geodesic dome

Background

A geodesic sphere is an arrangement of polygons that approximates a true sphere. A geodesic dome is a portion of a geodesic sphere. Buildings or roofs have been constructed out of geodesic domes that range from 5-100% of a sphere. Domes used for houses are usually arrays of triangles that form three-or five-eighths of a geodesic sphere.

Geodesic domes are efficient structures in several ways. The triangle is a very stable shape; for example, a force applied to the corner of a rectangle can deform it into a parallelogram, but the same force will not deform a triangle. This makes geodesic dome buildings highly resistant to such forces as snow coverings, earthquakes, wind, and even tornadoes. The surface area of a geodesic dome is only 38% of the surface area of a box-shaped building enclosing the same floor space. There is less surface exposed to outdoor temperature fluctuations, making the building cheaper to heat and cool than a rectilinear structure. Geodesic domes can be constructed quickly without heavy equipment. Using prefabricated components, it takes just a few people to erect the dome for a 2,000-sq ft (185-sq m) home in 10 hours or less.

A geometric dome supports itself without needing internal columns or interior load-bearing walls. This property makes such structures appealing for use as churches, sports arenas, and exhibition halls. The aesthetic appeal of lofty ceilings makes them attractive as homes, and full or partial second-story floors are easily suspended halfway up the enclosure without any support other than attachment to the dome itself.

History

In 1919, seeking a way to build a larger planetarium, German engineer Walter Bauersfeld decided to mount movable projectors within a stationary dome. Until that time, planetarium domes rotated while external light entered through holes on the dome shell to simulate stars and planets. This limited the practical size of the dome and the number of people it could hold. Bauersfeld's concept of interior projection would work in a much larger dome. The first model constructed was more than half of a sphere; 52 ft (16 m) in diameter. Bauersfeld solved the problem of how to construct such a large sphere by approximating it with an icosahedron (20-sided solid with equal triangular faces) and subdividing each face into smaller triangles. He framed the triangles from nearly 3,500 thin iron rods. To construct a spherical shell over this framework, he erected a sphefical wooden form inside the frame and sprayed on a pasty concrete mixture. The shell was designed to be the same proportional thickness as that of an eggshell compared to its diameter, a ratio later considered appropriate for geodesic domes.

Thirty years later, R. Buckminster Fuller, an American architect, engineer, poet, and philosopher, independently invented a similar structural system. Following World War II, Fuller wanted to design affordable, efficient housing that could be built quickly from mass-produced components. Willing to look outside of conventional approaches, Fuller began to work with spherical shapes because they enclose a given space with a minimum of surface area. He first framed spheres with a network of strips approximating great circles (circles on a sphere with centers that coincide with the sphere's center); the strips formed triangles as they crossed one another. He called the product a geodesic dome because great circles are known as geodesics (from a Greek word meaning earth dividing). Eventually, Fuller began forming spheres from hexagons and pentagons (like the panels on a soccer ball) and dividing them into triangles for strength and ease of construction.

In 1953, Fuller used his new system to cover the 93-ft (28-m) diameter courtyard surrounded by Ford Motor Company's headquarters building. The building was not designed to support the great weight of a traditional dome, but Fuller's creation weighed 95% less. He completed the design and construction in only three months. A temporary mast erected in the center of the courtyard supported the dome during construction, and the structure was incrementally raised and rotated following completion of each new section. The frame consisted of 12,000 aluminum struts weighing a total of 3,750 lb (1,700 kg) that were connected to form triangles and then lifted into position and riveted to the growing frame. When the dome was completed, it was gently lowered onto mounts that had been installed on the existing building. A clear fiberglass panel was installed in each triangle to complete the dome.

In 1954, Fuller received a patent on geodesic domes. During the 1960s and 1970s, an era in which unconventionality was prized, geometric domes became popular as an inexpensive way for environmentally conscious people to build their own homes. Instructions were widely available, but the quality of materials (including such strange choices as paper mache and discarded tin cans) and the skill of do-it-yourself builders were inconsistent. Amateur-built domes tended to leak when it rained, insufficient use of insulation limited their energy efficiency, and inadequate numbers of skylights left interiors dreary.

Fuller predicted that a million geodesic domes would be built by the mid-1980s, but by the early 1990s, estimates placed the worldwide number somewhere between 50,000 and 300,000. A small but persistent contingent of unconventional homebuilders continue to build geodesic dome homes, primarily from kits. However, Newsday reported in 1992 that the majority of geodesic dome structures have been built for green-houses, storage sheds, defense shelters, and tourist attractions. One of the most recognizable of these is the 165-ft (48-m) diameter sphere at Walt Disney World's Epcot Center. Built of composite panels of ethylene plastic and aluminum in 1982, the structure houses a ride called Spaceship Earth, a termed coined by Fuller himself.

Raw Materials

Geodesic domes range in size from the 460-ft (143-m) Poliedro de Caracas sports arena in Venezuela to temporary shelters that are 15 ft (5 m) or less in diameter. Consequently, construction materials vary widely. Simple, movable structures may be built of polyvinyl chloride (PVC) pipe or galvanized steel conduit frames covered with plastic sheeting or parachute canopies. Large, permanent structures like arenas and factories have been built from materials like aluminum and steel frame struts covered with aluminum, copper, structural gypsum, acrylic, or Plexiglas panels.

Most residential dome kit manufacturers use wood components, primarily kiln-dried Douglas fir struts covered with 0.5-in (1.3-cm) exterior-or structural-grade plywood. Such kits include various designs of connectors to securely fasten the wood struts together in the proper configuration; high-strength aluminum, or steel coated with zinc, epoxy, or industrial primer are commonly used for connectors. Zinc-plated steel bolts secure the connectors and paneling is nailed on.

A few kit manufacturers use altemative materials to make prefabricated panels that combine the frame and exterior covering. One, for example, makes molded fiberglass panels. Another supplies reinforced concrete panels; steel mesh extending from the panel edges is overlapped with mesh from the adjoining panel, and the joint is sealed with concrete.

Most dome kits are built atop concrete foundation slabs. Often, these slabs are recessed into the ground to provide a basement level. Foundation walls and riser walls (vertical walls below the dome that may be used to raise its overall height) are usually made of concrete or wood. Interior insulation generally consists of fiberglass batting or sprayed-on urethane, cellulose, or Icynene plastic foam.

Design

Although dome homes are built from manufactured kits, designs are flexible. As many as half of the triangles in the dome's lowest row can be removed without weakening the structure, so door and window openings can be plentiful. Vertical-walled extensions can be built out from such openings to increase the floor space. The dome can sit directly on ground-level footings (short walls recessed into the ground to bear the building's weight), or it can be erected atop a riser wall up to 8 ft (2.5 m) tall.

Space must be provided between the interior and exterior walls to accommodate insulation. Some manufacturers create this space by making the struts from wood that is 4-8 in (10-20 cm) thick. Others make this space 14.5-21 in (37-53 cm) thick by using compound struts consisting of two strips of lumber joined with plywood gussets.

The Manufacturing Process

The following is a composite of techniques used by several individuals using kits from various manufacturers.

The substructure

• After clearing and leveling the home site, a trench is dug for the foundation footing, following detailed drawings supplied by the kit manufacturer. The base of the dome is not circular; rather, it is outlined by five short walls alternating with five long walls (twice the length of the short walls). Forms are placed for the footings; many builders like to use permanent Styrofoam forms that need not be removed. Concrete is then poured in the footing forms.
• A layer of sand may be used to further level the surface and provide a base for the foundation slab. Reinforcing steel bars are tied together in a grid, and concrete is poured to form the foundation.
• Foundation walls are built atop the footings, up to approximately ground level. If desired, riser walls (which are provided as part of the kit) are installed atop the foundation walls and bolted to one another.
• Floor joists are installed by standing wooden 2x12 (1.5x1.5 in [3.8x29.2]) boards 16 in (40 cm) apart above the foundation. The joists are nailed to a perimeter wooden frame and a wooden crossbeam. Three-quarter-inch (1.9-cm) thick plywood sheets are laid across the joists and nailed in place.

The superstructure

The superstructure typically consists of 60 triangular panels. Depending on the desired size of the dome, the panels are usually 6-10 ft (1.8-3 m) on a side. They may be prefabricated with the exterior panels installed, or they may constructed on site from precut lumber and metal connectors.

If dome panels were supplied with the kit, they are set atop the foundation or riser walls and connected to one another in a sequence prescribed by the manufacturer. Until enough panels are connected to support themselves, they must be braced with poles radiating out from a block in the center of the floor. The following steps describe the more common case of frame erection followed by exterior panel installation:

• Base plates are installed atop the foundation or riser walls. These precisely beveled 4x6-in (lOx15-cm) wood strips provide a transition between the horizontal top edge of the walls and the slightly tilted triangles of the dome's bottom strip of panels.
• Matching the color coding on the kit's wooden struts and metal connectors, a triangle is formed and secured with bolts. The triangle is lifted into position and bolted to the wall and/or to the adjacent triangles. Successive rows of triangular elements are placed until the dome is completely formed. Because of their light weight, the triangles do not need supplementary bracing to hold them in place during construction.
• Wooden studs are nailed inside each triangle. Running perpendicular to one side of the triangle, they are placed about 16 in (40 cm) apart. If an odd number of studs is used, the center one is secured against a per-pendicular block near the triangle's vertex, rather than extending to the vertex.
• Matching color-coded edges, the plywood panels are lifted into position on the exterior of each triangle and nailed into place. By working downward from the top of the dome, the worker can stand on the open framework below while attaching each panel.
• Vertical walls and roofs are framed for any desired extensions that will project outward from the dome. Plywood panels are nailed to the exterior faces of the extensions. Dormer extensions can also be erected for second-story windows.

Finishing

• Windows, skylights, and exterior doors are installed.
• The roof is covered with rubber sheeting, and conventional roofing material (such as shingles or tiles) is applied.
• Conventional siding material (such as stucco or vinyl siding) is applied to the exterior of the riser walls.
• Insulation is placed between the struts and studs inside the dome and extension walls.
• Walls are framed to divide the interior into rooms. Conventional drywall sheets are cut according to patterns included in the kit, and they are nailed to the interior walls and the inside surfaces of the dome and riser walls. Because of the many angles between triangular sections of the dome, amateur builders often hire a professional to tape the drywall joints.

Quality Control

A quality geodesic dome structure is airtight and structurally sound. These are the factors that lower energy costs, the main consideration when building a geodesic home. Because the structure is basically airtight, condensation can sometimes be a problem. Normally it is controlled by the heating and cooling system but when the house has been closed up for a few days, moisture can build up. This is easily solved by turning the air system on or opening a door or window.

The Future

Future refinements in geodesic dome construction may come from improved building materials. For example, in 1997 a concrete block manufacturer developed a hollow, beveled, triangular block with scored edges that could interlock with adjacent blocks. Properly shaped, such blocks could be used to construct domes.

Another innovation involves designing domes based on a different mathematical premise. In a true geodesic dome, the edges of the triangular elements align to form great circles. Although not geodesic, a new design patented in 1989 uses hexagons and pentagons to form domes with an elliptical cross section. Because of its mathematical derivation, this design is called geotangent.

Although geodesic domes maximize strength while minimizing construction materials, elliptical-profile domes offer two different advantages. They can cover a circular area without rising as high as a spherical dome. And they can cover elongated or irregularly shaped areas that vary in elevation. Located in northern Mexico, the world's largest industrial domes are a pair of manufacturing buildings covered with elliptical roofs 735 ft (224 m) long and 260 ft (80 m) wide.

Where to Learn More

Periodicals

DiChristina, Mariette. "Elliptical Dome." Popular Science (January 1990): 74.

Horton, Ted. "The Dome." Mother Earth News (June/July 1999): 64.

Sieden, Lloyd Steven. "The Birth of the Geodesic Dome: How Bucky Did It." The Futurist (November/December 1989): 14+. http://www.Isi.usp.br/usp/rod/bucky/geodesic_domes.txt. (January 6, 2000).

Other

"An Introduction to Geodesic Domes." http://Owww.dnaco.net/-michael/domes/intro.html (December 2, 1999).

"Design and Construction of Alpine Dome Homes." Alpine Domes. http://www.freeyellow.com/alpinedomes (January 6, 2000).

"Home Sweet Dome." http://future.newsday.com (January 6, 2000).

Timberline Geodesics. http://www.dome-home.com (April 4, 2000).

[Article by: Loretta Hall]

A curved lattice grid dome that utilizes the equilateral triangle as the basis of itssurface grid geometry. R. Buckminster Fuller, the inventor and champion of the geodesic dome, obtained a patent in 1954 that described a method of dividing a spherical surface into equilateral triangles. The two regular polyhedra that can be inscribed in a sphere are the dodecahedron (12 faces, each of which is a regular polygon; illus. a) and the more utilized icosahedron (20 faces, each of which is an equilateral triangle;illus. b). See also Polyhedron.

pentagon is typical of each face; every point is an apex because all apexes are on the sphere; each strut (l) is the same length. (b) Icosahedron: an apex is above the center of each polygon and on the surface of the sphere; the equilateral triangle typical of each face is highlighted; each strut is the same length. (c) Larger dome based on the icosahedron: subdivision is formed by connecting mid points of struts of equilateral triangles (each half strut is labeled i/2); the original pentagon is shown at the top, and a formed hexagon is also shown.">
Geometry of geodesic domes. (a) Dodecahedron: a regular pentagon is typical of each face; every point is an apex because all apexes are on the sphere; each strut (l) is the same length. (b) Icosahedron: an apex is above the center of each polygon and on the surface of the sphere; the equilateral triangle typical of each face is highlighted; each strut is the same length. (c) Larger dome based on the icosahedron: subdivision is formed by connecting mid points of struts of equilateral triangles (each half strut is labeled i/2); the original pentagon is shown at the top, and a formed hexagon is also shown.

The geodesic dome has been used for everything from great exhibition spaces and halls to outdoor tent supports and jungle gyms. By utilizing the icosahedron as the basic building block ofthe geodesic dome, larger domes are possible with additional triangular subdivisions. This subdivision is known as the frequency. The first frequency is to interconnect the projected midpoints of the struts of each equilateral triangle of the icosahedron as they will project on the spherical surface. The result is four almost equilateral triangles where there was one before. The resulting lattice has similar but not exactly equilateral triangles if the grid is to remain on the spherical surface. This subdivision process can continue. The resulting grids have bothtriangular and hexagonal grids as a by-product within the basic geodesic dome geometry, with pentagons around the apex of the basic underlying icosahedron framework (illus. c).

A structure consisting of a multiplicity of similar, light, straight-line elements (usually in tension) which form a grid in the shape of a dome.

Geodesic Dome, a type of building invented by the American engineer R. Buckminster Fuller in the late 1940s. Geodesic domes are composed of triangles of various sizes that are assembled into roughly hemispherical structures. They are exceptionally lightweight, strong, and require no interior supports. Geodesic domes first came to prominence in the 1950s, when they were used as radar shelters in the Distant Early Warning line and for exhibit pavilions in international trade fairs (most notably the Montreal Expo in 1967). These uses helped solidify Fuller's reputation as a visionary yet practical thinker, and domes likewise became symbols of American ingenuity and the strength of Cold War capitalism. In the 1960s, domes were embraced by the counterculture, and thousands were built for use as homes, especially in rural communes. For these dome builders, domes were symbols of an ecologically friendly, pacifist, and anticorporate lifestyle—the rejection of precisely those values the dome embodied in the 1950s. The dome faded as countercultural architecture in the 1970s; since then, domes have principally been used in industrial applications requiring wide-span structures.

Bibliography

Kahn, Lloyd, ed. Domebook 2. Bolinas, Calif.: Pacific Domes, 1971.

Pang, Alex Soojung-Kim. "Whose Dome Is It, Anyway?" American Heritage of Invention and Technology (spring 1996), 28–31.

———. "Dome Days: Buckminster Fuller in the Cold War." In Cultural Babbage: Technology, Time, and Invention. Edited by Francis Spufford and Jenny Uglow. London: Faber and Faber, 1996.

Wong, Yunn Chii. "The Geodesic Works of Richard Buckminster Fuller, 1948–1968 (The Universe as a Home of Man)." Ph. D. diss. Massachusetts Institute of Technology, 1999.

—Alex Soojung-Kim Pang

Spaceship Earth at Epcot, Walt Disney World, a familiar geodesic sphere

A geodesic dome is a spherical or partial-spherical shell structure or lattice shell based on a network of great circles (geodesics) lying on the surface of a sphere. The geodesics intersect to form triangular elements that have local triangular rigidity and also distribute the stress across the entire structure. When completed to form a complete sphere, it is known as a geodesic sphere.

Typically the design of a geodesic dome begins with an icosahedron inscribed in a sphere, tiling each triangular face with smaller triangles, then projecting the vertices of each tile to the sphere. The endpoints of the links of the completed sphere would then be the projected endpoints on the sphere's surface. If this is done exactly, each of the edges of the sub-triangles is slightly different lengths, so it would require a very large number of links of different sizes. To minimize the number of different sizes of links, various simplifications are made. The result is a compromise consisting of a pattern of triangles with their vertices lying approximately on the surface of the sphere. The edges of the triangles form approximate geodesic paths over the surface of the dome that distribute its weight.

Geodesic designs can be used to form any curved, enclosed space. Oddly-shaped designs would require calculating for and custom building of each individual strut, vertex or panel—resulting in potentially expensive construction. Because of the expense and complexity of design and fabrication of any geodesic dome, builders have tended to standardize using a few basic designs.

Contents 1 Related patterns 2 History 3 Chord factors 4 Advantages of domes 5 Disadvantages of dome homes 6 Methods of construction 7 Largest geodesic dome structures 8 See also 9 References 10 External links

Related patterns

Similar non-geodesic structures may be based upon the pattern of edges and vertices of certain platonic solids, or upon various expansions of these called Johnson solids. Such structures may be composed of struts of uniform length while having faces other than triangles such as pentagons or squares, or these faces may be subdivided by struts of other than the basic length. Plans and licenses for such structures derived from licenses of the Fuller patents were produced during the 1970s by Zomeworks (now a manufacturer of solar trackers). Both geodesic and non-geodesic structures can be derived similarly from the archimedean solids and catalan solids.

The building of strong stable structures out of patterns of reinforcing triangles is most commonly seen in tent design. It has been applied in the abstract in other industrial design, but even in management science and deliberative structures as a conceptual metaphor, especially in the work of Stafford Beer, whose syntegration method is based so specifically on dome design that only fixed numbers of people can take part in the process at each deliberation stage.

History

The Montreal Biosphère, formerly the American Pavilion of Expo 67, by R. Buckminster Fuller, on Île Sainte-Hélène, Montreal, Canada

The first dome that could be called "geodesic" in every respect was designed just after World War I by Walther Bauersfeld,^[1] chief engineer of the Carl Zeiss optical company, for a planetarium to house his new planetarium projector. The dome was patented, constructed by the firm of Dykerhoff and Wydmann on the roof of the Zeiss plant in Jena, Germany, and opened to the public in July 1926.^[2] Some 30 years later, R. Buckminster Fuller named the dome "geodesic" from field experiments with artist Kenneth Snelson at Black Mountain College in 1948 and 1949. Snelson and Fuller worked together in developing what they termed "tensegrity," an engineering principle of continuous tension and discontinuous compression that allowed domes to deploy a lightweight lattice of interlocking icosahedrons that could be skinned with a protective cover. Although Fuller was not the original inventor, he developed the intrinsic mathematics of the dome, thereby allowing popularization of the idea — for which he received a U.S. patent in 1954.^[3]

The geodesic dome appealed to Fuller because it was extremely strong for its weight, its "omnitriangulated" surface provided an inherently stable structure, and because a sphere encloses the greatest volume for the least surface area. Fuller hoped that the geodesic dome would help address the postwar housing crisis. This was consistent with his prior hopes for both versions of the Dymaxion House.

The Climatron greenhouse at Missouri Botanical Gardens, built during 1960, inspired the domes in the science fiction movie Silent Running.

However, from a practical perspective, geodesic constructions have some disadvantages. They have a very large number of edges in comparison with more conventional structures which have just a few large flat surfaces. Each of the edges must be prevented from leaking, which can be quite challenging for a geodesic structure. Also, spaces enclosed within curved boundaries tend to be less usable than spaces enclosed within flat boundaries. (Since it would be impractical to produce sofas with every possible curved shape, they are normally constructed along straight lines, and so leave wasted space when placed in a curved space.)

The dome was successfully adopted for specialized industrial use, such as the 1958 Union Tank Car Company dome near Baton Rouge, Louisiana and specialty buildings like the Kaiser Aluminum domes (constructed in numerous locations across the US, e.g., Virginia Beach, VA), auditoriums, weather observatories, and storage facilities. The dome was soon breaking records for covered surface, enclosed volume, and construction speed. According to a WAFB-TV of Baton Rouge news report on November 27, 2007, the Union Tank Car Company Dome has been demolished.

Leveraging the geodesic dome's stability, the US Air Force experimented with helicopter-deliverable units.

The dome was introduced to a wider audience as a pavilion for the 1964 World's Fair in New York City. This dome is now used as an aviary by the Queens Zoo in Flushing Meadows Corona Park.

Another dome is from Expo 67 the Montreal, Canada World's Fair as part of the American Pavilion. The structure's covering later burned, but the structure itself still stands and, under the name Biosphère, currently houses an interpretive museum about the Saint Lawrence River.

During the 1970s, the Cinesphere dome was built at the Ontario Place amusement park in Toronto, Canada. During 1975, a dome was constructed at the South Pole, where its resistance to snow and wind loads is important.

Residential geodesic domes have been less successful than those used for working and/or entertainment, largely because of their complexity and consequent greater construction costs. Fuller himself lived in a geodesic dome in Carbondale, Illinois, at the corner of Forest and Cherry [1]. Residential domes have not become as popular as Fuller hoped. He thought of residential domes as air-deliverable products manufactured by an aerospace-like industry. Fuller's dome home still exists, and a group called RBF Dome NFP is attempting to restore the dome and have it registered as a National Historic Landmark.

Chord factors

A geodesic sphere and its dual.

The mathematical object "chord" of the "geodesic sphere" corresponds to the structural "strut" of the physical "geodesic dome". The general definition of a chord is a (straight) line segment joining two points on a curve. For simple geodesic domes we recognize the associated curve to be the surface of a sphere. Here is how chords of geodesic spheres are generated. We first choose an underlying polyhedron with equal triangle faces. The regular icosahedron is most popular. The sphere we use is specifically the "circumscribing sphere" that contains the points (vertices) of the underlying polyhedron. The desired frequency of the subsequent geodesic sphere or dome is the number of parts or segments into which a side (edge) of the underlying polyhedral triangle is subdivided. The frequency has historically been denoted by the Greek letter "ν" (nu). By connecting like points along the subdivided sides we produce a natural triangular grid of segments inside each underlying triangle face. Each segment of the grid is then projected as a "chord" onto the surface of the circumscribing sphere. The technical definition of a chord factor is the ratio of the chord length to the radius of the circumscribing sphere. It is therefore convenient to think of the circumscribing sphere as scaled to radius = 1 in which "chord factors" are the same as "chord lengths" (decimal numbers less than one).

For geodesic spheres a well-known formula for calculating any "chord factor" is

chord factor = 2 Sin (θ / 2) where θ is the corresponding angle of arc for the given chord, that is, the "central angle" spanned by the chord with respect to the center of the circumscribing sphere. Determining the central angle usually requires some non-trivial spherical geometry.

In Geodesic Math and How to Use It Hugh Kenner writes, "Tables of chord factors, containing as they do the essential design information for spherical systems, were for many years guarded like military secrets. As late as 1966, some 3ν icosa figures from Popular Science Monthly were all anyone outside the circle of Fuller licensees had to go on." (page 57, 1976 edition). Other tables became available with publication of Lloyd Kahn's Domebook 1 (1970) and Domebook 2 (1971). With advent of personal computers, the mathematics became more solvable. Rick Bono's Dome software outputs a script that can be used with the POV-ray raytrace to produce 3D pictures of domes. Domes based on the frameworks of different underlying polyhedra along with various methods for subdividing them will produce quite different results. Mathematical formulas developed by Peter W. Messer for calculating chord factors and dihedral angles for the general geodesic sphere appear in the Appendix of the 1999 Dover edition of Spherical Models by Magnus J. Wenninger.

Advantages of domes

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Inside the Eden Project tropical biome

Geodesic domes provide an enclosed space free of structural supports. The basic structure can be erected quickly from lightweight pieces by a small crew. Domes as large as 50 meters have been constructed in the wilderness from rough materials without a crane. The dome is also aerodynamic, so it withstands considerable wind loads, such as those created by hurricanes. Solar heating is possible by placing an arc of windows across the dome: the more heating needed, the wider the arc should be, to encompass more of the year.

Nowadays, there are many companies that sell both dome plans and frame material with instructions designed simply enough for owners to build themselves, and many do to make the net cost lower than standard construction homes. Construction techniques have improved based on real-world experience during the past several decades, and many newer dome homes can resolve some of the disadvantages that were true of the early dome homes.

Disadvantages of dome homes

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As a housing system, the dome can have numerous disadvantages and problems.

The shape of a dome house makes it difficult to conform to code requirements for placement of sewer vents and chimneys. Off-the-shelf building materials (e.g., plywood, strand board) normally come in rectangular shapes and so much material may have to be scrapped after cutting rectangles down to triangles, thus increasing the cost of construction. Fire escapes are problematic; codes require them for larger structures, and they are expensive. Windows conforming to code can cost anywhere from 5 to 15 times as much as windows in conventional houses. Professional electrical wiring costs more because of increased labor time. Even owner-wired situations are costly, because more of certain materials are required for dome construction.

Air stratification and moisture distribution within a dome are unusual, and these conditions tend to quickly degrade wooden framing or interior paneling. Privacy is difficult to guarantee because a dome is difficult to partition satisfactorily. Sounds, smells, and even reflected light tend to be conveyed through the entire structure.

As with any curved shape, the dome produces wall areas that can be difficult to use and leaves some peripheral floor area with restricted use due to lack of headroom. This can leave a volume that may require heating – representing a cost in energy – but that cannot be lived in. Circular plan shapes lack the simple modularity provided by rectangles. Furnishers and fitters usually design with flat surfaces in mind, and so placing a standard sofa (for example) results in a crescent behind the sofa being wasted. This is best overcome by purpose-built fittings, though it adds to cost.

Dome builders using cut-board sheathing materials find it hard to seal domes against rain, because of their many seams. Also, these seams may be stressed because ordinary solar heat flexes the entire structure each day as the sun moves across the sky.

The most effective waterproofing method with a wooden dome is to shingle the dome, but even this can be a problem at the top of the dome where the slope is less than that required by most roofing materials. (One solution is to add a peaked cap to the top of the dome or to modify the dome shape.) One-piece reinforced concrete or plastic domes are also in use, and some domes have been constructed from plastic or waxed cardboard triangles that are overlapped in such a way as to shed water. Buckminster Fuller's former student J. Baldwin insists that there is not any reason for a properly designed, well-constructed dome to leak, and that some designs cannot leak (Bucky Works: Buckminster Fuller's Ideas for Today). However, Lloyd Kahn, after writing two books on the subject (Domebook 1 and Domebook 2), became disillusioned with domes. He calls domes "smart but not wise",^[4] and has collected many of the criticisms given above.

Methods of construction

Construction details of a permanently installed tent-type geodesic dome by Buckminster Fuller.

Wooden domes have a hole drilled in the width of a strut. A stainless steel band locks the strut's hole to a steel pipe. With this method, the struts may be cut to the exact length needed. Triangles of exterior plywood are then nailed to the struts. The dome is wrapped from the bottom to the top with several stapled layers of tar paper, in order to shed water, and finished with shingles. This type of dome is often called a hub-and-strut dome because of the use of steel hubs to tie the struts together.

Panelized domes are constructed of separately-framed timbers covered in plywood. The three members comprising the triangular frame are often cut at compound angles in order to provide for a flat fitting of the various triangles. Holes are drilled through the members at precise locations and steel bolts then connect the triangles to form the dome. These members are often 2x4's or 2x6's, which allow for more insulation to fit within the triangle. The panelized technique allows the builder to attach the plywood skin to the triangles while safely working on the ground or in a comfortable shop out of the weather. This method does not require expensive steel hubs.

Temporary greenhouse domes have been constructed by stapling plastic sheeting onto a dome constructed from one-inch square beams. The result is warm, movable by hand in sizes less than 20 feet, and cheap. It should be staked to the ground to prevent it being moved by wind.

Steel-framework domes can be easily constructed of electrical conduit. One flattens the end of a strut and drills bolt holes at the needed length. A single bolt secures a vertex of struts. The nuts are usually set with removable locking compound, or if the dome is portable, have a castle nut with a cotter pin. This is the standard way to construct domes for jungle-gyms.

Concrete and foam plastic domes generally start with a steel framework dome, wrapped with chicken wire and wire screen for reinforcement. The chicken wire and screen is tied to the framework with wire ties. A coat of material is then sprayed or molded onto the frame. Tests should be performed with small squares to achieve the correct consistency of concrete or plastic. Generally, several coats are necessary on the inside and outside. The last step is to saturate concrete or polyester domes with a thin layer of epoxy compound to shed water.

Some concrete domes have been constructed from prefabricated, prestressed, steel-reinforced concrete panels that can be bolted into place. The bolts are within raised receptacles covered with little concrete caps to shed water. The triangles overlap to shed water. The triangles in this method can be molded in forms patterned in sand with wooden patterns, but the concrete triangles are usually so heavy that they must be placed with a crane. This construction is well-suited to domes because there is no place for water to pool on the concrete and leak through. The metal fasteners, joints and internal steel frames remain dry, preventing frost and corrosion damage. The concrete resists sun and weathering. Some form of internal flashing or caulking must be placed over the joints to prevent drafts. The 1963 Cinerama Dome was built from precast concrete hexagons and pentagons.

In 1986 a patent for a dome construction technique involving EPS triangles laminated to reinforced concrete on the outside, and wallboard on the inside was awarded to American Ingenuity of Rockledge Florida. The construction technique allows the domes to be prefabricated in kit form and erected by a homeowner. This method makes the seams into the strongest part of the structure, where the seams and especially the hubs in most wooden-framed domes are the weakest point in the structure. It also has the advantage of being watertight.

Largest geodesic dome structures

Many geodesic domes built are still in use. According to the Buckminster Fuller Institute,^[5] the world's ten largest geodesic domes are^{[clarification needed]}:

• Fantasy Entertainment Complex: Kyosho Isle, Japan, 710 ft (216 m) [2]
• Multi-Purpose Arena: Nagoya, Japan, 614 ft (187 m) [3]
• Tacoma Dome: Tacoma, Washington, USA, 530 ft (161.5 m)
• Superior Dome: Northern Michigan University. Marquette, Michigan, USA, 525 ft (160 m)[4]

• Walkup Skydome: Northern Arizona University. Flagstaff, Arizona, USA, 502 ft (153 m) [5]
• Round Valley High School Stadium: Springerville-Eagar, AZ, USA, 440 ft (134 m)
• Former Spruce Goose Hangar: Long Beach, California, USA, 415 ft (126 m)
• Formosa Plastics Storage Facility: Mai Liao, Taiwan, 402 ft (122 m)
• Union Tank Car Maintenance Facility: Baton Rouge, Louisiana, USA, 384 ft (117) m (Demolished in November 2007.) [6]
• Union Lehigh Portland Cement Storage Facility: Union Bridge, Maryland, USA, 374 ft (114 m)

See also

• Dome
• Concrete dome
• Cloud nine (Tensegrity sphere)
• Domed city
• Fullerenes, molecules which resemble the geodesic dome structure
• Hoberman sphere
• Monolithic dome
• Radome
• Silent Running 1972 science fiction film prominently featuring geodesic domes.
• Sindome An online Cyberpunk RPG that takes place in a giant geodesic dome.
• Space frames
• Stepan Center
• Shell structure
• Gridshell
• Truss
• Synergetics
• Geodesic tents
• Pentakis dodecahedron
• Truncated icosahedron

References

This article needs additional citations for verification. Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (August 2007)

1. ^ First Geodesic Dome: Planetarium in Jena 1922 incl. patent information
2. ^ according to http://www.planetarium-jena.de/Geschichte.43.0.html
3. ^ For a more detailed historical account, see the chapter "Geodesics, Domes, and Spacetime" in Tony Rothman's book "Science a la Mode", Princeton University Press, 1989.
4. ^ "Refried Domes" by Lloyd Kahn
5. ^ "World's 10 Largest Domes". Buckminster Fuller Institute. http://bfi.org/our_programs/who_is_buckminster_fuller/design_science/geodesic_domes/worlds_10_largest_domes. 

External links

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Look up geodesic dome in Wiktionary, the free dictionary.

Wikimedia Commons has media related to: Geodesic domes

• The R. Buckminster and Anne Hewlett Fuller Dome Home: the original R. Buckminster and Anne Hewlett Fuller Dome Home located at 407 S. Forest Ave. in Carbondale, Illinois, which was raised in just 7 hours on April 19, 1960.
• The R. Buckminster Fuller FAQ: Geodesic Domes
• Geodesic Dome Notes: 57 dome variants featured (1V to 10V) of various solids (icosa, cube, octa, etc)
• Article about the Eden Domes (PDF file 5.1 MB)
• Construction of the Eden Project Biomes
• Geodaetische Kuppeln (Geodesic Dome) by T.E. Dorozinski
• Geometry Dome: geodesic dome design without corner connectors, featured in the Guggenheim Museum and at BurningMan
• Shape optimization of Shell and Spatial structure
• 3D Warehouse - Geodesic Collection Catalog(s) of free 3D digital models for Google SketchUp and Google Earth

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