The 2022 Inflation Reduction Act transformed insulation economics. Federal 25C credit now covers 30% of insulation costs up to $1,200/year, making attic and wall insulation the highest-ROI home improvement available in 2026. Typical payback: attic insulation 3-7 years, wall insulation 5-12 years, spray foam 7-15 years depending on climate and fuel costs.
R-value targets by zone
DOE-recommended R-values by climate zone. Attic: R-30 (hot climates, Zone 1-2), R-38 (mixed, Zone 3-5), R-49 (cold, Zone 6-8). Walls: R-13 in 2x4 cavities, R-19 in 2x6, R-23 with continuous exterior insulation. Floor over crawlspace or basement: R-19 minimum. Basement walls: R-15 continuous. Most 1980s-1990s homes have attic insulation at R-19 or below — adding R-30 more on top is typically $1,200-$2,500 and saves $250-$600/year in heating and cooling.
Spray foam — when it's worth the premium
Closed-cell spray foam runs 3-5x the cost of batt but delivers R-6 to R-7 per inch (vs R-3.5 for batt) and acts as its own air seal and vapor barrier. Worth it in: rim joists (biggest air leak in most houses), cathedral ceilings, bonus rooms over garages, and any cavity where an air barrier matters more than raw R-value. Not worth it in: standard attics where loose-fill cellulose achieves the same R-value for 1/3 the cost.
Air sealing — the step most DIYers skip
Insulation without air sealing is roughly 30-40% less effective than advertised. Before any insulation install, seal: top plates penetrations (wiring, plumbing), can light housings (replace with IC-rated airtight), HVAC register boots, attic access hatch weatherstripping, and rim joists. Budget $500-$1,500 in air sealing products and labor before blown insulation goes in. Blower door testing after work confirms tightness and documents for tax credits.