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purlins for metal roof

Purlins for Metal Roof

Table of Contents


In structural engineering for metal building and construction of metal roofs, a purlin refers to a horizontal beam or bar that is used as structural support, mostly on roofs. Purlins get their support either from rafters or the walls of the building. The function of the purlin of a roof is to act as added support for the roof deck’s weight. The metal roofing deck comprises a metal roof sheet, which is the metal roof’s surface. 

introduction of purlin for metal

There are several types of purlins. The different types are divided into categories based on what the metal roof requires like the type of material and the shape. Different purlins offer different services that include; structural support for the floors and walls. Purlins are an important component to the structure of the roof as they offer additional support to the frame of the roof where the roof sheeting rests. 

Purlins For Metal Roof

Steel Purlin

Steel Purlin

This is a direct replacement of the wood purlin. Unlike wood purlin, steel roof purlins are lightweight, dimensionally stable, have more accuracy, and are straight. In extreme temperature changes, that is, cold or hot temperatures, the purlins expand and contract reasonably. 

Cold-formed steel is the main component that makes steel purlins. This type of steel is thin and allows for easy penetration by screws. The cold-formed steel is cost-effective compared to hot-rolled steel and is also easier to work with. 

Manufacturing of the purlins comprises lightweight steel structural building products combined with hot dipped galvanized steel coated. This composition of purlin gives it protection from exposed internal environments. Contact with materials that are not compatible with zinc should be avoided. However, this cannot be avoided at all times. Therefore, purlins are protected with a layer of paint. Paint and zinc produce corrosion protection in a process referred to as a synergistic effect. 

Purling as Secondary Framing

Purlin and girt are components that make up the secondary framing. Secondary framing is a fundamental component of a number of pre-engineered metal buildings. 

It is also known as “secondary structural.” Secondary framing distributes the weight from the surfaces of the building through to the main framing and, ultimately, to the foundation. The secondary framing is also fundamental in adding longitudinal support, which is essential in resisting earthquakes and winds. 

Roof framing members, which are part of the secondary framing, support the roof as reinforcements. They are created into a horizontal “diaphragm” upon which the weight of the building’s roof deck rests. They also make the entire roof structure firm. Since the purlins add mid-span support, purlins allow long spans that enable you to come up with a wider building. 

Purling as Secondary Framing

Eave struts are another type of secondary framing, which are also referred to as eave purlins. The eave purlins are fundamentally a combination of the two purlins. They are used in places where the sidewalls intersect with the roof, with the help of a flange that aids in support of the roof and a “web” that supports the walls. 

Secondary framing can be achieved in two configurations. CEE and ZED. The shape is achieved using the bending press, which creates a web with two flanges. Secondary framing comes in various sizes. Purlins, for instance, can be any length to 30 feet long.

Types of Steel Purlins

The following are the available types of steel purlins:

C Purlins

C Purlins

C purlins are formed in the shape of the alphabet C, whose primary use is to support floors and walls. C-section purlins also referred to as cee section purlins, are made to shape the shell structure of the walls and the floor joists, which makes them suitable to support flooring beams.

C-section purlins from our stores are made with an extension on their ends, which means they can be used in single spans. The purlins are free-standing, making them secure, which makes them easily manageable during mounting. 

We offer a wide range of thicknesses. 

Z Shaped Purlin

Another type of purlins is the z purlin, which are stronger than the C purlin and are used at overlaps and joints in most cases. Zed purlins are beams horizontally built to shape a metal structure’s wall joists and roof. The zed-shaped purlins sit between the building and the roofing sheets. Therefore, the purlins act as sheet support, ensuring that the sheets are attached firmly and securely into their place. Due to the peculiar capabilities of the zed purlins – lightweight and flexible – are commonly used in industrial and agricultural buildings.

We manufacture standard zed purlins and customized ones. We also manufacture the purlins in either un-drilled or pre-drilled holes, either oval shapes or round shapes. Web height can be achieved at varying dimensions up to 300mm, and a width of 3.2 mm is also achievable. 

C Shaped SIGMA Purlins

These are C-shaped purlins but with special ribs, which are referred to as “SIGMA” purlins. The SIGMA purlins have good structural properties. These purlins are manufactured and installed to shape the shell structure of the building and its walls and floor joists. This nature of the purlins makes them ideal also for supporting beams that are essential in flooring.

Red Oxide vs. Galvanized Metal Purlins

Red Oxide metal purlins
Galvanized Metal Purlins

Red oxide is a water-based paint that is safe for the environment. Once the red oxide paint has been applied to all the components of the structural steel, surface steel is inhibited.

Red oxide is durable. It can withstand loading and unloading abuse as well as field handling when being erected. The method also allows you to paint the building different colors as you wish. 

Galvanized metal is sometimes recommended when the environment has a potential corrosive effect, like salt water. However, galvanized steel is extremely abrasive; hence, it must always be handled with extreme care with gloves. When exposed to moisture, galvanized steel is not resistant to oxidation. This type of steel will produce unsightly rust.


Generally, red oxide primer is therefore considered a better material than galvanized steel.

Purlin Sizes

Purlins are manufactured in standard sizes of the nominal length of 100mm, which is 4inches, 150mm – 6 inches, 200mm – 8 inches, 250mm – 10 inches, and 300mm, equivalent to 12 inches. 

Cost of Metal Purlins

The pricing of metal purlins depends on the job size, size of the purlin, and steel thickness.

Size 14 Gauge, Galvanized 14 Gauge, Red Oxide
4” X 2”
$2.00- $3.00 Per linear Ft.
$2.00- $2.50 Per linear Ft.
6” X 2”
$3.00- $4.00 Per linear Ft.
$2.50- $3.00 Per linear Ft.
8” X 2.5”
$4.00- $5.00 Per linear Ft.
$3.50- $4.00 Per linear Ft.
10” X 2.5”
$4.50- $5.50 Per linear Ft.
$4.00- $5.00 Per linear Ft.
12” X 2.5”
$5.00- $6.00 Per linear Ft.
$4.50- $5.50 Per linear Ft.

Metal Purlin Spacing

The ideal spacing of purlins is determined by the weight that the structure will carry and the load that is to be carried by the metal panels. The heavier the expected load is, the shorter the distance between the purlins. 

The spacing of the same purlins will determine the number of metal purlins needed for the job. The shorter the spacing between purlins, the more purlins you need. More purlins account for increased cost of materials. 

Metal Purlin Gauges

The gauges for metal roof purlins are 12 gauge, 14 gauge, and 16 gauge. To determine the exact gauge for your building, consult an engineer. Our technical personnel can also determine the best gauge to fit your building.

Metal Purlins for Your Roof

Roofing is among the final steps in your building project. This means that you should ensure that you have put in place the best materials to give you a good final touch to your metal building. Metal purlins are essential for the stability and protection of your metal roof. Installation of the correct purlins placed with the right spacing for the same will provide your roof with an extra level of protection. 

The following is a chart of summarized features of the metal purlins. 


C Purlins, Z Purlins


12 ga, 14 ga, 16 ga


4”- 12”


Red Oxide, Galvanized

How To Install Metal Roof Purlins

Purlins are installed horizontally. They are to be installed strategically on top of the roof rafters. The first step in installing your metal roof purlin is determining the number of purlins used. This is achieved by taking measurements of the roof. 

Step two, snap a chalk line across the roof horizontally and two feet from the top. Lay the first purlin at the roof ridge beginning at either corner. Fated the purlin with nails into the vertical rafters. 

Step three, Place the second purlin right to the next one, also horizontally, and install it with the same 16d nails into the rafters. Continue this until you finish the first row, then cut to size the last purlin if necessary. 

Step four, Move two feet below the roof and snap another horizontal chalk line. From this, install another row of purlins, similar to the first one. Continue this until the roof is covered with purlins. Inspect the area and ensure that the nails are well driven and that all purlins are secured into the roof rafters.

How To Find The Best Metal Purlins Near You

Metal roof purlins can be found in steel stores near you, hardware stores, or other building and construction dealers. You can also purchase the metal roof purlins from Steel and Stud from any state in the US. Our orders can be made online, and we deliver all over the country. Apart from offering the item, we also give consultation services on the best practices to achieve a strong roof. Visit us today.