Tip
Attic insulation — the highest-ROI envelope move
What R-value to target
| Climate zone | Target attic R-value | Equivalent depth (loose-fill cellulose) |
|---|---|---|
| Zone 1-2 (FL, S TX, S CA, HI) | R-30 | ~9 inches |
| Zone 3 (most of South) | R-49 | ~14 inches |
| Zone 4 (Mid-Atlantic, mid US) | R-49 | ~14 inches |
| Zone 5-6 (Midwest, NE) | R-49 to R-60 | ~14-17 inches |
| Zone 7-8 (N tier, AK) | R-60 | ~17 inches |
Materials — what to use
- Loose-fill cellulose — most cost-effective; recycled content; install via blower
- Loose-fill fiberglass — cheaper than cellulose; lower density; settles less but R-value drops at low temperatures
- Spray foam (open or closed cell) — most expensive; adds air sealing; closed cell adds structural rigidity
- Fiberglass batts — DIY-friendly; gaps reduce effective R-value substantially
Air sealing FIRST
Before adding insulation, seal: top plates around interior walls, plumbing/electrical penetrations, recessed light cans (use IC-rated covers), attic hatch (gasket + weatherstripping), bathroom fan housings. Every air leak past the insulation reduces effective R-value.
Federal + utility stack
25C credit: 30% of cost (envelope $1,200/year cap). Most utilities offer $0.10-$0.50/sqft of attic insulation. DOE HOMES at the deep end if combined with whole-home retrofit. Total stack often covers 50-80% of cost.