Tri County Metals is committed to assisting our customers achieve a metal roofing system that will last a lifetime. One way to achieve this is to help educate our customers on key aspects to the installation process.

The topic we want to discuss today is the purlin installation.

What are purlins?

Purlins are non-pressure treated, 1” x 4” x 12’ lumber that is installed on to the roof in a specific layout pattern and screw pattern. The purpose of the purlins is to provide a solid foundation for the metal roofing panels and trim to be screwed to.

Do all roofing projects require purlins?

No. We do recommend it, however. For new construction, Florida building code does not require the use of a purlin system, and some profiles, like our TCM-LOC panel, does not require use of purlins. You will typically see purlins used for re-roof project over existing shingles or other situations.

What do I need to know about installing purlins for my metal roofing project?

There are a few common questions we see arise when discussing the installation of the purlin system.

  • Doubling up in the valleys – Refer to the installation manual for the proper on-center spacing and be sure that the purlin is attached to the roofing truss. In the valleys, due to the angle typically produced at the valley and the use of transition flashing, it is essential that the purlins are doubled in the valleys – that is, two purlins side-by-side on each side of the angle of the valley.
  • Purlins need to follow the sides / edges of the roof – It is important to note that in addition to the proper spacing and doubling of purlins the valleys, it is essential to include purlins along the entire perimeter of the roof. You will also need to install purlins around penetrations such as plumbing pipes, electrical pipes, and skylights among others.
  • Follow the proper screw pattern – The last common concern when discussing the installation of the purlin system is the screw pattern. The screws need to be placed every 2’ on-center as like the diagram below, but also the screws need to be doubled at every on-center location.

We are just a click or phone call away if we can answer any other installation or product questions for you.