Insulation R-Value Calculator

Calculate the cumulative R-value (thermal resistance) of your wall, ceiling, or floor assembly by stacking materials. 100% Client-side.

Assembly Layers

Thermal Resistance

Add layers and click Calculate to see results.

Understanding Insulation R-Values

Whether you're finishing a basement or building a new home, understanding R-value (Thermal Resistance) is critical for energy efficiency and comfort. It measures how well a material resists the conductive flow of heat.

1. The "System" vs. The Material

It's easy to look at a fiberglass batt labeled "R-13" and assume your wall is R-13. However, typical wood studs (thermal bridges) have a much lower R-value (around R-4 per 3.5 inches). Since studs take up 15-25% of the wall area, the effective R-value of the whole wall is often significantly lower than the insulation rating.

2. Material Guide

  • Fiberglass Batts (R-3.1 to R-4.3 per inch): The most common choice. Cheap and effective if installed perfectly, but gaps or compression ruin its performance.
  • Mineral Wool (R-4.0 to R-4.2 per inch): denser than fiberglass, fire-resistant, and water-repellent. Great for soundproofing.
  • Spray Foam:
    • Open Cell (R-3.5/in): Expands massively, stops air leaks, but allows moisture to pass.
    • Closed Cell (R-6.0 to R-7.0/in): Dense, acts as a vapor barrier, adds structural rigidity, and provides the highest R-value per inch.
  • Rigid Foam (XPS/Polyiso): Used for continuous exterior insulation to break thermal bridging. Polyiso degrades slightly in extreme cold, while XPS is stable.

3. Where to prioritize

Heat rises, making attic insulation the best ROI. Most codes recommend R-38 to R-60 for attics in cold climates, compared to R-13 to R-21 for walls.

5 Fun Facts About Insulation

Frozen Smoke

Aerogel is 99.8% air and holds the record for lowest thermal conductivity—up to R-20 per inch—but costs a fortune.

Super material

The Pink Panthoer

Fiberglass barely insulates on its own; it works by trapping pockets of still air. The glass just holds the air in place.

Trapped air

Straw Bales

Old-school sustainability: Compressed straw bales can offer R-1.5 to R-2 per inch, creating super-insulated R-50 walls.

Natural

Vacuum Power

Vacuum Insulation Panels (VIPs) can hit R-45 per inch by removing air entirely, but they fail instantly if punctured.

Tech

Snow Roofs

If snow melts quickly off your roof in winter, it’s a bad sign—it means heat is escaping your attic (and causing ice dams).

Visual check

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