CCAT greenhouse natural wall

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Background

Humboldt State Universities CCAT house once resided where the BSS building now is. At that time it had a green house which was a staple of CCAT's identity. When the CCAT house was moved to its current location the green house never made the move and is now long gone. With more funding at hand Co-Directors Adam and Eric both expressed great enthusiasm when pitching this new natural clay and straw slip wall. Adam and Eric said that they were purchasing an reasonably priced upper green house roof. This roof would attach to the south west side of the house at a point higher up then the top of the natural earthen wall that will be constructed, creating an angled roof.

Problem statement

The objective of this project is to construct a aesthetically pleasing natural earthen wall, by clay and straw slip methods. This will be built at the CCAT house near Humboldt States BSS building. Bottle bricks like those used for the green shed in 2008 are going to be added to the wall, as to allow ample light to enter. Plaster and lime will coat the exterior of the earthen wall.

Criteria

This section includes all possible aspects thought up by the group members for this project as well as the directors of CCAT. These criteria were chosen to evaluate the project based on the educational capacity. These criteria will help us to determine how much time, money, and effort needs to be invested in each aspect of the greenhouse natural wall based on our client's (CCAT) expectations.

Literature Review

The Steady state air to air thermal transmittance for buildings in the UK should be under 0.35 W/m(^2)K The three building materials that were tested in this report were Straw bale, Clay and Straw mixture and claytec bricks. The Volumetric heat capacity for Straw bale is .7 x10^(-3) J/m^(3)K, while the clay and straw mixture was measured with having 50 x10^(-3) J/m^(3)K. Seven times as much heat holding capability by mixing the straw with clay. The unfired claytec bricks measured in with having 20 x10^(-3) J/m^(3)K.^[1]

Some Common mistakes that are worth considering is the lack of incorporation of passive solar into these naturally built walls and buildings. Incorporating passive solar into a structure is beneficial for maximizing the efficiency of the structure. Taking into consideration the angle of the sun's rays and which way the structure will be oriented. Another common mistake is failure to construct a foundation between the straw-clay wall and the earth, better yet if the requirements for the structure wanted to retain heat then the foundation should be insulated. ^[2]

The R-value of a building material is the building materials ability to insulate. Tests done in North America and Canada show that the R-value of a 12 inch Clay and straw slip wall is R-19, this is with a density of 40 to 45 pounds per square foot. Meanwhile a 6 inch fiberglass wall about equals the R-value of the 12 inch clay and straw wall. This is for most of the country a sufficient R-value for an insulating wall to pass energy code. There is one more point I'd like to make and that is that the internal wooden structure of the wall is not adding to the insulation capabilities. Options include placing less internal wooden studs inside the wall would increase the walls thermal capabilities. Just have to make sure the building regulations are met and the strength of the wall is not jeopardized. ^[3]

A clay and straw slip wall is dense enough that the fire can not burn in an almost oxygen free environment. Tests were completed on a straw wall, a clay and straw slip wall, and a timber framed and cladded building. These mediums lasted for 30 minutes, 2 hours, and 8 minutes in the fire respectively. Straw bales can not contain a moisture content of more than 15%. This can be managed with the use of an appropriate foundation, overhangs, gutters, and splash rocks. Splash rocks are placed at the bottom of the wall covering the foundation, this helps protect the foundation and lower wall from getting wet.^[4]

To build with straw bales requires a good understanding of the basic characteristics of straw and how it behaves as a building material. In general, straw and other natural fibers have low compressive strength but when twisted, interwoven, bundled, baled or combined with other materials like clay, their compressive strength improves dramatically and they can then be used for a variety of structural and non-structural building applications. However, it is important to remember that despite the improvement in strength, bales do compress under loads. The more compact the bale, the less it will compress. Bales you use for building should be solid, compact, and keep their shape when you handle them, especially if they will be asked to support the kind of bearing walls that we will ask them to.^[5]

Another very important factor to the overall comfort experienced in a clay/straw building is the role of thermal mass. When walls containing thousands of pounds of clay are heated by the sun, they will very slowly transfer the heat from the outside in, and by nighttime they will have a warming, moderating effect on the interior. Likewise, at night these walls will slowly cool, transferring the "coolness" to the interior during the heat of the day. This delayed reaction that works to our comfort advantage is called the flywheel effect... In colder climates, where there is a long heating season, the thermal mass is also advantageous. When the space is heated the walls absorb and store the heat, creating a source of additional radiant heat and providing "surround comfort". ^[6] Template:Reflist <refrences/> Goodhew, Steven and Richard, Griffiths.2004."Sustainable earth walls to meet building regulations." Science Dircet 37(5): 451-459 <refrences/> Mack, Peter, Magwood, Chris and Tina,Therrien.2005.More straw bale building: a complete guide to desiging and building with straw.Canada:New Society Publishers. <refrences/> Baker-Laporte, Paula and Robert, Laporte.2005.EcoNest: Creating Sustainable Sanctuaries of Clay, Straw, and Timber.Utah:Gibbs Smith, Publisher. <refrences/> Mohamed Salah Gharib Elsayed.2000.Straw Bale is Future House Building Material.Egypt.