Section 501 specifies R-values for walls, roofs, foundations, and other envelope components by climate zone. Zone 1 (warmest) requires R-13 walls, R-19 roofs, and R-5 foundations. Zone 8 (coldest) requires R-21 walls, R-38-49 roofs, and R-15-21 foundations. Continuous insulation (outside the framing) provides additional thermal resistance and reduces thermal bridging through framing. Air leakage testing verifies the building envelope is adequately sealed, with maximum allowable rates of 3-7 air changes per hour at 50 pascals depending on building type. Blower door testing pressurizes the building and measures leakage rate, with sealing required where leaks are detected.