The attic is the highest-impact, most cost-effective insulation upgrade in most central Illinois homes. But "how much does it cost" is not a simple question because attic insulation projects vary significantly based on the material, the existing conditions, and whether air sealing is included. This guide breaks down attic insulation costs by material type, by project scenario, and by the factors that move your price up or down.
Here are the typical installed costs for attic insulation in central Illinois:
Blown-in cellulose (attic floor, R-49): $1.50 to $3.00 per square foot
Blown-in fiberglass (attic floor, R-49): $1.00 to $1.75 per square foot
Spray foam, open-cell (roof deck, 5.5"): $1.90 to $3.00 per square foot
Spray foam, closed-cell (roof deck, 3"): $3.00 to $4.50 per square foot
Fiberglass batts (new construction attic floor, R-38): $1.25 to $2.00 per square foot
Attic air sealing (comprehensive): $300 to $800 as an add-on to insulation
These are professional installation costs including material, labor, and equipment. The material you need depends on your attic type, your existing insulation, and whether your attic contains HVAC equipment. We explain each option below.
Blown-in cellulose on the attic floor is the most popular attic insulation upgrade for existing central Illinois homes. It is dense, fills irregularities in the joist bays, resists air movement through the insulation layer, and costs less per R-value than any other professional option.
| Project | Target R-Value | Depth | Approx. Cost |
|---|---|---|---|
| 1,000 sq ft attic | R-49 | 14-15" settled | $1,500 to $3,000 |
| 1,500 sq ft attic | R-49 | 14-15" settled | $2,250 to $4,500 |
| 2,000 sq ft attic | R-49 | 14-15" settled | $3,000 to $6,000 |
| Top-off R-19 to R-49 | R-30 additional | 8-9" additional | $1,000 to $2,000 |
Note: If your attic already has R-19 or more of clean, dry insulation, blowing additional cellulose on top to reach R-49 costs significantly less than insulating from bare joists because less material is needed.
Learn more about blown-in insulationBlown-in fiberglass is a strong alternative to cellulose, particularly for attics with a history of moisture issues (past roof leaks, condensation). Fiberglass does not absorb water and settles less than cellulose. It costs slightly less per square foot but requires more depth to reach the same R-value.
| Project | Target R-Value | Depth | Approx. Cost |
|---|---|---|---|
| 1,000 sq ft attic | R-49 | 16-20" | $1,000 to $1,750 |
| 1,500 sq ft attic | R-49 | 16-20" | $1,500 to $2,625 |
| 2,000 sq ft attic | R-49 | 16-20" | $2,000 to $3,500 |
Instead of insulating the attic floor, spray foam can be applied to the underside of the roof deck. This converts the attic into conditioned space. It is the right approach when HVAC ductwork or air handlers are located in the attic, when the attic is used as living or storage space, or when chronic ice dams cannot be solved with floor-level insulation alone.
Spray foam on the roof deck costs two to three times more than blown-in on the attic floor. The higher cost is justified only when the attic needs to be inside the conditioned envelope.
| Project | Foam Type | Thickness | Approx. Cost |
|---|---|---|---|
| 1,000 sq ft roof deck | Open-cell | 5.5" (R-20) | $1,900 to $3,000 |
| 1,500 sq ft roof deck | Open-cell | 5.5" (R-20) | $2,900 to $4,500 |
| 1,000 sq ft roof deck | Closed-cell | 3" (R-20) | $3,000 to $4,500 |
| 1,500 sq ft roof deck | Closed-cell | 3" (R-20) | $4,500 to $6,750 |
Fiberglass batts laid between attic floor joists are primarily used in new construction when the attic is open and accessible before drywall is installed. For existing homes, blown-in is almost always the better choice because batts cannot be installed over existing insulation or around obstructions without significant gaps.
| Project | Target R-Value | Approx. Cost |
|---|---|---|
| 1,000 sq ft attic floor | R-38 (batts) | $1,250 to $2,000 |
| 1,500 sq ft attic floor | R-38 (batts) | $1,875 to $3,000 |
Air sealing is not optional. It is the step that makes attic insulation effective. Without it, warm air convects through the insulation layer via gaps around electrical boxes, plumbing stacks, HVAC chases, recessed lights, and interior wall top plates. Adding insulation over unsealed penetrations improves thermal resistance but does not stop the air leakage that drives 25% to 40% of attic heat loss.
Most insulation contractors in central Illinois offer air sealing as part of a complete attic insulation project. Here is what it typically costs:
| Service | Approx. Cost |
|---|---|
| Comprehensive attic air sealing (caulk, foam, rigid board, fire-rated covers) | $300 to $800 |
| Air sealing + blown-in cellulose to R-49 (1,000 sq ft attic) | $1,800 to $3,800 |
| Air sealing + blown-in cellulose to R-49 (1,500 sq ft attic) | $2,550 to $5,300 |
When air sealing is combined with insulation in the same project, the per-square-foot cost is lower than hiring two separate contractors or scheduling two separate visits. We include air sealing in every attic insulation proposal because insulation without air sealing underperforms.
Learn more about our attic insulation and air sealing process| Add-On Service | Approx. Cost | When It Applies |
|---|---|---|
| Old insulation removal | $1.00 to $2.00 per sq ft | Existing insulation is pest-contaminated, moldy, or water-damaged |
| Rafter baffle installation | $5 to $15 per bay | Required in vented attics to keep insulation from blocking soffit vents |
| Bathroom vent extension to exterior | $150 to $400 per vent | Bathroom fan currently terminates in the attic (common in older homes) |
| Attic hatch or pull-down stair insulation | $50 to $200 | Uninsulated attic access point |
| Recessed light covers (IC-rated) | $10 to $25 per can | Required before burying recessed lights in insulation |
| Knob-and-tube wiring evaluation | Varies (electrician cost) | Must be assessed before insulation if present |
Not every project includes these costs. Old insulation removal is only needed when the existing material is genuinely compromised. Rafter baffles are standard on most projects and typically included in the base estimate. Bathroom vent extensions and recessed light covers are common add-ons that we identify during your free estimate.
Blown-in fiberglass is the least expensive. Blown-in cellulose costs slightly more but performs better in most applications. Spray foam on the roof deck costs two to three times more than blown-in on the floor. The right material depends on your attic type, not your budget.
Topping off an attic that already has R-19 costs less than insulating an attic with bare joists because less new material is needed. We measure your existing insulation depth during the estimate and calculate the material needed to reach R-49.
Larger attics cost more in total but less per square foot. A 2,000-square-foot attic costs less per square foot than a 1,000-square-foot attic because the crew and equipment setup is the same regardless of size.
Attics with tight access hatches, low roof pitches, HVAC equipment blocking work areas, or multiple levels are more labor-intensive. Walk-up attics with full standing height and clear floor space are the easiest and least expensive to insulate.
A newer home with minimal attic penetrations needs less air sealing work than a 1950s home with open top plates, unsealed plumbing stacks, and a dozen recessed light cans. The more penetrations that need sealing, the higher the air sealing cost.
If existing insulation needs to be removed (pest damage, mold, water damage), that adds $1.00 to $2.00 per square foot to the project. Most attics do not require removal. We recommend it only when the existing material is genuinely compromised.
For most central Illinois homes, attic insulation is the single highest-ROI energy upgrade available. Here is the math:
A typical central Illinois home spends $2,000 to $3,000 per year on heating and cooling. The attic is responsible for 25% to 30% of total heat loss in homes with inadequate insulation. Upgrading a 1,500-square-foot attic from R-19 to R-49 with air sealing typically costs $2,500 to $5,000 and reduces annual heating and cooling costs by 15% to 25%.
At a 20% energy savings on a $2,500 annual bill, the upgrade saves $500 per year. A $3,500 project pays for itself in seven years. The insulation lasts 30 to 50 years. That is 23 to 43 years of savings after payback.
Beyond energy savings, attic insulation eliminates ice dams, reduces temperature swings between floors, extends HVAC equipment life by reducing runtime, and improves comfort in every room directly below the attic.
Schedule your free attic insulation estimate| Factor | Blown-In Cellulose | Blown-In Fiberglass | Spray Foam (Roof Deck) | Fiberglass Batts |
|---|---|---|---|---|
| Cost Per Sq Ft (R-49) | $1.50 - $3.00 | $1.00 - $1.75 | $1.90 - $4.50 | $1.25 - $2.00 |
| R-Value Per Inch | R-3.2 - R-3.8 | R-2.2 - R-2.7 | R-3.5 - R-7.0 | R-3.1 - R-3.8 |
| Depth for R-49 | 14-15" | 16-20" | 5.5" - 8" | 12-13" |
| Air Sealing | Moderate | Minimal | Excellent | None |
| Best For | Existing home attic floors | Moisture-prone attics | Attics with HVAC equipment | New construction only |
| Settling | 15-20% (accounted for) | 5% or less | None | None |
| Lifespan | 30-50+ years | 30-50+ years | Life of building | 30-50+ years |
For existing central Illinois homes with standard unconditioned attics, blown-in cellulose on the attic floor with comprehensive air sealing delivers the best performance per dollar. It is what we recommend for the majority of our attic projects.
For a 1,500-square-foot attic in central Illinois, blown-in cellulose insulation to R-49 with air sealing typically costs $2,550 to $5,300. Blown-in fiberglass without air sealing runs $1,500 to $2,625. Spray foam on the roof deck (open-cell, 5.5 inches) runs $2,900 to $4,500. The right option depends on your attic type and existing conditions.
Topping off an attic that already has some insulation is less expensive than starting from bare joists. If your attic has R-19 of clean, dry insulation and you want to reach R-49, you need approximately 8 to 9 additional inches of cellulose. For a 1,000-square-foot attic, this typically costs $1,000 to $2,000.
Both. Air sealing addresses the air leakage that drives 25% to 40% of attic heat loss. Insulation addresses conductive heat transfer. Adding insulation without air sealing is like putting on a thicker coat while leaving the zipper open. Air sealing adds $300 to $800 to a typical attic project and significantly improves the performance of whatever insulation you install.
Insulating the attic floor with blown-in material is significantly cheaper. Blown-in cellulose at R-49 costs $1.50 to $3.00 per square foot. Spray foam on the roof deck costs $1.90 to $4.50 per square foot. The roof deck approach is only worth the extra cost when the attic contains HVAC equipment or needs to be conditioned space.
Only if the old insulation is contaminated by pests, wet from leaks, or containing mold. If it is dry and in reasonable condition, new blown-in material is installed directly on top. Removal adds $1.00 to $2.00 per square foot. We recommend it only when genuinely necessary.
Blown-in cellulose and fiberglass last 30 to 50 years or longer when kept dry and undisturbed. Spray foam lasts the life of the building. The primary reason attic insulation fails early is moisture from roof leaks, condensation, or bathroom fans venting into the attic.
You can rent a blowing machine from a home improvement store and blow fiberglass or cellulose yourself. The material cost is lower, but you will skip the air sealing step (which is what makes the insulation effective), you may not achieve uniform depth, and you risk blocking soffit vents without rafter baffles. Professional installation costs $1.00 to $3.00 per square foot and includes air sealing, baffle installation, depth verification, and proper coverage around all obstacles.
Yes. We provide free, on-site attic insulation estimates throughout our central Illinois service area. We enter the attic, measure existing insulation depth, identify air leakage points, and provide a written proposal with specific pricing. Call (217) 508-8095 or submit a request online.
The ranges in this guide give you a starting point, but your actual cost depends on your attic size, existing insulation, accessibility, and air sealing needs. We provide free, detailed estimates with exact pricing. No guesswork. No national averages. Just what your attic project will cost in central Illinois.