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Attic Insulation Upgrade Calculator

Find how many more inches of blown-in insulation to add to reach your target attic 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 2026-08-25 · v1.0.0

Market
Imperial · sales tax

Additional insulation depth needed

12 in of additional insulation

Check your inputs

R-per-inch varies somewhat by brand and how densely the material settles over time — check your specific product's published R-value chart.

Additional R-value needed
30 R

Running these inputs gives 12 in of additional insulation as the additional insulation depth needed. Expect some drift against the real job; the calculation is solid but conditions on site are not. Currently reading for United States under IRC 2024 — pick a different market above and the figures re-cast accordingly.

Add the equipment this sizes

This result is a specification — 12 in of additional insulation — 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

  • Standard published R-value per inch for loose-fill blown insulation: fiberglass ~2.5, cellulose ~3.7, mineral wool ~3.0
  • Additional depth needed (in) = (target R-value - current R-value) / R-value per inch of the chosen material

Your workspace

Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.

Frequently asked questions

Why does material type change how much depth I need?
Each material traps air differently at the same thickness — cellulose is denser and achieves a higher R-value per inch than fiberglass, so it needs less depth to hit the same target.
Can I mix a new layer of a different material over old insulation?
Yes, this is common practice — just make sure the new layer isn't a vapor barrier-faced batt laid over existing insulation, which can trap moisture. Unfaced batts or loose-fill are generally safe to layer.
Does adding attic insulation help with cooling too, not just heating?
Yes — attic insulation slows heat transfer in both directions, reducing summer heat gain into the living space as well as winter heat loss.