How to Insulate Walls
Learn how to insulate walls step by step, with the tools, materials, and a free calculator to estimate exactly what you need. To estimate insulation, multiply the length × width of the surface for the square footage, then multiply by the installed cost per square foot for your insulation type. Fiberglass batts run about $1–$2.40/ft², blown-in $1–$2.50, and spray foam $3–$7. A 600 ft² area in batts costs roughly $600–$1,440.
Get exact numbers
Use the free Insulation Calculator to estimate your project.
Tools
- Tape measure
- Utility knife
- Staple gun
- Caulk gun
- Safety glasses & mask
Materials
- Fiberglass batts or blown-in
- Vapor barrier
- Foam sealant
- Insulation supports
Step-by-step
- 1
Measure the surface
Multiply length × width for walls, or the attic floor area.
- 2
Pick an insulation type
Batts are cheapest; spray foam gives the highest R-value per inch and air-seals.
- 3
Check the R-value target
Aim for R-38 to R-60 in attics and R-13 to R-21 in walls, depending on climate.
- 4
Estimate cost
Multiply the area by the installed price per square foot for your type.
Pro tips
- Avoid: under-insulating the attic — The attic is where most heat is lost. Hitting R-38 to R-60 there gives the biggest energy savings.
- Avoid: ignoring air sealing — Insulation slows heat flow but doesn't stop air leaks. Seal gaps and penetrations first for full performance.
- Avoid: compressing batts — Squeezing batts into tight cavities lowers their R-value. Use the right thickness for the cavity.
- Avoid: skipping the vapor barrier — In cold climates, a vapor barrier on the warm side prevents condensation inside walls.