Passing New Mexico Energy Conservation and Building Codes in Traditional Adobe Construction
In New Mexico, the adobe builder is fortunate to be able to call on extensive traditional and modern resources, as well as an excellent and unique earthen building code. These advantages allow us to study and make use of methods that have succeeded over centuries, in addition to modern techniques that have not necessarily been strictly adapted into the codes. However, navigating the system of codes and the bureaucracy which supports them can be daunting and frustrating. Some choose to ignore the system and build without permits or any bureaucratic oversight. In rural New Mexico, because of isolation by distance and landscape; and low or no enforcement of codes, this remains an option. But those who build in more populated areas, more visibly, and perhaps with stricter oversight, or who are under mortgage constrictions, will have to walk the officially condoned path laid out by local, state and even international building codes.
There is another reason for working within the system. It is critical that traditional and sustainable earthen building practices be promoted and championed openly and legally, so that they are not forgotten, neglected - even outlawed - and eventually lost. As well, architects and engineers who design systems and stamp plans need to be brought into awareness and appreciation of traditional and sustainable alternative building methods so that they can foster them in their contact with code agencies.
When the authors moved to Santa Fe County from New York, where they had built using stick framing and post-and-beam methods, they were captivated by the examples of traditional adobe buildings still standing; still in use, or in some cases in ruins. Less interesting, and often confusing, were the adobe houses under construction in Santa Fe. The use of foam insulation and cement stucco, while providing defensible utility, seemed environmentally and aesthetically unsustainable. To us, the whole idea was to honor the earth, in every sense; and when we actually got our hands in the mud we were even more convinced. The specialist in adobe preservation, Ed Crocker, has put it this way: "Over the course of two generations adobe buildings with earthen plasters were replaced by soil blocks saturated with asphalt emulsion, laid up in Portland cement, tied with a concrete bond beam...[and] sprayed with polyurethane foam...This is not earthen construction: it is a composite with which one could build an adobe submarine."
Bound to build in adobe using traditional methods, we designed a small house built on a rubble trench foundation, with earthen floors, mud plaster inside and out and -most critically- no insulation on or in the walls. This decision was taken after extensive research on the subject, especially(and quite accessibly) in the work of Paul G. Mc Henry who, in his comprehensive study of insulation and thermal mass values in Adobe and Rammed Earth Buildings, covers the scientific as well as anecdotal evidence which lends support to the fact that traditional adobe buildings are cool in summer and warm in winter: "People who have lived in earth houses have stated a satisfactory comfort standard repeatedly, more comfortable than temperature measurements might lead us to believe." A statement something quite like this was heard from many others, including as an aside from a state building inspector who allowed that he lived comfortably in an uninsulated adobe house, but nevertheless officially stood by the International Building Code, which requires wall insulation.
The authors' decision to build on a rubble trench foundation was based on the determination to use as little Portland cement/concrete in the building as possible, given that the embodied energy in a 94 pound bag of Portland is 381,624 Btu, or the equivalent energy of about 3 gallons of gasoline. Consideration was given to building with no foundation at all, as have been many earthen structures in New Mexico, including much of the Taos pueblo. On high, stable ground this method, which requires nothing more than laying adobes directly on the earth, is a tempting and extremely sustainable alternative. However, it might be impossible to find an engineer who would sign off on it, and even then, the state might reject the plan. Buildings under 140 square feet are exempt from code oversight, so this method, or a variation - like setting a course of stones on the earth before laying the adobe wall - might be employed with good result.
We decided to put in a gravel-filled trench with a steel reinforced concrete grade beam on top. This resulted in about a 70% reduction in concrete and rebar as compared with a conventional footing/stemwall foundation. The design involved digging a 16" wide trench to below the frost line(about 2' in our case), making sure that the bottom of the trench was undisturbed ground and sloping slightly from one corner. This required continuing the trench about 50' from the low corner of the building until it reached daylight. This allows any water that runs toward the building to drain through the gravel trench and out. To facilitate this, we set a 4" PVC perforated pipe, holes down, on top of the first inch or two of gravel at the bottom, and ran that all the way around and to daylight as well. We set in vertically a 2' high panel of 2" thick styrofoam insulation inside and against the outer wall of the trench, holding it to the height of our eventual grade beam, and filled the trench to grade with gravel. We used one-and-a-half inch round stone, which settles very solidly with little or no tamping required, much as marbles poured into a jar naturally form their most compact arrangement.
On top of the gravel we formed an 8" high concrete grade beam, using the styrofoam we had set in the trench as the outside of the form. The grade beam was 12" wide plus the thickness of the styrofoam, which allowed a 14" adobe to be laid flush, inside and out. Eventually, we brought our mud plaster right down to the ground, over the styrofoam(no lath or other preparation)and, more than a year later, it's still sticking well.
This method: the rubble trench foundation, has been employed extensively in myriad variations over centuries and has proven to be effective and lasting. However, the practice has not been accepted in the International Building Code, and the Portland intensive method of concrete footing/stemwall/slab has become the standard in practice as well as code. While a few architects and engineers know about the rubble trench foundation as a sustainable alternative, they are unwilling to incorporate it into their designs, most likely because they are leery of taking the risk of pushing through an innovation which is not in accepted practice. Inspectors at New Mexico CID knew of the method, probably because of traditional use of it, but would not take the risk of approving our plans without a stamp from engineer or architect. The authors were fortunate to find, with the help of Ed Crocker, and at the eleventh hour, (trenches were dug, and we could have poured either concrete or gravel into them) an engineer in Santa Fe who was willing to stick his neck out on a practice he knew to be sound.
Neither a rubble trench foundation nor uninsulated adobe walls are allowed in the International Building Code. A few days after submitting our plans to NM Construction Industries Division, we got a call from an inspector in the Santa Fe office. "You're going to need to insulate your walls; and that foundation isn't in the codes." We told him we wanted to build in a sustainable way, and as close to the traditional as possible.
"You're going to have to get an engineer or architect to sign off on that foundation. But you still need to insulate your walls to R 19." We asked him if there was no alternative. At first he said there was none, but after persistent questioning, told us:
"Well you can fill out a trade-off worksheet and try that."
The 2003 New Mexico Energy Conservation Code Residential Applications Manual is a comprehensive and fairly easy to navigate 41 page book ( available at www.energycodes.gov/rescheck/download.stm), which includes tables and data on various thermal building characteristics including passive solar, mass wall allowance, building material thermal data, etc. Its stated intent is to:
1. Allow the use of a worksheet to trade off R-values between various parts of the
house, without increasing the energy use of the house.
2. Make it easier to demonstrate code compliance for passive solar heated homes.
3. Make it easier for massive construction to achieve code compliance.
Included are worksheets by which allowances and tradeoffs are calculated. Most important of these, for builders who want to use uninsulated adobe walls, is the Tradeoff Worksheet. Essentially this allows you to balance positive thermal and insulative values against lesser or no values to achieve an overall compliance with the Energy Code. In our case, high insulation values in the ceiling, demonstrated passive solar heating and allowance for the mass of our walls allowed us to exceed the code requirements while having no added insulation on the walls.
Essentially what the Tradeoff Worksheet in the manual does is to compare total roof, wall and foundation R values in the proposed house to the values of a hypothetical code-compliant house. It does this by requiring the applicant to enter figures which are attained by dividing square foot area by the R value of the materials comprising that area. For instance, a 14" adobe wall, with an inch of mud plaster inside and out, adding the Mass Wall Allowance given in the worksheet manual, has an R value of 7.3. Divide this into the square footage of wall area and enter at the right. Thus, the higher the R value the lower the end number. Enter all walls, ceiling, windows, skylight and uninsulated slab edge, add these numbers together, and if the sum comes out to less than the sum for the hypothetical code house of the same square footage, voila! you pass. If not, you must add insulation somewhere to bring down your numbers. A 1000 square' house with R 25 in the ceiling gives an end number of 40. Double your insulation and you halve your end number. Without much adjustment, the authors were able to come in at about 15% lower than the code house.
As is frequently found with codes on the books in government agencies, recognition and enforcement appear to be matters of group or individual convenience and discretion. Permit reviewers and inspectors may be ignorant of the Tradeoff Worksheet, or may be reluctant to accept it. One official at Santa Fe CID refused to say whether a Worksheet in compliance would necessarily be accepted, saying that permits were reviewed on a case-by-case basis and that the International Building Code(which requires wall insulation) was used and enforced in New Mexico. The Residential Applications Manual gives inspectors an out by saying, "This publication does not intend to negate any of the standards found in the International Energy Conservation Code."
After completing the process, and having received a certificate of occupancy for our house, our sense is that greater leeway is given to the homeowner/builder over contractors, but this should not deter the contractor or the client from completing the worksheet and submitting it. Our experience has been that politely standing ones ground and continuing to ask for an alternative to what is often a kneejerk "No," will win out in the end.
Presumably, codes are put in place to protect the public. In New Mexico, at least, we have found that working within the system, the builder can pursue traditional, sustainable and alternative methods by using implemented paths as well as making full use of unofficial openess to these methods, when presented properly. By building openly and legally, we are helping to continue tradition and to bring back or present new sustainable building practices. To us, this is critically important if the promise of true earthen building is to be fulfilled.