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Posted by McElroy Metal ● Jul 11, 2024 8:00 AM

A to Zee’s: Choose The Correct Substructure Component For Your Project

A to Zee’s: Choose The Correct Substructure Component For Your Project

The popularity of metal roofing has been on the rise in recent years because of numerous benefits. It offers a 50-60 year life expectancy, is energy efficient, durable, and gives a home or building a beautiful look. But underneath those shiny panels is a substructure designed to support the roof’s overall performance.

The substructure acts as the backbone of a metal roof system, and its components work together to provide support, stability, and protection against sagging, leaks, and structural failure. In this blog, we will review substructural components, cees, zees, and custom options.

Substructural Components

Before we can dive deep into this topic, it’s important to understand the basic definitions and purposes of various structural members.

Purlins: Purlins are horizontal structural members that run perpendicular to the roof trusses. Their primary purposes include tying the rafters or trusses together to provide structural stabilization, transferring building loads to columns, and serving as an attachment point for panels and flashings.

Eave Struts: As the name might imply, eave struts are horizontal structural members in a building located at the eave. This structural member is responsible for two primary things: transferring weight and building loads to the walls or columns; and supporting the attachment of roof panels, flashings, soffit, fascia, and gutters.

Girts: Girts are horizontal structural members that run parallel to the building walls. Much like eave struts, girts also transfer the load to other points, such as columns and footings. They also serve as a primary attachment point for panels and flashings.

Base Angles: Base angles are most often small L-shaped structural members with two legs bent to 90 degrees attached to the concrete foundation. Base angles provide support for wall panels and flashings. Beyond that, they can also be used effectively to prevent water intrusion into the building envelope.

Punching: During the manufacturing process, a series of holes can be punched in secondary substructural members. During the installation process, bolts are inserted through the holes to join two or more parts together.

Eave struts are typically punched in the flange, while cees and zees are punched in the web. Angles are not typically punched but can be if requested. Punch patterns sent in with an order will be verified against our capabilities for hole sizes and spacing.
Deep Dive into Shapes


ceeA Cee-shaped profile is a secondary steel framing component with a return flange on each side. Cees can be used as roof purlins, wall girts, headers, jambs, and sills for windows and doors on metal buildings. The “C” shape does not allow for end lapping. Instead, they must be butted together. Cees are typically fastened with bolts, but they can be fastened with self-drilling screws or welded together to form columns, braces, and ties.


zeeZee profiles are shaped like a “Z” and are used most often as purlins to tie rafters or truss systems together. Zee shapes offer a distinct advantage over cee shapes in that they have the ability to be lapped together. Lapping a Zee effectively doubles the part’s strength in the lap area. Many years ago, the Light Gauge Steel Institute (LGSI) standardized the shape of zees amongst most component manufacturers. To make the lapping process easier, the LGSI standard-shaped zee profile offered two slightly different flange sizes, effectively making it a non-symmetrical structural member. This seemingly slight change allowed manufacturers to ship products more effectively and installers to much more easily nest the products together for lap applications. While non-LGSI, or Symmetrical zees, can also be lapped, they generally require more effort.

McElroy Metal’s standard zee is an asymmetrical zee. For example: if a customer orders an 8” x 2.5” Zee, the flat portion of the top and bottom flange will be 2.125” and 2.375”, respectively.

McElroy Metal Custom Options and Considerations

Standard Zee and Cee shapes have many benefits; however, some applications require custom secondary substructural components. At McElroy Metal, we can produce many customized parts outside of our standard offering.

For example, we press brake up to 32’ on most of our production lines and can produce a variety of web sizes starting at 4” wide up to 24” on several of our purlin XL lines. For customer parts, flange sizes vary from 2 ½” up to 5”. Other options may be available depending on production plant and coil availability.

McElroy Metal cannot slit our purlin coil stock. Therefore, we must use a standard-width blank for all custom parts. This means that when a custom part doesn’t fall within our standard coil widths we’ll need you to supply its critical leg(s) and also tell us which legs are noncritical for the placement of excess material. For example: 8 ½” x 3” x 3” would use a 15.9375” coil to produce the desired part; however, our closest stock width is ½” wider. When placing the order, you would need to tell us if you wanted the extra ½” of material on the 8 ½” or one of the 3” legs.

NOTE: Any custom option may raise the cost of the item.

About McElroy Metal

Since 1963, McElroy Metal has served the construction industry with quality products and excellent customer service. The employee-owned components manufacturer is headquartered in Bossier City, La., and has 14 manufacturing facilities across the United States. Quality, service and performance have been the cornerstone of McElroy Metal’s business philosophy and have contributed to the success of the company through the years. As a preferred service provider, these values will continue to be at the forefront of McElroy Metal’s model along with a strong focus on the customer.

Topics: Metal Roofing, Substructural Components

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