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 mothers 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, quentinwilson.com, lists the course schedule and many other resources related to working with adobe.
Q: I am working on a school project in sustainable design and have chosen to work using adobe, knowing that the California Missions used the same material. There will be 6 in of styrofoam blocks between 9 in of bricks on either side just to make no mistake that the LEED R-value is met. Do you find this a practical approach?
A: Insulation added to the exterior of a mass wall will result in a higher R-Value than would be predicted by normal methods (simple addition of the assembly's component R-Values.) Insulation added to the interior of mass wall does not benefit from this effect of "Phantom R-Values." This information is hidden deep in the tables of the International Energy Conservation Code (IECC) where they show that R-13 insulation added to a mass wall will result in R-21 even though the mass wall is only considered to be around R-4 or less. Simple addition would have arrived at R-17 so that acknowledges 4 Phantom R's.
So, your double wall system will benefit highly from the combination of the 6-inch styrofoam and the interior adobe wall. However, I do not advise the use of styrofoam which is not closed cell. I would recommend polystyrene and 2- or 3-inch thickness should be sufficient. However, We do not want so see the dew point occur at or near the insulation and I don't know how to figure that for your climate mainly because I don't know what your climate might be.
However, the International Building Code requires a minimum thickness of 10-inches for an adobe wall. Unless you can create a very powerful way to connect the two walls across the bridge of the insulation, the system will perform as two independent 9-inch walls.
LEED R-values are derived from steady state laboratory studies where heat is applied to one side of a material and once steady state conditions are achieved where the heat in and heat out numbers become constant the value is determined. California, Arizona, New Mexico, Texas, Colorado, Oklahoma, Utah, Nevada and eastern Oregon and Washington - the list goes on - happen to have climates where the sun comes up and goes down on a very regular basis. Therefore, steady state is never achieved as the heat flow in mass walls pulses back and forth following the Second Law of Thermodynamics as it tries to go from hot to cold. This means that LEED, ASHRAE, ASTM and nearly any other published numbers on adobe and other mass walls are wrong, specious, and incorrect and have no meaning in the world of thermal dynamic systems.
In 1981 the State of New Mexico developed the Applications Manual of the New Mexico Energy Conservation Code. This official document was the first to publish dynamic state derived Effective U-Values (The reciprocal of R) for several cases of earthen walls that could be used in calculations required to demonstrate thermal performance that would meet the requirements of the Energy Conservation Code. Empirical and calculated results became the Effective U-Values for adobe and other materials. These numbers depended on three things: the climatic zone of the building, the cardinal direction each wall faced, and the color - light, medium, dark - of the exterior surface. By 2015 this important information and thoroughgoing integration of a building into its site has been forgotten and largely ignored. Only the aforementioned table buried in the IECC now officially exists to corroborate my wild-eyed, worldwide, wake-up call to the construction industry and its attendant engineers, architects, researchers and building officials.
Q: I am involved in the design for a passive solar home in Maryland. We are investigating materials to use for interior thermal wall mass, and adobe seems like an excellent choice.
A: Adobe would indeed be a good choice. Besides the fact that it has a specific heat of 0.2 which is the same as concrete, stone, brick and some concrete blocks, adobe has a wonderful coefficient of heat diffusiveness which results in its releasing heat more slowly that the other materials which all have higher diffusively.
Q: There seems to be some discrepancy as to whether adobe is an effective insulator. Adobe is a tremendous capacitor of heat. Can you clarify this for me?
A: In non-steady state situations - such as our planet- capacity mimics insulation. Insulation cannot mimic capacity. Some sources cite it as a good thermal mass, but poor insulator.
Q: I’m grad student currently working on modeling the energy efficiency of a passive-solar adobe home. I been having a lot of trouble trying to find the physical properties of adobe, thermal conductivity, absorptance and specific heat. Can you guide me on this matter? I would really like to find a reliable (quotable) source for these parameters.
A: Specific Heat: 0.20 BTU/DEG F/LB Source: Passive Solar Home Book by Edward Mazria, Rodale Press about 1982, out of print but in many libraries and at amazon.com Absorptance depends on the color of the wall presented to the sun and varies incredibly from light to dark colors. Source: New Mexico Energy Conservation Code Applications Manual available from the State of New Mexico Construction Industries Division, 725 St Michaels Drive, Santa Fe, 87501
Thermal Conductivity, BTU/SQ FT/DELTA T/HR also known as or related to thermal diffusivity, rho, has never been determined as far as I know. It is the most important number and its value, whatever it is, is what makes adobe the planet's best passive solar storage medium. Rho is less than concrete, stone, brick, and concrete block so it does not loose its heat as fast as those materials which have nearly the same specific heats. Its rho-value is higher than wood or paper which are so low that they are very slow to transfer their stored heat even though they also have nearly the same specific heat. The paper I refer to is in the form of books or other tightly packed forms of paper. Mazria hints at these relative conductivity in a table of appropriate wall thicknesses for Trombe Walls. A person might use Mazria's table and extrapolate for adobe if the numbers can be found for the other building materials.Ed Mazria, himself, is a well-known architect practicing in Santa Fe. He might respond to a well structured question requiring a short answer.
Sometimes, Thermal Conductivity or its reciprocal, Thermal Resistance is quoted from determinations made by standard laboratory calorimeter tests at steady state. As soon as steady state is mentioned, the results should be thrown out. The planet is not steady state. The sun comes up and goes down, the air cools off and warms up. The NM Energy Code Applns Manual hints at these planetary truths in the several tables that give Effective U-Values for adobe walls depending upon:Climatic Zone in NM Orientation of the wall (n,s,e,w) Color of wall (light, medium, dark)
The State of NM got its numbers from computer simulations run in the mid-1970's. Along with that, four adobe buildings and buildings of several other types of materials were built at the Tesuque Pueblo Solar Thermal Project at the same time. Real data points measured on the buildings confirmed the millions of bits of information produced by the computer simulations to convince the researchers at the University of New Mexico to publish the tables of Effective U-Values in the Manual.
Q: My adobe house is always freezing. It can be 85 outside, but the house never warms up. I live in northern NM with lots of sun and warm days in fall, but cold nights. Even in the daytime its so cold in here. I hate to be using the heat so early in the year- when its 80 outside. I come from the northeast, so was not aware that an adobe house meant a freezing house year round! I only rent this place and will surely move after winter, but is there anything I can cheaply do to make it livable in here?
A: Adobe is noted for being warm in the winter and cool in the summer. There is something basically wrong with your house but it is not the adobe. Perhaps there is shade on the south wall and/or the building is oriented so that the south wall is narrow and the east and west walls are wide. Maybe there is ground moisture coming up through the floors and acting like a full-house evaporative cooler. Perhaps the ceilings are high and the warm air moves up there. Giant cottonwoods shading the house? The contributing factors to a year round comfortable house and especially adobe are: Proper orientation to the sun with the south wall elongated and containing ample windows; fewer windows on the north, east and west walls and exterior insulation on those three or at least the north wall; roof insulation of R-40 or more; airtight, double glazed windows or at least windows with storm glazing; tight fitting doors; modest ceiling height: ten-foot max; attention to other possible sources of air infiltration such as exhaust fans, fireplaces without dampers.
While the temperature may be 85 at the warmest point of the day, the nighttime temperature will be 50 or 55. The average between 85 and 55 is 70 and adobe normally delivers that average temperature. One trick is to close up tight when temperatures are too low or too high and then close up when temperatures are the opposite to tilt the house in the direction you want to go.
Rich folks in the middle ages had cold castles to deal with. A major solution was to hang large, thick tapestries on many of the wall surfaces to give some protection from the low temperature of those walls which sucked the heat out of occupants. Four poster beds with lots of fabric served the same purpose.
Short of a major insulation overhaul of the house by the owner there may not be much you can do other than drape some walls or line a north wall on the inside with 2" polystyrene insulation boards or straw insulation boards which are hard to find in this country. Short of comprehensive construction details on the house, all is conjecture.
Pity poor Emily Dickinson. She talks of dinner in her brother's house with the curtains lifting in the wind and air moving through the wood clapboards. Meanwhile, Canadian immigrants in the Finger Lakes region and clustered around Geneva were sitting tight in their 1850's adobe homes. They brought the adobe technique south from Ontario. Thirteen of those homes still exist to our knowledge and there may be more found soon. At the time of their construction they outperformed wood framed homes. Back then no one understood insulation and airtight construction.
Q: I am trying to find the R-value on 9" thick adobe brick. I live 12 miles from Oklahoma in Texas, 75 miles north east of Dallas. I do a/c for a living and need to figure a heat load on two houses.
A: That's a mighty tough question. Adobe has about 140 Effective U-Values according to the NM Energy Conservation Code Applications Manual. I am looking at Zone 9 which is Clovis and Roswell which is as close to the Dallas area as we are going to get minus some of the humidity. For a Medium Colored Wall the U-Values are North: 0.227; East: 0.198; South: 0.160: West: 0.204 For dark colored walls the values go down 10 to 30%. For light colored walls the values go up 8 to 15%. The ASHRAE Steady State U-Value is 0.263. Those numbers are for 10-inch thick adobe walls.
R-factor is the reciprocal of U-Value. ( R = 1/U ) Because adobe is a storage device rather than a resistance device it generally performs well beyond predictions based on steady state numbers. The NM numbers are based on the Tesuque Thermal Study Project of the 1970's which used full-sized adobe test cells and computer numbers to mimic adobe's dynamic performance. I do know that there was an entire school district built in the Dallas area with adobe in the 1930's.
Q: I would like to build a home with some adobe walls. One of the walls I would like to be adobe would be on the south side of the home but would also between the living space and an attached greenhouse. I still need to explore the attached greenhouse option, but would you recommend adobe in this application? I am concerned about the higher humidity levels. Are there any changes you would suggest? i.e. a vapor barrier between the stucco and adobe?
A: This is a perfect use of adobe. It stores the excess heat of the greenhouse and conducts it to the interior of the home. The elevated humidity will not hurt the adobe one bit. Adobes achieve their maximum strength at 60% humidity. They also have a great ability to soak up moisture and return it as the atmosphere inside dries out. We are starting to see some papers to this effect at our yearly Adobe Conferences here in El Rito. May 20-22 in 2005. The Germans have long been aware of adobe's moisture modulating capabilities and Gernot Minke has a chapter in his Handbook of Earthen Construction.
If the adobe wall is between the living space and the greenhouse, you can save money by omitting stucco. Exposed adobes, a mud wash or mud plaster will work fine. Try to find a light color to avoid having to paint the wall. Paints are less breathable than is desirable in this situation.
Q: Do you know of any instances where this type of setup was used as a significant portion of heating a residence? I was looking to use the thermal mass and attached sunspace as a means of heating the conditioned space and also tempering the thermal conditions in the greenhouse. I have heard rumors that this can be effective in both these goals.
A: (Kelly) Yes, Quentin suggests that this is a good strategy, and I agree. I know of one home where an adobe Trombe wall has been used quite effectively in heating the home during the winter in New Mexico.
Q: I live in western North Dakota which typical sees 12-15" of moisture(6-8" as rain) a year. Winter temperatures can be arctic (-10 to -30 F for a week at a time) I am most curious about insulating properties. What exactly are the R-factors for an eight inch, ten inch and twelve inch adobe walls? How many R-factors does outer insulation (polypropylene?) add to a wall? I ask these questions because I wonder if adobe would work as a basement wall if adequate moisture barriers were installed? (I am thinking a trench filled with bentonite.) However is the effort, lower cost and mainly the R-factors, worth the effort?
A: Adobe walls don't have any specific R-values. In the State of New Mexico it is recognized that adobe walls will perform as if they have different R-values depending on the thickness of the wall, the climatic zone, the cardinal direction that the wall faces and the color of the wall. The walls can range from 2.5R to 22R. In your case a wall on the north side or below grade would act like the 2.5R. The preferred insulation to add to the exterior of a wall is 2-inch polystyrene. Dow Styrofoam Utilityfix xps has a rated R-value of 10 and a crush resistance of 15psi. It is a closed cell foam and will not loose its R-value to moisture uptake if it is below grade.
I don't recommend that you use adobes below grade even with the Styrofoam. If there is one little pinhole, moisture will get through and cause trouble for the adobes. I would stick with concrete or pumice or cinder blocks for below grade construction basement walls.
Strange things will happen if you add insulation to the adobe. The wall will perform better than the sum of the two R-values. I call it phantom R's. It's because the adobe is not an insulator but a capacitor and conductor that mimics insulation in certain situations. When you couple capacity with resistance you get more resistance than expected in a non-steady state situation. Electrical engineers understand this as capacitive reactance or a band pass filter.
Down in the basement in Western North Dakota, you are as close as anyone will get to steady state on this planet. Adobe will be at its least wonderful state there. If you can have an adobe wall where some sunlight hits it, it will start to perform as a low grade, unglazed Trombe wall. That's adobe at its best level of performance.
Q: My wife and I recently bought a rambling adobe house outside Ranchos de Taos. The house is not that old, but when it seems as though relatively little attention to insulation was paid when it was built. The roof is a straightforward viga/truss/brai structure, and it does have about 4" or so of blown in insulation. The walls are 20" of adobe - but with no insulation of any kind.
Here's the problem - the place is a propane black hole in the winter, with prodigious quantities of the stuff being burned for seemingly little/no internal temperature rise. (Plus, the house was conventionally designed in the Northern NM vernacular, and it would be difficult to attempt to retrofit passive solar features without messing up the "feel".) An architect we know in Taos (Karlis Viceps) has suggested that we should put a bunch of active solar heating on the roof in an attempt to warm the mass up in the daytime. One of the local solar contractors reckons that is pointless until the house is better insulated.
So, here's the question - would it be better to: a) insulate the walls (styrofoam panels, and then re-stucco; or spray foam on), b) add extra blown-in insulation to the roof, or c) add active solar hot air heating? The driver is less cost, per se, but more about cost effectiveness and comfort.
A: I'm gonna have to shoot that Carlos Biceps! Talk about blowing the NNM vernacular, not to mention the heat cart before the insulation horse. I agree that the house needs to be insulated better. It will cost more, but if you can afford it, spray on polyurethane on the North East and West walls then restucco. Two inches works well. Nail-on
polystyrene, two-inches thick gives R 10 or 11 but, coupled with the Capacity/Conductivity of the adobe, an unexpected boost in performance will occur as if there are additional phantom R's
If there is space in the roof cavity add all the blown in cellulose or loose fiberglass or fiberglass bats possible. Current standards require roof insulation to be R-38. 40 or 45 would be nice, beyond that is beyond the
point of diminishing returns. Or have the wall foamer foam the roof too. I favor TC&I in Santa Fe. They have developed the best coating for the top of the roof insulation - gravel.
Just promise me no solar warts on the roof. I would think the same amount of tempered glass could be used in a solarium, greenhouse, sun gallery, glassed in south porch, or to fill giant holes blasted into the south wall for direct gain. There are plenty of stately vernacularly aligned solar adobes in Taos. If hot air collectors cannot be avoided, give some thought to ground mounting them in front of the house or behind it beyond the winter shade line.
C and Q: I should note, in Karlis' defense, that he was familiar with the house (he designed the retrofit rainwater collection system). It's a somewhat unusual house layout and I agree with him that it would be very hard to do a retrofit of passive solar features. (We discussed that as the first option.) It's also true that, because of the way the house lies on the land that the solar collectors would be totally invisible from most angles. So, solar warts might be in our future - after we've improved the insulation... One last question on the wall insulation - the local spray on foam guy in Taos drives a brand new shiny full-size pickup. Like you, I am extremely suspicious about that, on the basis that folks like me are paying for it! On the other hand, I have a certain amount of construction experience and could install the blue styrofoam panels, along with the self-furring mesh, myself. (I would get someone else to do the three coat plaster, regardless.) So, here's the question - given those parameters, would you go with spray on foam or the styrofoam blocks?
A: Sorry, I over-reacted on Karlis as I certainly know him to be a careful, thoughtful designer. Of course, he is a little too open minded on certain non-adobe types of construction.
As for the insulation, it's true that all the foamers drive big, diesel, dually, crew cab trucks that cost as much as a baby Freightliner. Being the simple guy that I am, I just bought the Freightliner. I make sure that no prospective clients see it until the contract is signed. One client was sure he had paid for my Dodge Dakota in 1992 so I learned my lesson.
My choice on my own home was to install the blue, rigid Dow foam myself and even do the three coat stucco myself. That saves a lot on the insulation but there are hairline cracks at the joints in the insulation. One solution is to tape the joints with some now forgotten waterproof tape and follow it with two layers of Jumbotex building paper before the wire and stucco.
Q: I bought an adobe construction home in Pueblo Co last summer. This is my first winter here and I am freezing in this home. The walls are 14" thick adobe with 2" of foam board over that, then stucco. I expected to be living in a cozy warm home, instead the cold goes right threw me. My propane bill is running $100 per week with me keeping the temp at 72 during the day and 66 during bed time. I just don't understand what the problem is. Can you help?
A: Something is very wrong. Pueblo has a relatively mild climate and no house there should be using so much propane. It could be that there is little insulation in the roof or there may be a source of air leaking into the house. Perhaps there is a heating flue or kitchen range vent or bathroom vent that is loosing heat upward. Too many windows on the north? French doors are the most notorious for infiltration. (Letting cold air in.) There could be a problem with the heater. There are some installations of radiant floor heating which had no insulation under the floor. We have always known that to be a problem but the plumbers were slow to catch on. Uninsulated radiant floors use twice the fuel as insulated floors. Once adobe walls cool down, they are hard to warm up and they suck the heat right out of you. But they should work the other way, be toasty warm, and radiate back at you. We will keep thinking. We might have to send a deputation team up to visit to see if we can determine the problem. An electric blanket would help until help arrives.
R: I have checked for air leaks etc. and not found the place too drafty. Most windows are on the south and west. I don't think I've ever been able to pump enough heat into the place to heat these walls up. The walls are COLD. The furnace takes hours to raise the heat in the house just a few degrees. My rooms are large and I feel a damp coldness everywhere. I'm thinking of having a fireplace insert installed just so I can get a lot of heat in here for several days in order to heat the walls. What do you think?
A: (Penny, if you have been putting $100 worth of heat into your home each week, the adobe walls should be very warm by now. Rather than, or in addition to, spending the money on an insert, you might consider having an energy audit done on the house. There should be one or two certified home inspectors in Pueblo who can do this. A blower door test will determine the airtightness of your home and pinpoint the area of loss if there is one. A house that does not feel drafty can still have major infiltration problems. An infrared camera will find conduction losses through the walls or roof. Clever use of a non-contact thermometer such as a Raytech can find floor problems.
An adobe house performs differently than a lightweight structure. We were in a student's home last week that she is renovating. She has installed radiant floor heating, new doors and windows but no roof insulation yet. The original dirt is still in place on the roof. Her living room and kitchen felt warm to us. We found that the floor surfaces were averaging 74 degrees. The walls averaged 66 and the ceiling was about 68. In standard lightweight construction with conventional heating we would have expected to have found the floor to be around 68 degrees, the walls around 72 degrees and the ceiling around 80 degrees. It is not uncommon to find a temperature difference of fifteen degrees between the floor and ceiling due to heat stratification. This is why ceiling fans have become popular in the winter. With your walls any surface temperature below 80 degrees would feel cold to the touch as the adobe would draw heat out of your hand rapidly. This thermodynamics is tricky stuff and not for sissies.
This time of year is best for heat problems diagnosis. As the spring warms up and summer arrives the heat starts moving the other direction. See if you can verify the wall and ceiling insulation.
Q: I have some land in Southern Colorado and I am starting to make choices necessary to start building a 1200 Sq. Ft. house on it. Your web page is very, very helpful. Right now I am looking at the possibilities of using either Shotcrete Sandwich Panels or adobe. It is very cold in the mountains of Southern Colorado so I need heavy insulation want materials that hold head and radiate it out. But I also have to look at cost. I'm trying to figure out how to cost compare a house with Shortcrete Sandwich Panels and an adobe house build with two rows of brick and insulation between them with both structures having the same R Factor. Can you tell me where I can start to get information to calculate this?
A: Adobe is always my choice because besides having the thermal capacity needed, it also has a slower rate of heat transfer than concrete, stone or brick. Therefore for a given thickness of wall, the heat is returned to the living space over a longer period of time
Q: My husband and are retirees and are currently negotiating to purchase an adobe home in Green Valley, AZ, south of Tucson. We are from California and know nothing about adobe construction. The house was built in 1969 by Fairfield (a big Green Valley builder), the "Hermosa" model, and all exterior walls are adobe brick which we are told are 8" thick (but not sure). It doesn't have any other insulation on the walls, inside or out. It is a 1378 sq. ft. house, with standard 8 foot walls, and a tile roof. We asked the realtors for information re: insulation "R" values for this house, and no one can give us a clue. We are on a limited retirement income and don't want to fall into a "propane black hole" in the winter, like I read in one of the posted Q & A's on your website. The house has a forced air gas heater and electric "refrigeration" type cooling. Can you please enlighten us as to what we might expect to encounter to heat and cool this house year around?
A: That's a tough one. On our adobe discussion group right now, we are hearing about some wonderfully cool adobe houses in Texas and Arizona from our roving Butopia2003. Most of them have very well insulated roofs or thick dirt roofs. And most of them have thicker walls than your house of interest. I don't know about Green Valley, but much of the area around Phoenix is
covered by the codes of several counties most all of which require 16-inch thick walls.
Adobe itself is not an insulator. It is a capacitor and stores heat nicely. On big thick walls, heat or coolth does not get to the interior before the next phase of the sun cycle starts and the heat, or cool starts to move back out. With an 8-inch wall, heat or coolth might get to the interior before the sun comes up or goes down and reverses the cycle. It would work badly.
I don't know if there is anyway to figure it out short of finding a smart heating cooling engineer who actually has an idea how adobe performs. It can't be all bad or the miners in Death Valley or the Mormons by Safford, Arizona would not have used adobe. But again, they had the thicker walls.
Or ask for utility records, or get a trial month. If you can survive August, you can survive anything. If it stays cool then, it will most certainly stay warm in January.
Q: I'm a student at university in Tanzania, East Africa and am searching for a PhD thesis topic. My interest is the use of clay/mud/ soil to achieve thermal performance in walls. Its almost hot throughout the year here. Could you please advise?
A: Give me a little time to think this over. Adobe works well where there are differences in temperature throughout the 24-hour daily cycle. With it's thermal flywheel effect, it can capture the desirable temperature at the cool or hot part of the day and save it for the hot or cool part of the day. If it's always hot, we have to think this through very carefully.
Q: My walls are two courses thick (10 by 14 by 4) with two inches of airspace in between, making a 22 inch wall. I read the previous questions and answers, some of which touched on the use of the air space, but the other folks all talked about putting some kind of insulation in that airspace. It seems to me that simple dead air, with no insulating substance, would be just as effective as any insulation. Do you have any thoughts on that?
A: Dead airspace is around an R-value of 1. Fill the two-inch space with rigid polystyrene insulation and you will have R-11. Several lightweight loose insulation materials can be poured in later and will give similar R's. If you have gone to all the trouble to build double walls with an airspace, fill it. It would not hurt to bridge across the two walls with JDurowall to tie them together about every four courses.
Q: I am considering employing a builder within the next year or more to build an adobe home for me in the southwest. I am concerned with extreme heat and extreme moisture. How will the structure respond to both heat and moisture?
A: I would love to find a place with extreme moisture here in the Southwest. Adobe and other types of earthen structures are found in hot arid climates because the material is near at hand but also because the material is simply the best at moderating heat. There are many ways in which the adobe building can be built to enhance its abilities to fend off the unwanted extremes of the climate. There are also ways in which the building can be designed to enhance the climate's ability to create thermal discomfort. The key, then, is to make sure the house is designed by someone who understands how to make it work with the climate. In extreme moisture, wood rots, steel rusts and microbes eat most everything else so adobe is no more delicate than any other material.
Q: I am from Philippines. They have said that adobe isn't a good insulator. Is it possible to make adobe hollow blocks and then use rice hulls as mortar in green building? How can I make it strong enough just like reinforced concrete so that it could pass the specifications?
A: Adobe is not an insulator at at all. It is a capacitor and stores heat wonderfully. No heat can be stored in insulation. So adobe does wonderful things when it is understood and for that reason much of the world's population lives in earthen homes quite comfortably while nearby homes of new, manufactured, technological sources leave the occupants panting for air conditioning or screaming for heat. All those engineers who grin and leer at adobe are just plain dead wrong. They can't fool 3 billion people.
You can certainly add rice hulls. There are a couple of papers in our AdobeUSA 2007 proceedings from Argentineans regarding rice hulls. The bricks are not hollow but have a large percentage of hulls. It is in essence what some call "cob". We call it monolithic adobe or "daub." Adobe without hotrodding is the original green building material. It is as autochthonous as anything can get.
It won't be as strong as concrete hollow blocks since concrete is around 3000psi and adobe runs around 300psi. We do not see much hollow adobe production in the USA but several German companies do it routinely. You will just have to do some experimentation but do it with the knowledge that it is possible.
Q: I want an adobe or comparable earth home. I am a long time crafter, always thinking of alternative ways to do things! Can I build a curvy (pine wood) facade and other walls, then add adobe brick (while wet) mixture one stage at a time, meaning wait till dry then go along say a day or two later and add another, till the wall height is reached, considering doing it in summer, hot dry? What benefit could I have from using a series of wood forms and how thick do you envision I could go? Also in one wall, a rustic fireplace with stone inside and outside?
A: That would be a good system for building. Systems with two walls and adobe mud filled in between are found in various parts of the world. It is sometimes called cribbing as in corn crib. It is also one permutation of wattle and daub. Doing it with just one wall will work as you propose by waiting for each layer to dry. The truth is you can even do it with no wood wall. Hand formed stiff mud layer by layer is the world's most widespread building system over history. It is called cob in some areas, monolithic adobe in others, and perhaps the root word for adobe was dub which became a'tob or daub as in wattle and daub. The problem with building the curvy pine wood wall is thermal. An inch of thickness of pine is enough to isolate the interior of the building from the powerful ability of adobe to store heat. The result is a wall with thermal properties more like a pine paneled room.
Also, it just might turn out that a brick and mortar wall is easier to build with curves than is a pine wood wall.
You can certainly make forms that are 4- to 6-inches high and build your wall in lifts as the drying time permits. One of my students, Dave C, left some of those type of forms hanging on the wall of our shop should you wish to see them. Curved forms could be built with several thin strips bent around a form and then glued together. This system saves human energy since the adobe is only placed once. However, the process stretches over more time as you wait for each lift to dry.
New Mexico now requires construction permits throughout the state. Remote sites have been known to escape detection. For permitted construction it will be hard to build a stone fireplace without a liner of fire brick that meets several requirements. It is hard to prove to the officials that stones do not burn. For an energy efficient home it is a disadvantage to have the fireplace pierce through the building envelope and present a stone exterior surface. Stone transmits heat much faster than adobe or insulated frame construction. It would be a cold spot in the room when a fire was not blazing.
Q: I live in southern Arizona and am told my home is of adobe brick. The brick is 15"x7". The interior of the exterior walls has 2x2's nailed to the walls with 1.75 insulation batting. I am having to rip the walls out due to termite damage. What would be the best method to put in a vapor and/or moisture barrier between the new walls and the exposed, uncoated interior adobe. I have been told everything from do nothing, to seal the wall, to install tar paper on the inside of the new frame. Code requires R13 insulation, which apparently requires new 2x4 walls. Cost has become a real factor. What would you suggest?
A: The best thing would indeed be to do nothing. The thermal power of adobes are lost once there is insulation applied to the inside of the wall. What is left is the thermal power of insulated frame construction which is nearly nothing. A vapor barrier should go on the warm side of a wall assembly which normally is on the inside surface of a wall or just under the sheetrock so tarpaper, but better yet, a real vapor barrier would be best located on the inside of the new frame. Just in case an inspector is advocating tarpaper, then he is to be ignored since dedicated vapor barriers have long since replaced tarpaper.
I would cast about for an architect or engineer or smart permit desk person who might certify that the adobe walls in your climate would perform as if they were equivalent to R-13. Then you can leave out the furring and insulation completely and enjoy the thermal power of your adobe walls. Adobe is how pioneers survived in Death Valley and Safford, Arizona.
Q: I have a 2 story adobe house in Silver City, NM that I am trying to get insulated and re-stuccoed. I am having a very difficult time finding someone with skills to either put on 2" insulation board or spray on insulation. Do you know where I can find a list of contractors in my area that might have these skills. So far the only person I found locally has given me an estimate of $34000 to insulate and stucco. The area of the house is approximately 240 sq. yds that need insulation and 185 sq. yds. that are insulated frame and just need matching stucco.
A: I am out of touch with the contracting scene in Silver City. The yellow pages might be your best bet and you might have to look at Las Cruces or even El Paso. Start looking for an insulation company and see if they have their own stucco crew or one they work with frequently. Foam and stucco are fairly routine from Santa Fe North. It might be more rare around Silver City.
I figure 240 yards of 2" foam @ $21 to be $5040
240 yards of stucco @ $40 to be $9600
185 yards of color coat @ $18 is $3230
I am thinking in terms of Espanola area costs which are lower than Taos, Santa Fe but about equal to Albuquerque. There would be an expected extra charge for the two-story height since everything goes up on scaffolds. Still, $34, 000 seems at the upper end of the spectrum.
Nailed on 2" blue polystyrene rigid insulation boards would save money but I think professionally sprayed 2" polyurethane is a better choice.
Q: I am working with a team on a greenhouse. We are a group of Engineers and architects. The house is located in Jordan, near the Dead Sea. My question is what materials we should use for insulation, and is it recommended to have airspace insulation?
A: Most often we insulate the exterior of an adobe wall with nailed on rigid polystyrene insulation or sprayed on polyurethane foam. We would rather use a more planet friendly insulation but have not yet found one. Architects in Portugal have used cork which is wonderful but not easily available or affordable in sufficient quantity in the USA.
An airspace is a historical solution in New Mexico and Colorado here in the United States. Most of us do feel that if we have gone to the trouble to build two walls to create the space then we might as well fill the airspace with some form of insulation. We have volcanic pumice available and vermiculite is also a possibility. There might be wonderful local materials in Jordan that would be insulative.
Q: I have a recently constructed adobe with 2" of sprayed foam insulation on the outside of the outer walls. My issue is that the bedrooms are on the north side of the house and this winter, our first, have been cool to cold. I would like to add 2"-4" over the outside wall and replaster. Can the insulation (rigid foam board) be applied directly to the current plastered wall and then be re-plastered with no problem?
A: That will probably work Jim. If you are in a dry climate then you do not have to worry about moisture migration through the assembly and possible entrapment in the plaster between the two applications of foam. Another consideration is the weight of the foam and plaster which will be hung on the existing plaster. It might be worth considering long screws that will go from the stucco netting al the way through and two or more inches into the adobe.
Spend some time looking for other possible causes for your home being cold. There might be some heat loss through the ceiling/roof system or even the floor. Windows can loose heat through conduction and air infiltration. The new, cheap infrared thermometers give quick point and shoot temperature readings of surfaces. Sometimes they uncover a surprise cold spot. A little smoke can help show an air infiltration source.
I live in Arroyo Hondo, just north of Taos so it is pretty dry. Would it be better to go with spray foam insulation rather than rigid foam board?
The spray foam will cost more but it has an R-value of around 7 or 7.5 per inch. Rigid polystyrene is around R-5.5. The spray is preferred if the cost is not prohibitive since it is polyurethane which is the basic ingredient in Gorilla glue and other glues. The spray will stick to almost any substrate including existing stucco. The foam is closed cell and is a very good moisture and moisture vapor barrier. There are no seams and most applicators do a good job going right up to window and door frames so that the house is very air tight. The foam is self supporting but might need help to support the stucco and you would still need to attach the stucco netting mechanically through the insulation, the stucco and the first insulation into the adobe. I think. Your spray insulation application contractor might have another opinion. I would trust that opinion over mine.
Q: I have an adobe home built in 1968 with adobes 14" think laid for extra thickness. It is so cold in winter and I have been thinking about the spray foam insulation on the exterior. I live in the cold north of Taos County and I have been advised to use 4 inches. Recently I attended an event and spoke with some construction/contractor people here in NM. I am concerned about moisture and a vapor barrier. I had always heard to put the insulation on the outside. Now this contractor is advising 3 layers of regular stucco on the outside, and placing a vapor barrier on the inside walls, and then the insulation over that, on the interior, and finally the cosmetic plaster over that. What do you think?
A: Totally wrong.
Q: I live in Queretaro state (central plateau of Mexico) at about 6500' elevation. 18-20" of rain per year. Summer temps run 60º nights/75º-80º days. Winters run 33º nights/65º days. I would like rooms that are 12' wide with 24" adobe walls (14' on centers).
A: (Kelly) I lived in Bernal, Queretero for awhile, so I know that region pretty well. While a thick adobe-walled home will certainly be more comfortable than the common brick or cement block, especially in the spring, summer, and autumn, the winter time might be a bit chilly. You might consider leaving a cavity in the middle of those 24" adobe walls and fill it with pumice to isolate the inside from the outside. This will definitely help with the thermal properties of the home.
Q: I would like to make use of the thermal mass properties of Adobe. I have a freestanding fireplace against a wall in my lounge. Behind that wall is a bedroom which I would like to keep reasonably warm during the night. I was thinking of replacing the current timber wall with an Adobe wall, so that the heat, which is emitted from the fireplace can heat up the Adobe wall in the evening and then later when I go to bed I am hoping that the wall would release the stored heat during the course of the night. Do you think this will work well and, if so, what would an ideal wall thickness be so that the warmth will not be lost too quickly? (Note: The wall is not structural)
A: A ten-inch wall will give a heat lag of about six- to eight-hours. A fourteen-inch wall will add another two hours. This will work well if there is a way for the freestanding fireplace to put its heat into the wall. Direct contact is the best method.
Q: I have the idea to build a compressed earth block (CEB) or compressed stabilized earth block (CSEB) adobe style house in Australia. I like the idea of using natural materials in the house's construction that won't off gas VOCs in/around the house. I appreciate that the CEB / adobe style house has great thermal mass but understand that it needs a layer of insulation too. I thought about building a double wall with insulation or just air in between the two layers. I though to make the inside wall a the typically thick CEB/adobe block and the outer wall a thinner smaller block similar to the size of a regular brick (to save on labour). Now, in terms of insulation, I know that what is often talked about with adobe is the hard polystyrene panels tacked on the outside and then stuccoed. I don't like this idea because the polystyrene panels are not a natural material and it also seems to go against the idea that the house would breathe if made from CEBs. My question is, in this double cavity wall I have described above would it be suitable/acceptable to insert wool insulation batts instead? I think this would provide the insulation needed but also be 1) natural and 2) breathable.
A: (Kelly) Yes, I think that you could fill that void with wool, and this would effectively insulate the structure and keep it breathable. Another natural material for that is sawdust mixed with some lime. With either of these you would want to assure that they stay dry and don't settle too much.
Q: I am doing research to prepare for building an adobe home in Southwest AZ (Bisbee). I was told that for maximum insulation benefits that I should use 4x8x12 bricks with 4inches in between and then a second wall of same size bricks. Is this logical and if so what should be put into the 4 inch space if anything? Also how deep and wide would the footings need to be?
A: Is each wall to be 8 inches thick or 12 inches thick? I know that in parts of Arizona, minimum wall thickness is 16 inches but it seems that every county has its own code. Are you in Cochise County?
Certainly a double wall is one way to achieve good insulation value if the cavity is filled with insulation. A cavity with just air has been used historically but if you can find a proper insulation such as rigid polystyrene, all the better. Fiberglass batts can be used and are a step down the chemical pyramid. Cotton from SE Arizona is being marketed as insulation batts also.
The bottom of the footings need to be down at the frost line if there is one around Bisbee. Otherwise, deep enough to be on really solid ground - no fluffy top soil. That might be 12 or 16 inches. Local builders or inspectors would be able to tell you that. Foundation width would be four inches wider on each side than the two walls. That could be 4 + 8+ +4+ 8+ 4 equaling 28 inches or 4 + 12 + 4 + 12 + 4 equaling 36 inches is my addition is good at this hour of the night. In New Mexico, exterior walls must be a minimum of 10 and interior a minimum of 8. Arizona might accept a 12 and an 8.
I personally found it to be too much trouble to build double walls with a space so we just built 10 inch walls exterior and interior and put 2 inches of polystyrene or polyurethane over the exterior walls. There are plenty of Arizona adobe houses built without double walls. The common technique was to have overhanging roofs or porches that kept the summer sun off the walls on all four sides. Then the emphasis was to have super insulation in the roof. Sawdust was sometimes used.
Yes I am in Cochise County. The walls would each be 8 inches thick. I have never heard of this polyurethane technique on adobe. Then do you paint over it and does it jeopardize the integrity of the adobe? It seems like 12 inch walls would be sufficient. The weather is so temperate here...
Two 8-inch walls will result in a powerfully built building if they are tied together at several levels as you go up. This can be done with steel ties as used in the standard brick industry or with Durowall a heavy wire ladder shaped material used to tie concrete block assemblies together. These ties should be at every sixteen or twenty-four inches in height. The Durowall, if used, should be a continuous horizontal band at each level around the building. Brick ties, if used, will need to have someone else familiar with them determine the spacing horizontally and vertically.
The polyurethane we use is stuccoed over its exterior with standard cement/lime/sand stucco which is in common use throughout the United States. Pairing foam with simple adobe bothers some people but if you have a cavity wall you do not need to do that. But do consider filling the cavity with some form of insulation which will not settle. It will make a big difference winter and summer and besides what seems sufficient you may need to satisfy code officials or the building inspector that you meet the local energy efficiency code assuming that there is one.
Q: Our house, which had been stuccoed long ago, needs a bit of a facelift on the exterior, as the color coat is delaminating. I am inclined to attach foam insulation on the outside and apply a new stucco, but am getting different input from various people about the efficacy of doing this. One person says it won't make much difference; another warns that the stucco will crack badly because of its different coefficient of expansion relative to the insulation. The local stucco people say there is no problem. What has been your experience with this?
A: The local stucco people are correct. There is now a lot of experience with foam insulation covered with new stucco. Rigid boards or sprayed foam work well. My preference is the sprayed foam since its stickiness to the original stucco solves a lot of problems. It is more costly. At any rate, stucco over foam is a well-developed technique.
Q: For single wall adobe, are there any alternatives to polyurethane foam spray being commonly used these days?
A: (Kelly) Well one alternative is what I have done with the traditional adobe house that I bought in Silver City, NM, which is to attach rigid panels of insulation to the outside, covered with netting to hold the stucco. This has worked quite well, and I expect it to last a very long time.
Q: I have a warehouse full of my late husband's books. A couple of people told me I could use the books as building blocks inside the walls of adobe/ cob small houses/units. I am wondering if you know if this is possible?
A: Books have been used to build houses. An adobe house stands on its own and needs no additional structural materials. Books have mass and thermal mass and store heat although they are very slow to accept or reject heat. The Monastery at Pecos was in the publishing business and the tons of books they had in the warehouse were factored into the passive solar calculations for the building. Students at the College of Wooster in Ohio once determined that the grilled cheese sandwiches served in the dining halls could be used to build structures but no lasting housing movement came of that.
Q: We live in Dixon, NM in an old abode that badly needs new attic insulation. 20 years ago cellulose was blown in and now it’s a compacted mass about 4” thick. We’re considering blowing in additional cellulose but received advice that we should use blown fiberglass to achieve R-60.
A: R-60 seems a bit high. R-45 to 50 ought to do it. Beyond that, I would expect diminishing returns. Early day blown cellulose did tend to compact over time. It probably should be removed rather than having more cellulose added on top. Newer cellulose formulations maintain the loft of the material better. The same is true of fiberglass. If you should happen to have any dirt under the insulation it is best to keep it. Dirt/adobe/earth have heat storage capacity but when coupled with insulation on the cold side the R-values do not add up. Instead there is some basic physics going on with the coupling of heat capacity on the warm side with insulation on the cold side so that phantom R-values appear. The effective U-Value will be less than predicted by adding the two R-Values and taking the reciprocal. Heat loss through a construction assembly is calculated using the U-Value where lower numbers are better.
Q: How do we find adobe insulation?
A: Adobe walls are most commonly insulated in New Mexico with nailed on two-inch rigid polystyrene boards in 2 x 8 or 4 x 8 sheets. This can be done casually since it is then followed by stucco net nailed through the insulation with long nails - or sometimes screws. Cement/lime/sand stucco is then applied in the three layers: scratch, brown, color. Western one-coat combines the scratch and brown but I like the standard three-coat. Polystyrene is the blue stuff at Lowe's and Home Depot.
Several spray foam insulation companies in NM will spray two-to three-inches of polyurethane insulation onto adobe walls. It is more expensive and better in my opinion. Foamers leave a wire protruding every 16-inches horizontally and vertically. These wires are bent over to hold the stucco net and we then proceed as above. Foamers are in the Yellow Pages or on Google under spray foam insulation or sometimes roofing.
There are those adobe citizens who hate the idea of such synthetic materials going over natural walls so there are other options: A 2 x 4 wall can be attached to the exterior of the adobe walls and filled with fiberglass, cotton, hemp, cellulose insulations which are either in batts or blown in. Good old-fashioned Celotex or 1/2-inch plywood go over the frame and then two layers of building paper and the above stucco sequence follow. Two friends have mud plastered onto the stucco net.
We are still waiting after fifteen years for straw board insulation which has been promised by several manufacturers but none has come to market. Common in Europe and heading our way is multiple layers of reeds. We can see this at garden supply centers. It insulates and also serves as a base for plaster. I anticipate a short wait for hemp insulation boards. The industrial hemp industry is up and running in Colorado and we had two papers on hemp at Earth USA last September. Just nail it on and commence mud or stucco plastering is how I hope it will work out.
The old tried and true method that offends no one is to build two walls with an air space of 4- to 10-inches. In modern times the air space should be filled with insulation. Rigid, poured in, blown in. Don't use pumice. It is monstrously hygroscopic and pulls moisture out of the air and it supports capillary movement of any moisture from plumbing or roof leaks or rising damp from the foundation.
Adobe walls should always be insulated on the exterior side so that the mass of the wall is inside where it can participate in the warm/cool heat cycles that it moderates so well. If insulation is on the inside, the structure is demoted to the thermal equivalent of sheetrock on frame construction. In NM insulation is mandated by the NM Energy Conservation Code. Elsewhere it is mandated and enforced by the Second Law of Thermodynamics. No one thought to insulate wood frame construction whether sticks or timbers until just before and after World War II. Now, no one would dream of not insulating a frame structure. We are just at the point of realizing the benefits of insulating north adobe walls always, east and west walls often and south walls almost never. (This applies to NM, CO, AZ.) Because of the way adobe thermal mass reacts with sunlight, seasons, wind and winter/summer severity at any particular location, it makes a big difference to tune an adobe structure wall by wall to its surroundings. Phoenix and Bombay are not like Taos and Tibet.
The Holy Grail of adobe will be the discovery and/or adoption of a simple, waterproof, natural insulating material. So far, reeds has my vote but I recommend that people invest in industrial hemp.
We recently purchased an adobe home near Pueblo, Colorado. The property included an adobe barn. Both house and barn were built around 1984. The barn has a loft that was never insulated except for a few rigid panels, and now that the loft has been cleaned up, we would like to insulate properly. What type of insulation for an adobe barn loft would you recommend? We were fortunate to be able to meet with the couple who personally built the home. They shared many details (such as two rows of bricks with a 3" gap in the middle filled with perlite insulation-- 18" thick total, We do love the house -- and the exposed adobe brick construction of the barn is simply terrific. We just don't want to spend more of our retirement savings on propane than necessary. And we'd like to make the best use of the barn and its lovely storage loft.
A: I am on propane for back-up to my solar and wood heated house. Nothing like the cost of propane to catch your attention. In your house, your double wall with perlite insulation should be about as good as it can get. I don't have experience with perlite but we used pumice in wall cavities for the Sundwellings at Ghost Ranch. Pumice got wet over time in two of them and any insulation loses most of its value when it gets wet. If properly detailed in your walls, that should not happen. (Meaning that there should be a moisture barrier at the bottom of the perlite that stops moisture from the ground and foundation from moving up.)
To fully understand where the heat goes and where the cold comes from the best approach is to have a full house energy audit. An auditor with an infrared camera can spot problems' if any, in your walls. It is possible that there are problems in the ceiling/roof insulation system and a camera can work there too. A blower door test will find air leaks around windows, doors and anywhere else cold might be sneaking in. Short of that, you can buy one of the $30 infrared thermometers shaped like a pistol and take lots of readings on a cold day to see what floor, wall and ceiling surfaces are doing. A telltale - long, light fibers on the end of a stick - will let you trace air currents around your house. An adobe house was meant to feel warm in the winter and cool in the summer. Yours just needs a nudge or a bit of intervention.
If the loft in the barn can be closed off and separated from the rest of the barn, standard insulation such as fiberglass batts can be used between roof joists and any frame walls. If the loft is integral with the whole barn then you need to consider two inches of insulation - polystyrene or polyurethane applied to the outside followed by stucco to cut down heat loss through the adobe walls. If the barn is elongated in the east-west direction you are in luck and can insulate the north wall for sure and probably the east and west walls for good measure. Uninslated, the south wall will perform almost as well or better than an insulated wall due to your abundant sunshine and moderate winters. If the exterior is the exposed adobe that you highly value, then there is a dilemma. Dress warmly for the barn.
Thermally, the interior walls of adobe are the most valuable. Any BTU's they soak up from solar or any other heat source are returned to the living space. Frame walls cannot soak up much heat so when room temperatures go down they are unable to contribute any heat. Exterior adobe walls around the perimeter soak up lots of heat but they also lose some fraction of heat out to the atmosphere so they are not as effective as interior walls.
Q: I am designing a timber frame home with a desire to eliminate thermal bridges. My idea is to construct the timber frame and interior wall surfaces separate from a free standing compressed earth block wall, resulting in a cavity wall of timber on the inside, earth block on the outside, air in the void, no additional foam or infill insulation. Thoughts?
A: I don't know of anyone who has built a home as you describe it. There are some cases where people have built an insulated frame wall for the exterior perimeter with adobe as the interior wall. Architect Mark Chalom of Santa Fe has done this with at least three houses. I myself would favor this approach since the massive wall would be on the interior where it would be available to act as a heat sink for whatever type of heating you might be contemplating. Passive solar would be a natural - direct gain, Trombe wall, or greenhouse.
Any time you have an air cavity no matter the order in which you place the CEB walls and the timber frame walls, it's worthwhile to fill it with some sort of insulation. Several possibilities would be blown-in or poured-in cellulose; pressed straw insulating board (if the straw industry can just produce a stable company that can stay in business and market the product which is common in Europe); hemp fibers loose or in pressed boards (again it might be hard to find a company producing insulation but it can only be a matter of months); a company in SE Arizona has been producing cotton insulation at a premium price. Or... just build with the air cavity with some sort of access and once a reliable and affordable source for loose insulation appears, pour or blow it in. It will make a thermal difference.
Q: My wife and I are looking to build a very energy efficient home in Tucson, AZ. I have spoken to a couple of adobe builders and they both said that a 16" adobe wall will perform about as well as a 36" adobe wall with a 4" gap between bricks. What will the benefit be of building a 36" wall with 4" gap (insulated in the gap with what? and on all sides of home or just North?)
A: In Tucson the dominant energy consideration is staying cool in the summer. Oddly enough the north wall receives about the same number of BTU's of summer solar insolation as on the south - about 450 BTU/Sq Ft/of wall per day. East and west walls receive around 1100 and the roof is pounded by about 2400 BTU/Sq Ft of roof per day. At any rate you want to defend the home from roof heat intrusion with lots of insulation there. And you want to defend the east and west walls from as much direct solar insolation as possible. Probably a double wall with an insulation cavity is not cost effective on the north. It might be on the east and west. To know for sure, you need to have someone do a complete thermal analysis of the house for the Tucson climate. Should you go the double wall route, don't use pumice - a lesson we learned at Ghost Ranch Sundwellings. Loose fiber might be best: cellulose, hemp, straw, glass fiber, mineral wool, the list goes on.
I am also wondering about having the foundation and footing be 1-2' below grade to further increase thermal capacity, I know adobe contacting ground is a NO, but what about the 1-2' below grade with the footing for adobe wall above (2-4") grade?
A: If you want to store solar heat from direct gain or a greenhouse in a floor, a total of 8-inches depth is more than sufficient. Four- to six-inches will do. But it must be insulated below. If it is in ground contact, any heat that goes into the floor just keeps going down. It never comes back up and that's strongly enforced by the Second Law of Thermodynamics. However, for Tucson where cooling is so important it would be better to have an adobe floor (or concrete or bricks or flagstone) with no thermal breaks below so that the house can take advantage of summer cooling by the floor.
If I were building there, I would have a pitched roof over the ceiling so there was room for lots of insulation and provision for hot air above the insulation to escape. I would have wide porches on the east, west and north to keep the sun off the walls and 18" to 24" eyebrows along the south side to keep the summer sun out of windows and off the walls.