{
  "id": "insulation",
  "version": "b3c2cfd67efd",
  "status": "published",
  "name": "Insulation Calculator",
  "question": "How much insulation do I need?",
  "summary": "Finds the R-value to add to an attic or floor for your climate zone, the depth of insulation that gives it, and the volume to cover the area.",
  "category": "construction",
  "subcategory": "materials",
  "url": "https://www.acalculator.org/construction/insulation-calculator",
  "markdown": "https://www.acalculator.org/construction/insulation-calculator.md",
  "kind": "function",
  "method": "R to add = the zone’s value for the place; depth (in) = R ÷ R per inch; volume = area × depth.",
  "assumptions": [
    "The R-values are ENERGY STAR’s recommendations for adding insulation to existing wood-framed homes; your local code may ask for more in new work.",
    "R-value per inch differs by product and how it is installed; use the number on the bag or batt label when you have it.",
    "Blown insulation settles; the bag label gives the installed depth and the number of bags for each R-value, which this page does not count."
  ],
  "inputs": {
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "type": "object",
    "properties": {
      "zone": {
        "title": "Climate zone",
        "description": "Your IECC climate zone, from 1 (hottest) to 8 (coldest).",
        "type": "string",
        "enum": [
          "1",
          "2",
          "3",
          "4",
          "5",
          "7"
        ]
      },
      "where": {
        "title": "Where",
        "description": "An attic with no insulation, an attic that already has 3 to 4 inches, or a floor over an unheated space.",
        "type": "string",
        "enum": [
          "attic",
          "topup",
          "floor"
        ]
      },
      "a": {
        "title": "Area to insulate",
        "description": "The floor area of the attic, or the area of the floor.",
        "type": [
          "number",
          "string"
        ],
        "x-quantity": "area",
        "minimum": 0.1,
        "maximum": 1000000
      },
      "rpi": {
        "title": "R-value per inch",
        "description": "The R-value one inch of your insulation gives, from its label (about 3 for blown fiberglass or cellulose).",
        "type": "number",
        "minimum": 1,
        "maximum": 8
      }
    }
  },
  "outputs": {
    "r": {
      "label": "R-value to add",
      "description": "The recommended R-value to add for this zone and place (US units, ft²·°F·h/Btu).",
      "format": "integer"
    },
    "inches": {
      "label": "Depth (in)",
      "description": "R-value to add ÷ R-value per inch.",
      "format": "number"
    },
    "cm": {
      "label": "Depth (cm)",
      "description": "The same depth in centimetres.",
      "format": "number"
    },
    "cubicFeet": {
      "label": "Volume (ft³)",
      "description": "Area × depth: the insulation to fill the space, in cubic feet.",
      "format": "number"
    },
    "cubicMeters": {
      "label": "Volume (m³)",
      "description": "The same volume in cubic metres.",
      "format": "number"
    },
    "rsi": {
      "label": "RSI to add",
      "description": "The R-value in metric units (m²·K/W): R × 0.1761102.",
      "format": "number"
    }
  },
  "defaultAnswer": {
    "inputs": {
      "zone": "4",
      "where": "attic",
      "a": 92.90304,
      "rpi": 3
    },
    "outputs": {
      "r": 60,
      "inches": 20,
      "cm": 50.8,
      "cubicFeet": 1666.6666666666667,
      "cubicMeters": 47.19474432,
      "rsi": 10.566612
    },
    "text": "Add R-60: about 20 inches of insulation, 1,667 cubic feet over the area."
  },
  "examples": [
    {
      "given": {
        "zone": "4",
        "where": "attic",
        "a": 92.90304,
        "rpi": 3
      },
      "expect": {
        "r": 60,
        "inches": 20,
        "cm": 50.8,
        "cubicFeet": 1666.6666666666667,
        "rsi": 10.566612
      },
      "source": "ENERGY STAR, Recommended Home Insulation R-Values (retrofit of existing wood-framed buildings, based on 2021 IECC Table R402.1.3), https://www.energystar.gov/saveathome/seal_insulate/identify-problems-you-want-fix/diy-checks-inspections/insulation-r-values (zone 4A and 4B, uninsulated attic: R60); ENERGY STAR, How to Check Your Home’s Attic Insulation Level (fiberglass, cellulose and mineral wool about R-3 to R-3.5 per inch; depth × 3), https://www.energystar.gov/products/ask-the-experts/how-check-your-homes-attic-insulation-level; hand calculation in content.mdx: 60 ÷ 3 = 20 in; 1,000 × 20 ÷ 12 = 1,666.7 ft³"
    },
    {
      "given": {
        "zone": "2",
        "where": "topup",
        "a": 139.35456000000002,
        "rpi": 2.5
      },
      "expect": {
        "r": 38,
        "inches": 15.2,
        "cubicFeet": 1900
      },
      "source": "ENERGY STAR, Recommended Home Insulation R-Values (retrofit of existing wood-framed buildings, based on 2021 IECC Table R402.1.3), https://www.energystar.gov/saveathome/seal_insulate/identify-problems-you-want-fix/diy-checks-inspections/insulation-r-values (zone 2, 3–4 in existing: add R38); hand calculation in content.mdx: 38 ÷ 2.5 = 15.2 in; 1,500 × 15.2 ÷ 12 = 1,900 ft³"
    },
    {
      "given": {
        "zone": "7",
        "where": "floor",
        "a": 100,
        "rpi": 3.5
      },
      "expect": {
        "r": 38,
        "inches": 10.857142857142858,
        "cubicMeters": 27.577142857142857
      },
      "source": "ENERGY STAR, Recommended Home Insulation R-Values (retrofit of existing wood-framed buildings, based on 2021 IECC Table R402.1.3), https://www.energystar.gov/saveathome/seal_insulate/identify-problems-you-want-fix/diy-checks-inspections/insulation-r-values (zones 7 and 8, floor: R38); hand calculation in content.mdx: 38 ÷ 3.5 = 10.857 in = 27.58 cm; 100 × 0.27577 = 27.58 m³",
      "tolerance": 1e-12
    },
    {
      "given": {
        "zone": "1",
        "where": "attic",
        "a": 92.90304,
        "rpi": 3
      },
      "expect": {
        "r": 30,
        "inches": 10
      },
      "source": "ENERGY STAR, Recommended Home Insulation R-Values (retrofit of existing wood-framed buildings, based on 2021 IECC Table R402.1.3), https://www.energystar.gov/saveathome/seal_insulate/identify-problems-you-want-fix/diy-checks-inspections/insulation-r-values (zone 1, uninsulated attic: R30); DOE, Energy Efficient Home Improvement Credit: Insulation and Air Sealing (zone 1 uninsulated attic R30), https://www.energy.gov/cmei/buildings/articles/energy-efficient-home-improvement-credit-insulation-and-air-sealing"
    }
  ],
  "sources": [
    "ENERGY STAR (US EPA), Recommended Home Insulation R-Values: recommended insulation levels for retrofitting existing wood-framed buildings by zone (attic uninsulated, attic with 3–4 in, floor), based on the 2021 IECC Table R402.1.3. https://www.energystar.gov/saveathome/seal_insulate/identify-problems-you-want-fix/diy-checks-inspections/insulation-r-values (retrieved 2026-10-02)",
    "US Department of Energy, Energy Efficient Home Improvement Credit: Insulation and Air Sealing: minimum ceiling R-value in an uninsulated attic by climate zone under the 2021 IECC (R30, R49, R49, R60 …). https://www.energy.gov/cmei/buildings/articles/energy-efficient-home-improvement-credit-insulation-and-air-sealing (retrieved 2026-10-02)",
    "ENERGY STAR, How to Check Your Home’s Attic Insulation Level: fiberglass, cellulose and mineral wool have an R-value of about 3 to 3.5 per inch; depth in inches × 3 estimates the R-value. https://www.energystar.gov/products/ask-the-experts/how-check-your-homes-attic-insulation-level (retrieved 2026-10-02)",
    "NIST Special Publication 811, Appendix B (1 ft²·h·°F/Btu = 0.1761102 m²·K/W; 1 in = 2.54 cm, 1 ft = 0.3048 m exactly). https://www.nist.gov/pml/special-publication-811 (retrieved 2026-10-02)"
  ],
  "related": [
    "btu",
    "square-footage",
    "roofing",
    "drywall"
  ],
  "changelog": []
}