For Those Considering Building with Adobe in California
Due to both seismic risk and regulatory disinterest, building with adobe in California is more complicated than in adobe friendly states like New Mexico. While not insurmountable, the barriers to building with adobe in California are significant. For the persistent individual, the owner-builder, or the environmentally concerned, these regulatory hurdles can be overcome. What follows below is an outline of factors within California confronting the prospective adobe builder or client which should be considered early in a project’s inception:
Supply Considerations
Perhaps the most significant barrier to adobe construction within California is the lack of commercially available brick. As of the spring of 2012, there are no commerical adobe manufacturers operating within the state. Adobe yards require large amounts of space for material handling and brick curing, and logistical considerations naturally favor locations near major highway corridors. Real estate costs, low market demand, air quality and mining regulations have all been significant barriers to the entry of additional producers. Fortunately, small scale adobe manufacturing can be accomplished by contractors and owner-builders alike; commercially produced bricks can also be obtained from yards in Arizona and New Mexico.
For those interested in making their own bricks, the process is simple though labor intensive (refer to the excellent Earthbuilder’s Encyclopedia or P.G. McHenry’s books listed in our Bibliography [link] for more information). Appropriate soil is not available in all areas – in portions of the Mojave, for example, clay soil is often found only in dry lake beds and is not easily procured on site or from sand and gravel companies. Geologists, excavation contractors or agricultural extension agents are often good resources in the search for appropriate soil.
Whether made on site or purchased, adobe brick needs to comply with strength, modulus of rupture and moisture resistance requirements detailed in California Building Code Section 2109.3. For example, under these requirements, bricks need to have an average compressive strength of at least 300psi when tested according to ASTM C 67 (five brick minimum sample size). Similarly, the adobe brick’s average modulus of rupture must achieve at least 50psi under the specified test procedure, with no individual unit testing at less than 35 psi. In practice, bricks that are sufficiently strong to survive handling on the job site usually do not have difficulty meeting these criteria, and adobe manufacturers can usually provide test results demonstrating that their product satisfies code requirements. For those making their own bricks, private engineering test labs that can quantify brick performance for a few hundred dollars are located throughout the state.
Labor Considerations
Although it may be initially difficult to find local contractors advertising experience in adobe construction, they do exist. Adobe construction was not uncommon in California until the mid 1990′s, and many masonry contractors are still capable of building with adobe. Additionally, the masonry trades within the state draw heavily from labor pools south of the border where adobe construction is still common.
Structural Considerations
California exists in an area of seismic hazard, and adobe construction needs to be designed in anticipation of the inevitable earthquake. Any adobe building within the state will be required to to have its structural system designed by a licensed structural engineer. Appropriate design will probably be accomplished in one of three ways: by designing the walls as cantilevers (taking no or little credit for the contribution of roof structure); as walls stabilized against lateral movement by the diaphragm action of the roof; or by designing the structure as wood or concrete frames with non-structural adobe infill. Whatever the approach, rebar will need to be provided within the adobe walls. This can be achieved by laying up a single width (wythe in masonry parlance) of “holey” adobes which have cavities through which rebar may pass, by coring in rebar or threaded rod once the wall is nearly complete, or by providing a double wythe wall in which a mud-packed cavity containing rebar is provided. The last is the most conservative approach, and likely most appropriate. In all cases, the adobes will need to be firmly seated against a strong foundation at the foot, and stabilized at the top by a bond beam of wood or concrete.
Energy Considerations
Construction within California is governed by the State’s energy code, commonly called “Title 24″. California provides two paths for demonstrating compliance with the requirements of the energy code: a prescriptive path, for which compliance is achieved by showing that the building meets or exceeds performance values for all building components (wall and roof assemblies, window frames and glazing, etc); and a performance path which attempts to show performance by computer modeling components of the building with respect to published weather data, building orientation and massing against an energy budget.
For reasons too technical to address here, many of the computer modelling tools recognized by the California Energy Commission are thought to do very poorly at documenting the performance of adobe walls. For this reason, the prescriptive approach to demonstrating performance will usually fair better, and in all but the most extreme climate zones within the State no additional insulation beyond the adobe wall construction itself will be required. Individuals pursuing earthen construction are often told incorrectly by contractors and consultants unfamiliar with how Title 24 addresses massive wall construction that adobe cannot meet energy code requirements – this is fictive, and these individuals should be referred to the Residential Compliance Manual published by the California Energy Commission for more information.
|
|
For Those Considering Owning and Maintaining an Adobe building
Although some of the oldest surviving buildings in the world are made of earth, owning or maintaining an adobe structure requires a different type of care than a wood frame building. In fact, well intentioned measures taken by uninformed owners or contractors can in even hasten or cause damage to the structure.
The following “Dos and Don’ts” will help avoid some major mistakes, and when in doubt, it is never a bad idea to obtain advice from an adobe professional.
In a historic structure, do not undertake any work without consulting a preservation professional
Do maintain roofs, canales, scuppers, gutters and downspouts. Address the causes of water damage as soon as they occur.
Do not allow sprinklers or irrigation equipment to spray the building, or saturate the soil at the base of the walls.
Do not install concrete collars/contra pareds, pavement or sidewalks at the base of adobe walls. Although it may seem that such additions will prevent water damage, generally they only capture moisture within adobe walls, exacerbating deterioration. Adobe structures will
Do not install stucco/portland cement based plaster on an adobe building without the consultation of an expert familiar with adobe construction. While cement-based plasters are durable and low-maintenance, an improperly detailed or installed stucco finish can destroy an adobe building.
Do not add soil or allow grading to direct water towards the building.
Do not paint adobe walls with vapor impermeable paints such as gloss paints, elastomeric coatings, et cetera.
Do have on hand these two excellent references on the conservation of adobe buildings:
Preservation Brief on Preserving Historic Adobe Building
National Park Service
http://www.nps.gov/hps/tps/briefs/brief05.htm
Adobe Conservation
by Cornerstones Community Partnership
http://www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=cornerstones+adobe+preservation |
|
