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EIFS Insulation Board Thickness Calculator

Calculate the EIFS foam insulation board thickness needed to achieve a target R-value.

Computed in your browser — nothing you enter is uploaded. Figures are presented for United States against IRC 2024, and every formula is cited under regulatory standards below.

Last verified 2026-08-26 · v1.0.0

Market
Imperial · sales tax

Required insulation thickness

3.33 in

Check your inputs

R-value per inch varies by foam type (EPS, graphite-enhanced EPS, XPS) and manufacturer — use your specific product's rated value, not a generic assumption.

With the figures above, the required insulation thickness comes to 3.33. The method behind this is well established, though site conditions and material batches will move it somewhat. This is calculated for United States and cites IRC 2024. Building in another market? Change the selector above so the units and code reference follow.

Add the equipment this sizes

This result is a specification — 3.333 in — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — confirmed fixes become pinned regression tests.

[Schema Verified] Computed in alignment with American Concrete Institute (ACI 318-19) formulas and International Residential Code (IRC 2024) spatial boundaries.

Regulatory standards & verification citations

  • Required thickness = target R-value ÷ the foam board's rated R-value per inch (commonly ~4.5-5.0 for EPS/XPS insulation board)

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Frequently asked questions

Why does R-value per inch vary by foam type?
EPS, graphite-enhanced (gray) EPS, and XPS foam boards all have different cell structures and densities, which give each type a different rated R-value per inch — commonly in the range of about 4.5 to 5.0 for these EIFS insulation board types.
Should I use the manufacturer's rated value or a generic assumption?
Always use your specific product's rated R-value per inch from its technical data sheet rather than a generic figure, since the result scales directly with this value.
Do EIFS foam boards come in the exact thickness this calculator returns?
Not necessarily — insulation board is manufactured in stock thicknesses, so round up the calculated thickness to the nearest available stock size, or check whether boards can be doubled up to reach a non-stock thickness.