The provisions contained in this appendix are not mandatory unless specifically referenced in the adopting ordinance.
About this appendix:While heavier forms of straw-clay construction have been used in various parts of the world for thousands of years, light forms of straw-clay construction began to appear in Europe in 1950 and in the United States in 1990. These lighter forms of straw-clay construction are intended as infill materials in nonload-bearing walls. The advantages of light straw-clay construction, such as regulated by Appendix R, include thermal performance and low environmental impact.
This appendix shall govern the use of light straw-clay as a nonbearing building material and wall infill system in Seismic Design Categories A and B. Use of light straw-clay in Seismic Design Categories C, D0, D1 and D2 shall require an approved engineered design by a registered design professional in accordance with Section R301.1.3.
The following words and terms shall, for the purposes of this appendix, have the meanings shown herein. Refer to Chapter 2 for general definitions.
CLAY. Inorganic soil with particle sizes of less than 0.00008 inch (0.002 mm) having the characteristics of high to very high dry strength and medium to high plasticity.
INFILL. Light straw-clay that is placed between the structural and nonstructural members of a building.
NONBEARING. Not bearing the weight of the building other than the weight of the light straw-clay itself and its finish.
STRAW. The dry stems of cereal grains after the seed heads have been removed.
VOID. Any space in a light straw-clay wall wider than 1/4 inch (6 mm), greater than 2 inches (51 mm) in horizontal length and greater than 2 inches (51 mm) in depth.
The requirements and properties of light straw-clay mixtures shall be in accordance with Table AR103.2.3.
REQUIREMENTS AND PROPERTIES OF LIGHT STRAW-CLAY MIXTURESa
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- Vertical stabilization shall be of structural or nonstructural wood framing in accordance with Figure AR103.2.4(1), AR103.2.4(2) or AR103.2.4(3). Framing members that are both load-bearing and stabilization members shall meet the requirements of Section R602 and this section. Nonstructural stabilization members shall be not more than 32 inches (813 mm) on center.
- Horizontal stabilization shall be installed at not more than 24 inches (610 mm) on center and in accordance with Figure AR103.2.4(1), AR103.2.4(2) or AR103.2.4(3). Horizontal stabilization shall be of any of the following with the stated minimum dimensions: 3/4-inch (19.1 mm) bamboo, 1/2-inch (12.7 mm) fiberglass rod, 1-inch (25 mm) wood dowel or nominal 1-inch by 2-inch (25 mm by 51 mm) wood.
Light straw-clay shall be installed in accordance with the following:
- Formwork shall be sufficiently strong to resist bowing where the light straw-clay is compacted into the forms.
- Light straw-clay shall be uniformly placed into forms and evenly tamped to achieve stable walls free of voids. Light straw-clay shall be placed in lifts of not more than 6 inches (152 mm) and shall be thoroughly tamped before additional material is added.
- Temporary formwork shall be removed from walls within 24 hours after tamping, and walls shall remain exposed until moisture content is in accordance with Section AR103.5.1. Visible voids shall be filled with light straw-clay or other insulative material prior to plastering.
Openings in walls shall be in accordance with the following:
- Rough framing for doors and windows shall be fastened to structural members in accordance with the International Residential Code. Windows and doors shall be flashed in accordance with the International Residential Code.
- An approved moisture barrier shall be installed at window sills in light straw-clay walls prior to installation of windows.
Where wood framing occurs in light straw-clay walls, such wood surfaces shall be separated from exterior plaster with No.15 asphalt felt, Grade D paper or other approved material except where the wood is preservative treated or naturally durable.
Exception: Exterior clay plasters shall not be required to be separated from wood.
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