Metal Roofing Systems: Types, Materials, and Code Context

What Is a Metal Roofing System?

Metal roofing has been used on commercial, industrial, and residential buildings for well over a century. Today it is one of the fastest-growing roofing categories because of its long service life, durability, and recyclability. As a roofer, you need to know the major system types, the metals used to make them, and the material properties that shape every installation decision.

Four Major Metal Roofing System Types

1. Standing-Seam Systems

Standing-seam panels run vertically from ridge to eave. Their side edges are folded up and mechanically seamed or snap-locked together above the panel surface, hiding all fasteners. Because no fasteners pierce the weather side of the panel, standing-seam systems offer superior leak resistance. Clips attached to the structure hold the panels while still allowing them to slide as the metal expands and contracts. Standing-seam is common on low-slope and steep-slope commercial roofs and high-end residential projects.

2. Exposed-Fastener (Lap-Seam) Systems

These panels overlap at their edges, and screws with neoprene or EPDM washers pass through the overlap and into the substrate. Installation is faster and less expensive than standing-seam, but fastener holes are a potential leak point if washers degrade. Exposed-fastener panels are widely used on agricultural, industrial, and light commercial buildings where long-term aesthetic expectations are lower.

3. Metal Shingle and Shake Systems

Individual metal panels are shaped to resemble asphalt shingles, wood shakes, clay tile, or slate. They interlock and are typically nailed or screwed through a concealed flange. Metal shingles work well on steep-slope residential roofs and are popular in re-roofing projects because their lighter weight reduces structural load.

4. Batten and Rib Systems

Panels attach over horizontal or vertical wood or metal battens fastened to the deck. The batten creates an air space that improves thermal performance. Bermuda rib and classic barrel profiles fall into this category. Batten systems are common in historic renovation and in regions where a traditional look is required.

Common Metals and Their Properties

Galvanized Steel (G-90)

Galvanized steel is carbon steel coated with zinc by hot-dipping. The "G-90" designation means the coating weight is 0.90 oz of zinc per square foot of sheet (both sides combined). Zinc sacrificially protects the steel if the coating is scratched. G-90 is economical and widely available but can corrode in coastal or highly acidic environments if the zinc layer is compromised.

Galvalume Steel

Galvalume is steel coated with an aluminum-zinc alloy (approximately 55% aluminum, 43.4% zinc, 1.6% silicon by weight). The aluminum provides excellent heat and corrosion resistance; the zinc provides sacrificial protection at cut edges. Galvalume typically outperforms standard galvanized steel in corrosion resistance in most environments and is the predominant substrate for exposed metal roofing today.

Aluminum

Aluminum is lightweight (roughly one-third the weight of steel at the same thickness) and naturally forms an oxide layer that resists corrosion without a separate coating. It is an excellent choice for coastal and high-humidity environments. Aluminum expands and contracts at a higher rate than steel, so thermal movement must be carefully addressed in the installation design. Because aluminum is softer than steel, it dents more easily.

Copper

Copper is one of the most durable roofing metals, with documented service lives well over 100 years on historic structures. It requires no paint or coating. Over time it develops a blue-green patina (verdigris) that protects the base metal. Copper is expensive and must be isolated from incompatible metals (such as steel and aluminum) to prevent galvanic corrosion. Runoff from copper can stain adjacent materials.

Zinc

Zinc is self-healing: surface scratches fill in as the metal oxidizes to form a protective patina called zinc carbonate. It is used frequently in European architectural roofing and is growing in the US market. Like copper, it must be separated from dissimilar metals.

Gauge: Thickness Matters

Steel panel thickness is described by gauge number — a higher gauge number means a thinner sheet. Common roofing gauges for steel panels range from 22 gauge (thicker, used on heavy commercial work) to 29 gauge (thinner, common on agricultural exposed-fastener panels). Aluminum thickness is usually stated in decimal inches or millimeters rather than gauge. Always verify the gauge specified in the project documents; installing thinner material than specified can void warranties and may not meet local code requirements.

Coatings and Finishes

Most factory-finished metal panels receive a Kynar 500® or similar polyvinylidene fluoride (PVDF) coating. PVDF coatings resist fading, chalking, and chemical attack better than polyester paints. Coating warranties typically cover film integrity and fade limits, and they depend on maintaining the correct substrate (for example, Galvalume is required under most PVDF coating warranties for steel panels).

Thermal Expansion: The Critical Installation Variable

All metals expand when heated and contract when cooled. The coefficient of thermal expansion tells you how much a given length of material changes per degree of temperature change. Steel expands at approximately 6.5 × 10⁻⁶ in/in/°F; aluminum at approximately 13 × 10⁻⁶ in/in/°F — roughly twice that of steel. On a long panel run in a climate with wide temperature swings, the total movement can be significant. Failing to allow for this movement causes panels to buckle, fasteners to work loose, or seams to fail. Standing-seam clips are specifically designed to float, letting panels slide freely. Exposed-fastener systems use slotted holes or limit panel run lengths.

Code Context

Metal roofing installations must comply with the adopted edition of the International Building Code (IBC) or International Residential Code (IRC) in your jurisdiction, as well as local amendments. The SMACNA Architectural Sheet Metal Manual is the standard industry reference for fabrication details, flashing, and expansion joint design. Always check the current adopted code before you specify or install a system. Fire ratings, wind uplift resistance, and impact ratings (Class 1–4 per FM or UL testing) may all be required by the authority having jurisdiction.

Safety on Metal Roofing Work

Metal panels have sharp edges and cut ends — always wear cut-resistant gloves when handling panels. Metal roofs can be extremely slippery, especially when wet or covered with morning dew. Fall protection is required any time you are working at heights where a fall could cause injury; follow your site fall-protection plan and OSHA requirements. Never work on a metal roof during lightning or when a storm is approaching. Wear eye protection when cutting or drilling panels.