Charles writes from Greenland, New Hampshire: "We are about to build a home for a client. His architect has specified 2x6 walls, 1/2" drywall interior and white cedar over 7/16" osb and housewrap exterior. He also specified R-25. R-21 fiberglass is all that will fit in the cavity. How can we pick up the additional R-4?"

Answer: You can achieve an additional R-5 by installing one inch of FOAMULAR® extruded polystyrene insulation over the OSB before applying housewrap and white cedar.