Metal Wall Panels

What it is

“Metal wall panel” is a family rather than a product. The systems within it differ enough that a specification naming only the family has not said much:

• Single-skin profiled sheet — formed metal fixed to a support structure.
• Cassette rainscreen — flat panels folded into trays, hung on a carrier system with open or gasketed joints.
• Aluminium composite material (ACM/MCM) — two thin metal skins bonded to a core.
• Insulated metal panels (IMP) — metal skins with a factory-applied insulating core.

The fire discussion below is mostly about the composite systems, because that is where the core material sits inside the wall.

Which metal panel to use on an exterior wall

Start from what the wall needs the panel to do, then check the fire route for that system. The table uses only the distinctions this guide can support; it is not a product ranking.

Composite and insulated panels follow different code routes. In the 2024 IBC text, exterior walls on Type I, II, III and IV buildings that contain a combustible wall covering, insulation or water-resistive barrier must meet the flame-propagation provisions. Metal composite material is sent to the MCM section, while walls containing foam plastic insulation are sent to the foam plastic provisions in Chapter 26. An insulated panel with a foam core is therefore not checked the same way as a composite panel, even when the two look alike on the elevation. Confirm the edition adopted for the project and the route your panel falls under before comparing products.

If you only know the look you want, you have not yet chosen a system. Flat metal can be a cassette, a composite panel or the face of an insulated panel, and each brings a different fire, movement and support question.

The core is a fire variable, not a fire result

Composite panels are sold with different cores, usually described as polyethylene (PE), fire-retardant (FR) or mineral. The core is the first thing to identify in a composite-panel specification, because it is part of what burns or does not burn inside the wall.

What the core name does not do is settle the fire question. NFPA 285 tests a complete exterior wall assembly, so there is no test result for “PE core” or “mineral core” in general — only for a particular panel, with its core, built into a particular wall. Statements that a core type always passes or always fails go beyond what an assembly test can show.

The useful sequence is:

1. Identify the core of the exact panel being offered, not the product family.
2. Find the tested assembly that includes that panel and core.
3. Compare the build-up — insulation, cavity, water-resistive barrier, attachment and joints — with the one that was tested.

Why “the panel is rated” is the wrong sentence

NFPA 285 evaluates the performance of the entire exterior wall assembly, not the panel on its own. Insulation type, cavity depth, the water-resistive barrier, the attachment system and joint detailing may all influence whether the finished facade satisfies the requirement.

The practical consequence: a manufacturer’s NFPA 285 listing applies to the assembly configurations that were tested. Substituting the insulation, changing the cavity or altering the attachment can put the wall outside what was tested, even with the same panel.

Common formats

Panel size, joint type and attachment method vary by system. Cassette rainscreen and open-joint systems deliberately admit some water and rely on the drainage plane behind, which changes what the water-resistive barrier has to do compared with a sealed system.

What governs performance

Thermal movement has to be accommodated by panel size, joints and fixing type. How much a panel moves can be calculated, as the next section shows.

Metal selection governs corrosion behaviour. Coastal and industrial exposures, and any contact between dissimilar metals, need to be resolved at design stage.

Finish — architectural fluoropolymer coatings and polyester systems have different warranty and fade profiles. Ask for the coating warranty separately from the panel warranty.

Allowing for thermal movement at the joints

Movement can be estimated before the fixing detail is drawn. One ACM manufacturer’s fabrication manual gives the calculation as:

Expansion or contraction (in) = 12 × coefficient × temperature change (°F) × panel length (ft)

using a coefficient of 13 × 10⁻⁶ per °F for its panels. The temperature change is measured from the temperature at which the panel was fabricated or installed, so the same wall moves in both directions from the day it went up.

As a worked illustration with that coefficient: a 10 ft panel seeing a 100 °F swing from its installation temperature moves about 0.16 in (roughly 5/32 in). That is a calculation, not a measured value for any wall, and other metals and products have their own coefficients — use the figure from the datasheet for the panel you are buying.

What the number changes in practice:

• Joint width has to take the movement without the panel edges meeting or a sealed joint tearing.
• Fixings have to let the panel move. The same manufacturer’s installation examples describe the hanging method as one that easily lets thermal expansion and contraction take place, because the panels are suspended rather than tightly fastened to the sub-frame.
• Panel length is the variable you control: movement scales with it, which is why thermal movement constrains panel size.

Those installation examples are published as concepts: the manufacturer states that its sections are for conceptual use only and that suitability, design and installation are the purchaser’s responsibility. Read them for the principle, not for joint widths or fixing dimensions — those come from the system manufacturer’s project details and the design team.

Using metal wall panels indoors

Inside the building the panel is an interior finish, and the question changes. NFPA 285 is an exterior wall assembly test. Interior wall and ceiling finishes are classified in the IBC by ASTM E84 (or UL 723) flame spread: Class A is 0–25, Class B 26–75 and Class C 76–200, each with a smoke-developed index no greater than 450. Which class is required depends on the occupancy and where in the building the finish is used.

For a composite panel, ask for the E84 report on the panel as supplied, core included. Temperature swings in a conditioned interior are usually smaller than on an exposed facade, so the movement calculation above normally gives a smaller figure — but run it rather than assume it.

Advantages

Long spans, large formats and precise lines. Low water absorption and no rot or insect concerns. On a rainscreen the system is drained and back-ventilated by design.

Limitations

Fire compliance is an assembly exercise with real cost and real substitution risk. Thermal movement constrains panel size. Denting and oil-canning are appearance issues that appear on site rather than in a sample. And the specification burden is higher than for Fiber Cement Cladding, because more of the outcome depends on components you are not looking at.

Installation overview

Support structure and carrier system, water-resistive barrier and drainage plane, panel attachment following the tested configuration, then joints and terminations. Where NFPA 285 compliance is required, the installed build-up has to match a tested assembly — that check happens before procurement, not after.

Maintenance

Washing per the coating manufacturer, plus inspection of joints, gaskets and fixings. Coating failure and fastener corrosion are the two things worth looking for.

Selection checklist

• Which system is specified — profiled sheet, cassette, composite or insulated panel?
• For composites, what is the core, and is it PE, FR or mineral?
• Is there an NFPA 285 tested assembly that matches the actual build-up, including insulation and cavity?
• Has thermal movement been calculated for the specified panel length and the temperature range at the site, and do the joints and fixings take it?
• Is the metal appropriate for the exposure, and are dissimilar-metal contacts resolved?
• For interior use, which ASTM E84 class does the location require, and is there a report for the panel as supplied?

For the direct comparison, see Fiber Cement vs Metal Cladding, see how metal assemblies fit into exterior wall specifications, and for the rest of the family, browse wall cladding.