Cost Estimators · Interior Work
Blown-In Insulation Cost Per Sq Ft Calculator
Enter your attic or wall area and instantly estimate blown-in insulation cost — fiberglass or cellulose.
Blown-in insulation is the most cost-effective way to insulate an attic and one of the highest-ROI home improvements you can make. Fiberglass and cellulose blown insulation fill gaps that batt insulation leaves behind — giving you a more complete thermal envelope at a competitive price per sq ft. Use this calculator to estimate your project cost before calling insulation contractors.
Enter an area above to see your estimate
Using national average: $1–$2.5/sq ft
Estimates are based on national averages and are for planning purposes only. Actual costs vary by location, contractor, and material choice.
Example: 1,000 sq ft attic floor
Area
1,000
sq ft
Low Estimate
$1,000
@ $1/sq ft
High Estimate
$2,500
@ $2.5/sq ft
Based on national average rates of $1–$2.5/sq ft. Actual costs will vary by location and contractor.
What does blown-in insulation cost per square foot?
Blown-in fiberglass insulation costs $1–$2 per sq ft installed in an attic. Cellulose blown insulation runs $1–$2.50 per sq ft. Both are significantly cheaper per sq ft than spray foam while still achieving high R-values when applied at the correct depth. Attic air sealing before blowing in insulation adds $0.20–$0.50/sq ft but dramatically improves performance. For wall cavity insulation using injection foam or drill-and-fill cellulose, expect $2–$4/sq ft. For a full insulation type comparison, see our insulation cost per sq ft calculator.
Cost by project size
| Project size | Low estimate | High estimate |
|---|---|---|
| 500 sq ft (small attic) | $500 | $1,250 |
| 800 sq ft | $800 | $2,000 |
| 1,000 sq ft (average attic) | $1,000 | $2,500 |
| 1,500 sq ft | $1,500 | $3,750 |
| 2,000 sq ft (large attic) | $2,000 | $5,000 |
Approximate 2026 US national averages at $1–$2.5/sq ft installed. Actual costs vary by location, contractor, and project complexity.
What affects interior work cost per square foot?
Material: fiberglass vs cellulose
Fiberglass blown insulation costs slightly more per bag but settles less over time. Cellulose is made from recycled paper, has better air resistance, and is often slightly cheaper per sq ft. Both achieve similar R-values per inch when installed correctly.
Target R-value depth
R-38 (about 12 inches of blown cellulose) is the minimum recommended for most US climates. R-49 to R-60 (16–20 inches) is recommended for Climate Zones 5–7. More depth = more material = higher cost per sq ft, but the energy savings justify it.
Air sealing first
Blowing insulation over unsealed gaps and penetrations locks air leaks under the insulation rather than fixing them. Air sealing top plates, penetrations, and attic hatches before blowing adds $0.20–$0.50/sq ft and is the single most impactful step for energy performance.
Existing insulation removal
If the attic has old vermiculite, asbestos-contaminated insulation, or pest-damaged material, it must be professionally removed first — costing $1–$3/sq ft. Clean, dry existing insulation can typically be left in place and new material blown on top.
Attic access & ventilation
Attics with limited access hatches slow installation and may require temporary removal of existing materials. Blown insulation must not block soffit vents — installers use baffles to maintain airflow, which adds a small amount of labour time.
Labour & equipment
Blown insulation requires a blowing machine — most contractors include this in the quote. DIY is possible with rental machines (available at big-box stores for $150–$300/day), but professional installation is typically faster and ensures uniform coverage depth.
Frequently asked questions
How much does blown-in insulation cost per square foot?
Blown-in fiberglass or cellulose insulation costs $1–$2.50 per sq ft installed in an attic. For a 1,000 sq ft attic floor insulated to R-38, expect $1,000–$2,500. Achieving R-49 to R-60 adds about 30–50% more material cost.
Is blown-in insulation better than batts?
Blown-in insulation fills gaps and irregular spaces that batt insulation leaves behind — particularly around joists, wiring, and odd-shaped areas. This makes it a better air barrier in practice. For attics, blown-in is the preferred professional choice. In open wall cavities during construction, batts are faster to install.
What is the difference between fiberglass and cellulose blown insulation?
Fiberglass blown insulation is made from glass fibres and is non-combustible. Cellulose is made from recycled newsprint treated with fire retardant. Cellulose has slightly better air resistance per inch and is more environmentally friendly. Both achieve similar R-values. Fiberglass settles slightly less over time.
Can blown-in insulation be added over existing insulation?
Yes — in most cases, new blown-in insulation can be added directly over existing fiberglass batts or blown material. The existing insulation provides a base layer and reduces how much new material is needed. If the existing insulation is damaged, wet, or pest-contaminated, it must be removed first.
How long does blown-in insulation installation take?
A professional crew can insulate a 1,000 sq ft attic floor in 2–4 hours. Air sealing adds 1–2 hours. The entire project including prep and clean-up is typically completed in half a day to a full day for an average home.