Sunday, December 4, 2011

Dome Sweet Dome - Housing for the Future

Dome structures made of various materials have a long architectural lineage extending into prehistory. Most people think of domes that sit atop structures like the Capitol Building in Washington, DC or St. Peter's Basilica in Rome.  

A monolithic dome (from Greek mono- and -lithic, meaning "one stone") is a structure cast in a one-piece form. The form may be permanent or temporary and may or may not remain part of the finished structure.  Forms have been made using nearly every common structural material including air pressure supported fabric.

The earliest form of monolithic dome structure could be considered to be the igloo. While it is constructed of blocks of compressed snow, these blocks melt and re-freeze to form a strong, homogeneous structure. The dome-like shape of the igloo exhibits the two major advantages of a dome-shaped structure: great strength, and good insulation. The strength is due to the natural strength of the arch, and the insulation is due to the minimal surface area of a spherical section.

The Inuit's of Canada's Central Arctic, and Greenland's Thule region were the predominant builders of igloos. Architecturally, the igloo is unique in that it is a dome that can be raised out of independent blocks leaning on each other and polished to fit without an additional supporting structure during construction. An igloo that is built correctly will support the weight of a person standing on the roof.  Igloos are energy-efficient. On the outside, temperatures may be as low as −45 °C (−49 °F), but on the inside the temperature may range from −7 °C (19 °F) to 16 °C (61 °F) when warmed by body heat alone.

The first modern monolithic dome structure was built in Provo, Utah and opened in 1963 as an ice skating rink. Called Ream's Turtle after its 1967 conversion into a general store by new owner Paul Ream, the building stood until it was demolished in 2006 for new construction.

Ream's Turtle was built by first creating a mound of dirt in the desired shape of the shell, an ellipsoidal section 240 feet (73 m) long, 160 feet (49 m) wide and 40 feet (12 m) high. The mound was then covered in a grid of rebar, to provide strength, and a layer of concrete approximately 4 inches (100 mm) thick. After the concrete was cured, the dirt was excavated through the doorways, leaving the roof standing in its place. The floor was then poured to finish the structure.

Modern construction differs significantly from the original concrete-over-dirt method. The current methods were developed by three brothers from Idaho: Barry, Randy, and David South. The first dome built using these method was constructed in Shelley, Idaho:
  • A reinforced concrete foundation, or "ring beam", is constructed, defining the shape of the base of the structure.
  • The fabric form, or air form, is attached to the foundation and inflated with an air blower. The air form contains an airlock to allow workers to enter the form while it is inflated.
  • A layer of polyurethane foam is sprayed on the interior of the form. (Its purposes are to give rigidity to the air form, secure the rebar in place, provide support for spraying in the concrete mixture, and insulate the final structure.)
  • Rebar is attached to the outside layer of foam, using clips that are attached to the foam.
  • Several inches of concrete are sprayed over the rebar frame.
  • After the concrete has set, the blower is turned off.
  • The exposed surface of the air form may be left as is, or a surface treatment such as paint, tile, etc., may be applied. (Proper selection of air form material will ensure prevention from long-term degradation due to ultraviolet radiation.)
In instances where necessity requires economical construction for multiple small and basic dwellings, the dome can be built without insulation and the air form can be removed after completion and re-used to build additional domes.

In 1979, David South, president of Monolithic, and Barry South, David’s younger brother, as co-inventors, were awarded a patent for the Monolithic Dome. The USPTO awarded this patent because the structure called a Monolithic Dome was substantially different from all other types of structures, in use, in America. What made it different was its construction process that stipulated using an inflatable Airform, polyurethane foam insulation and steel-reinforced concrete.

The dome, when finished, is earthquake, tornado and hurricane resistant (FEMA rates them as "near-absolute protection" from F5 tornadoes and Category 5 Hurricanes). Recently, a number of monolithic domes constructed using MDI techniques have survived major disasters:
  • Several monolithic domes in Florida survived direct hits by Hurricane Katrina in 2005.
  • Several monolithic domes were in the path of the 2005 and 2006 wildfires in Oklahoma and Texas, and survived with only slight charring of the exterior foam insulation.
  • In 2003, a monolithic dome government building in Iraq survived a direct hit by a 5,000 lb (2,300 kg) bomb. The interior of the structure was totally destroyed, but the dome itself remained standing.

Today, Monolithic is a family of companies sharing a mutual goal: to improve the lives of people worldwide through the introduction and construction of Monolithic Domes, for personal and public use, that are superior in strength, energy-efficiency and cost control. Monolithic Dome Institute (or MDI) is the information-generating and educational branch of the Monolithic family.  Their website is an excellent resource for learning more about this type of architecture and construction technique.

With natural disasters always a consideration in structural safety, exhorbitant energy costs, and sky-rocketing insurance premiums, monolithic domes are a logical answer to humanity's future housing needs.  I urge anyone who is thinking about building a home to do the research on the MDI website.  

Until next time...become the change you imagine.