Calculate insulation R-value, heat loss, energy savings, and payback period for walls, attics, and floors. Compare materials and recommended levels.
R-value measures thermal resistance — how well insulation resists heat flow. Higher R-values mean better insulation and lower energy bills. Understanding R-values is essential for meeting building codes, reducing heating/cooling costs, and improving comfort. It also helps explain why two wall assemblies with similar thickness can perform very differently. The details of layering and thermal bridging matter just as much as the insulation label. In practice, assembly-level performance is what determines comfort and load.
This calculator computes the total R-value of a wall, ceiling, or floor assembly from individual material layers, then estimates heat loss, energy cost, and savings from upgrading. It covers all common insulation materials from fiberglass batts to spray foam, with recommended R-values by climate zone.
Whether you're building a new home, retrofitting insulation, or comparing material options, this tool provides the thermal performance data and financial analysis to make informed decisions. The payback calculator shows how quickly insulation upgrades pay for themselves in energy savings.
Use this calculator when you want to compare insulation layers, estimate heat loss, or see whether an upgrade meaningfully changes the thermal performance of an assembly. It is useful for retrofit planning, code discussions, and deciding where added insulation is likely to pay back first. It also helps turn a nominal R-value into an energy and comfort tradeoff you can explain clearly.
R-total = ΣRᵢ where Rᵢ = thickness / conductivity. Heat loss: Q = A × ΔT / R-total. U-value = 1/R-total. Annual energy cost = Q × degree-days × 24 / (efficiency × 1000000) × rate.
Result: R-13 wall, 3,077 BTU/h heat loss, ~$480/year heating cost
3.5 inches of fiberglass batt in a 1000 sq ft wall with 40°F temperature difference yields R-13, typical for a 2×4 wall assembly.
R-value (thermal resistance) is the inverse of thermal conductivity per unit thickness: R = thickness / k. Materials with low k values (like foam and fiberglass) make excellent insulation. Still air has very low conductivity (k = 0.024 W/m·K at 20°C), which is why most insulation works by trapping air in small pockets.
The total R-value of a wall or ceiling assembly is the sum of all layer R-values, including interior and exterior air films (typically R-0.7 interior, R-0.2 exterior). The whole-assembly R-value determines actual thermal performance.
The US DOE defines 8 climate zones. Zone 1 (Miami) needs minimal insulation, while Zone 7-8 (Alaska, northern Minnesota) needs maximum. Current IECC codes require R-49 to R-60 attic insulation in cold climates and R-20 + R-5 continuous for walls. These requirements have steadily increased as energy costs rise.
The payback period for insulation depends on climate severity, energy prices, and existing insulation level. Going from R-0 to R-13 in walls saves dramatically, while going from R-30 to R-50 in an attic provides smaller incremental savings. The law of diminishing returns applies — each additional R-value provides less energy savings than the previous one.
It depends on climate zone. Zone 1-2 (hot): R-13 walls, R-30 attic. Zone 3-5 (mixed): R-20 walls, R-38 attic. Zone 6-8 (cold): R-21+ walls, R-49-60 attic.
U-value = 1/R-value. U-value measures heat transfer rate (lower is better); R-value measures resistance (higher is better). Windows are typically rated by U-value.
Yes — R-values are additive when layers are in series. R-13 fiberglass + R-5 foam board = R-18 total. This is one of the most useful properties of R-value.
Closed-cell spray foam has the highest R-value per inch (R-6.5-7). But fiberglass (R-3.2-3.8/inch) is much cheaper. The "best" depends on space constraints and budget.
A still air gap provides about R-1 per inch. But if air can circulate (convection), the effective R-value drops near zero. Air barriers are essential for any insulation system.
Studs, joists, and other solid members bypass insulation, creating paths of high heat flow. Wood studs reduce effective wall R-value by 15-25%. Steel studs are worse.