In building codes, what does "R-value" measure?

R-value is a measure of thermal resistance, specifically indicating how effectively insulation can resist heat flow. The higher the R-value, the better the insulation's ability to limit heat transfer, making buildings more energy-efficient. This is particularly important in maintaining consistent indoor temperatures and reducing heating and cooling costs. The R-value is used in various building codes to ensure that structures meet energy conservation standards.

In contrast, the other options focus on different aspects of building materials. Fire resistance pertains to a material's ability to withstand fire and prevent it from spreading. Moisture resistance involves a material's capacity to withstand water exposure without degrading. Structural integrity refers to the ability of a building or material to support loads without failure. Each of these factors is important in construction, but R-value specifically relates to thermal properties, confirming the correctness of the chosen answer.