steel constructionA steel structure is not a building without a building envelope, or the shell that separates the interior space from the exterior space. There are several cladding types used to distinguish these two spaces in industrial steel structures.

No steel building is complete without a building envelope. This is the shell that protects and separates the interior environment of the structure from its exterior environment. In order for the building envelope to properly do its job, it should consist of the right components. Listed below are metal cladding systems that are commonly used for a steel structure’s building envelope. Note that these are the most often used for industrial steel buildings.

Single-skin trapezoidal sheeting

The name of this cladding system says it all: it makes use of a single sheet, typically manufactured from pre-coated steel (0.7 mm gauge). The sheeting also gets its name thanks to the metal’s trapezoidal profile, whose depth measures about 32 to 35 mm. This use of the cladding system is pretty straightforward—the sheeting is attached directly to the purlins. This cladding system does not come with insulation, and is often utilized for steel structures to be used for industrial and agricultural purposes.

Built-up cladding system

This cladding system is more commonly used and more complicated than single-skin sheeting because it consists of more components, all of them built on site (as the name implies). Aside from the outer metal liner itself (known as the weather sheet), it also has an insulation layer, a system for spacing as well as another metal liner. This cladding system has limited spans mainly because the cladding sheets used have limited spans (between 2 to 2.5 m), and it requires additional support in the form of side rails or purlins.

The liner sheet, usually made from cold formed pre-coated steel or aluminium and has a trapezoidal profile, serves as support to the thermal insulation; it also gives restraint to the purlins and allows an airtight layer to be created. For insulation, mineral wool slabs may be used, but mineral wool quilts are most recommended; the latter is cheaper, lighter, easier to handle and has lower thermal conductivity. As for the spacer system (which often consists of a bar and bracket), its main function is to support the weather sheet and allow the right spacing between that and the liner sheet. As its name suggests, weather sheets protect the structure from the weather.

Insulated panels

This type of cladding is sometimes called composite or ‘sandwich’ panels, and for a reason: it consists of an insulation layer inserted between two metal sheets. This makes for a lightweight but durable panel that has notable spanning capabilities.

This cladding system is typically used as an alternative to built-up cladding for industrial and retail structures. However, sandwich panels are quite different from the aforementioned cladding type. For instance, this cladding system does not require a spacer system—the insulation layer is stiff and strong, so it can properly keep the space between the metal skins. Loads applied to the surface of the cladding shift from the external sheet through the adhesive and insulation layer to the internal metal sheet and supporting steelwork.

For insulated panels, the material most commonly utilized for the middle layer is polyisocyanurate or PIR. This material does not need adhesive to attach to the sheets; when sprayed on the metal, it immediately expands and sticks to the sheets. Nonetheless, there are other materials used, most of which need adhesive. These include mineral wool.

When it comes to steel buildings construction, profiled composite panels are most preferred for roofs to allow rainwater runoff but the flat panels are often chosen for walls because they are more aesthetically pleasing.

Standing seam systems

This type of cladding is known by another name—secret fix. A standing seam system is called as such because it does have a ‘secret fix’ in the form of a clipped joint for the weather sheet. Such joint is placed between adjoining metal skins so that there is no need to have fasteners exposed. This unique feature also makes the cladding system more weather tight. Usually made from steel or aluminium, this type of cladding is ideal for low roof slopes. A standing seam joint in the outer sheet can be incorporated in an insulated panel cladding system.

One disadvantage of the standing seam system is that unlike a fixed system, its make allows for less restraint to the purlins. Fortunately, this problem can be addressed with the addition of a properly fixed liner.

Structural liner trays

This cladding system is often used in place of composite wall panels. This type is made up of a structural profile that has an insulation slab inserted into it. The insertion of the insulation on the profile is done on site. Structural liner trays differ from built-up systems because they do not need secondary cladding rails; the former comes with liner trays that span directly between the key structural columns, so additional support is not required. Because it can do without more steelwork, it is faster and easier to install. This type of cladding may be added with perforations to meet acoustic requirements.

Structural deck and membrane roof systems

Another alternative to built-up cladding, these systems are favoured on low pitched or flat roofs. This type of cladding consists of a metal deck (with a trapezoidal profile) with enough depth and gauge to span directly between trusses, roof beams or rafters. The deck, which is usually 100 mm high and 0.75 to 1 mm thick, supports a insulation layer which in turn supports a waterproof membrane. The membrane, which is made rigid, allows the loads to transfer from it through the insulation to the deck without a spacer system or external metal skin. Because the structural deck can restrain the top of the truss or beam, this cladding type can be suitable for steel buildings whose roof structures are designed to be simply supported.

Michael Harrington penned this article. The author, who has written many articles about a wide range of topics, now writes steel building-related content for Steel Buildings Design.