Home Insulation R-Value Calculator

ANA›Life Services Authority›National Calculator Authority›Home Insulation R-Value Calculator

.calc-container { max-width: 640px; margin: 2rem 0; padding: 1.5rem; background: #fff; border: 1px solid #ddd; border-radius: 8px; box-shadow: 0 1px 3px rgba(0,0,0,0.06); font-family: system-ui, -apple-system, sans-serif; } .calc-container h3 { font-family: Georgia, serif; font-size: 1.15rem; color: #1a1a1a; margin-bottom: 1rem; padding-bottom: 0.5rem; border-bottom: 2px solid var(--ac, #3d5a80); } .calc-row { display: flex; align-items: center; gap: 0.75rem; margin-bottom: 0.75rem; flex-wrap: wrap; } .calc-row label { min-width: 160px; font-size: 0.9rem; color: #333; font-weight: 500; } .calc-row input[type="number"], .calc-row select { flex: 1; min-width: 120px; max-width: 200px; padding: 0.5rem 0.6rem; border: 1px solid #ccc; border-radius: 4px; font-size: 0.9rem; font-family: system-ui, sans-serif; color: #1a1a1a; background: #fafaf8; } .calc-row input:focus, .calc-row select:focus { outline: none; border-color: var(--ac, #3d5a80); box-shadow: 0 0 0 2px rgba(26,74,138,0.12); } .calc-row .unit { font-size: 0.82rem; color: #888; min-width: 30px; } .calc-btn { display: inline-block; margin-top: 0.5rem; padding: 0.55rem 1.5rem; background: var(--ac, #3d5a80); color: #fff; border: none; border-radius: 4px; font-size: 0.9rem; font-weight: 600; cursor: pointer; font-family: system-ui, sans-serif; } .calc-btn:hover { opacity: 0.9; } .calc-result { margin-top: 1.25rem; padding: 1rem 1.25rem; background: #f0f6fc; border-left: 3px solid var(--ac, #3d5a80); border-radius: 0 6px 6px 0; display: none; } .calc-result.visible { display: block; } .calc-result-label { font-size: 0.78rem; text-transform: uppercase; letter-spacing: 0.06em; color: #666; margin-bottom: 0.25rem; } .calc-result-value { font-size: 1.6rem; font-weight: 700; color: var(--ac, #3d5a80); } .calc-result-detail { font-size: 0.85rem; color: #555; margin-top: 0.5rem; line-height: 1.5; } .calc-note { margin-top: 1rem; font-size: 0.8rem; color: #888; font-style: italic; } .calc-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 0.75rem; margin-top: 0.75rem; } .calc-grid-item { padding: 0.6rem 0.8rem; background: #f8f9fa; border-radius: 4px; border: 1px solid #eee; } .calc-grid-item .label { font-size: 0.75rem; color: #888; text-transform: uppercase; letter-spacing: 0.04em; } .calc-grid-item .value { font-size: 1.1rem; font-weight: 600; color: #1a1a1a; } @media (max-width: 720px) { .calc-row { flex-direction: column; align-items: flex-start; gap: 0.3rem; } .calc-row label { min-width: auto; } .calc-row input[type="number"], .calc-row select { max-width: 100%; width: 100%; } .calc-grid { grid-template-columns: 1fr; } } .calc-chart { margin: 1rem 0; text-align: center; } .calc-chart svg { max-width: 100%; height: auto; } .calc-chart-legend { display: flex; flex-wrap: wrap; justify-content: center; gap: 0.6rem 1.2rem; margin-top: 0.6rem; font-size: 0.8rem; color: #555; } .calc-chart-legend span { display: inline-flex; align-items: center; gap: 0.3rem; } .calc-chart-legend i { display: inline-block; width: 10px; height: 10px; border-radius: 2px; font-style: normal; } .calc-related { max-width: 640px; margin: 2rem 0 1rem; padding: 1.25rem 1.5rem; background: #f8f9fa; border: 1px solid #e8e8e8; border-radius: 8px; } .calc-related h3 { font-family: Georgia, serif; font-size: 1rem; color: #1a1a1a; margin: 0 0 0.75rem; padding-bottom: 0.4rem; border-bottom: 2px solid var(--ac, #3d5a80); } .calc-related-list { list-style: none; padding: 0; margin: 0 0 0.75rem; display: grid; grid-template-columns: 1fr 1fr; gap: 0.4rem 1.5rem; } .calc-related-list li a { font-size: 0.88rem; color: var(--ac, #3d5a80); text-decoration: none; } .calc-related-list li a:hover { text-decoration: underline; } .calc-browse-all { margin: 0.5rem 0 0; font-size: 0.9rem; font-weight: 600; } .calc-browse-all a { color: var(--ac, #3d5a80); text-decoration: none; } .calc-browse-all a:hover { text-decoration: underline; } @media (max-width: 720px) { .calc-related-list { grid-template-columns: 1fr; } }

Home Insulation R-Value Calculator

Calculate the total thermal resistance (R-value) of your home insulation to determine energy efficiency. Add multiple insulation layers for a complete wall or ceiling assembly.

Building Location / Climate Zone

Zone 1 (Hot – Hawaii, S. Florida) Zone 2 (Hot-Humid – Gulf Coast) Zone 3 (Mixed – SE/SW US) Zone 4 (Mixed-Humid – Mid-Atlantic) Zone 5 (Cool – Great Lakes, NE) Zone 6 (Cold – Upper Midwest) Zone 7 (Very Cold – N. Minnesota, Montana) Zone 8 (Subarctic – Alaska)

Assembly Type

Attic / Ceiling Exterior Wall Floor / Crawlspace Basement Wall

### Insulation Layers

Add one or more insulation layers. R-values are additive for layers in series.

Add Layer

### Surface Air Films (Auto-included)

Interior Air Film

Still air – vertical wall (R-0.68) Still air – horizontal, heat up (R-0.61) Still air – horizontal, heat down (R-0.92)

Exterior Air Film

15 mph wind (R-0.17) 7.5 mph wind (R-0.25)

Calculate R-Value

#### Formulas Used

Total R-Value (series layers):

Rtotal = Rint.film + Σ(Rlayer) + Rext.film

Where for each layer: Rlayer = rmaterial × thickness (inches)

rmaterial = R-value per inch of the selected insulation material (h·ft²·°F/BTU per inch)

U-Factor: U = 1 / Rtotal

Heat Loss (BTU/hr): Q = U × A × ΔT, where A = area (ft²), ΔT = indoor–outdoor temperature difference (°F)

#### Assumptions & References

R-values per inch are based on ASHRAE Handbook of Fundamentals and DOE/Oak Ridge National Laboratory data.
Air film resistances follow ASHRAE 90.1 standard surface conditions.
Recommended R-values by climate zone are from DOE Energy Saver / IECC 2021 guidelines.
Calculations assume 1-D steady-state heat transfer (no thermal bridging through studs or framing).
R-values are in imperial units: h·ft²·°F/BTU.

// ── Material database: { label, rPerInch } const HOM_MATERIALS = [ { label: "Fiberglass Batt", rPerInch: 3.14 }, { label: "Mineral Wool / Rock Wool Batt", rPerInch: 3.70 }, { label: "Cellulose (blown-in)", rPerInch: 3.70 }, { label: "Fiberglass (blown-in, attic)", rPerInch: 2.50 }, { label: "Fiberglass (blown-in, wall)", rPerInch: 3.20 }, { label: "Open-Cell Spray Foam", rPerInch: 3.70 }, { label: "Closed-Cell Spray Foam", rPerInch: 6.50 }, { label: "Rigid EPS Foam Board", rPerInch: 3.85 }, { label: "Rigid XPS Foam Board", rPerInch: 5.00 }, { label: "Rigid Polyisocyanurate (Polyiso)", rPerInch: 6.50 }, { label: "Vermiculite / Perlite (loose)", rPerInch: 2.70 }, { label: "Cotton / Denim Batt", rPerInch: 3.50 }, { label: "Sheep Wool Batt", rPerInch: 3.50 }, { label: "Reflective Foil (dead air space)", rPerInch: null, fixedR: 1.00 }, { label: "OSB Sheathing (per inch)", rPerInch: 1.25 }, { label: "Plywood Sheathing (per inch)", rPerInch: 1.25 }, { label: "Drywall / Gypsum Board (per inch)", rPerInch: 0.90 }, { label: "Brick (per inch)", rPerInch: 0.20 }, { label: "Concrete Block (per inch)", rPerInch: 0.08 }, { label: "Wood Siding (per inch)", rPerInch: 1.23 }, ];

// DOE recommended minimum R-values [zone1..zone8] for [attic, wall, floor, basement] const HOM_RECOMMENDED = { attic: [30, 30, 38, 38, 49, 49, 49, 49], wall: [13, 13, 20, 20, 20, 20, 21, 21], floor: [13, 13, 19, 19, 30, 30, 38, 38], basement: [0, 0, 5, 10, 10, 15, 15, 20], };

let homLayerCount = 0;

function homMaterialOptions(selectedIdx) { return HOM_MATERIALS.map((m, i) => ${m.label} ).join(''); }

function homAddLayer(matIdx, thickness) { homLayerCount++; const id = homLayerCount; const mat = matIdx !== undefined ? matIdx : 0; const thick = thickness !== undefined ? thickness : 3.5; const container = document.getElementById('hom-layers-container'); const div = document.createElement('div'); div.id = hom-layer-${id}; div.style.cssText = 'background:#f7fafc; border:1px solid #e2e8f0; border-radius:8px; padding:14px; margin-bottom:12px;'; div.innerHTML = `

Layer ${id} Remove

Material ${homMaterialOptions(mat)}

Thickness (inches)

; container.appendChild(div); homToggleThickness(id); homPreviewLayer(id); // attach live preview document.getElementById(hom-mat-${id}).addEventListener('change', () => homPreviewLayer(id)); document.getElementById(hom-thick-${id}) && document.getElementById(hom-thick-${id}`).addEventListener('input', () => homPreviewLayer(id)); }

function homRemoveLayer(id) { const el = document.getElementById(hom-layer-${id}); if (el) el.remove(); }

function homUpdateRecommended() { / called on assembly change, no-op here / }

function homCalc() { const resultEl = document.getElementById('hom-result');

// Collect layers const layerDivs = document.querySelectorAll('[id^="hom-layer-"]'); if (layerDivs.length === 0) { resultEl.style.display = 'block'; resultEl.innerHTML = '⚠ Please add at least one insulation layer.'; return; }

let errors = []; let layerResults = []; let totalInsulationR = 0;

layerDivs.forEach((div) => { const idStr = div.id.replace('hom-layer-', ''); const id = parseInt(idStr); if (isNaN(id)) return;

const matIdx = parseInt(document.getElementById(hom-mat-${id}).value); const mat = HOM_MATERIALS[matIdx];

if (mat.fixedR !== undefined) { layerResults.push({ name: mat.label, thickness: '—', rPerInch: '—', rValue: mat.fixedR }); totalInsulationR += mat.fixedR; } else { const thickEl = document.getElementById(hom-thick-${id}); const thick = parseFloat(thickEl ? thickEl.value : ''); if (isNaN(thick) || thick 36) { errors.push(Layer ${id}: thickness seems unrealistically large (max 36 inches).); return; } const r = mat.rPerInch * thick; layerResults.push({ name: mat.label, thickness: thick, rPerInch: mat.rPerInch, rValue: r }); totalInsulationR += r; } });

if (errors.length > 0) { resultEl.style.display = 'block'; resultEl.innerHTML = '⚠ ' + errors.join('') + ''; return; }

const intFilm = parseFloat(document.getElementById('hom-interior-film').value); const extFilm = parseFloat(document.getElementById('hom-exterior-film').value); const totalR = intFilm + totalInsulationR + extFilm; const uFactor = 1 / totalR;

const zone = parseInt(document.getElementById('hom-location').value); const assembly = document.getElementById('hom-assembly').value; const recommended = HOM_RECOMMENDED[assembly][zone - 1];

const meetsCode = totalInsulationR >= recommended;
const statusColor = meetsCode ? '#276749' : '#c53030';
const statusIcon = meetsCode ? '✅' : '⚠';
const statusText = meetsCode
? Meets DOE recommendation (R-${recommended}) for Zone ${zone}: Below DOE recommendation of R-${recommended} for Zone ${zone} — consider adding R-${(recommended - totalInsulationR).toFixed(1)} more;

// Build layer table let tableRows = layerResults.map(l => ${l.name} ${l.thickness === '—' ? '—' : l.thickness + '"'} ${l.rPerInch === '—' ? '—' : l.rPerInch} **R-${l.rValue.toFixed(2)}** ).join('');

tableRows += `

Interior Air Film R-${intFilm.toFixed(2)}

Exterior Air Film R-${extFilm.toFixed(2)}

resultEl.style.display = 'block'; resultEl.innerHTML = ` ### Results

Material Thickness R/inch R-Value

${tableRows}

Insulation R-Value R-${totalInsulationR.toFixed(1)}

Total Assembly R-Value R-${totalR.toFixed(1)}

U-Factor (BTU/hr·ft²·°F) ${uFactor.toFixed(4)}

DOE Recommended (Zone ${zone}) R-${recommended}

${statusIcon} ${statusText}

#### Estimated Heat Loss (per 100 ft²)

Q = U × A × ΔT | A = 100 ft²

ΔT (°F) Scenario Heat Loss (BTU/hr)

${[[20,'Mild day (70°F inside, 50°F outside)'],[40,'Cool day (70°F inside, 30°F outside)'],[60,'Cold day (70°F inside, 10°F outside)'],[80,'Very cold (70°F inside, -10°F outside)']].map(([dt, label]) => ${dt}°F${label}**${(uFactor * 100 * dt).toFixed(1)} BTU/hr** ).join('')}

`; }

// Initialize with two default layers (fiberglass batt 3.5" + OSB sheathing 0.5") homAddLayer(0, 3.5); homAddLayer(14, 0.5);

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References

10 CFR § 460.103 — Installation of insulation

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