Define "R-value per inch" and how it informs selection for different climates?

• A. R-value per inch indicates resistance per unit thickness; materials with higher R per inch allow thinner assemblies to meet code; climate determines required total R, so per-inch value helps compare materials.
• B. R-value per inch measures color of insulation.
• C. R-value per inch is unrelated to thickness.
• D. R-value per inch is about cost efficiency only.

Answer: (A)

R-value per inch measures the thermal resistance you get for each inch of insulation. This means materials with a higher R-value per inch provide more resistance for every added inch, so you can reach the required performance with a thinner layer. Climate and building codes set a target total R for assemblies, like walls or roofs. The per-inch rating helps you compare materials and figure out how thick each layer must be to meet that target. In short, you multiply the R-value per inch by the thickness to get the layer’s total R, and then add up all layers to see if the whole assembly meets the climate requirement. For example, if you need R-30, a material with R-3 per inch would require about 10 inches, while one with R-5 per inch would need about 6 inches. The overall choice comes down to achieving the required total R efficiently, balancing space, cost, and performance.