When it’s time for a new metal roof, material selection is often based on the knowledge available to the specification writer or project team. The better-informed architects and specifiers are about the wide variety of metal roofing materials available and the ideal applications for each type of material, the more successful and seamless their projects will be.
When specifying a metal roof, some of the most basic questions are also some of the most important:
- Who is the final user/owner of the project?
- What is the purpose/goal of the project?
- Where is the project located? (In many cases, location plays into material, usage, and application methods.)
- Why is metal being selected for the project (aesthetics, function, integrity)?
- How much is the budget? (Prices vary widely for both roofing and wall applications, from around $6 per square foot to cover a roof with prefinished metal to well above $80 per square foot based on metal wall panel systems, materials and applications.)
Choosing a Base Metal Roof Panel Material
One of the most basic choices that architects and specifiers will have to make is between aluminum and steel roof panels. Each material has its own advantages and drawbacks.
Pluses and minuses of aluminum panels:
- More corrosion-resistant than steel.
- Lighter than steel, but softer. Therefore, while aluminum is less of a load on your structure, it won’t stand up to the punishment of a severe hailstorm as well as steel.
- Suitable for corrosive environments and marine environments.
- Can be used for water treatment and chemical storage.
- Warrantable.
Pluses and minuses of steel panels:
- Structural applications.
- More budget friendly than aluminum.
- Heavier and less resistant to corrosion than aluminum.
- Excellent resistance to fire.
- Warrantable.
The better-informed architects and specifiers are about the wide variety of metal roofing materials available and the ideal applications for each type of material, the more successful and seamless their projects will be.
Choosing a Material Thickness and Gauge
This decision is largely based on the purpose and final usage of the project. A lower gauge—and thus greater thickness—is typically preferred for its durability in steel substrates. For aluminum substrates, a higher number gauge means a thicker product.
However, the heavier weight or thicker material can make fabrication and installation more difficult since thicker metal is harder to bend and work.
Choices: 22-/24-/26-gauge; 0.032/0.040/0.050 aluminum
Residential/agricultural roofing and cladding
Good options: 24-/26-gauge
Reasons for selection: Cost, varied pricing in finishes (PVDF-Kynar to structural metal panels) with varied warranties and material costs, easy to work with, lower freight and fabrication costs, can be easily roll-formed into various profiles.
Industrial/military/commercial roofing and cladding
Good options: 24-/22-gauge; 0.032/0.040
Reasons for selection: Thicker is better mentality, more resilient to damage, higher structural loads, higher end finishes are available as well as lower-cost finishes.
Commercial/industrial/military wall panels, plates, rainscreens, roof edge flashing
Good options: 0.032, 0.040, 0.050, 0.063, 0.080, 0.125; 24-/22-/20-gauge
Reasons for selection: Highly visible and takes a considerable amount of contact, manages expansion with thicker base material, and displays less visual distortion. Perceived duration is extended. In many cases, specifications are driven to eliminate competition by high-end companies. This can also be driven by high-end coatings, thick mil paint specification, and multicoat finishes.
Choosing a Roof Underlayment
It’s crucial to specify a metal roofing underlayment material that is designed to protect the structure from extreme weather elements specific to the region where the roof is being installed. This can include water seepage caused by ice dams and wind-driven rains, as well as extremely hot and/or cold weather.
Self-Adhering Membrane Underlayment
Ideal for high-temperature roof underlayment applications, these high-tensile-strength rubberized asphalt underlayments are specifically designed to withstand temperatures up to 250 F (121 C) without degradation of the adhesive. Self-adhering underlayments seal around roofing nails, staples, and screws and bond directly to the roof substrate for fast and easy installation without the need for additional adhesives.
Synthetic Sheet Underlayment
The textured woven fabric surface of synthetic sheet underlayments offers dynamic traction and is ideal for steep slopes in a variety of weather conditions. The heavyweight woven polymer fabric provides superior strength and durability, dynamic steep-slope traction, water resistance, a wrinkle-free surface, and excellent resistance to UV breakdown.
Synthetic sheet underlayments are typically rated for commercial and residential applications using standard roofing nails (3/8-inch head) and are ideal under asphalt shingles, metal, tile, slate and a variety of other sloped roofing materials.
Ken McLauchlan is the director of sales for Louisville, Ky.-based Drexel Metals, a division of Carlisle Construction Materials. Drexel Metals is a member of the Metal Roofing Alliance. He can be reached at ken.mclauchlan@carlisleccm.com. For more information on Drexel Metals, visit www.drexelmetals.com.