Barrel Arch Roofs Made Easy
by Rick Dill
Architects love the opportunity to add creativity and beauty, especially to a high-end custom home design. The barrel arch roof/ceiling has been an attractive design choice for centuries, but not all architects and engineers know that this beautiful design doesn't need to cost a fortune or to be labor intensive.
For a custom home, one of the most efficient ways to design a barrel arch roof is to use prefabricated, custom open web trusses that use wood chords with tubular steel webs, connected with steel pins. The truss chords can bend to form an arch because of the way the 2-by-4 flat chords are connected to the webs using steel pins (typically to a maximum 50-foot radius, sometimes even tighter). This allows the architect to design a barrel arch roof that will clear span most custom home distances?up to 36 feet under normal loading conditions. When a tighter radius is desired, a custom arched glulam beam will do the trick.
Another way to create a barrel arch is to use plated scissor trusses and drop the frame below with two-by-four materials, each one curved and varying in depth to form the arch. This method is very messy, labor intensive and costly, and it is nearly impossible to obtain a perfect radius.
Radiused Pin-Connected Open Web Trusses
The pin-connected, open web truss has been around since the early 1960s, but not everyone knows about their benefits?both design and economical?or that they are available for shipping anywhere in the country. This type of truss gives one of the highest strength-to-weight ratios of any structural member.
The typical truss ismade of 2-by-4 top and bottomchords and tubular steel webs, which are connected to the chords using steel pins. The webs are flattened at each end, with a hole for the pin to connect to the web. The manufacturer uses a jig to bend the chords to the desired radius and then the webs and pins are connected to the top and bottom chords.
These trusses are available from14 to 36 inches deep, spanning up to 36 feet under normal loading conditions and can be top or bottom chord bearing. The simple top chord bearing connection is designed to handle eccentric load and eliminate the need of increased building height and notched plates. The bearing connection promotes ease of installation, requiring only two nails driven through predrilled holes. For a typical custom home application, these trusses are so lightweight that they can often be lifted into place without the need for a forklift or crane.
Another benefit of using an open web truss, without the messy drop framing, is the flexibility to run ductwork, piping and electrical through the trusses, eliminating the need for soffit framing and keeping an exquisite barrel arch ceiling. Typical spacing of these trusses is 24 inches on center, with plywood or OSB sheathing attached to the top chords. The ceiling is typically one-fourth inch of drywall dipped in water before installation so it can bend to the radius.
This type of system is custom-engineered and comes with stamped calculations and placement plans to assist the design professional and builder. Manufacturers typically have technical representatives across the country that can provide direct job-by-job assistance for architects, engineers and contractors, giving the kind of special attention that a high-end custom home project deserves.
Exposed Applications
Some choose to leave the openweb trusses exposed, painted or left as-is with its bare wood chords connected with the diagonal tubular steel webs and pins. Architectural grade chords and upgraded web and hardware are typically available upon request for an additional charge. This truss provides a unique tech-industrial design. As an attractive ceiling solution, T & G woodmembers can be installed perpendicular to the trusses at the top chords. These trusses can be made into several different profiles. For example, the top chord can be pitched, while the bottom chord is radiused to form the barrel arch. Other profiles include bow string (flat bottom chord and radiused top chord), or even parabolic (radius top chord and inverted radius bottom chord).
Pin-connected open web trusses are common in commercial construction, especially in the West, but few architects and engineers know how beneficial they can be for custom home projects, and with the ability to barrel arch these trusses, architects can provide home owners with a unique, beautiful roof/ceiling design. The industry is seeingmore andmore of these pin-connected trusses specified in high-end customhomes because of their ability to span long roof distances, eliminating columns and beams and opening up larger, more open rooms typical of high-end homes.
Radiused Glulam Beams
For a barrel arch roof that requires a radius tighter than the 50-foot limit of a pin-connected open web truss, a custom glulam beam can be specified. Glulam beams can be made as tight as a four-foot radius by using thinner laminations. For example, the tightest possible radius of four feet can be achieved using one-fourth-inch laminated veneers.
Although the curved glulams costmore than a radiused pin-connected open web truss, they also domore.While there are some limitations to the profiles of a pin-connected open web truss, a glulam beam can be made into almost any customshape, including the formof an "s" shape. This allows architects to let their creativity and imaginations run wild, and when custom glulams are used, the end result could actually be cost-saving and easy to construct.
The other benefit of custom glulam beams is their warmth and appeal when left exposed with either smooth or rough-sawn texture, left as-is, painted or stained. Glulams can generally span farther than trusses and can also be spaced farther apart, leaving room for an attractive wood ceiling design. As an added design element, Redwood laminations can be mixed with Douglas Fir or Alaskan Yellow Cedar.
If all or part of the beam is exposed to the weather, Alaskan Yellow Cedar is recommended since it is naturally resistant to decay. Redwood is also resistant to decay and provides a unique color but is more expensive and also carries less load than the Alaskan Yellow Cedar glulam beams. The barrel arch design is an efficient and popular design for covering a pool house.While these beams are not exposed to the weather, they are subject to more moisture than allowed for a typical glulam, so this is an attractive and ideal application for the custom arched Alaskan Yellow Cedar glulam beam.
FSC Certified Available
Designing a LEED or green building? These glulam beams can be made using FSC certified lumber, which help add points toward the "green" status. According to APA-The Engineered Wood Association, wood products make up 47 percent of all industrial raw materials manufactured in the U.S., yet consume only 4 percent of the total energy needed to manufacture all industrial raw materials. Compared with the energy required to produce one ton of wood, it takes five times more energy to produce one ton of concrete, 14 times more energy to produce one ton of glass and 24 times more energy to produce one ton of steel.
By designing the structure using the warmth of wood with the option of FSC certified lumber, a building is created that is not only "green" but is easier to construct, more efficient in thermal protection and generally less expensive to build.
Barrel Arch Roofs Made Easy
BarrelArch roof designs that use pin-connected open web trusses or arched glulam beams are economical, easy to install and beautiful to look at. The flexibility of design allows architects to expand their creative minds and realize that even their wildest dreams and ideas can become reality using custom engineered wood products.
Rick Dill is General Manager of the Custom Home Division of Precision Component Systems, LLC, an engineered wood products supplier based in Newport Beach, California, with technical representatives throughout the U.S. Dill has 21 years' experience in the industry including sales and management positions with Trus Joist and Precision Component Systems, LLC, a distributor of Standard Structures, Inc.
