heat transfer, A=area, TD = temperature difference
Lets say you had a wall that was 50% R=1, 50% R=99.
If you average the R-Value, you'd get a wall with R=50. But in fact, the effective R-value of that wall is about R-2.
This is why thermal bridges matter.