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Metal Buildings – Roof Systems

One of the things that separates a metal building system from more conventional methods of construction is the fact that the building structure and the envelope can be provided by a single source. In this article we will review the common roof panel systems utilized in metal building systems.

Purlin Bearing Rib Panels

Purlin Bearing Rib Panels, or PBR panels, are panels that attach directly to the roof purlin utilizing through fasteners.

PBR style panels are typically 36″ wide and formed using 26 or 24 gauge steel sheets. Panels can be installed on roofs with slopes of 1/2:12 or greater.

PBR is the most economical roof system because it utilizes 26 gauge material and it requires less parts and pieces to install. However it has its draw-backs; most notably the fact that the entire roof has exposed fasteners which increases the likelihood of leaks. Additionally it does not allow for thermal expansion/contraction as well as a standing seam roof system.

PBR panels were once the mainstay in the market, but today they are typically only utilized in unheated, uninsulated spaces.

Trapezoidal Rib Standing Seam Roof Panels

Trapezoidal standing seam roof panels are by far the most common panels utilized in today’s metal building systems.

Standing seam roof panels are attached to the roof structure utilizing a panel clip that attaches to the purlin. The panel is locked into the clip and eventually the panel is manually or mechanically seamed to lock in place permanently. The end result is single watertight membrane. Through fasteners are only utilized at trim conditions.

The clips utilized include a mix of fixed and sliding clips. The sliding clips allow for thermal movement. When designed and installed properly, the mix of sliding and fixed clips allows the roof to expand/contract as desired.

Standing seam roof panels are typically 24″ wide with a 3″ seam height and formed from 24 gauge steel sheets. The panels can be utilized on roofs with a slope as low as 1/4:12.

Vertical Standing Seam Roof Panels

Vertical standing seam roof panels function much like a trapezoidal rib standing seam roof panel. The difference is in their appearance. The panels are typically 16″ wide with a 2″ high vertical seam formed from 24 or 22 gauge steel. Panels are completely flat between the seams, so 22 gauge is often utilized to minimize “oil canning” or panel waviness.

Vertical standing seam panels are most commonly utilized on roofs that require a more architectural appearance and specifically roofs with a steeper slope. They can be installed on roof slopes as low as 1/4:12 but they are much more aesthetically appealing than a trapezoidal rib panel when you get roof slopes greater than 4:12.

In this article we focused on panels that are typically manufactured by metal building manufacturers. Insulated metal panels are becoming much more common in the industry, but these panels are typically manufacturer by insulated panel manufacturers and not the actually building manufacturers. We will dive into insulated panels and their roof & wall applications in a subsequent article.