What is concealed-fix roofing and what makes it unique? 

The concealed-fix roofing system was developed to accommodate the effect of thermal expansion and contraction of roofing sheets under extreme temperatures, and to provide a watertight low-pitch roof in heavy storms. 

It is a modern development of the “standing seam” roofing used successfully throughout the world for generations. The concealed-fix system has been on the South African market since 1964 and has earned an excellent reputation over the years by professionals and contractors.  

St Thomas Aquinas School’s new pavilion roof coverings are a concealed-fix profile, roll-formed in continuous lengths. Credit: Global Roofing Solutions/Monro Roof Sheeting (Pty) Ltd. (Contractor)

Benefits 

A concealed fix roofing system provides numerous advantages, making it an ideal choice for both commercial and residential buildings. A key benefit is superior leak prevention, as there are no exposed fasteners, ensuring a watertight structure that minimizes the risk of water infiltration.  

The system’s clean, sleek appearance enhances the aesthetic appeal of the building, making it a popular choice for modern architectural designs.  

Concealed fix systems accommodate natural thermal expansion and contraction, reducing stress on the roof sheeting and significantly increasing its durability, particularly in areas with fluctuating temperatures. Its robust design also allows it to withstand extreme weather conditions such as strong winds, further enhancing its longevity. 

With fewer exposed components, maintenance is minimal, reducing long-term costs. 

Moreover, the system can contribute to energy efficiency by reducing heat transfer into the building, creating a more comfortable indoor environment and lowering energy consumption. 

The quicker and more efficient installation process translates into lower labour and construction costs, making it a practical and cost-effective roofing solution. 

Ease of use 

Concealed fix systems offer significant ease of use, combining streamlined installation with long-term benefits. It utilises clips and brackets hidden beneath the roofing panels, eliminating the need for visible fasteners and direct drilling, which simplifies the installation process. 

The panels, which can be rolled on-site using mobile mills, come in longer lengths than transportable ones, reducing the number of joints and seams needed. However, it does require skilled labour for installation, as it is not a typical pierced roof system. Precision is crucial, as the underlying structure must be accurate and square, to ensure proper fit and function.  

The absence of exposed screws minimises the risk of leaks and damage, enhancing the roof’s weather resistance and durability. The system also accommodates thermal expansion and contraction, reducing stress and preventing buckling. 

The concealed fix roof demands less maintenance over time, making it a highly practical and efficient roofing solution. 

Transverse stiffeners form structural members spanning across the width of the pan, reducing deflection. Image credit: Global Roofing Solutions KLIP-TITE™

Structural performance 

These systems are designed to resist weather-related issues effectively, as the concealed fixings prevent water ingress and reduce the risk of corrosion. Concealed fix sheeting delivers exceptional durability and structural integrity, with their interlocking design improving stability and load distribution. 

Additionally, these systems can be paired with insulation to enhance thermal performance, contributing to energy efficiency and consistent indoor temperatures.  

Despite requiring specialised installation, the ease of working with concealed fix systems and their long-lasting performance make them a favoured choice for various building projects. 

Roofing sheets are available in a wide range of materials and colours. Image credit: Safintra

Load resistance 

The main parameters that determine the load resistance of the roof covering are: 

• Bending Resistance: The ability of the profiled sheeting to withstand bending under both positive and negative moments, coupled with the load resistance of the fastening system. 
• Sheeting Thickness: The thickness of the sheeting profile significantly impacts its load-bearing capacity. 
• Profile Dimensions: The dimensions of the profile, particularly its overall depth, are critical in determining its structural performance. 

Together, these factors underscore the importance of both the sheeting profile and the fastening system in enhancing the roof system’s overall wind load resistance. 

6 key issues on site 

• Care and storage: material should be stored dry at all times, therefore cover the stack with a tarp, and stack sheets or bundles clear of the ground to avoid material getting wet. 
• Swarf removal: remove all metal scraps, pop rivet mandrels and excess fasteners from the roof at least daily to avoid rust stains. 

When cleaning up after having installed roof sheets clean out the gutters, ensuring not to leave metal tailings. 

• Walking on roof sheeting: clean, soft-soled shoes should be worn when installing and inspecting roof sheets. Keep weight evenly distributed over the soles of the feet, as new sheets may be slippery. Walk on purlin lines wherever possible. 
• As fasteners are supplied in different classes, it is important to match these to the roof sheeting material to ensure longevity of the installation. 
• Compatible products between new and old materials are key for refurbishment projects, to prevent rust. Always use coated steel purlins and girts to avoid steel or pre-painted steel contact with bare steel or treated timber. 
• Due to the low slopes’ characteristic of a concealed fix roof, effective drainage is crucial. Water ponding on the roof can lead to deterioration, and damage of the sheets over time. 

Concealed-fix roofing profiles not only enhance the aesthetics, durability, and performance of a metal roof but also offer the advantages of reduced costs and shorter lead times. 

Full acknowledgement and thanks go to https://www.globalroofs.co.za/, https://www.clotansteel.co.za/ and https://www.safintra.co.za/ for the information in this article.