Our Methodology
We do not guess. The calculator uses published standards, climate averages, and transparent formulas.
The Science Behind the Score
The Insulation ROI Calculator uses a deterministic model based on the 2021 International Energy Conservation Code (IECC), U.S. Department of Energy (DOE) retrofit guidance, and state-level energy price averages.
1. Climate Zone Selection
We use a conservative ZIP lookup for supported locations and ask for manual climate-zone selection when a ZIP is not in the local lookup yet. That avoids silently assigning the wrong zone to your home.
2. R-Value Calculation
We calculate your current thermal resistance using standard industry multipliers:
- Fiberglass Batts: about R-3.2 per inch
- Blown-in Cellulose: about R-3.5 per inch
- Closed Cell Spray Foam: about R-6.5 per inch
3. The Efficiency Gap
Your efficiency score represents how close your current insulation is to the retrofit target recommended for existing homes. We use retrofit targets because they are more realistic for attic upgrades than new-construction requirements.
4. Savings and Payback
Savings estimates combine climate load, attic size, current insulation level, heating system efficiency, and state-level fuel costs. Payback is the estimated upgrade cost divided by yearly savings.