Illinois Insulation Planner: Climate Zone & R-Value Guide
Plan additional attic, wall, floor, or basement/crawlspace insulation using your own current R-value and a fully editable planning target, with broad Illinois regional climate context — never a code or jurisdiction determination.
Estimate how much additional insulation you may need based on your own planning target. This tool provides broad regional climate context only — it does not determine your county, township, or municipal jurisdiction, and the target R-value below is a user-selected planning goal, not a legal or code requirement.
Existing insulation value, if any. Use 0 if uninsulated.
Your own goal — pre-filled with a typical attic / roof reference for central illinois, but fully editable. Not a code requirement.
Area to insulate is required.
Optional — used to estimate approximate added thickness.
Optional — from the product label, at your planned thickness/R-value.
Package coverage at planned thickness is required.
Central Illinois — IECC Zone 5 (cool)
Roughly the Springfield / Peoria / Bloomington corridor. Broad climate context only — not a jurisdiction or county determination.
Enter a current R-value, planning target, and area to see your estimate.
Before you buy or install
- Air-sealing (gaps, penetrations, top plates, attic hatches) is typically more cost-effective than added insulation alone and should be addressed first.
- Resolve roof leaks, plumbing leaks, or moisture/condensation problems before insulating — trapping moisture inside an assembly can cause rot or mold.
- In attics, keep soffit vents clear of insulation (use baffles) to preserve roof/attic ventilation.
- Maintain clearance around chimneys, flues, recessed lighting, and electrical components per the product's fire-safety instructions.
- If you suspect vermiculite insulation, asbestos-containing materials, or mold, stop and consult a qualified professional before disturbing any material.
Always verify your specific county/municipal requirements, the current Illinois-adopted energy code edition, and any local amendments with your local building department before starting work. Use the Illinois Permit Finder to find a likely local permit authority and contact information.
This tool provides a planning estimate only. Always verify field measurements, product packaging and supplier yields, manufacturer instructions, and local code and permit requirements before purchasing materials or beginning work. This calculator does not collect or save any personal information — nothing you enter here is stored.
How this is calculated
The planner works from a simple gap calculation, then converts that gap into practical shopping numbers:
additional R needed = planning target R − current Rapproximate added thickness (in) = additional R ÷ product R-per-inch(only shown once you enter a product R-value per inch)packages needed = area ÷ package coverage at your planned thickness(only shown once you enter package coverage)
The pre-filled planning target for each region/assembly pair is a general reference point only — you can change it at any time, and your own value is preserved even if you switch region or assembly afterward.
Worked example
For a central Illinois attic with 1,200 sq ft of floor area, an existing R-19, a planning target of R-49, a product rated R-3.7 per inch, and package coverage of 32 sq ft at that thickness:
- Additional R needed49 − 19 = R-30
- Approximate added thickness30 ÷ 3.7 ≈ 8.1 in
- Estimated packages1,200 ÷ 32 ≈ 38 packages
Measuring tips
To estimate your current R-value, measure the depth of existing loose-fill or batt insulation with a tape measure at several spots and compare it to your material's R-per-inch rating (often printed on attic joist rulers or the original product packaging).
Measure area as the floor footprint of the space (attic floor, wall face, or basement wall), subtracting areas you won't insulate such as mechanical platforms or storage decking, and round up slightly to account for framing members and irregular corners.