About Natural Building Straw Bale Cob Other Walls Plastering
Framing Roofs Floors Foundations Design

Natural Design

Designing the natural building is, in many respects, a more difficult proposition than designing a conventional structure. A greater understanding of engineering — structural, thermal, moisture — is required of the designer when working with materials that are not standardized, quantified, specified, or otherwise controlled, and with strategies that are designed to work with, not in spite of, the forces of nature. That said, there is nothing to stop the intrepid designer from creating a successful design if careful observation, dutiful research, and good common sense are employed. There is a growing trend in the building world to integrate the design/build process, to see it as one process rather than two separate jobs to be done by two separate people (the architect and the builder). This is only more relevant in natural building, where a deep and intuitive knowledge of one's materials is required to offset the lack of quantifiable testing data and to respond gracefully to the vagaries of non-industrial, unrefined, natural materials. The design/build process not only becomes directly integrated into one process, it becomes not a linear but a cyclical process, in which design decisions are able to be re-evaluated on the jobsite, and new designs can evolve out of the hands of the builder. Add onto this challenging and unique process the burden of answering to code and zoning officials, as well as a climate with 100 degree temperature swings from the interior to exterior and throughout the seasons, and exterior humidity swings of 100% from winter to summer, and one can see the importance of good design practices to guide a successful construction process.

Cold Climate Approach
To ensure a successful execution of a natural building project in this climate, careful planning must begin at the inception of the project, and be well-executed throughout the design and construction process. First and foremost, the planning starts with careful evaluation of the site. Seasonal and dominant wind patterns, soil type, drainage, solar orientation, and slope are only some of the features that will affect the performance of any structure — natural or otherwise — day in and day out, for the life of the structure.
Additionally, design of the structure itself must be executed with protection of the structure — particularly the moisture-sensitive walls — in mind. The "Cap 'n' Boots" approach speaks to giving the walls of a building good protection from below, by raising them a minimum of 12-18" up off the ground (the "Boots"), and protecting them from above, by careful top-of-wall detailing and generous roof overhangs of a minimum of 18" on the eaves (the "Cap"). Additional wall protection, such as the appropriate choice of exterior render, the use of a rainscreen siding system, or the inclusion of covered porches, may also be necessary in the design.
Once a design is ready for execution, an appropriate construction schedule is the next key to the success of the building; this schedule may well influence the design itself, and should be considered throughout the design process. For example, straw bales must remain protected from moisture and fire at all times. To achieve this, in addition to ensuring proper pre-construction protection, certain guidelines must be followed throughout the construction process. In a climate in which rain, snow, or sometimes both, can be expected any day of the year, having unroofed — and therefore unprotected — load-bearing walls can be a difficult situation; therefore, non-load-bearing — commonly known as infill, or occasionally wrap — systems are used, and bales are not installed until the frame, complete with protective roof, has been built to protect the walls; after the walls are up, they must continue to be fully protected until the base coat of plaster has been applied. As the plasters best suited for straw bale construction cannot be applied in freezing conditions (see Plasters for more information), the timing of the construction process must be done carefully to ensure the walls receive the protection they need in a timely manner, before the onset of the long, cold winter.
And, as with any well-built structure, attention to detail and quality of construction is where the rubber meets the road, and this process can be greatly informed by a well-detailed, thorough, comprehensive design. To use our straw structure again as an example: From choosing construction-grade bales, to quality installation, to thorough pre-plaster preparation, to adequate bottom-of-wall and top-of-wall detailing, to mitigating air leaks and achieving an air-tight seal on the wall inside and out with a developed strategy and pre-meditated approach, are all aspects of quality construction practice requisite for a high-performing, long-lasting, aesthetically pleasing structure. This begins with the design.
[back to top]

Breathing Walls, Breathing Homes
"Sick building syndrome" is a recent phenomenon that has resulted from a combination of newer energy-efficient super-tight structures, a lack of adequate ventilation, and indoor air quality (IAQ)-compromising contaminants, such as off-gassing carpets, furnishings, and finishes, as well as mold, dust, and other airborne pollutants. We are finding that, in addition to concerns about IAQ and "sick building syndrome" in air-tight natural houses (particularly those that may contain conventional carpeting, wood-burning stoves, or other VOC off-gassing or air pollutants), the need for positive ventilation is critical in these structures — especially those with straw-based insulation — to address potential moisture concerns for the walls themselves. A common feature in natural wall systems is their 'breathable' nature. This does not mean that air moves through them — quite the opposite, as they should be built to be air-tight. Rather, water vapor is able to pass into and out of the wall assembly, allowing for any vapor within the wall to safely exfiltrate before it concentrates into damaging concentrations. The term for this is 'vapor permeability'. In that the walls are vapor-permeable, and that in the winter time there are extreme temperature and humidity differentials between indoor and outdoor environments, the need not only for air-tight construction but for controlled ventilation becomes critical to minimize excessive vapor infiltration (and therefore potential condensation, when that vapor gets in contact with a cool surface and condenses into liquid) into the wall system and thus promote its longevity. This is just one of a variety of techniques and practices being developed in this region to ensure the viability of natural wall systems in this climate.
[back to top]

Democratic Energy and Ecologically Informed Design
The sun radiates free energy down onto our houses every day — all we have to do is let it in, and learn to work with it. Passive solar heating strategies should be employed not just in natural buildings, but in every building. Simple techniques, such as designing adequate glazing on the south sides and reducing excess glazing on the north, using high-efficiency windows to allow sun energy in yet insulate from exterior temperatures, and having high levels of mass to store the sun's energy within a well-insulated building envelope, will have a profound, daily effect on the structure, from reducing heating and lighting loads to improving mental health in the dark winter months by receiving more full-spectrum light. This is only one of a host of energy efficient and climatically adaptive design strategies to minimize impact and maximize efficiency and livability. Of course, these strategies must be deployed skillfully to avoid issues such as summer overheating; working with a skilled and knowledgeable professional — or as an owner-designer, educating yourself well — is key to making the most of this resource. As mentioned above, siting the house appropriately on the site is the beginning of a successful design, and from that point all the way through to installing solar hot water panels and compact fluorescent light bulbs will afford the designer the opportunity to create a structure that is of the highest possible good, to the inhabitants, and to the world in which it is inhabited.
[back to top]

Integrated Design and Code Compliancy
Ultimately, natural buildings are rarely, if ever, purely 'natural', especially in our demanding climate. Herein lies one of the most important challenges in designing natural buildings - achieving successful integration of natural and non-natural building elements. Whether it be mechanical systems, insulation, structural framework - whatever the context, there will be features in a building that will be of a vastly different medium than the clay and straw with which it interfaces. As can be found in any ecological system, all the action happens at the edge; where the two worlds meet will define the ultimate result of how well the building functions as a whole. Sometimes these 'compromises' will be born of intentional choice; sometimes, they may be imposed to comply with code or zoning requirements. It is critical to evaluate what potential administrative obstacles may lie in your path as early on as possible. Research your local zoning ordinances, code restrictions, and conditions of your lending agency; develop relationships with your zoning administrator, building inspector, and loan officer. Be prepared to educate, compromise, and integrate as gracefully as possible the elements of natural building with the elements of conventional building, taking the best - or at least the necessary - of both worlds to create a successful home.
[back to top]