Wall insulation
Dense-pack cellulose for existing walls: process, cost, and performance. When exterior rigid foam makes sense.
How wall insulation fits in
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.
This page is part of our insulation guide, written by people who install this stuff for a living. For the full picture — costs, sizing, and every rebate that applies — start from the insulation overview.
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. |
More on insulation
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.
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.
Costs are step one
Once you know what it costs, here's how the rest of the project goes.