When executed properly, metal roofs are notably robust structures.
They exhibit an impressive level of resistance to weather, strength, and minimal upkeep needs – all these factors contribute to their extraordinarily long anticipated lifespans.
A critical element of a metal roof structure is the roof purlins. These provide the roof with support and stability, thus playing a crucial role in guaranteeing its enduring strength.
Continue reading for a comprehensive guide on roof purlins, and a detailed explanation of how roof purlins are utilized during the installation of a metal roof.
What is the definition of roof purlins, and what is their purpose?
Roof purlins are composed of a series of horizontal beams, located beneath the roof covering.
They are employed in roof construction to provide the structure with support, strength, and stability. They are engineered to distribute the weight of the roof covering uniformly, while also preventing sagging and ensuring a high level of overall structural support.
Roof purlins come in a broad variety of types and materials, such as steel purlins, timber purlins, and composite material purlins. These purlin materials provide an optimal solution to factors like design requirements, local building regulations, and strength needs.
Typically, the purlins are spaced at regular intervals, running parallel to each other, across the entire length of the roof. Subsequently, they can bear the load of the roof covering. Thus, once the purlins are in place, roof tiles or metal sheets can be layered on top.
In this manner, roof purlins function in conjunction with all other components of the roof, to form a single, high-performance system.

What makes roof purlins essential?
Roof purlins are crucial for several key reasons:
Structural support
Purlins provide the roof with a substantial level of support and strength. In collaboration with the other components of the roof, purlins play a crucial role in ensuring the roofing system’s stability, both now and in the future.
Load distribution
The primary objective of purlin installation is to distribute the weight of the roof covering. By doing this, no single roof component will have to endure excessive stress.
Material conservation
The use of purlins can actually help to reduce the amount of material needed to construct the roof structure. This not only simplifies and streamlines the construction process, but also helps to keep project costs low.
Cost reduction
As an extension of the previous point, purlins help to decrease the quantity of roof structure materials required, thereby keeping this aspect of project costs low. Additionally, purlins themselves typically cost less than most other roof elements.
Facilitating wider roof areas
Purlins can facilitate the construction of broader roof areas in buildings with open floor plans, as they eliminate the need for additional support columns or walls.
Durability and resistance to weather
By providing additional strength and rigidity to the roof, they enable the roof to withstand heavy snow, wind uplift, and the weight of maintenance teams when they need to access the roof.
Minimizing the chance of roof failure
Roof purlins, due to the amalgamation of the aforementioned factors, serve as an exceptional method to considerably mitigate the likelihood of your roof collapsing or drooping over time.
Adaptable, pliable, and multifaceted solutions
Purlins come in an extensive array of materials and can be tailored to accommodate a vast array of distinct roof types or profiles.
What distinguishes ‘c’ and ‘z’ roof purlins?
The distinction between ‘c’ and ‘z’ roof purlins is evident in their form, load-bearing capability, and installation procedure.
Each type of purlin offers a set of unique advantages and is engineered to deliver optimal solutions for slightly varying project types.
The primary distinctions between ‘c’ and ‘z’ roof purlins are:
Their form
As implied by their names, c purlins resemble the letter c (when viewed laterally). They comprise two flanges on one side, leaving an open space on the other. Conversely, z purlins, when viewed laterally, mimic the letter z, as their two flanges are on opposing sides.
Their installation method
C purlins are installed with the flanges facing outwards, whereas z purlins are installed with the flanges facing inwards.
Their load-bearing capability
The form adopted for z purlins endows them with superior resistance to applied forces. Consequently, z purlins possess a higher load-bearing capability and are more apt for heavier loads.
Their typical uses
Both types of purlins are prevalently used in the construction of roof and wall systems, however, c purlins are typically employed for projects with lighter and smaller roofs.
Procedure for installing roof purlins
The standard procedure for installing roof purlins is as follows:
- Initially, ensure that the roof structure is prepared for the commencement of the purlin installation. For instance, the roof should already have rafters or trusses and sheathing installed, completely and accurately.
- Based on the design and load requirements of the roof, ascertain the type of purlin needed, and the spacing and size for the purlin’s placement.
- Mark the positions of the roof purlins.
- Commence with the first purlin, secure it to the roof. Start by affixing one end of the purlin to the structure, and fastening the purlin’s flange to the roof’s rafters or trusses (this is commonly done using a screw or bolt, but we recommend referring to the manufacturer’s guidelines for the most effective fastener type).
- Subsequently, secure the other side of the purlin.
- Ensure that the purlin is level and accurately positioned.
- Proceed with securing the remaining purlins, one at a time.
If you have additional queries regarding metal roofing, or if you require specific metal roofing installation guidance for your forthcoming project, the Zinc & Copper Works team is available to assist.
Reach out to our team today for a metal roofing estimate, we provide services throughout the UK