Roof Rafter Cross Ties: Understanding the Importance of Engineered Wood Products (EWP) in Roof Construction

When it comes to building a strong and durable roof, one crucial aspect is often overlooked - roof rafter cross ties. These vital components play a significant role in ensuring the structural integrity of a roof, particularly when using engineered wood products (EWP) like Weyerhaeuser's EWP.

To qualify as a substitute for traditional lumber, EWPs must meet or exceed the specifications of the item it replaces. This sometimes leads to requests for sealed documentation and calculations, as the used product is 'engineered' and not specified in the building code. Framers often favor using single long pieces of Microllam instead of multiple dimension lumber pieces, especially in ridge board applications.

Weyerhaeuser's EWP is available in lengths up to 48 feet, making it an attractive option for builders seeking a more efficient solution. According to chapter 8 of the 2018 IRC, the total system (ridge board, rafters, collar ties, and ceiling joist) must be specified by the code.

The ceiling joist (tension tie) at the rafter low end resists the thrust generated as those ends tend to shift outward and push the supporting wall. Under load, the rafters will experience both axial and bending stresses. With a non-structural ridge board at the top, the two opposing rafters basically prop each other up.

In a conventionally framed roof system, the ceiling joist spans from opposite exterior walls, connecting the lower ends of the rafters together to form the base and complete the triangle. The ridge board connects the upper ends of the rafters, forming the apex of the triangle. This system is known as a compression roof or 'prescriptive roof,' as the construction details are prescribed in the code.

In this article, we will explore three types of roofs: compression roofs, Weyerhaeuser EWP roofs, and structural roofs. The structure type will dictate what technical support services Weyerhaeuser can provide for individual components used in that structure.

Roof rafter cross ties play a vital role in ensuring the structural integrity of a roof, particularly when using engineered wood products (EWP) like Weyerhaeuser's EWP. By understanding the importance of these components and how they interact with other elements in a roofing system, builders can create stronger, more durable roofs that withstand various environmental conditions.