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Steel Roofing

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Pre-painted Galvalume® Sheet:
A Guide to Best Practices

Design
A Guide to Best Practices

Steel Roofing A wide variety of seams, joints, ribs, fastening devices and surface treatments is possible, enabling designers to develop almost any desired effect. Prepainted GALVALUME sheet in building systems and components can be designed to match or coordinate with textures and patterns produced by many other building and cladding materials, including exposed concrete, wood and glass curtain-wall systems.

Building systems and components fabricated of prepainted GALVALUME sheet are strong and lightweight, permitting their use for special effects not possible with other materials. Their light weight means less structural deadloading and greater freedom in the use of slender architectural elements.

Flexibility in color choice also provides greater opportunity for the selective use of metal on facades, in combination with masonry, concrete, wood and other materials. For projects that combine other exterior finishes and materials with metal, the availability of prepainted GALVALUME sheet facilitates matching or complementing desired colors.

Roofs and Mansards

The superior appearance and performance of today’s prepainted steel sheets has resulted in a resurgence of interest among architects and owners to make the roof visible. Roofs have become a design feature and are no longer just an element to keep out water. Metal roofing systems produced from prepainted GALVALUME sheet offer potential for using roof colors that complement the color of the other architectural elements. A wide variety of roof panel widths and seam effects can be achieved.

The slope of prepainted architectural GALVALUME roofs is generally steep, typically 3:12 or greater, to provide fast runoff of water. Roofs with lower slopes often are not visible, so unpainted GALVALUME sheet is the material of choice. For lower roof slopes down to 1/4:12, unpainted GALVALUME roofs are more economical and have demonstrated excellent performance after more than 20 years.

Architectural roof panels are usually applied to a solid deck rather than directly to the roof purlins. Decking can be wood or steel. Thirty-pound felt paper or equivalent is typically used between the panel and deck. Some architectural prepainted GALVALUME roof systems are designed for direct attachment to the roof substructure. Panel profiles are generally flat and about 10 - 24 in. wide. Minor longitudinal ribs may be formed in the panel for strength and form.

Panels can be fastened to the deck using through-panel, exposed fasteners or by concealed clips or fasteners. Panels are lapped or joined at longitudinal seams. Seams are generally variations of standing snap-together seams or batten seams. Batten seams can be traditional box batten or cap batten, as well as integral batten seams. Snap-together and batten seams typically range from about ¾ in. to about 2 in. high. Panels with snap-together seams or traditional batten seams are attached to the deck with concealed clips or cleats that are fastened to or fixed into the seam. Integral batten panels are fastened with clips or directly to the deck with concealed fasteners. Clips and cleats are typically designed to be movable so that thermal expansion and contraction of the panels can be accommodated.

Siding

Building panel manufacturers offer a wide range of prepainted GALVALUME sheet profiles for siding. Large facade areas can be covered so that panel appearances and desired architectural effects will be uniform over the entire area of application. High-quality prepainted GALVALUME sheet panels assure that color rendition and panel appearance will be uniform throughout the project.

Similarly, trimwork, stops, copings and other elements critical to the overall design effect can be executed using the same materials, treatments and colors that are used for coverage of larger exterior areas. The technical problems of transitions and joining are minimized by using identical materials.