Attic insulation provides best ROI. 25-35% of heat escapes through roof - easiest and cheapest to fix. Target R-38 to R-60 for attics. Cost: $1.50-$3.50 per sq ft installed. Typical savings: 15-25% on heating bills. Payback: 2-7 years. Second priority: basement/crawl space, then walls.

Depends on climate zone. Cold climates: Attic R-49 to R-60, walls R-18 to R-21. Moderate climates: Attic R-38 to R-49, walls R-13 to R-15. Warm climates: Attic R-30 to R-38, walls R-13. Check current insulation first - adding to R-19 attic is much more valuable than R-30 to R-40.

Spray foam is superior (R-6.5 per inch, air sealing) but 3-4x cost of fiberglass (R-3.2 per inch). Best strategy: spray foam for rim joists, knee walls, and problem areas; fiberglass for large areas like attics. Cellulose is middle ground - good R-value, eco-friendly, moderate cost.

DIY attic insulation is feasible with fiberglass batts or blown cellulose rental ($50/day). Safety: wear mask, goggles, gloves, long sleeves - insulation irritates skin/lungs. Avoid covering recessed lights or blocking ventilation. Wall and spray foam insulation requires professional installation. DIY saves 30-50% on labor ($500-1,500) but takes 1-3 days.

Quality varies by type. Fiberglass/cellulose: lasts 80-100 years if dry and undisturbed, but settles 10-20% over decades (reducing R-value). Spray foam: 80+ years with no settling. Moisture is enemy - wet insulation loses 50%+ R-value and grows mold. Check attic insulation every 5-10 years for settling, moisture damage, or pest infestation. Add more if compressed or degraded.