• APPENDIXS
    STRAWBALE CONSTRUCTION

    The provisions contained in this appendix are not mandatory unless specifically referenced in the adopting ordinance.

    SECTIONAS101
    GENERAL

    AS101.1 Scope.

    This appendix provides prescriptive and performance-based requirements for the use of baled straw as a building material. Other methods of strawbale construction shall be subject to approval in accordance with Section R104.11 of this code. Buildings using strawbale walls shall comply with the this code except as otherwise stated in this appendix.

    SECTIONAS102
    DEFINITIONS

    AS102.1 Definitions.

    The following words and terms shall, for the purposes of this appendix, have the meanings shown herein. Refer to Chapter 2 of the International Residential Code for general definitions.

    BALE. Equivalent to straw bale.

    CLAY. Inorganic soil with particle sizes less than 0.00008 inch (0.002 mm) having the characteristics of high to very high dry strength and medium to high plasticity.

    CLAY SLIP. A suspension of clay particles in water.

    FINISH. Completed compilation of materials on the interior or exterior faces of stacked bales.

    FLAKE. An intact section of compressed straw removed from an untied bale.

    LAID FLAT. The orientation of a bale with its largest faces horizontal, its longest dimension parallel with the wall plane, its ties concealed in the unfinished wall and its straw lengths oriented across the thickness of the wall.

    LOAD-BEARING WALL. A strawbale wall that supports more than 100 pounds per linear foot (1459 N/m) of vertical load in addition its own weight.

    MESH. An openwork fabric of linked strands of metal, plastic, or natural or synthetic fiber, embedded in plaster.

    NONSTRUCTURAL WALL. Walls other than load-bearing walls or shear walls.

    ON-EDGE. The orientation of a bale with its largest faces vertical, its longest dimension parallel with the wall plane, its ties on the face of the wall and its straw lengths oriented vertically.

    PIN. A vertical metal rod, wood dowel or bamboo, driven into the center of stacked bales, or placed on opposite surfaces of stacked bales and through-tied.

    PLASTER. Gypsum or cement plaster, as defined in Sections R702 and AS104, or clay plaster, soil-cement plaster, lime plaster or cement-lime plaster as defined in Section AS104.

    PRECOMPRESSION. Vertical compression of stacked bales before the application of finish.

    REINFORCED PLASTER. A plaster containing mesh reinforcement.

    RUNNING BOND. The placement of straw bales such that the head joints in successive courses are offset not less than one-quarter the bale length.

    SHEAR WALL. A strawbale wall designed and constructed to resist lateral seismic and wind forces parallel to the plane of the wall in accordance with Section AS106.13.

    SKIN. The compilation of plaster and reinforcing, if any, applied to the surface of stacked bales.

    STRUCTURAL WALL. A wall that meets the definition for a load-bearing wall or shear wall.

    STACK BOND. The placement of straw bales such that head joints in successive courses are vertically aligned.

    STRAW. The dry stems of cereal grains after the seed heads have been removed.

    STRAW BALE. A rectangular compressed block of straw, bound by ties.

    STRAWBALE. The adjective form of straw bale.

    STRAW-CLAY. Loose straw mixed and coated with clay slip.

    TIE. A synthetic fiber, natural fiber or metal wire used to confine a straw bale.

    TRUTH WINDOW. An area of a strawbale wall left without its finish, to allow view of the straw otherwise concealed by its finish.

    SECTIONAS103
    BALES

    AS103.1 Shape.

    Bales shall be rectangular in shape.

    AS103.2 Size.

    Bales shall have a height and thickness of not less than 12 inches (305 mm), except as otherwise permitted or required in this appendix. Bales used within a continuous wall shall be of consistent height and thickness to ensure even distribution of loads within the wall system.

    AS103.3 Ties.

    Bales shall be confined by synthetic fiber, natural fiber or metal ties sufficient to maintain required bale density. Ties shall be not less than 3 inches (76 mm) and not more than 6 inches (152 mm) from the two faces without ties and shall be spaced not more than 12 inches (305 mm) apart. Bales with broken ties shall be retied with sufficient tension to maintain required bale density.

    AS103.4 Moisture content.

    The moisture content of bales at the time of application of the first coat of plaster or the installation of another finish shall not exceed 20 percent of the weight of the bale. The moisture content of bales shall be determined by use of a moisture meter designed for use with baled straw or hay, equipped with a probe of sufficient length to reach the center of the bale. Not less than 5 percent and not less than 10 bales used shall be randomly selected and tested.

    AS103.5 Density.

    Bales shall have a dry density of not less than 6.5 pounds per cubic foot (104 kg/cubic meter). The dry density shall be calculated by subtracting the weight of the moisture in pounds (kg) from the actual bale weight and dividing by the volume of the bale in cubic feet (cubic meters). Not less than 2 percent and not less than five bales to be used shall be randomly selected and tested on site.

    AS103.6 Partial bales.

    Partial bales made after original fabrication shall be retied with ties complying with Section AS103.3.

    AS103.7 Types of straw.

    Bales shall be composed of straw from wheat, rice, rye, barley or oat.

    AS103.8 Other baled material.

    The dry stems of other cereal grains shall be acceptable where approved by the building official.

    SECTIONAS104
    FINISHES

    AS104.1 General.

    Finishes applied to strawbale walls shall be any type permitted by this code, and shall comply with this section and with Chapters 3 and 7 of this code unless stated otherwise in this section.

    AS104.2 Purpose, and where required.

    Strawbale walls shall be finished so as to provide mechanical protection, fire resistance and protection from weather and to restrict the passage of air through the bales, in accordance with this appendix and this code. Vertical strawbale wall surfaces shall receive a coat of plaster not less than 3/8 inch (10 mm) thick, or greater where required elsewhere in this appendix, or shall fit tightly against a solid wall panel. The tops of strawbale walls shall receive a coat of plaster not less than 3/8 inch (10 mm) thick where straw would otherwise be exposed.

    Exception: Truth windows shall be permitted where a fire-resistance rating is not required. Weather-exposed truth windows shall be fitted with a weather-tight cover. Interior truth windows in Climate Zones 5, 6, 7, 8 and Marine 4 shall be fitted with an air-tight cover.

    AS104.3 Vapor retarders.

    Class I and II vapor retarders shall not be used on a strawbale wall, nor shall any other material be used that has a vapor permeance rating of less than 3 perms, except as permitted or required elsewhere in this appendix.

    AS104.4 Plaster.

    Plaster applied to bales shall be any type described in this section, and as required or limited in this appendix. Plaster thickness shall not exceed 2 inches (51 mm).

    AS104.4.1 Plaster and membranes.

    Plaster shall be applied directly to strawbale walls to facilitate transpiration of moisture from the bales, and to secure a mechanical bond between the skin and the bales, except where a membrane is allowed or required elsewhere in this appendix.

    AS104.4.2 Lath and mesh for plaster.

    The surface of the straw bales functions as lath, and other lath or mesh shall not be required, except as required for out-of-plane resistance by Table AS105.4 or for structural walls by Tables AS106.12 and AS106.13(1).

    AS104.4.3 Clay plaster.

    Clay plaster shall comply with Sections AS104.4.3.1 through AS104.4.3.6.

    AS104.4.3.1 General.

    Clay plaster shall be any plaster having a clay or clay-soil binder. Such plaster shall contain sufficient clay to fully bind the plaster, sand or other inert granular material, and shall be permitted to contain reinforcing fibers. Acceptable reinforcing fibers include chopped straw, sisal and animal hair.

    AS104.4.3.2 Lath and mesh.

    Clay plaster shall not be required to contain reinforcing lath or mesh except as required in Tables AS105.4 and AS106.13(1). Where provided, mesh shall be natural fiber, corrosion-resistant metal, nylon, high-density polypropylene or other approved material.

    AS104.4.3.3 Thickness and coats.

    Clay plaster shall be not less than 1 inch (25 mm) thick, except where required to be thicker for structural walls as described elsewhere in this appendix, and shall be applied in not less than two coats.

    AS104.4.3.4 Rain-exposed.

    Clay plaster, where exposed to rain, shall be finished with lime wash, lime plaster, linseed oil or other approved erosion-resistant finish.

    AS104.4.3.5 Prohibited finish coat.

    Plaster containing Portland cement shall not be permitted as a finish coat over clay plasters.

    AS104.4.3.6 Plaster additives.

    Additives shall be permitted to increase plaster workability, durability, strength or water resistance.

    AS104.4.4 Soil-cement plaster.

    Soil-cement plaster shall comply with Sections AS104.4.4.1 through AS104.4.4.3.

    AS104.4.4.1 General.

    Soil-cement plaster shall be composed of soil (free of organic matter), sand and not less than 10 percent and not more than 20 percent Portland cement by volume, and shall be permitted to contain reinforcing fibers.

    AS104.4.4.2 Lath and mesh.

    Soil-cement plaster shall use any corrosion-resistant lath or mesh permitted by this code, or as required in Section AS106 where used on structural walls.

    AS104.4.4.3 Thickness.

    Soil-cement plaster shall be not less than 1 inch (25 mm) thick.

    AS104.4.5 Gypsum plaster.

    Gypsum plaster shall comply with Section R702. Gypsum plaster shall be limited to use on interior surfaces of nonstructural walls, and as an interior finish coat over a structural plaster that complies with this appendix.

    AS104.4.6 Lime plaster.

    Lime plaster shall comply with Sections AS104.4.6.1 and AS104.4.6.3.

    AS104.4.6.1 General.

    Lime plaster is any plaster with a binder that is composed of calcium hydroxide (CaOH) including Type N or S hydrated lime, hydraulic lime, natural hydraulic lime or quicklime. Hydrated lime shall comply with ASTM C 206. Hydraulic lime shall comply with ASTM C 1707. Natural hydraulic lime shall comply with ASTM C 141 and EN 459. Quicklime shall comply with ASTM C 5.

    AS104.4.6.2 Thickness and coats.

    Lime plaster shall be not less than 7/8 inch (22 mm) thick, and shall be applied in not less than three coats.

    AS104.4.6.3 On structural walls.

    Lime plaster on strawbale structural walls in accordance with Table AS106.12 or Table AS106.13(1) shall use a binder of hydraulic or natural hydraulic lime.

    AS104.4.7 Cement-lime plaster.

    Cement-lime plaster shall be plaster mixes CL, F or FL, as described in ASTM C 926.

    AS104.4.8 Cement plaster.

    Cement plaster shall conform to ASTM C 926 and shall comply with Sections R703.7.2, R703.7.4 and R703.7.5, except that the amount of lime in plaster coats shall be not less than 1 part lime to 6 parts cement to allow a minimum acceptable vapor permeability. The combined thickness of plaster coats shall be not more than 11/2 inches (38 mm) thick.

    SECTIONAS105
    STRAWBALE WALLS—GENERAL

    AS105.1 General.

    Strawbale walls shall be designed and constructed in accordance with this section. Strawbale structural walls shall be in accordance with the additional requirements of Section AS106.

    AS105.2 Building requirements for use of strawbale non-structural walls.

    Buildings using strawbale nonstructural walls shall be subject to the following limitations and requirements:

    1. 1.Number of stories: not more than one, except that two stories shall be allowed with an approved engineered design.

    2. 2.Building height: not more than 25 feet (7620 mm).

    3. 3.Wall height: in accordance with Table AS105.4.

    4. 4.Braced wall panel length, and increase in Seismic Design Categories C, D0, D1 and D2: the required length of bracing for buildings using strawbale nonstructural walls shall comply with Section R602.10.3 of this code, with the additional requirements that Table R602.10.3(3) shall be applicable to buildings in Seismic Design Category C, and that the minimum total length of braced wall panels in Table R602.10.3(3) shall be increased by 60 percent.

    AS105.3 Sill plates.

    Sill plates shall support and be flush with each face of the straw bales above and shall be of naturally durable or preservative-treated wood where required by this code. Sill plates shall be not less than nominal 2 inches by 4 inches (51 mm by 102 mm) with anchoring complying with Section R403.1.6 and the additional requirements of Tables AS105.4 and AS106.6(1), where applicable.

    AS105.4 Out-of-plane resistance and unrestrained wall dimensions.

    Strawbale walls shall employ a method of out-of-plane resistance in accordance with Table AS105.4, and comply with its associated limits and requirements.

    TABLE AS105.4

    OUT-OF-PLANE RESISTANCE AND UNRESTRAINED WALL DIMENSIONS

    METHOD OF OUT-OF-PLANE RESISTANCEaFOR WIND DESIGN SPEEDS (mph)FOR SEISMIC DESIGN CATEGORIESUNRESTRAINED WALL DIMENSIONS, HbMESH STAPLE SPACING AT BOUNDARY RESTRAINTS
    Absolute limit in feetLimit based on bale thickness Tc in feet (mm)
    Nonplaster finish or unreinforced plaster≤ 100A, B, C, D0H ≤ 8H ≤ 5TNone required
    Pins per Section AS105.4.2≤ 100A, B, C, D0H ≤ 12H ≤ 8TNone required
    Pins per Section AS105.4.2≤ 110A, B, C, D0, D1, D2H ≤ 10H ≤ 7TNone required
    Reinforcedc clay plaster≤ 110A, B, C, D0, D1, D2H ≤ 10H ≤ 8T0.5 (H ≤ 140T0.5)≤ 6 inches
    Reinforcedc clay plaster≤ 110A, B, C, D0, D1, D210 < H ≤ 12H ≤ 8T0.5 (H ≤ 140T0.5)≤ 4 inchese
    Reinforcedc cement, cement-lime, lime or soil-cement plaster≤ 110A, B, C, D0, D1, D2H ≤ 10H ≤ 9T0.5 (H ≤ 157T0.5)≤ 6 inches
    Reinforcedc cement, cement-lime, lime or soil-cement plaster≤ 120A, B, C, D0, D1, D2H ≤ 12H ≤ 9T0.5 (H ≤ 157T0.5)≤ 4 inchese

    For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm.

    1. a.Finishes applied to both sides of stacked bales. Where different finishes are used on opposite sides of a wall, the more restrictive requirements shall apply.

    2. b.H = Stacked bale height in feet (mm) between sill plate and top plate or other approved horizontal restraint, or the horizontal distance in feet (mm) between approved vertical restraints. For load-bearing walls, H refers to vertical height only.

    3. c.T = Bale thickness in feet (mm).

    4. d.Plaster reinforcement shall be any mesh allowed in Table AS106.16 for the matching plaster type, and with staple spacing in accordance with this table. Mesh shall be installed in accordance with Section AS106.9.

    5. e.Sill plate attachment shall be with 5/8-inch anchor bolts or approved equivalent at not more than 48 inches on center where staple spacing is required to be ≤ 4 inches.

    AS105.4.1 Determination of out-of-plane loading.

    Out-of-plane loading for the use of Table AS105.4 shall be in terms of the design wind speed and seismic design category as determined in accordance with Sections R301.2.1 and R301.2.2 of this code.

    AS105.4.2 Pins.

    Pins used for out-of-plane resistance shall comply with the following or shall be in accordance with an approved engineered design. Pins shall be external, internal or a combination of the two.

    1. 1.Pins shall be 1/2-inch-diameter (12.7 mm) steel, 3/4-inch-diameter (19.1 mm) wood or 1/2-inch-diameter (12.7 mm) bamboo.

    2. 2.External pins shall be installed vertically on both sides of the wall at a spacing of not more than 24 inches (610 mm) on center. External pins shall have full lateral bearing on the sill plate and the top plate or roof-bearing element, and shall be tightly tied through the wall to an opposing pin with ties spaced not more than 32 inches (813 mm) apart and not more than 8 inches (203 mm) from each end of the pins.

    3. 3.Internal pins shall be installed vertically within the center third of the bales, at spacing of not more than 24 inches (610 mm) and shall extend from top course to bottom course. The bottom course shall be similarly connected to its support and the top course shall be similarly connected to the roof- or floor-bearing member above with pins or other approved means. Internal pins shall be continuous or shall overlap through not less than one bale course.

    AS105.5 Connection of light-framed walls to strawbale walls.

    Light-framed walls perpendicular to, or at an angle to a straw bale wall assembly, shall be fastened to the bottom and top wood members of the strawbale wall in accordance with requirements for wood or cold-formed steel light-framed walls in this code, or the abutting stud shall be connected to alternating straw bale courses with a 1/2-inch diameter (12.7 mm) steel, 3/4-inch-diameter (19.1 mm) wood or 5/8-inch-diameter (15.9 mm) bamboo dowel, with not less than 8-inch (203 mm) penetration.

    AS105.6 Moisture control.

    Strawbale walls shall be protected from moisture intrusion and damage in accordance with Sections AS105.6.1 through AS105.6.8.

    AS105.6.1 Water-resistant barriers and vapor permeance ratings.

    Plastered bale walls shall be constructed without any membrane barrier between straw and plaster to facilitate transpiration of moisture from the bales, and to secure a structural bond between straw and plaster, except as permitted or required elsewhere in this appendix. Where a water-resistant barrier is placed behind an exterior finish, it shall have a vapor permeance rating of not less than 5 perms, except as permitted or required elsewhere in this appendix.

    AS105.6.2 Vapor retarders.

    Wall finishes shall have an equivalent vapor permeance rating of a Class III vapor retarder on the interior side of exterior strawbale walls in Climate Zones 5, 6, 7, 8 and Marine 4, as defined in Chapter 11. Bales in walls enclosing showers or steam rooms shall be protected on the interior side by a Class I or Class II vapor retarder.

    AS105.6.3 Penetrations in exterior strawbale walls.

    Penetrations in exterior strawbale walls shall be sealed with an approved sealant or gasket on the exterior side of the wall in all climate zones, and on the interior side of the wall in Climate Zones 5, 6, 7, 8 and Marine 4, as defined in Chapter 11.

    AS105.6.4 Horizontal surfaces.

    Bale walls and other bale elements shall be provided with a water-resistant barrier at weather-exposed horizontal surfaces. The water-resistant barrier shall be of a material and installation that will prevent water from entering the wall system. Horizontal surfaces shall include exterior window sills, sills at exterior niches and buttresses. The finish material at such surfaces shall be sloped not less than 1 unit vertical in 12 units horizontal (8-percent slope) and shall drain away from bale walls and elements. Where the water-resistant barrier is below the finish material, it shall be sloped not less than 1 unit vertical in 12 units horizontal (8-percent slope) and shall drain to the outside surface of the bales wall’s vertical finish.

    AS105.6.5 Separation of bales and concrete.

    A sheet or liquid-applied Class II vapor retarder shall be installed between bales and supporting concrete or masonry. The bales shall be separated from the vapor retarder by not less than 3/4 inch (19.1 mm), and that space shall be filled with an insulating material such as wood or rigid insulation, or a material that allows vapor dispersion such as gravel, or other approved insulating or vapor dispersion material. Sill plates shall be installed at this interface in accordance with Section AS105.3. Where bales abut a concrete or masonry wall that retains earth, a Class II vapor retarder shall be provided between such wall and the bales.

    AS105.6.6 Separation of bales and earth.

    Bales shall be separated from earth by not less than 8 inches (203 mm).

    AS105.6.7 Separation of exterior plaster and earth.

    Exterior plaster applied to straw bales shall be located not less than 6 inches (102 mm) above earth or 3 inches (51 mm) above paved areas.

    AS105.6.8 Separation of wood and plaster.

    Where wood framing or wood sheathing occurs on the exterior face of strawbale walls, such wood surfaces shall be separated from exterior plaster with two layers of Grade D paper, No. 15 asphalt felt or other approved material in accordance with Section R703.7.3.

    Exceptions:

    1. 1.Where the wood is preservative treated or naturally durable and is not greater than 11/2 inches (38 mm) in width.

    2. 2.Clay plaster shall not be required to be separated from untreated wood that is not greater than 11/2 inches (38 mm) in width.

    AS105.7 Inspections.

    The building official shall inspect the following aspects of strawbale construction in accordance with Section R109.1:

    1. 1.Sill plate anchors, as part of and in accordance with Section R109.1.1.

    2. 2.Mesh placement and attachment, where mesh is required by this appendix.

    3. 3.Pins, where required by and in accordance with Section AS105.4.

    SECTIONAS106
    STRAWBALE WALLS—STRUCTURAL

    AS106.1 General.

    Plastered strawbale walls shall be permitted to be used as structural walls in one-story buildings in accordance with the prescriptive provisions of this section.

    AS106.2 Loads and other limitations.

    Live and dead loads and other limitations shall be in accordance with Section R301 of the International Residential Code. Strawbale wall dead loads shall not exceed 60 psf (2872 N/m2) per face area of wall.

    AS106.3 Foundations.

    Foundations for plastered strawbale walls shall be in accordance with Chapter 4.

    AS106.4 Configuration of bales.

    Bales in strawbale structural walls shall be laid flat or on-edge and in a running bond or stack bond, except that bales in structural walls with unreinforced plasters shall be laid in a running bond only.

    AS106.5 Voids and stuffing.

    Voids between bales in straw-bale structural walls shall not exceed 4 inches (102 mm) in width, and such voids shall be stuffed with flakes of straw or straw-clay, before application of finish.

    AS106.6 Plaster on structural walls.

    Plaster on load-bearing walls shall be in accordance with Table AS106.12. Plaster on shear walls shall be in accordance with Table AS106.13(1).

    AS106.6.1 Compressive strength.

    For plaster on straw-bale structural walls, the building official is authorized to require a 2-inch (51mm) cube test conforming to ASTM C 109 to demonstrate a minimum compressive strength in accordance with Table AS106.6.1.

    TABLE AS106.6.1

    MINIMUM COMPRESSIVE STRENGTH FOR PLASTERS ON STRUCTURAL WALLS

    PLASTER TYPEMINIMUM COMPRESSIVE STRENGTH (psi)
    Clay100
    Soil-cement1000
    Lime600
    Cement-lime1000
    Cement1400

    For SI: 1 pound per square inch = 6894.76 N/m2.

    AS106.7 Straightness of plaster.

    Plaster on strawbale structural walls shall be straight, as a function of the bale wall surfaces they are applied to, in accordance with all of the following:

    1. 1.As measured across the face of a bale, straw bulges shall not protrude more than 3/4 inch (19.1 mm) across 2 feet (610 mm) of its height or length.

    2. 2.As measured across the face of a bale wall, straw bulges shall not protrude from the vertical plane of a bale wall more than 2 inches (51 mm) over 8 feet (2438 mm).

    3. 3.The vertical faces of adjacent bales shall not be offset more than 3/8 inch (9.5 mm).

    AS106.8 Plaster and membranes.

    Strawbale structural walls shall not have a membrane between straw and plaster, or shall have attachment through the bale wall from one plaster skin to the other in accordance with an approved engineered design.

    AS106.9 Mesh.

    Mesh in plasters on strawbale structural walls, and where required by Table AS105.4, shall be installed in accordance with Sections AS106.9.1 through AS106.9.4.

    AS106.9.1 Mesh laps.

    Mesh required by Table AS105.4 or AS106.12 shall be installed with not less than 4-inch (102 mm) laps. Mesh required by Table AS106.13(1) or in walls designed to resist wind uplift of more than 100 plf (1459 N/m), shall run continuous vertically from sill plate to the top plate or roof-bearing element, or shall lap not less than 8 inches (203 mm). Horizontal laps in such mesh shall be not less than 4 inches (102 mm).

    AS106.9.2 Mesh attachment.

    Mesh shall be attached with staples to top plates or roof-bearing elements and to sill plates in accordance with all of the following:

    1. 1.Staples. Staples shall be pneumatically driven, stainless steel or electro-galvanized, 16 gage with 11/2-inch (38 mm) legs, 7/16-inch (11.1 mm) crown; or manually driven, galvanized, 15 gage with 1-inch (25 mm) legs. Other staples shall be permitted to be used as designed by a registered design professional. Staples into preservative-treated wood shall be stainless steel.

    2. 2.Staple orientation. Staples shall be firmly driven diagonally across mesh intersections at the required spacing.

    3. 3.Staple spacing. Staples shall be spaced not more than 4 inches (102 mm) on center, except where a lesser spacing is required by Table AS106.13(1) or Section AS106.14, as applicable.

    AS106.9.3 Steel mesh.

    Steel mesh shall be galvanized, and shall be separated from preservative-treated wood by Grade D paper, No. 15 roofing felt or other approved barrier.

    AS106.9.4 Mesh in plaster.

    Required mesh shall be embedded in the plaster except where staples fasten the mesh to horizontal boundary elements.

    AS106.10 Support of plaster skins.

    Plaster skins on straw-bale structural walls shall be continuously supported along their bottom edge. Acceptable supports include: a concrete or masonry stem wall, a concrete slab-on-grade, a wood-framed floor blocked with an approved engineered design or a steel angle anchored with an approved engineered design. A weep screed as described in Section R702.7.2.1 is not an acceptable support.

    AS106.11 Transfer of loads to and from plaster skins.

    Where plastered strawbale walls are used to support superimposed vertical loads, such loads shall be transferred to the plaster skins by continuous direct bearing or by an approved engineered design. Where plastered strawbale walls are used to resist in-plane lateral loads, such loads shall be transferred to the reinforcing mesh from the structural member or assembly above and to the sill plate in accordance with Table AS106.13(3).

    AS106.12 Load-bearing walls.

    Plastered strawbale walls shall be permitted to be used as load-bearing walls in one-story buildings to support vertical loads imposed in accordance with Section R301, in accordance with and not more than the allowable bearing capacities indicated in Table AS106.12.

    TABLE AS106.12

    ALLOWABLE SUPERIMPOSED VERTICAL LOADS (LBS/FOOT) FOR PLASTERED LOAD-BEARING STRAWBALE WALLS

    WALL DESIGNATIONPLASTERa (both sides) Minimum thickness in inches each sideMESHbSTAPLEScALLOWABLE BEARING CAPACITYd (plf)
    AClay 11/2None requiredNone required400
    BSoil-cement 1RequiredRequired800
    CLime 7/8RequiredRequired500
    DCement-lime 7/8RequiredRequired800
    ECement 7/8RequiredRequired800

    For SI: 1 inch = 25.4mm, 1 pound per foot = 14.5939 N/m.

    1. a.Plasters shall conform to Sections AS104.4.3 through AS104.4.8, AS106.7 and AS106.10.

    2. b.Any metal mesh allowed by this appendix and installed in accordance with Section AS106.9.

    3. c.In accordance with Section AS106.9.2, except as required to transfer roof loads to the plaster skins in accordance with Section AS106.11.

    4. d.For walls with a different plaster on each side, the lower value shall be used.

    AS106.12.1 Precompression of load-bearing strawbale walls.

    Prior to application of plaster, walls designed to be load bearing shall be precompressed by a uniform load of not less than 100 plf (1459 N/m).

    AS106.12.2 Concentrated loads.

    Concentrated loads shall be distributed by structural elements capable of distributing the loads to the bearing wall within the allowable bearing capacity listed in Table AS106.12 for the plaster type used.

    AS106.13 Braced panels.

    Plastered strawbale walls shall be permitted to be used as braced wall panels for one-story buildings in accordance with Section R602.10 of the International Residential Code, and with Tables AS106.13(1), AS106.13(2) and AS106.13(3). Wind design criteria shall be in accordance with Section R301.2.1. Seismic design criteria shall be in accordance with Section R301.2.2.

    TABLE AS106.13(1)

    PLASTERED STRAWBALE BRACED WALL PANEL TYPES

    WALL DESIGNATIONPLASTERa (both sides)SILL PLATESb (nominal size in inches)ANCHOR BOLTc SPACING (inches on center)MESHd (inches)STAPLE SPACINGe (inches on center)
    TypeThickness (minimum in inches each side)
    A1Clay1.52 × 432NoneNone
    A2Clay1.52 × 4322 × 2 high-density polypropylene2
    A3Clay1.52 × 4222 × 2 × 14 gage4
    BSoil-cement14 × 4242 × 2 × 14 gage2
    C1Lime7/82 × 43217-gage woven wire3
    C2Lime7/84 × 4242 × 2 × 14 gage2
    D1Cement-lime7/84 × 43217 gage woven wire2
    D2Cement-lime7/84 × 4242 × 2 × 14 gage2
    E1Cement7/84 × 4222 × 2 × 14 gage2
    E2Cement1.54 × 4242 × 2 × 14 gage2

    SI: 1 inch = 25.4 mm

    1. a.Plasters shall conform with Sections AS104.4.3 through AS104.4.8, AS106.7, AS106.8 and AS106.12.

    2. b.Sill plates shall be Douglas fir-larch or southern pine and shall be preservative treated where required by the International Residential Code.

    3. c.Anchor bolts shall be in accordance with Section AS106.13.3 at the spacing shown in this table.

    4. d.Installed in accordance with Section AS106.9.

    5. e.Staples shall be in accordance with Section AS106.9.2 at the spacing shown in this table.

    TABLE AS106.13(2)

    BRACING REQUIREMENTS FOR STRAWBALE BRACED WALL PANELS BASED ON WIND SPEED

    • EXPOSURE CATEGORY Bd• 25-FOOT MEAN ROOF HEIGHT• 10-FOOT EAVE-TO-RIDGE HEIGHTd• 10-FOOT WALL HEIGHTd• 2 BRACED WALL LINESdMINIMUM TOTAL LENGTH (FEET) OF STRAWBALE BRACED WALLPANELS REQUIRED ALONG EACH BRACED WALL LINEa, b, c, d
    Basic wind speed (mph)Story locationBraced wall line spacing (feet)Strawbale braced wallpanele A2, A3Strawbale braced wallpanele C1, C2, D1Strawbale braced wallpanele D2, E1, E2
    ≤ 85One-story building106.43.83.0
    208.55.14.0
    3010.26.14.8
    4013.36.95.5
    5016.37.76.1
    6019.48.36.6
    ≤ 90One-story building106.43.83.0
    209.05.44.3
    3011.26.45.1
    4015.37.45.9
    5018.48.16.5
    6021.48.87.0
    ≤ 100One-story building107.14.33.4
    2010.26.14.8
    3014.37.25.7
    4018.48.16.5
    5022.49.07.1
    6026.59.87.8
    ≤ 110One-story building107.84.73.7
    2012.26.65.3
    3017.37.96.3
    4022.49.07.1
    5026.59.87.8
    6031.611.48.5

    For SI: 1 inch = 25.4 mm, 1 foot = 305 mm, 1 mile per hour = 0.447 m/s.

    1. a.Linear interpolation shall be permitted.

    2. b.All braced wall panels shall be without openings and shall have an aspect ratio (H:L) ≤ 2:1.

    3. c.Tabulated minimum total lengths are for braced wall lines using single braced wall panels with an aspect ratio (H:L) ≤ 2:1, or using multiple braced wall panels with aspect ratios (H:L) ≤ 1:1. For braced wall lines using two or more braced wall panels with an aspect ratio (H:L) > 1:1, the minimum total length shall be multiplied by the largest aspect ratio (H:L) of braced wall panels in that line.

    4. d.Subject to applicable wind adjustment factors associated with “All methods” in Table R602.10.3(2)

    5. e.Strawbale braced panel types indicated shall comply with Sections AS106.13.1 through AS106.13.3 and with Table AS106.13(1).

    TABLE AS106.13(3)

    BRACING REQUIREMENTS FOR STRAWBALE BRACED WALL PANELS BASED ON SEISMIC DESIGN CATEGORY

    • SOIL CLASS Dd• WALL HEIGHT = 10 FEETd• 15 PSF ROOF-CEILING DEAD LOADd• BRACED WALL LINE SPACING ≤ 25 FEETdMINIMUM TOTAL LENGTH (FEET) OF STRAWBALE BRACED WALL PANELS REQUIRED ALONG EACH BRACED WALL LINEa, b, c, d
    Seismic Design CategoryStory locationBraced wall line length (feet)Strawbale Braced Wall Panele A2, C1, C2, D1Strawbale Braced Wall Panele B, D2, E1, E2
    COne-story building105.74.6
    208.06.5
    309.87.9
    4012.99.1
    5016.110.4
    D0One-story building106.04.8
    208.56.8
    3010.98.4
    4014.59.7
    5018.111.7
    D1One-story building106.35.1
    209.07.2
    3012.18.8
    4016.110.4
    5020.113.0
    D2One-story building107.15.7
    2010.18.1
    3015.19.9
    4020.113.0
    5025.116.3

    For SI: 1 inch = 25.4 mm, 1 foot = 305 mm, 1 pound per square foot = 0.0479 kPa.

    1. a.Linear interpolation shall be permitted.

    2. b.Braced wall panels shall be without openings and shall have an aspect ratio (H:L) ≤ 2:1.

    3. c.Tabulated minimum total lengths are for braced wall lines using single braced wall panels with an aspect ratio (H:L) ≤ 2:1, or using multiple braced wall panels with aspect ratios (H:L) ≤ 1:1. For braced wall lines using two or more braced wall panels with an aspect ratio (H:L) > 1:1, the minimum total length shall be multiplied by the largest aspect ratio (H:L) of braced wall panels in that line.

    4. d.Subject to applicable seismic adjustment factors associated with “All methods” in Table R602.10.3(4), except “Wall dead load.”

    5. e.Strawbale braced wall panel types indicated shall comply with Sections AS106.13.1 through AS106.13.3 and Table AS106.13(1).

    AS106.13.1 Bale wall thickness.

    The thickness of the stacked bale wall without its plaster shall be not less than 15 inches (381 mm).

    AS106.13.2 Sill plates.

    Sill plates shall be in accordance with Table AS106.13(1).

    AS106.13.3 Sill plate fasteners.

    Sill plates shall be fastened with not less than 5/8-inch-diameter (15.9 mm) steel anchor bolts with 3-inch by 3-inch by 3/16-inch (76.2 mm by 76.2 mm by 4.8 mm) steel washers, with not less than 7-inch (177.8 mm) embedment in a concrete or masonry foundation, or shall be an approved equivalent, with the spacing shown in Table AS106.13(1). Anchor bolts or other fasteners into framed floors shall be of an approved engineered design.

    AS106.14 Resistance to wind uplift forces.

    Plaster mesh in skins of strawbale walls that resist uplift forces from the roof assembly, as determined in accordance with Section R802.11, shall be in accordance with all of the following:

    1. 1.Plaster shall be any type and thickness allowed in Section AS104.

    2. 2.Mesh shall be any type allowed in Table AS106.13(1), and shall be attached to top plates or roof-bearing elements and to sill plates in accordance with Section AS106.9.2.

    3. 3.Sill plates shall be not less than nominal 2-inch by 4-inch (51 mm by 102 mm) with anchoring complying with Section R403.1.6.

    4. 4.Mesh attached with staples at 4 inches (51 mm) on center shall be considered to be capable of resisting uplift forces of 100 plf (1459 N/m) for each plaster skin.

    5. 5.Mesh attached with staples at 2 inches (51 mm) on center shall be considered to be capable of resisting uplift forces of 200 plf (2918 N/m) for each plaster skin.

    SECTIONAS107
    FIRE RESISTANCE

    AS107.1 Fire-resistance rating.

    Strawbale walls shall be considered to be nonrated, except for walls constructed in accordance with Section AS107.1.1 or AS107.1.2. Alternately, fire-resistance ratings of strawbale walls shall be determined in accordance with Section R302 of the International Residential Code.

    AS107.1.1 One-hour rated clay plastered wall.

    One-hour fire-resistance-rated nonload-bearing clay plastered strawbale walls shall comply with all of the following:

    1. 1.Bales shall be laid flat or on-edge in a running bond.

    2. 2.Bales shall maintain thickness of not less than 18 inches (457 mm).

    3. 3.Gaps shall be stuffed with straw-clay.

    4. 4.Clay plaster on each side of the wall shall be not less than 1 inch (25 mm) thick and shall be composed of a mixture of 3 parts clay, 2 parts chopped straw and 6 parts sand, or an alternative approved clay plaster.

    5. 5.Plaster application shall be in accordance with Section AS104.4.3.3 for the number and thickness of coats.

    AS107.1.2 Two-hour rated cement plastered wall.

    Two-hour fire-resistance-rated nonload-bearing cement plastered strawbale walls shall comply with all of the following:

    1. 1.Bales shall be laid flat or on-edge in a running bond.

    2. 2.Bales shall maintain a thickness of not less than 14 inches (356 mm).

    3. 3.Gaps shall be stuffed with straw-clay.

    4. 4.11/2-inch (38 mm) by 17-gage galvanized woven wire mesh shall be attached to wood members with 11/2-inch (38 mm) staples at 6 inches (152 mm) on center. 9 gage U-pins with not less than 8-inch (203 mm) legs shall be installed at 18 inches (457 mm) on center to fasten the mesh to the bales.

    5. 5.Cement plaster on each side of the wall shall be not less than 1 inch (25 mm) thick.

    6. 6.Plaster application shall be in accordance with Section AS104.4.8 for the number and thickness of coats.

    AS107.2 Openings in rated walls.

    Openings and penetrations in bale walls required to have a fire-resistance rating shall satisfy the same requirements for openings and penetrations as prescribed in the International Residential Code.

    AS107.3 Clearance to fireplaces and chimneys.

    Strawbale surfaces adjacent to fireplaces or chimneys shall be finished with not less than 3/8-inch (10 mm) thick plaster of any type permitted by this appendix. Clearance from the face of such plaster to fireplaces and chimneys shall be maintained as required from fireplaces and chimneys to combustibles in Chapter 10, or as required by manufacturer’s instructions, whichever is more restrictive.

    SECTIONAS108
    THERMAL INSULATION

    AS108.1 R-value.

    The unit R-value of a strawbale wall with bales laid flat is R-1.3 per inch of bale thickness. The unit R-value of a strawbale wall with bales on-edge is R-2 per inch of bale thickness.

    SECTIONAS109
    REFERENCED STANDARDS

    ASTM

    C 5—10

    Standard Specification for Quicklime for Structural Purposes

    AS104.4.6.1

    C 109/C 109M—12

    Standard Test Method for Compressive Strength of Hydraulic Cement Mortars

    AS106.6.1

    C 141/C 141M—09

    Standard Specification for Hydrated Hydraulic Lime for Structural Purposes

    AS104.4.6.1

    C 206—03

    Standard Specification for Finishing Hydrated Lime

    AS104.4.6.1

    C 926—12a

    Standard Specification for Application of Portland Cement Based Plaster

    AS104.4.7AS104.4.8

    C 1707—11

    Standard Specification for Pozzolanic Hydraulic Lime for Structural Purposes

    AS104.4.6.1

    EN

    459—2010

    Part 1: Building Lime. Definitions, Specifications and Conformity Criteria; Part 2: Test Methods

    AS104.4.6.1

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