Published on September 5th, 2008 | by Philip Proefrock


Are Extruded Houses Green?

Contour Crafting extruded housesFor several years, Professor Behrokh Khoshnevis at the University of Southern California has been working on systems for rapidly creating buildings with system that is essentially a very large 3-dimensional printer.  Called Contour Crafting, the equipment is able to rapidly build up walls.  Already, test runs have been able to produce six-foot high concrete walls.

One goal of the team developing this technology is to be able to build a house in a day, a goal that they hope to reach within the next few years.  There is some merit to this goal, and the benefits of being able to rapidly and inexpensively produce houses are obvious, though not without some attendant problems.

This research has been going on for a number of years.  (Inhabitat wrote about the concept in 2005.) The team has recently received funding support from Caterpillar for further development of the system.

At present, the system has only limited ability to work with multiple materials. They are working on printing buildings using a “special concrete formulation provided by USG, the multi-national construction materials company.” Many of the same criticisms I wrote about earlier about Concrete Housing pertain here, as well.

The issue of concrete as an unsustainable material has also been addressed by the inventor: “Another question came from the direction of the material currently used in Contour Crafting, which is primarily some top secret fibre reinforced concrete. A student pointed out that concrete is not sustainable, and why are there no sustainable materials being developed along side contour crafting. To this the Dr. responded by saying that while he does use concrete, there are definitely possibilities for other materials in contour crafting. His main concern is introducing the technology. He says he has enough work on his hands to just make this technology available.”

Part of the difficulty of building construction is that many different materials are needed to accomplish all the various things that are expected of modern buildings. One material serves to keep the water out; another one provides a durable exterior; yet another helps by reducing the transmission of heat, and so forth. Working with only one or two materials typically means that there are more compromises, or that the system does not perform as well as some other alternatives.

One of the materials that needs to be included in the mix that Contour Crafting supplies is a good insulation. If the wall is solid concrete, or even a specialty concrete with improved thermal properties and air spaces to help with insulation and reducing thermal bridging, it is still going to have poor thermal performance in a heating climate. Some insulation materials may be able to be extrusion formed in a manner that is compatible with the system. However, the interactions between different materials – for example, the wetness of one material being detrimental to the application of another material – may add further complexity to the development of the system.

Adaptability and repairability is another issue to be considered. A monolithic building system that embeds the various services in the structure makes it difficult to access them for repair or expansion. This is true for a number of building systems besides this one. Expansion and modification of a building built by this extrusion method will likely be more difficult than a building built with other methods.

The first applications this system is being proposed for include rapid creation of shelter in the wake of a large-scale disaster and the production of mass low-cost housing in areas where there is great demand.  In the long run, it has also been suggested that this technology might be utilized to create structures for astronauts to use on the Moon or on Mars.

At present, the Contour Crafting system has some claim to being a green building method. The extrusion construction offers some benefits, including:
• less total material use
• less total energy use for all construction activities
• less material and energy waste during construction
• less transportation of material, equipment, and people
However, such extensive use of concrete as a material is not an especially sustainable approach. With continued development, the possibility is certainly there that further development of the technology and materials that are used in the system could lead to a greener method of building.

Related articles on Green Building Elements:
Weighing the Value of Concrete Housing
Green Prefab — Everyone’s into Modular Homes
Green Builders, Inc. Bringing Green Homes to the Masses

links: USC ISI, Contour Crafting, USC Viterbi School of Engineering, Live Architecture Blog

image sources: Contour Crafting, USC Viterbi School of Engineering

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