Wall Insulation (Blown-In) Cost in 2026: What to Expect

Blown-in wall insulation costs $1-$4 per square foot installed. A 1,500 sq ft ranch home typically has 800-1,200 sq ft of exterior wall (accounting for windows and doors). A two-story 2,500 sq ft home may have 1,500-2,000 sq ft of exterior wall. Measure the exterior perimeter, multiply by wall height, and subtract window and door area for a rough estimate.

Blown-in cellulose is the most common choice ($0.50-$0.80/sq ft material) - it is recycled paper with excellent air-sealing properties and achieves R-13 to R-15 in a 3.5-inch wall. Blown-in fiberglass achieves similar R-value. Spray foam (open-cell or closed-cell) costs significantly more ($1.50-$3/sq ft material) but provides superior moisture control and air sealing in high-performance applications.

Drilling from the exterior ($0.20-$0.40/sq ft) means holes in siding that are plugged and painted - cheaper labor but more visible patch work. Drilling from the interior means going through drywall, filling with insulation, and patching - slightly more expensive ($0.30-$0.50/sq ft) but the holes are easier to hide. Homes with composite or fiber cement siding often prefer interior drilling to avoid siding damage.

Many walls in pre-1980 homes have no insulation at all - a blower door test can confirm this. Homes built in the 1980s-1990s may have R-11 fiberglass batts that are adequate. Before spending money on blown-in insulation, confirm your walls are actually empty. Drilling a small test hole is the most reliable way to check.

Standard 2x4 walls (3.5-inch cavity) achieve R-13 to R-15 with blown-in. Homes built with 2x6 framing (5.5-inch cavity) can achieve R-19 to R-21. Older homes sometimes have irregular cavities or fire blocks that interrupt the fill path, requiring additional drilling locations and adding labor cost.

“Will you drill from the interior or exterior, and how will you patch the holes?”

Why this matters: The patching quality determines whether the job is invisible or obvious. Ask to see photos of previous patching work, especially on your siding type.

“What fill density will you achieve, and how do you verify it?”

Why this matters: Dense-pack cellulose should achieve 3.5 lbs/cubic ft. Contractors who can't describe their fill density measurement process may be under-filling, which leads to settling.

“How do you handle fire blocking and horizontal obstructions in the wall cavities?”

Why this matters: Many homes have fire blocks (horizontal 2x4s) that interrupt cavity fills. A good contractor explains how they address this - typically by drilling above and below each block.

“Do you carry thermal imaging equipment to verify complete fill after installation?”

Why this matters: Thermal imaging is the only reliable way to confirm every cavity bay was completely filled. Contractors who won't provide this check leave you guessing about quality.