Compute the total R-value of your attic insulation from depth and material type. Compare to DOE recommended ranges and IECC code minimums for your climate zone. Supports multi-layer attics where new insulation has been added over old.
Reviewed May 22, 2026
Add one layer per distinct material in your attic (e.g., original fiberglass batts plus newer blown-in cellulose). Measure depth in inches at multiple points and use a typical value. Click Calculate to see your total R-value, status against DOE recommendations, an R-value gauge, and upgrade depth by material if needed.
Insulation layers
Layer 1
inches deep
Enter your insulation layers above, then click Calculate
Result will appear here with the total R-value, R-value gauge, layer breakdown, upgrade material options, and energy savings estimate.
Climate zone is the single most important input in any HVAC sizing decision — it drives both heating and cooling design temperatures and the equipment-class recommendation. The reference card below covers all eight US climate zones with sample cities and design temperatures.
The single most important reference for attic insulation decisions is the DOE / ENERGY STAR recommended R-value range for your climate zone. The chart below shows the recommended range across all eight IECC climate zones — from R-30 in the south (where heating loads are minimal) to R-60 in the far north (where every inch of insulation cuts winter heat loss).
The calculator above checks your computed R-value against this DOE range AND against the IECC code minimum (the legal floor for new construction). Most older homes are grandfathered to the code that existed when they were built — often well below current DOE recommendations. Topping off to the upper end of the DOE range is the cost-optimal target for retrofits in cold climates.
The default state shows the calculator's answer for a typical attic with 8 inches of blown-in cellulose insulation, in IECC climate zone 5 (most of the northern US).
The math:
The calculator uses the following R-per-inch values, documented in our attic R-value article. These align with major insulation manufacturer literature and DOE Energy Saver values.
| Material | R per inch | Depth for R-49 |
|---|---|---|
| Fiberglass batt | 3.0 | 16.3″ |
| Loose-fill fiberglass (blown) | 2.3 | 21.3″ |
| Loose-fill cellulose (blown) | 3.6 | 13.6″ |
| Mineral wool batt | 3.6 | 13.6″ |
| Open-cell spray foam | 3.6 | 13.6″ |
| Closed-cell spray foam (aged) | 6.5 | 7.5″ |
| Polyiso rigid (aged) | 6.5 | 7.5″ |
| XPS rigid | 5.0 | 9.8″ |
| EPS rigid | 4.0 | 12.3″ |
The calculator compares your total R-value to two benchmarks: DOE recommended ranges (for existing-home retrofits, slightly aspirational) and IECC 2021 code minimums (legal floor for new construction). Older homes are typically grandfathered to the code in effect when built; DOE recommendations target the higher of the two ranges as the cost-effective target for retrofits.
Air leakage. The biggest limitation. R-value rates resistance to conductive heat flow. It does nothing for air infiltration through unsealed penetrations (recessed lights, top plates, plumbing chases, the attic hatch). Field studies routinely find 30-50% effective R-value reduction in attics with code insulation but no air sealing. Air seal first.
Compression and settling. Compressed batts (foot traffic) and settled loose-fill insulation read lower than nominal. Measure current depth, not what was installed.
Moisture damage. Wet insulation is approximately R-0 until dried. Visible water staining or mold indicates the layer may need removal, not just top-off.
The energy savings from added attic insulation come from two physical effects. First, R-value reduces conductive heat loss through the ceiling proportional to the inverse of total R. Going from R-19 to R-49 (typical retrofit) cuts ceiling conduction by roughly 60-65% in heating mode. Second, a well-insulated ceiling keeps the radiant surface temperature closer to room air temperature, improving occupant comfort and allowing the same thermostat setting to feel warmer in winter / cooler in summer.
For a typical 2,000 sq ft home in zone 5 with 1,500 sq ft of attic area, going from R-19 to R-49 cuts heating load by roughly 1,500 BTU/hr at the design temperature and reduces annual heating cost by about $200-$400 depending on fuel and price. Cooling savings are smaller (about $50-$100) because cooling design conditions involve smaller temperature differences. The cellulose top-off cost ($2,000-$3,500 for 1,500 sq ft) pays back in 6-12 years in cold climates and longer in mild ones. The attic R-value article walks through the cost-payback math by climate zone with worked examples.
A professional energy audit measures attic insulation depth at multiple points, identifies thermal bridging through joists, performs a blower-door test for air leakage, runs a thermal imaging scan to find missing insulation and air leakage paths, and produces a Home Energy Rating System (HERS) Index score. The output is a comprehensive whole-home retrofit plan, not just an R-value number.
This calculator answers the narrow question "what is my attic R-value and how does it compare to recommendations?". For HEEHRA rebate eligibility, IRA 25C tax credit documentation, and HERS-based new-construction certification, a credentialed audit is required. The HERS Index article covers what a professional audit produces and how it differs from a calculator output like this one.
The most frequent attic-insulation errors that show up in DOE Building America field studies and BPI certified-auditor reports.
Insulation rated R-49 in a leaky attic performs as if it were R-25 to R-30 because warm interior air rushes through gaps around top plates, recessed lights, plumbing chases, and the attic hatch — bypassing the insulation entirely. Air seal first. The DOE air-sealing guide identifies bath fan housings, recessed lights, plumbing penetrations, the attic hatch perimeter, and top-plate gaps as the priority targets.
A R-30 batt rated at full thickness (8.25" fiberglass batt) compressed to 6" of depth delivers about R-21, not R-30. Compression reduces effective R-value proportionally to the compression ratio. The fix is to use loose-fill blown insulation in irregular cavity geometries instead of cut-to-fit batts.
Standard recessed light cans are not rated for direct insulation contact (non-IC). Burying them in loose-fill insulation creates a fire hazard. Either replace with IC-rated airtight LED cans before insulating, or build airtight enclosures around non-IC cans. Many older homes have a mix that needs inventory before insulation.
The attic hatch is typically R-2 to R-5, surrounded by R-49 insulation. The hatch becomes a thermal bridge that conducts proportionally more heat than its area suggests. Weatherstrip the hatch perimeter and install a removable insulating cover above it (R-30+ rigid foam) for an inexpensive but high-impact upgrade.
Cathedral ceilings, vaulted living rooms, and second-floor knee-wall systems have their own insulation challenges that loose-fill attic insulation does not solve. These spaces typically need rigid foam between rafters or spray foam, both of which have different cost and contractor-skill requirements than blown-in attic floor work.
Pre-computed R-value calculations for typical attic insulation scenarios across climate zones. Each example shows total R-value, DOE comparison, and upgrade recommendation.
R-18.9 · zone 4
R-29.9 · zone 4
R-37.8 · zone 4
R-49.0 · zone 5
R-60.1 · zone 6
R-18.0 · zone 5
R-43.2 · zone 5
R-46.8 · zone 5
R-32.5 · zone 5
R-29.9 · zone 3
R-37.8 · zone 5
R-18.9 · zone 7
DOE recommended R-values by climate zone, insulation types, and methodology behind this calculator.
DOE recommended R-values by climate zone, R-per-inch by material, payback analysis, and the air-sealing primacy discussion.
U-factor is R-value's cousin; both express resistance to heat flow.
Reviewed May 22, 2026