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Foundations for Adobe |
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Q: How do you build foundations for an adobe house (2 floors) on the sand? The location would be on a stable sand dune. I don't know yet if there's any layer of rock at a decent distance from the surface. But, in the case the layer is very deep, what can we do? A: Sand is not such a bad base for a house. The foundation needs to get down to the frost level if there is one at your location. The foundation needs to be a minimum of 8-inches thick and should be at six-inches wider than the wall on each side. For two story construction the first floor needs to be at least 14-inches thick and the second should step back to 10-inches. Adobe walls should not go higher than ten times their thickness so if the wall does not step back for the second floor then it needs to be twenty-inches thick all the way up. My best recommendation is to stick to a single story if you have not built adobe before and given that you are on a sand base. Q: If one followed the 10 to 1 width/height ratio, could we build a relatively self standing adobe wall (used like a fence) at the heights mentioned? We had learned that if building a cement block wall of over 4 feet tall, one has to reinforce with mortar & rebar. We would also love our 'wall' to have some curves. Thanks for any hints on reading material and whether homemade sun baked adobe bricks would support this wall project. A: It will work just fine. Just stay a bit below the height limitation of a 10" or 12" wall. A good foundation to the frost line or else a Frank Lloyd Wright gravel trench with or without the concrete grade beam will work. Curves in the wall make it stronger. We do have an adobe discussion group at adobe-subscribeATyahoogroups.com I normally don't recruit for that group but you might benefit from it more than most. Q: Could it be useful to use tires for the foundation of an adobe house? A: Tires rammed tightly with soil make a reasonably acceptable foundation. I don't think that it saves time or energy. My preference would be large flat stones dry stacked or round stones laid up in the minimum amount of cement/lime mortar. Q: I am designing an adobe house. Since abode walls have to be protected from rain I was thinking of elevating my house and using rocks up to the plinth height. Will it be structurally safe as the house elevation will be partially in a artificial pond? If yes/no what kind of foundation should I go in for? Q: I am wondering though about the capillary action of the concrete foundation. Our house site is in a Very dry area with the water table down around 200 feet or so, so I'm not worried about that. My question: Is the capillary action of concrete such that, during mild to heavy New Mexico snow melt or summer monsoons, enough moisture could wick up into the foundation from the ground to threaten the integrity of the structure, given that the first course of the house is all of unstabilized adobes? A: It is useful to paint emulsified asphalt on top of the foundation or trowel on one of the roofing asphalt coatings. Since your adobes are already in place, you might coat the exterior surface of the foundation with asphalt or Bituthene or similar sheet material. In the long run, I don't think you have much to worry about. The traditional response to the snow problem was to sweep or shovel it away from the building.You will do fine. Worst case is that the house might only last 200 years instead of 2000. Q: Firstly, my plan is to build a small (10' diameter dome) using earth, with an earthbag stem wall filled with pumice (on site). Thoughts? A: Over the years, I have worked with pumice in a variety of forms. In ground contact it becomes damp and looses its insulating abilities. In walls, it has higher moisture content than the ambient atmosphere and surrounding materials. Pumice is well designed to be a fine capillary action medium and any moisture in pumice becomes well disbursed and uniformly damp or dry very quickly. Therefore you will want to introduce a good moisture and vapor barrier between the bag wall and the adobe. I am no fan of the use of bag walls at the lower part of the building. Filled with pumice and no binder such as clay or cement, the system depends entirely on the polypropylene material. As evidenced by the short lifetime of blue poly tarps found at most construction sites, the material has little resistance to ultraviolet degradation. Therefore, you will want to have a very good plaster or some other form of covering over the stem wall to protect the bag material. You will want to be careful to maintain that coating for the life of the building. ironically, the old burlap material which has now been replaced by poly for sand bags lasted far longer out in the open. Q: I plan to use a compacted gravel trench foundation, with a 14" wide and 8" thick bond beam sitting on top of that to support the exterior walls, post and beam, with straw clay infill. I wonder what type of foundation is required for the interior adobe walls. The finished adobe floor will come to the top of the exterior wall's bond beam. Q: I am designing a small house to be built in Torrance County NM. It will be passive solar design, post and beam, with light straw clay infill for exterior walls, adobe floor. At least two major walls on the interior are to be 10" thick adobe brick wall. These are in the south rooms of the building and will serve as solar mass. These are non bearing walls. One runs parallel to the roof trusses above. This connects with the south exterior wall. The other will be midway beneath the trusses, and will run perpendicular to them. Loading, however, will be on adequate post and beam structure for that wall. I plan to use a compacted gravel trench foundation, with a 14" wide and 8" thick bond beam sitting on top of that to support the exterior walls, post and beam, with straw clay infill. I wonder what type of foundation is required for the interior adobe walls. The finished adobe floor will come to the top of the exterior wall's bond beam. If I use gravel trench for interior walls, how deep, and will I need an equally large bond beam? Is a bond beam necessary to tie the buildings foundation together? A: For your interior walls a gravel trench that is four inches wider on each side will be fine. There should be 8-inches of gravel and as long as you are on undisturbed earth, there is no need to go down to the frost line. Myself and PG McHenry never did the concrete grade beam as we call it but just started with the adobe coursework right on top of the gravel. It would be advisable to have the adobe walls start about four inches above the mud floor for protection from the possibility of a burst pipe somewhere in the future or the possibility of moisture wicking up from the floor. Solid ground ties the building together well enough at the bottom so the concrete is optional or something to get adobe above exterior grade and interior floor levels. Q: Is it possible to establish a lawn around an adobe house? I'm considering using native, drought resistant grass (blue grama) but have been told that a lawn and an adobe house are not compatible. A: The traditional adobe house enjoyed flowers and other plants at some distance from the house and kept the soil around the house free of plants, well packed and sloped to drain water away from the house. If your house has a modern foundation that is waterproof and has a membrane or tar on top of the cement to stop upward migration of water into the adobe, then a lawn will be fine. I have a small lawn that abuts one adobe wall and has shown that my foundation is not 100% waterproof. Q: I used to live in Logan in Northern Utah and the land moved a lot causing many broken foundations. One old house across the street had a fine foundation. When I asked the elderly Lady who lived there about it she told me that it had had some work done now and then. She also said that the thing she found most interesting was the last contractor had told her that the interior part of the foundation was adobe brick. She didn't know what it was covered with. The house itself was built around WW1 and was a stick built house. Was the contractor just confused? If not how would this be done? A:
That's a great story and I hope its true. Adobe bricks can tolerate some movement without a house being totally damaged but we would rather is did not have to move. If the adobes were used below grade there might have been stucco or parging as it is called on a foundation. Logan is a fairly dry climate and if there is not much water in the surrounding soil then adobe bricks would hold up over the years. Modern codes don't allow us to place adobes below grade and that is a reasonable rule. Sometimes we find old houses that broke the rule before it was written and the houses have survived just fine. |
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Quentin
Wilson and
Associates, specializes in solar adobe design and construction. He grew
up in the South Valley of Albuquerque, New Mexico where he watched adobe
bricks being made. In the fifth grade, he made miniature adobes on cookie
sheets in his mother’s oven in order to construct house models for
a class assignment. By age thirteen he made full-sized adobes in the back
yard and ruined the grass. Later, he traveled a bit, went through the
Army, and graduated eventually from the University of New Mexico with
a major in physics, minors in math, chemistry, and education in 1970.
After teaching high school two years and community college math for three
more, Quentin moved into professional solar adobe construction in 1976
as the Project Manager and Instructor for the Sundwellings Demonstration
Project at Ghost Ranch, Abiquiu, NM. He became a licensed general contractor
in the State of New Mexico in 1982. He has been building homes and teaching
seminars and workshops ever since. In the fall of 1995 he established
and taught the full-time Adobe Construction Program at Northern New Mexico
Community College. His website, 
