13.3. Circular Dome with Flat Seam System

Description: Flat seam roofing is very well-suited for use on domes and other more complex shapes. The dome panels are based on the 18"x 24" flat seam system design concepts. On the low-pitch areas near the top of the dome, the seams must be soldered to ensure watertightness. As the pitch of the dome increases, sealant may be used in the seams. Near the base of the dome, where the pitch exceeds 6" per foot, no solder or sealant is required. See Roofing Systems - Special Design and Installation Considerations, for more information. For information on cornice and gutter treatments, see Domes, Spires, and Vaults - Circular Dome with Diagonal Flat Panels.

Battens or ribs are used with flat seam roofing for decorative or functional reasons. If fully soldered seams are used, expansion battens,ribs, or seams must be used to allow for expansion and contraction. Battens can be made watertight, as shown in Detail 13.7A, for use where water, snow, or ice can build-up. In other areas, the batten and rib designs shown in Details 13.3C and D can be used.

The minimum recommended weight for the flat seam panels is 20 ounce copper.

Substrate: Continuous nailable substrate.

Fastening Method: Cleats.

13.3A. Elevation

The elevation shows flat seam roofing with and without battens, on a circular dome. The battens or ribs can be purely for aesthetic purposes, and they can have a wide variety of shapes and sizes. The detail shows a decorative cupola at the top of the dome. If desired, a flat, copper cap can be formed to provide a very low profile at the top. The cap should be locked and soldered to adjacent flat seam roofing panels.

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13.3B. Plan

The detail shows the overall layout of the flat seam dome. Note that the panels decrease in size as they converge towards the dome apex. Alternate panels can be deleted and replaced with larger panels in order to facilitate installation.

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13.3C. Dome

The flat seam panels are laid out from the base of the dome to its apex. Once the number of panels for the first course has been determined, the panels can be cut, formed, and cleated to the dome. Unlike some other roofing patterns, the number and size of panels for each course can vary, as long as the transverse seams are staggered on adjacent courses.

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13.3D. Typical Panel

The panels are trapezoidal to fit the dome's curved surface. The upper edge and one side are folded over; the lower edge and second side are folded under. A minimum of 3/4" fold is required to ensure interlocking of adjacent panels.

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13.3E. Typical Batten

Where battens are used, a wide range of sizes and shapes can be designed. This detail shows a typical batten. An important consideration is space for expansion, which can be accommodated as shown, or by tapering the battens as shown in the Batten Seam Roofing.

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13.3F. Alternate Ribs

These designs provide the space for expansion.

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Detail 1 is recommended for warm climates with low wind conditions. Detail 2 is recommended in climates with high winds, or ice or snow accumulations. In both cases, the ribs should be filled with sealant for slopes less than 6 inches per foot.

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