Joined: Jun 26, 2004 Posts: 1189 Location: Madison,Wisconsin
Posted: Sun Mar 18, 2007 8:46 pm Post subject: Re: dome housing
It entirely depends on what your using as your building materials. This post is slightly offtopic, as I'm not talking about domes. I personally always thought domes where a cool idea, but after actually studying them, I far prefer Cylinders as a home building shape.
I very much like them because they make maximum useage of a central radient heat source, and are a very strong structure. In addition, they don't make the assumption that people will somehow come up with very inventive ways to make use of living space that is varyingly smaller and bigger depending on the height your at. _________________ Azreal60
Posted: Wed Mar 21, 2007 3:18 pm Post subject: Re: dome housing
If your property is located anywhere near an earthquake fault zone and you are considering "earth" architecture, I would really be concerned with the possibility of the structure collapsing during a major earthquake.
Some well-meaning organizations sell plans for earthbag architecture that are claimed to be "earthquake safe". These structures are constructed from a concrete-like mixture of earth and portland cement, which is placed into bags with layers of barbed wires between the rows of bags.
While the barbed wire provides structural reinforcement to support the weight of the structure, no vertical structural reinforcement exists between the bag layers. The lack of vertical structural reinforcement could cause separation to occur between the bag layers during an earthquake, and may result in all or part of the structure to come crashing down on the occupants.
After submitting earth architecture plans to the building department, in many cases the owner/builders have received comments from the engineering review process, such as "provide vertical connections between bag layers." While it is possible to make these structures reasonably "earthquake safe", it only adds to the cost.
One assumption people make is that earth architecture is inexpensive to build compared to conventional construction. Actual experience has shown that only the cost of building materials is less. These structures take a lot of time and effort to build, and the cost of labor is many times more expensive per square foot compared to conventional construction. If you factor in additional costs for modifications required by the building department to make these structures reasonably earthquake safe, these structures wind up costing 3-4 times more per square foot than conventional construction.
One compromise solution I have seen is to use the earthbag technique for the foundation and walls up to a few feet, and attach a yurt or framed dome structure to the earthbag foundation. I would feel much more comfortable with this arrangement, having a lighter structure above.
Posted: Wed Mar 21, 2007 3:32 pm Post subject: Re: dome housing
Some earth bag construction has been approved for use, but CA's earthquake regulations may be lax. Using a Yurt or framed dome definitely seems like the best of both worlds, so long as the top of the earthen walls are reinforced with beams going across.
Quote:
Superadobe Technology, U.S. patent #5,934,027, has been tested on individual dome and vaults (1993-1996) for the City of Hesperia, California, Building and Safety Department, in consultation with I.C.B.O. These structures passed the California required codes.
Posted: Wed Mar 21, 2007 5:37 pm Post subject: Re: dome housing
yesplease wrote:
Some earth bag construction has been approved for use, but CA's earthquake regulations may be lax. Using a Yurt or framed dome definitely seems like the best of both worlds, so long as the top of the earthen walls are reinforced with beams going across.
Quote:
Superadobe Technology, U.S. patent #5,934,027, has been tested on individual dome and vaults (1993-1996) for the City of Hesperia, California, Building and Safety Department, in consultation with I.C.B.O. These structures passed the California required codes.
Yes, I happen to have a copy of the complete engineering review process for this, where the City of Hesperia granted a building permit for superadobe. The permit approved by the City of Hesperia was for a non-residential structure, the Hesperia Lakes Nature Center and Museum. This structure was actually built and later bulldozed with the explaination given that shoddy construction was to blame.
During the review process, the engineer hired by CalEarth made the following statement regarding vertical ground movement:
Quote:
Upward vertical motion in a seismic event will not create a problem. The mass of the structure reduces as we approach the top and the continuous wall provides a large amount of surface area to distribute any dynamic stresses induced by a vertical rising motion. Downward vertical motion in a seismic event should also not create a problem since the shear mass of the structure would make vertical seperation virtually impossible
That's it. There are no references or calculations to support the claims made by this engineer that "the shear mass of the structure would make vertical separation virtually impossible." In addition this statement was not challenged by the Hesperia building department. I would not want to bet the lives of my family and myself on unsupported statements such as this.
The structures were required to undergo dynamic load testing, where asymetric horizontal stresses were applied to the structure. These tests passed with no problems. However, no testing or simulations have been performed on these structures where vertical seismic motion is involved. This type of motion is present to varying degrees in almost all earthquakes. As a general rule vertical motion is defined to be 2/3 of the horizontal motion. But depending on characteristics specific to the site, such as terrain or soil, the vertical ground motion can actually be greater than the horizontal motion.
Other building departments are more cautious about granting approval for these structures. For instance, when submitting plans for a superadobe structure to the San Bernadino County building department, the following comment was received from the engineering review process:
Quote:
Provide positive connection between the sand bags and between each layer of sand bags per CBC section 161633.2.5. The bar wires between the bags are not approved connectors.
They also wanted a study on the "Known Active Fault Near-Source Zones", and soil profile, which indicates that they are looking for the potential vertical ground motion at the site.
A superadobe structure was built on the Pomona College campus in the county of Los Angeles. The county required welded wire mesh to be installed on both the inside and outside of the structure, and shotcrete applied over the wire mesh, which increased the expense of building the structure.
So, while superadobe has passed the "required California codes" in some cases, it is still up to the owner/builder to decide if they are comfortable with being a guinea pig. I decided to pass on this opportunity and stick with something that has been proven over the test of time.
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