According to the 2012 International Energy Conservation Code (IECC), R-Values assigned to central Texas for climate zone 2 prescribe ceiling insulation at an R-38 and wood framed walls at R-13.  Creating an unvented attic assembly by applying spray foam along the roof line at R-Values nearly half the prescribed method – 19 to 21 – outperforms fibrous ceiling insulation meeting the energy code minimum of R-38.  This performance level allows spray foam a method of compliance without needing to meet prescribed R-values.  2x4 stud walls are sprayed with a nominal 3.5 inches of open-cell to achieve an R-13.  2x6 stud walls only require 3.5 inches of open-cell but can be filled with 5.5 inches for additional insulation.        

Closed-cell has double the R-value per inch of open-cell and can achieve higher R-values with lower thicknesses.    This characteristic is handy when less space needs maximized R-value, especially for commercial and industrial projects including metal buildings.  For crawlspaces, closed-cell is sprayed at a nominal 2 inches under floor for an R-value no less than 13.