What should be used for support along the fascia edge when plywood is used for the boxed cornice soffit?

Using a fascia backer for support along the fascia edge when plywood is used for the boxed cornice soffit is appropriate because the fascia backer provides a solid and stable surface for attaching the plywood. It also helps to ensure that the edge of the soffit is properly supported and that the finished appearance is clean and professional. The backer can help in distributing loads evenly and reducing the risk of sagging or deforming over time.

While wood blocking, metal braces, and support beams might serve various support purposes in carpentry construction, they do not specifically cater to the unique requirements of a fascia edge when dealing with plywood and soffits. Wood blocking may be used in several applications but is typically less standardized than fascia backers in terms of fitting around the edge detailing of cornices. Metal braces are more suited for different structural applications, while support beams are used in larger framing contexts rather than specifically for the fascia edge. The fascia backer is tailored for the application at hand, ensuring optimal support and adherence to best practices in soffit installation.