Roof Raising

This weekend we undertook the raising of the roof of Cabin 1, with 9 students, 1 professor, 1 alumni and 1 construction guru over the course of 2 and a half days. We were lucky to have perfect 68 degree and sunny weather for the entire time, especially considering that two days later it snowed. With a handful of hammers and alot of sweat equity we lifted in place the large framing beams, ridge beam and rafters. Our construction guru Chris Wilson walked us through the rough spots, helping us to figure out how to get up by transforming the building itself into temporary scafollding, and guided us through feats we weren’t sure were possible. The ridge beam, a solid piece of 6″ x 16″ x 16′ douglas fir timber, managed to levitate into place 14′ up with a dozen hands, through shear strength in numbers. Saturday night, one of the student workshop leaders, Peter Lee, cooked us a special Korean dinner, Kim Chi soup, inspiring us to keep going. Piece by piece the roof took shape and by Monday afternoon we were wrapping up the OSB sheathing. Not bad for a weekend.

Filed under: Workshops, construction, roof

Earth Bags

Description:

Using soil-filled sacks (earthbags) for construction has been recently revived as an important natural building technique for several reasons. It is inexpensive, using locally available site soil and polypropylene or burlap sacks, which often can be obtained free or at low cost. The technique demands few skills, and is easy to learn. In addition, building with the bags goes extremely quickly, much faster than any other earth-building technique. They are adaptable to numerous site conditions and can be used with just about any type of fill material available. When built properly, earthbags are extremely strong, and as the bags themselves are lightweight and easily transported, they are useful for remote locations or emergency shelter. Thus, it is a flexible means of construction usable in a wide range of situations to create a variety of forms and structures.

Applications:

The essential material in building with bags is, of course, the bags themselves. Most commonly the bags used are made of polypropylene or burlap. Polypropylene sacks come in a variety of sizes, and are extremely common. It is important that UV resistant bags be used, as deterioration by sunlight is the biggest danger. Recycled seed or feed sacks of polypropylene are often available for free from various sources. The sacks come in a variety of sizes and also come in a tube form, which is much cheaper to buy per square foot. Burlap sacks have also been used, but are not as durable and can also be more expensive, although they are a “natural” material. Custom-sewn bags have been created for special shapes, and “site sewn” custom bags can easily be made using bent nails or wire.

The other essential material is that which fills the bag. A number of materials have been used, including sand, clay and gravel. While an ideal mixture would be a standard adobe mix of sand and clay, pretty much whatever subsoil is available is what has been used. The fill material can be used either wet or dry, but moistened material creates a more stable structure. An efficient system is to create your sack foundation and/or walls using soil from site excavation.

The most important consideration for bag choice is the material used to fill it. A good rule of thumb is the weaker the fill material, the stronger the bag material must be. In some cases, once a strong fill material has set, the bags could be removed from the exposed areas of the structure without any structural loss of integrity. On the other hand, if a weak material such as dry sand is used, it is essential that the bags be kept integral, and plastered as soon as possible.

Filed under: Materials, building, construction, earth, natural, soil

CordWood

Description:

Cordwood construction (also called “cordwood masonry,” “stackwall construction” or “stackwood construction”) is a term used for a natural building method in which “cordwood” or short lengths pieces of debarked tree are laid up crosswise with masonry or cob mixtures to build a wall.

Application:

Cordwood construction is an economical use for log ends or fallen trees in heavily timbered areas. Other common sources for wood include sawmills, split firewood, utility poles (without creosote), split rail fence posts, and logging slash. It is more sustainable and often economical to use recycled materials for cordwood walls. Regardless of the source, all wood must be debarked before construction begins. While over 30 different types of wood can be used, the most desirable rot resistant woods are Pacific yew, bald cypress (new growth), cedars, and juniper. Acceptable woods also include Douglas fir, western larch, Eastern White Pine, Spruce Pine, Poplar, Tamarack, Western red cedar and Monterey pine.  Less dense, airy woods are superior because they shrink and expand in lower proportions than dense hardwoods like elm, maple, oak, and beech. Most wood can be used in a wall if it is dried properly and stabilized to the external climate’s relative humidity. Furthermore, logs of identical species and source are preferred because they limit expansion/ contraction variables.

Environmental Impact:

Depending on a variety of factors (wall thickness, type of wood, particular mortar recipe), the insulative value of a cordwood wall, as expressed in R-value is generally less than that of a high-efficiency stud wall. Cordwood walls have greater thermal mass than stud frame but less than common brick and mortar. This is because the specific heat capacity of clay brick is higher (0.84 versus wood’s 0.42), and is denser than airy woods like cedar, cypress, or pine. Thermal mass makes it easier for a building to maintain median interior temperatures while going through daily hot and cold phases. In climates like the desert with broad daily temperature swings thermal mass will absorb and then slowly release the midday heat and nighttime cool in sequence, moderating temperature fluctuations. Thermal mass does not replace the function of insulation material, but is used in conjunction with it.

Filed under: Materials, building, building system, construction, natural

AgriBoard

Description:

We consider the Agriboard compressed agricultural fiber panel (CAFP) product a marvelous tool for the design of the structures for many of our projects. AgriBoard is made of compressed wheat straw.  It simplifies the structural design and allows the reduction of the number of trades and suppliers on the job. By this simplification we have been able to save weeks from the schedule, freed the plenum space for duct work and electrical/data distribution and deliver a shell that is insulated, air tight and quiet. For us, it simplifies the sometime endless coordination and shop drawing reviews over those of traditional structures.

Applications:

In high wind load zones and seismic areas the product allows less detailing and calculations to meet the structural demands. Because of the fire rating of the panels, less material and concerns of fire proofing is eliminated. In the interior fit-out, we are able to wall mount furniture and equipment without the necessity of blocking or plywood.  Agriboard panels have unmatched strength in the Structural Insulated Panel (SIP) industry. Available in lengths up to 24 feet, they can be utilized as self-supporting wall, roof and floor panels. If columns and beams are required to provide additional supports for the panels, they are far fewer in number than in conventional structures. The panels are joined together with a system that transfers forces across the panel joints, creating incredibly sound building structures.  Agriboard engineers each panel for the span and loading conditions required by the project design team. The panels can support concentrated loads (such as roof-top mechanical equipment), and can be customized for unique profiles. In addition, the panels can accommodate large openings, such as windows and roof hatches.

Overall, Agriboard panels are a very effective structural system for numerous building types.

Environmental Impact:

The embodied energy is a measurement of the amount of energy required to produce the product(s) in the analysis time frame. The result between 58 and 90 GJ is fairly high, particularly due to the use of natural gas in the production of oriented strand board (OSB).

Comparison: The embodied energy of one cubic meter of plywood is 9.44 GJ.

The embodied water, similar to embodied energy, is a measurement of the amount of water required to produce the product(s) in the analysis time frame.

Comparison: An Olympic-size swimming pool holds 2.5 million liters of water.

The carbon footprint is a measurement of the amount of carbon dioxide emitted during the production of the product(s) in the analysis time frame. The particular result in this case is surprising because it is negative. The growth of wheat (and the unattributed removal of waste from disposal) counteracts the requirements for transport to the manufacturing facility.

Comparison: A car emits approximately 5.91 metric tons of CO2 at 15 mpg and 10,000 miles per year

AGRIBOARD

Thickness                                                                                                             4-3/8″

Panel Size                                                                                                            24×9

Embodied Energy (GJ)                                                                                    58.82

Embodied Water (L)                                                                                    19702.01

CO2 Emitted (metric tons)                                                                            -0.42

Filed under: Materials, construction, SIP, Structural, wheat, wood