EIFS and total R-values
Considering EIFS on a new house in zone 4/5, and I have a question about the effect the ventilated drainage gap has on the R-Value, since it’s behind the EPS. Does that exposed gap introduce cold air and compromise the R-value provided by the EPS, or is the effect insignificant?
The closest info I could find was from BSC:
“Installed insulation R-value: The framed portion of this wall assembly typically has an R-value of R-19-20 when insulated with fiberglass batt or cellulose. Exterior insulation for EIFS is typically EPS at R-4/inch.
Whole-wall R-value: Using two-dimensional heat flow analysis with thermal bridging effects and average framing factors demonstrates improvements in the efficiency of the fiberglass batt or cellulose in the stud space by decreasing the thermal bridging effects of the framing and the rim joist. Adding 4” of EPS insulation for a total increase of R-16 increases the clear-wall R-value of standard construction by slightly more than R-16 because of thermal bridging of the framing and rim joist. The whole-wall R-value for this system is approximately R-30.”
Should I just take that whole-wall R-value estimate as gospel?
Second question: Is there a minimum EPS thickness for an EIFS wall in Zone 4/5?