What type of insulation is usually installed between floor joists in crawl spaces?

The installation of insulation between floor joists in crawl spaces typically involves using R-11 fiberglass batt insulation. This type of insulation is preferred in such applications because it strikes a balance between thermal resistance and ease of installation in the confined spaces of crawl areas.

R-11 fiberglass batts are designed to fit snugly between standard 2x8 floor joists, providing effective thermal insulation while minimizing the risk of moisture issues that can arise in crawl spaces. Furthermore, R-11 is suitable for the height of most crawl space joists and provides sufficient insulation value for the relatively mild climate control required in these areas.

Other options may not be as practical. For instance, R-19 fiberglass batt insulation may be too thick for typical joist spacing in crawl spaces, while R-30 cellulose insulation is generally used in higher ceiling applications and is not typically suited for horizontal installations. Similarly, R-15 foam insulation, while effective in certain scenarios, may not fit well between joists and is often more expensive and complex to install compared to the simplicity of fiberglass batts. Therefore, R-11 fiberglass batt insulation stands out as the optimal choice for insulating between floor joists in crawl spaces.