The thrill of a curve:
Diverse roofing applications offer daring displays
Dan Vinet,
Posted
05/01/2009
Taking a mountain
curve in a high-speed sports car offers a quick thrill. But
it can be fraught with danger. Taking a curve to a metal panel is a
lot safer
and adds a long-term, one-of-a-kind visual thrill to a
building.Getting up to
speed on curved panels isn't complicated. It just takes some
planning. Whether
it's for a roof, an architectural enhancement or even a structural
element,
metal's adaptability to be curved into convex, concave, elliptical
or
hyperbolical shapes offers extensive options for unique designs and
functions.
Roofs
Curved aluminum panels have been most widely used to create
great-looking roofs, and curved perforated aluminum has been used
to screen rooftop mechanical units or act as sunshades on the
structure.
With the right combination of material and expertise, creating a
curved or tapered roof can be a lot easier and more durable than
other roof forms. For example, a curved roof with a barrel shape
removes the need for a ridge cap normally placed on a sloped roof.
The curved roof also can eliminate initial costs for rooftop
components and reduce future maintenance issues and costs.
A curved roof still can accommodate the typical rooftop elements
placed on a sloped roof, such as skylights, heat pipes or exhaust
pipes. However, we encourage architects to keep the roof opening's
exterior skin penetration-free because it enhances the
weathertightness offered by a continuous sheet going across a
curved roof.
Engineering
Curved panels primarily are made from aluminum in natural or
painted finishes. Aluminum is preferred because it is lightweight
yet strong and very adaptable to meet demanding geometric shapes.
Additionally, it has high recycled content with residual value.
Curved panels also may be offered in copper, steel or zinc. Each
one offers different options that can be discussed with potential
suppliers in the early design stage.
The method of curving the material depends on the manufacturer, the
type of standing-seam profile and the material. One of three
methods is typically used: natural curved, machine- or
smooth-curved, and crimp-curved.
If the curve is gradual enough, the panels are naturally curved. In
this case, the product is delivered straight and laid on top of the
curved roof form. Usually with a radius of 150 feet (46 m) or
larger, aluminum panels can lay on the roof without precurving.
Below this radius, separately curving the sheets would be necessary
either in the factory or on the job site, depending on the final
size of the panels and related shipping needs.
Before panels are factory-curved, we evaluate capabilities that can
be applied to different panel widths and materials. These are
specific to the size of the panel, the thickness of the materials
and the desired curve. This determines whether the material needs
to be precurved in the factory or on the job site. For instance, if
the final size of the panels would be too large to ship, they would
have to be formed on-site.
This early evaluation is critical to a quality outcome-both for
appearance and for technical accuracy. That's why we encourage all
architects to use manufacturer design and technical support early
in the project so that issues can be identified and acted upon
early.
Installation
Although curved panels are no more difficult to install than
straight sheets, we prefer to train and qualify installers to
maintain consistent quality. Typically, curved panels are attached
by placing concealed clips on the substructure and installing the
panels on top of the clips. This creates a standingseam roof with
no exposed fasteners and offers a great appearance. A curved roof
simplifies installation by eliminating hips, valleys and ridges
that require more detail and time to install.
Other
Applications
Curved panels are easily applied to other building functions. The
University Federal Credit Union in Austin, Texas, used curved
panels for a unique decorative element. The architect wanted to
replicate a water cistern, so we worked with him to determine the
right material and radius. We used perforated aluminum panels
curved to a 5-foot (1.5-m) radius to create a cylinder that was
factory-formed in two pieces and placed together on the job site.
The 5-foot convex radius is close to the extreme limits of how
tight a radius can be curved.
The Illinois Tollway Authority used curved panels as a structural
element for several of its toll collection plazas. This is far from
a standard application, so the aluminum painted sheets were
precurved in our factory and applied to a roof that spans the width
of the structure, which is a walkway used by employees to go from
one location to another.
The 14-foot- (4-m-) wide roof is freestanding with a beam on each
side and no panel supports in the middle. The curved panels are
attached to an arched truss used as a structural element in the
roof. This design reduced costs because mo additional steel framing
or supports were needed. It also takes advantage of the strength of
the 1/2-inch- (13-mm-) thick aluminum. We consulted with the
architect from the beginning and provided a detailed structural
engineering drawing to show exactly how the support system would
work. The project is a great example of the benefits of early
communication between the architect and manufacturer.
A more traditional application is now in progress at a
40,000-square-foot (3,716-m2) Big Ass Fan Co. facility in
Lexington, Ky., where aluminum sheets are being laid on a curved
roof.
No matter the type of application, the range of available materials
and expertise from manufacturers can help keep architects from
taking a wrong turn when trying to navigate the road to curved
metal panels.
Dan Vinet is general manager of the North American headquarters of
Kalzip Inc. located in Michigan City, Ind. He previously served as
Kalzip's technical director for North America. Visit www.kalzip.com
for more information.
www.kalzip.com