Energy Code and Building Envelope Performance
Massachusetts enforces energy requirements in layers. The base residential requirements sit in 225 CMR 22 and commercial in 225 CMR 23, both built on the IECC with Massachusetts amendments; the state is climate zone 5. Many municipalities have adopted the Stretch Code, and a newer specialized opt-in code exists for communities going further - so the first question on any energy problem is which code that town has adopted.
Concepts: a continuous air barrier and a continuous thermal envelope; the difference between cavity insulation and continuous insulation (thermal bridging through studs cuts effective R-value); proper installation with no gaps, compression or voids; and moisture management with the correct vapor retarder for a cold climate. Typical zone 5 targets: ceiling around R-49 to R-60, wood-frame walls around R-20 plus 5 continuous or R-13 plus 10, basement walls around R-15 continuous, slab edge R-10, windows around U-0.30. Verify against the edition in force.
Verification: blower-door testing to a leakage target (about 3 ACH50 in the base code, tighter in stretch towns), duct leakage testing, and an insulation certificate posted at the electrical panel. Stretch-code towns generally require a HERS rating and third-party verification, including insulation inspection before drywall.
Traps: assuming the base code applies in a stretch town; confusing R-value with U-factor; and forgetting that a tight house needs mechanical ventilation - bath fans ducted outdoors and a whole-house system such as an ERV.
Rule of thumb: seal first, insulate second. Air leakage can waste more energy than a missing R-5.