A brief comparative analysis of several commonly used metal roofing systems

A metal roofing system refers to a roof form that uses metal sheets as roofing material, integrating structural support, waterproofing, and thermal insulation layers. According to the definition in the "Technical Specification for Skylights and Metal Roofs (JGJ255-2012)": a metal roof is composed of metal panels and a support system, which does not bear the load of the main structure and has an angle of less than 75° with the horizontal direction. The main materials used for the panels include: steel plates, aluminum plates, aluminum alloy plates, as well as copper plates and stainless steel plates.

The basic characteristics of metal roofs:

A. Strong functionality.

Under the premise of meeting architectural functional requirements, it can better achieve all requirements such as drainage, thermal insulation, ventilation, and sound insulation.

B. Lightweight and simple structure.

Compared with concrete roofing systems, metal roofing systems have thinner structural layers, lighter support structures, larger spans, and can adapt to complex architectural shapes.

C. Flexible construction and short installation cycle.

During construction, metal roofing systems can basically achieve a fully prefabricated installation method, and most of the work can be completed in the factory or on-site processing workshop. On-site construction is less affected by seasons and weather. Compared with traditional roofs, the installation efficiency is extremely high, which can significantly shorten the installation cycle.

D. Good economic efficiency.

Compared with traditional roofs, it has obvious economic advantages in large spans and complex roof forms.

Classification and Basic Structure of Metal Roof Panels

Currently, in engineering practice, various metal roofs are usually distinguished and classified according to the fixing method of the metal roof panels. Several common basic methods used in engineering are as follows:

1. Through-fastened Metal Roofing System

This type of roofing system has been used for a long time and is relatively common. In this system, the roof panels are fixed to the supporting purlins with screws. The connecting screws directly penetrate the roof panels. To prevent leakage at penetration points, connecting screws are generally equipped with special compression gaskets and waterproof washers. Another method involves using sealed blind rivets with rubber gaskets to secure the panels.

Advantages

• Simple structure, easy to install
• Lower cost, suitable for projects with limited budgets
• Easy to maintain and replace

Limitations

• Potential risk of leaks at penetration points
• Fastener components are prone to aging due to long-term exposure
• Relatively poor aesthetic appeal

Applications

Industrial plants, warehouses, temporary structures, etc.

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2. Concealed Fastener Metal Roofing System

This type of roofing system first appeared in Australia, hence it is also called the Australian concealed fastener panel. Specific panel types are matched with corresponding mounting brackets. During installation, the mounting brackets are first fixed to the supporting purlins or substrate, and the roof panels are fixed to each other and to the brackets using concealed snap-fit ​​connections.

Advantages

• Clean, neat appearance with excellent aesthetics
• Superior waterproofing performance compared to penetrating systems
• No exposed fasteners, resulting in greater durability

Limitations

• Requires a certain degree of installation precision
• Limited ability to accommodate thermal expansion and contraction

Applications

Commercial buildings, office buildings, and small-to-medium-sized industrial projects

3. Standing Seam Metal Roofing System(Low-rise seam)

This type of roofing system is usually also called a low-profile standing seam metal roofing system. To differentiate it, this document refers to it as a standing seam metal roofing system. It is divided into single-lock and double-lock types according to the degree of interlocking. The roof panels are mechanically formed. During installation, the special fasteners are first fixed to the supporting purlins, and the adjacent roof panels and connecting fasteners interlock with each other, and then locked, shaped, and fixed mechanically or manually.

Advantages

• Good structural stability
• Superior waterproofing performance
• Suitable for complex roof structures

Limitations

• Relatively complex installation process
• High requirements for construction equipment

Applications

Industrial plants, logistics centers, and certain public buildings

4. Standing Seam Metal Roofing System (Standing seam/Upright seam)

This type of roofing system is usually called a high-profile standing seam metal roofing system, also known as a standing seam Lok panel. The metal panels are mechanically roll-formed to create male and female interlocking edges. During installation, the special aluminum alloy T-shaped clips are first connected to the supporting purlins. Then the roof panels and T-shaped clips are interlocked, and finally locked and shaped mechanically or manually.

Advantages

• Excellent waterproofing performance (no perforations)
• Superior resistance to thermal expansion and contraction
• Suitable for large-span roofs
• Modern appearance with a cohesive aesthetic

Limitations

• Relatively high cost
• Requires high-level construction expertise

Applications

Airports, convention centers, sports arenas, high-end industrial facilities

5. Flat Lock Panel Metal Roofing System

This type of metal panel is generally formed by mechanical stamping or manual cutting. During installation, the special locking clips are first fixed to the substrate, and then the edges of the panels are folded and interlocked with the locking clips for fixing.

Advantages

• Flexible design, suitable for complex surfaces
• Strong architectural expressiveness
• Enables personalized design

Limitations

• Lower installation efficiency
• Higher labor costs
• Greater reliance on construction experience

Applications

Building facades, irregularly shaped roofs, high-end architectural projects

Comparison Chart of Metal Roofing Systems

Based on the above and engineering experience:

a. The main metal roofing system surface materials all use thin metal sheets. Due to the influence of mechanical processing and the limitations of the material's physical properties, the thickness is mostly below 1.0mm. Therefore, when selecting surface materials, the corrosion resistance of the material itself becomes the primary consideration.

b. In addition to thermal insulation performance, the fire resistance of roofing insulation materials must also be considered. Therefore, the main roofing insulation materials currently used are rock wool and glass wool, while some new insulation materials are also gradually being applied, such as foamed glass.

c. The types and quantities of main accessories do not differ significantly. Relatively speaking, low-profile standing seam metal roofs require fewer accessories.

Based on the above analysis, when selecting a suitable metal roofing system for a building, it is necessary to consider not only the design life, local climate conditions, and system performance, but also the building's shape and aesthetic requirements. In reality, the appearance of the metal roofing system often plays a dominant role in construction projects. Therefore, when construction companies propose or design roofing solutions, they first need to understand the architect's or owner's specific requirements for the building's appearance, and then consider the building's specific performance requirements.

Generally, buildings with low aesthetic requirements can choose through-fastened or concealed-fastened metal roofs. However, through-fastened roofs are best used in temporary buildings or buildings with low waterproofing requirements, so that subsequent maintenance and replacement will not affect normal use. For public buildings with high aesthetic requirements, large area or span, and long service life, standing seam or interlocking seam metal roofing systems are preferred. If the building roof needs to present different materials, such as stone, various types of metal panels, or glazed glass, requiring a double-layer roof system, the standing seam metal roofing system is the first choice.

When the metal roof panel is used directly as the surface layer, or for buildings with smaller size, complex shapes, and high aesthetic requirements, the standing seam interlocking metal roofing system is preferred. The application of flat lock seam roofing systems is usually directly requested by the architect or owner, but it should be noted that it must be attached to an inner waterproof system, and the application area should not be too large, and the size of the panels themselves is relatively small.