CMUs are often used in all except?

Concrete Masonry Units (CMUs), commonly known as cinder blocks or concrete blocks, are integral to various construction applications due to their strength, durability, and versatility. In structural projects, CMUs are typically utilized for foundation walls, retaining walls, and load-bearing walls because they provide significant structural support and can effectively withstand the loads imposed on them.

When it comes to rafter construction, the scenario changes. Rafters are structural components that support the roof of a building and are usually made from wood or metal, chosen for their lightweight characteristic and ease of installation, which is optimal for roof framing. CMUs, due to their weight and the nature of their construction, aren't employed in rafter designs because they don’t serve the necessary function in that context.

The other applications—foundation walls, retaining walls, and load-bearing walls—leverage the compressive strength and stability of CMUs, making them excellent choices for these critical elements in building construction. Therefore, the choice that identifies where CMUs are not typically used reflects their suitability and function in structural applications.