Matt Risinger discusses how the International Energy Conservation Code change impacts the usage of spray foam. He outlines the differences in ceiling and wall insulation specifically. Hot attics are now required to go from R-30 to R-38. Conditioned attics must be R-25 rather than R-21 to meet code. For wall insulation, R-15 OR R-13+2 is now up to code instead of R-13. Also the old fiberglass batts no longer are efficient. Replace them with total fill BIBS or Spray Foam to attain the R-15 necessary. According to Risinger, total fill insulation and open cell foam combined do good job of filling the space between studs and air sealing.
Read the full article here: Insulation Code Change & How Spray Foam Meets 2012 IECC Code