Insulation: what to know before you upgrade.
Types, R-values, costs, and which rebates cover the work. The envelope is the foundation — everything else performs better when insulation is right.
What to know about insulation
Insulation slows heat transfer through your home's envelope: attic, walls, basement, and crawlspace. The R-value measures resistance to heat flow — higher is better. Most older homes are significantly under-insulated by modern standards. Upgrading insulation is typically the highest-ROI energy improvement because it reduces both heating and cooling loads, makes heat pumps perform better, and improves comfort. Dense-pack cellulose and rigid foam are preferred for retrofits; fiberglass batts are common but often poorly installed.
What does it cost?
Typical installed costs before rebates. Your actual cost depends on home size, accessibility, and local labor rates.
| Type | Low | High | Notes |
|---|---|---|---|
| Attic insulation (blown-in cellulose) | $1,500 | $3,500 | Most common upgrade. R-49 to R-60 target. |
| Wall insulation (dense-pack cellulose) | $3,000 | $8,000 | Requires drilling and filling wall cavities. |
| Basement / crawlspace (rigid foam) | $2,000 | $5,000 | Rim joist + foundation wall. |
| Spray foam (closed-cell) | $5,000 | $12,000 | Highest R-value per inch. Best for rim joists and cathedral ceilings. |
Everything about insulation
7 in-depth guides covering costs, rebates, types, and installation.
Insulation costs
Cost per square foot by type and location. What affects price: accessibility, prep work, and health & safety.
Insulation rebates
State and utility rebates for insulation upgrades. Many programs cover 40-100% of the cost.
Attic insulation
R-value targets by climate zone, blown-in vs. batts, air sealing the attic floor first, and common mistakes.
Wall insulation
Dense-pack cellulose for existing walls: process, cost, and performance. When exterior rigid foam makes sense.
Basement insulation
Rim joist, foundation walls, and floor insulation. Moisture management is critical.
Blown-in cellulose
Why cellulose is the preferred retrofit material: fire resistance, air sealing, moisture buffering, and environmental profile.
Spray foam
Open-cell vs. closed-cell, where each is appropriate, health considerations, and cost comparison.
Common questions
What R-value do I need?
It depends on your climate zone and where in the home. Attics in Climate Zones 5-7 (northern US) should target R-49 to R-60. Walls should be R-13 to R-21. Basement rim joists R-15 to R-30. Use the DOE's climate zone map and our Guided Audit to get a specific recommendation.
Is cellulose or fiberglass better?
For retrofit applications, dense-pack cellulose outperforms fiberglass batts in real-world conditions. Cellulose fills cavities completely (no gaps), provides better air sealing when dense-packed, has superior fire resistance due to borate treatment, and buffers moisture. Fiberglass batts often leave gaps at wiring, pipes, and irregular framing.
How much can insulation save on energy bills?
Typical savings range from 15-40% of heating and cooling costs, depending on how under-insulated the home was. An attic upgrade from R-11 to R-49 in a northern climate can save $400-$800/year. The payback period after rebates is usually 2-5 years.
Do I need air sealing too?
Yes. Air sealing and insulation should always be done together. Air leaks can carry 10-20x more heat through an insulated wall than conduction alone. Seal penetrations, top plates, rim joists, and attic bypasses before adding insulation.