Which spacing for rafters, roof joists, and ceiling joists is least common?

The least common spacing for rafters, roof joists, and ceiling joists is 36 inches. This spacing is not widely used in standard construction practices. Most building codes and industry standards favor closer spacing for structural integrity and to better support roofing materials and insulation.

Typical spacing options include 12 inches, 16 inches, 20 inches, and 24 inches, with 16 inches on center being the most common. Larger spacings, such as 24 inches, are used but are generally reserved for specific types of materials or construction methods that can handle such spans without compromising strength and stability.

In contrast, 36-inch spacing is relatively rare because it may lead to insufficient support and structural problems, especially when dealing with heavy roofing materials or adverse weather conditions. This makes 36 inches the least favorable choice in most residential and commercial construction scenarios.