|CALIFORNIA HEALTH AND SAFETY CODE
Guidelines for Straw Bale Structures
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HEALTH AND SAFETY CODE
18944.30. The Legislature finds and declares all of the following:
(a) There is an urgent need for low-cost, energy-efficient housing
(b) The cost of conventional lumber-framed housing has risen due
to a shortage of construction-grade lumber.
(c) Straw is an annually renewable source of cellulose that can
be used as an energy-efficient substitute for stud-framed wall
(d) The state has mandated that the burning of rice straw be
(e) As a result of the mandated burning reduction, growers are
experimenting with alternative straw management practices. Various
methods of straw incorporation into the soil are the most widely used
alternatives. The two most common methods are nonflood
incorporation and winter flood incorporation. Economically viable
off-farm uses for rice straw are not yet available.
(f) Winter flooding of rice fields encourages the natural
decomposition of rice straw and provides valuable waterfowl habitat.
According to the Central Valley Habitat Joint Venture component of
the North American Waterfowl Management Plan, in California's Central
Valley, over 400,000 acres of enhanced agricultural lands are needed
to restore the depleted migratory waterfowl populations of the
Pacific flyway. Flooded rice fields are a key and integral part of
the successful restoration of historic waterfowl and shorebird
(g) Winter flooding of rice fields provides significant waterfowl
habitat benefits and should be especially encouraged in areas where
there is minimal potential to impact salmon as a result of surface
(h) An economically viable market for rice straw bales could
result from the use of rice straw bales in housing construction.
(i) Practicing architects and engineers have determined that the
statutory guidelines established by Chapter 941 of the Statutes of
1995 contain specific requirements that they believe are either
unnecessary or detrimental. Some of the requirements are considered
costly and severely restrict the development of straw-bale housing.
(j) Statutory guidelines for the use of straw-bale housing would
significantly benefit energy conservation, natural resources,
low-cost housing, agriculture, and fisheries in California.
(k) Tests and experience with straw-bale construction demonstrate
that it is a strong, durable, and thermally superior building system
that deserves a larger role in modern construction.
18944.31. (a) Notwithstanding any other provision of law, the
guidelines established by this chapter shall apply to the
construction of all structures that use baled straw as a loadbearing
or nonloadbearing material within any city or county that adopted the
guidelines established by Chapter 941 of the Statutes of 1995 prior
to January 1, 2002. This requirement shall not preclude the city or
county from making changes or modifications to the guidelines
pursuant to subdivision (b). Notwithstanding any other provision of
law, the guidelines established by this chapter shall not become
operative in a city or county that has not adopted the guidelines
prior to January 1, 2002, unless and until the legislative body of
the city or county makes an express finding that the application of
these guidelines within the city or county is reasonably necessary
because of local conditions and the city or county files a copy of
that finding with the department.
(b) A city or county may, by ordinance or regulation, make any
changes or modifications in the guidelines contained in this chapter
as it determines are reasonably necessary because of local
conditions, provided the city or county files a copy of the changes
or modifications and the express findings for the changes or
modifications with the department. No change or modification of that
type shall become effective or operative for any purpose until the
finding and the change or modification has been filed with the
(c) Nothing in this chapter shall be construed as increasing or
decreasing the authority to approve or disapprove of alternative
construction methods pursuant to the State Housing Law, Part 1.5
(commencing with Section 17910) or the California Building Standards
Code, Title 24 of the California Code of Regulations.
(d) It is the intent of the Legislature that the statutory
guidelines of this chapter serve as an interim measure pending the
evaluation of straw bales as a construction material through the
normal processes used for the testing and listing of building
materials, the determination of construction standards, and the
adoption of those materials and construction standards into the
California Building Standards Code.
18944.32. Nothing in this chapter shall be construed as an
exemption from Chapter 3 (commencing with Section 5500) of, or
Chapter 7 (commencing with Section 6700) of, Division 3 of the
Business and Professions Code relative to preparation of plans,
drawings, specifications, or calculations under the direct
supervision of a licensed architect or civil engineer, for the
construction of structures that deviate from the conventional framing
requirements for wood-frame construction.
18944.33. For the purposes of this chapter, the following terms are
defined as follows:
(a) "Bales" means rectangular compressed blocks of straw, bound by
strings or wire.
(b) "Department" means the Department of Housing and Community
(c) "Flakes" means slabs of straw removed from an untied bale.
Flakes are used to fill small gaps between the ends of stacked bales.
(d) "Laid flat" refers to stacking bales so that the sides with
the largest cross-sectional area are horizontal and the longest
dimension of this area is parallel with the wall plane.
(e) "Laid on edge" refers to stacking bales so that the sides with
the largest cross-sectional area are vertical and the longest
dimension of this area is horizontal and parallel with the wall
(f) "Loadbearing" refers to plastered straw-bale walls that bear
the dead and live loads of the roof and any upper floor.
(g) "Nonloadbearing" refers to plastered straw-bale walls that
bear only their own weight, such as infill panels within some type of
post and beam structure.
(h) "Plaster" means lime, gypsum, lime cement, or cement plasters,
as defined by the California Building Standards Code, or earthen
plaster with fiber reinforcing.
(i) "Straw" means the dry stems of cereal grains left after the
seed heads have been substantially removed.
18944.34. (a) Subject to the availability of funds, on or before
January 1, 2002, the California Building Standards Commission shall
transmit, to the department and to the Legislature, a report
regarding the implementation of this chapter.
(b) The implementation report shall describe which cities and
counties have utilized this chapter, and the number and type of
structures that have been built pursuant to local ordinances. The
implementation report may include recommendations to amend the
guidelines established by this chapter, or any other related matters.
(c) The California Building Standards Commission may accept and
use any funds provided or donated for the purposes of this section.
HEALTH AND SAFETY CODE
18944.35. (a) Bales shall be rectangular in shape.
(b) Bales used within a continuous wall shall be of consistent
height and width to ensure even distribution of loads within wall
(c) Bales shall be bound with ties of either polypropylene string
or baling wire. Bales with broken or loose ties shall not be used
unless the broken or loose ties are replaced with ties which restore
the original degree of compaction of the bale.
(d) The moisture content of bales, at the time of installation,
shall not exceed 20 percent of the total weight of the bale.
Moisture content of bales shall be determined through the use of a
suitable moisture meter, designed for use with baled rice straw or
hay, equipped with a probe of sufficient length to reach the center
of the bale, and used to determine the average moisture content of
five bales randomly selected from the bales to be used.
(e) Bales in loadbearing walls shall have a minimum calculated dry
density of 7.0 pounds per cubic foot. The calculated dry density
shall be determined after reducing the actual bale weight by the
weight of the moisture content.
(f) Where custom-made partial bales are used, they shall be of the
same density, same string or wire tension, and, where possible, use
the same number of ties as the standard size bales.
(g) Bales of various types of straw, including wheat, rice, rye,
barley, oats, and similar plants, shall be acceptable if they meet
the minimum requirements of this chapter for density, shape, moisture
content, and ties.
HEALTH AND SAFETY CODE
18944.40. (a) Straw-bale walls, when covered with plaster, drywall,
or stucco, shall be deemed to have the equivalent fire resistive
rating as wood-frame construction with the same wall-finishing
(b) Minimum bale wall thickness shall be 13 inches.
(c) Buildings with loadbearing bale walls shall not exceed one
story in height without substantiating calculations and design by a
civil engineer or architect licensed by the state, and the bale
portion of the loadbearing walls shall not exceed a height-to-width
ratio of 5.6:1 (for example, the maximum height for a wall that is 23
inches thick would be 10 feet 8 inches).
(d) The ratio of unsupported wall length to thickness, for
loadbearing walls, shall not exceed 15.7:1 (for example, for a wall
that is 23 inches thick, the maximum unsupported length allowed is 30
(e) The allowable vertical load (live and dead load) on top of
loadbearing bale walls plastered with cement or lime cement plaster
on both sides shall not exceed 800 pounds per linear foot, and the
resultant load shall act at the center of the wall. Straw-bale
structures shall be designed to withstand all vertical and horizontal
loads, and the resulting overturning and base shear, as specified in
the latest edition of the California Building Standards Code.
Straw-bale walls plastered with cement or lime cement plaster on both
sides shall be capable of resisting in-plane lateral forces from
wind or earthquake of 360 pounds per linear foot.
(f) Foundations shall be designed in accordance with the
California Building Standards Code to accommodate the load created by
the bale wall plus superimposed live and dead loads. Supports for
bale walls shall extend to an elevation of at least six inches above
adjacent ground at all points, and at least one inch above floor
(g) (1) Bale walls shall be anchored to supports to resist lateral
forces, as approved by the civil engineer or architect. This may be
accomplished with one-half inch reinforcing bars embedded in the
foundation and penetrating the bales by at least 12 inches, located
along the center line of the bale wall, spaced not more than two feet
apart. Other methods as determined by the engineer or architect may
also be used.
(2) Nonbale walls abutting bale walls shall be attached by means
of one or more of the following methods or by means of an acceptable
(A) Wooden dowels of 5/8 inch minimum diameter and of sufficient
length to provide 12 inches of penetration into the bale, driven
through holes bored in the abutting wall stud, and spaced to provide
one dowel connection per bale.
(B) Pointed wooden stakes, a minimum of 12 inches in length and
11/2 inches by 31/2 inches at the exposed end, fully driven into each
course of bales, as anchorage points.
(C) Bolted or threaded rod connection of the abutting wall,
through the bale wall, to a steel nut and steel or plywood plate
washer, a minimum of 6 inches square and a minimum thickness of 3/16
of an inch for steel and 1/2 inch for plywood, in a minimum of three
(3) (A) Bale walls and roof bearing assemblies shall be anchored
to the foundation where necessary, as determined by the civil
engineer or architect, by means of methods that are adequate to
resist uplift forces resulting from the design wind load. There
shall be a minimum of two points of anchorage per wall, spaced not
more than 6 feet apart, with one located within 36 inches of each end
of each wall.
(B) With loadbearing bale walls, the dead load of the roof and
ceiling systems will produce vertical compression of the walls.
Regardless of the anchoring system used to attach the roof bearing
assembly to the foundation, prior to installation of wall finish
materials, the nuts, straps, or cables shall be retightened to
compensate for this compression.
(h) (1) A moisture barrier shall be used between the top of the
foundation and the bottom of the bale wall to prevent moisture from
migrating through the foundation so as to come into contact with the
bottom course of bales. This barrier shall consist of one of the
(A) Cementitious waterproof coating.
(B) Type 30 asphalt felt over an asphalt emulsion.
(C) Sheet metal flashing, sealed at joints.
(D) Another building moisture barrier, as approved by the building
(2) All penetrations through the moisture barrier, as well as all
joints in the barrier, shall be sealed with asphalt, caulking, or an
(3) There shall also be a drainage plane between the straw and the
top of the foundation, such as a one inch layer of pea gravel.
(i) (1) For nonloadbearing walls, bales may be laid either flat or
on edge. Bales in loadbearing bale walls shall be laid flat and be
stacked in a running bond, where possible, with each bale overlapping
the two bales beneath it. Overlaps shall be a minimum of 12 inches.
Gaps between the ends of bales which are less than 6 inches in
width may be filled by an untied flake inserted snugly into the gap.
(2) Bale wall assemblies shall be held securely together by rebar
pins driven through bale centers as described in this chapter, or
equivalent methods as approved by the civil engineer or architect.
(3) The first course of bales shall be laid by impaling the bales
on the rebar verticals and threaded rods, if any, extending from the
foundation. When the fourth course has been laid, vertical #4 rebar
pins, or an acceptable equivalent long enough to extend through all
four courses, shall be driven down through the bales, two in each
bale, located so that they do not pass through the space between the
ends of any two bales. The layout of these rebar pins shall
approximate the layout of the rebar pins extending from the
foundation. As each subsequent course is laid, two pins, long enough
to extend through that course and the three courses immediately
below it, shall be driven down through each bale. This pinning
method shall be continued to the top of the wall. In walls seven or
eight courses high, pinning at the fifth course may be eliminated.
(4) Alternative pinning method to the method described in
paragraph (3): when the third course has been laid, vertical #4
rebar pins, or an acceptable equivalent, long enough to extend
through all three courses, shall be driven down through the bales,
two in each bale, located so that they do not pass through the space
between the ends of any two bales. The layout of these rebar pins
shall approximate the layout of the rebar pins extending from the
foundation. As each subsequent course is laid, two pins, long enough
to extend through that course and the two courses immediately below
it, shall be driven down through each bale. This pinning method
shall be continued to the top of the wall.
(5) Only full-length bales shall be used at corners of loadbearing
(6) Vertical #4 rebar pins, or an acceptable alternative, shall be
located within one foot of all corners or door openings.
(7) Staples, made of #3 or larger rebar formed into a "U" shape, a
minimum of 18 inches long with two 6-inch legs, shall be used at all
corners of every course, driven with one leg into the top of each
abutting corner bale.
(j) (1) All loadbearing bale walls shall have a roof bearing
assembly at the top of the walls to bear the roof load and to provide
the means of connecting the roof structure to the foundation. The
roof bearing assembly shall be continuous along the tops of
loadbearing bale walls.
(2) An acceptable roof bearing assembly option shall consist of
two double 2-inch by 6-inch, or larger, horizontal top plates, one
located at the inner edge of the wall and the other at the outer
edge. Connecting the two doubled top plates, and located
horizontally and perpendicular to the length of the wall, shall be
2-inch by 6-inch cross members, spaced no more than 72 inches center
to center, and as required to align with the threaded rods extending
from the anchor bolts in the foundation. The double 2-inch by 6-inch
top plates shall be face-nailed with 16d nails staggered at 16-inch
o.c., with laps and intersections face-nailed with four 16d nails.
The crossmembers shall be face-nailed to the top plates with four 16d
nails at each end. Corner connections shall include overlaps nailed
as above or an acceptable equivalent, such as plywood gussets or
metal plates. Alternatives to this roof bearing assembly option
shall provide equal or greater vertical rigidity and provide
horizontal rigidity equivalent to a continuous double 2 by 4 top
(3) The connection of roof framing members to the roof plate shall
comply with the appropriate sections of the California Building
(k) All openings in loadbearing bale walls shall be a minimum of
one full bale length from any outside corner, unless exceptions are
approved by an engineer or architect licensed by the state to
practice. Wall or roof load present above any opening shall be
carried, or transferred, to the bales below by one of the following:
(1) A frame, such as a structural window or door frame.
(2) A lintel, such as an angle-iron cradle, wooden beam, or wooden
box beam. Lintels shall be at least twice as long as the opening is
wide and extend a minimum of 24 inches beyond either side of the
opening. Lintels shall be centered over openings.
(3) A roof bearing assembly designed to act as a rigid beam over
(l) (1) All weather-exposed bale walls shall be protected from
water damage. No vapor impermeable barrier may be used on bale
walls, and the civil engineer or architect may design the bale walls
without any membrane barriers between straw and plaster, except as
specified in this section, in order to allow natural transpiration of
moisture from the bales and to secure a structural bond between
plaster and straw.
(2) Bale walls shall have special moisture protection provided at
all horizontal surfaces exposed to the weather. This moisture
protection shall be installed in a manner that will prevent water
from entering the wall system.
(m) (1) Interior and exterior surfaces of bale walls shall be
protected from mechanical damage, flame, animals, and prolonged
exposure to water. Bale walls adjacent to bath and shower enclosures
shall be protected by a moisture barrier.
(2) Cement stucco shall be reinforced with galvanized woven wire
stucco netting or an equivalent, as approved by the building
official. The reinforcement shall be secured by attachment through
the wall at a maximum spacing of 24 inches horizontally and 16 inches
vertically, unless substantiated otherwise by a civil engineer or
(3) Where bales abut other materials, the plaster or stucco shall
be reinforced with galvanized expanded metal lath, or an acceptable
equivalent, extending a minimum of 6 inches onto the bales.
(4) Earthen and lime-based plasters may be applied directly onto
bale walls without reinforcement, except where applied over materials
other than straw.
(n) (1) All wiring within or on bale walls shall meet all
provisions of the California Electrical Code. Type "NM" or "UF"
cable may be used, or wiring may be run in metallic or nonmetallic
(2) Electrical boxes shall be securely attached to wooden stakes
driven a minimum of 12 inches into the bales, or an acceptable
(o) Water or gas pipes within bale walls shall be encased in a
continuous pipe sleeve to prevent leakage within the wall. Where
pipes are mounted on bale walls, they shall be isolated from the
bales by a moisture barrier.
(p) Bales shall be protected from rain and other moisture
infiltration at all times until protected by the roof of the
18944.41. Sections 18944.30, 18944.31, 18944.33, 18944.35, and
18944.40 shall become inoperative when building standards become
effective after approval by the California Building Standards
Commission pursuant to Chapter 4 (commencing with Section 18935) that
permit the construction of structures that use baled straw as a
loadbearing or nonloadbearing material and that are safe to the