International Building Code Section 1805 – International Building Code 2006 Discussions

International Building Code 1805.1

General. Footings and foundations shall be designed
and constructed in accordance with Sections 1805.1 through
1805.9. Footings and foundations shall be built on undisturbed
soil, compacted fill material or CLSM. Compacted fill material
shall be placed in accordance with Section 1803.5. CLSMshall
be placed in accordance with Section 1803.6.
The top surface of footings shall be level. The bottom surface
of footings is permitted to have a slope not exceeding one
unit vertical in 10 units horizontal (10-percent slope). Footings
shall be stepped where it is necessary to change the elevation of
the top surface of the footing or where the surface of the ground
slopes more than one unit vertical in 10 units horizontal
(10-percent slope).
2006 INTERNATIONAL BUILDING CODE 345
SOILS AND FOUNDATIONS

International Building Code 1805.2

Depth of footings. The minimum depth of footings
below the undisturbed ground surface shall be 12 inches (305
mm). Where applicable, the depth of footings shall also conform
to Sections 1805.2.1 through 1805.2.3.

Frost protection. Except where otherwise protected
from frost, foundation walls, piers and other permanent
supports of buildings and structures shall be protected
by one or more of the following methods:
1. Extending below the frost line of the locality;
2. Constructing in accordance with ASCE 32; or
3. Erecting on solid rock.
Exception: Free-standing buildings meeting all of the
following conditions shall not be required to be protected:
1. Classified in Occupancy Category I, in accordance
with Section1604.5;
2. Area of 600 square feet (56 m2) or less for
light-frame construction or 400 square feet (37m2)
or less for other than light-frame construction; and
3. Eave height of 10 feet (3048 mm) or less.
Footings shall not bear on frozen soil unless such frozen
condition is of a permanent character.

Isolated footings. Footings on granular soil shall
be so located that the line drawn between the lower edges of
adjoining footings shall not have a slope steeper than 30
degrees (0.52 rad) with the horizontal, unless the material
supporting the higher footing is braced or retained or otherwise
laterally supported in an approved manner or a greater
slope has been properly established by engineering analysis.

Shifting or moving soils. Where it is known that
the shallow subsoils are of a shifting or moving character,
footings shall be carried to a sufficient depth to ensure stability.

International Building Code 1805.2.1

International Building Code 1805.2.2

International Building Code 1805.2.3

Shifting or moving soils. Where it is known that
the shallow subsoils are of a shifting or moving character,
footings shall be carried to a sufficient depth to ensure stability.

International Building Code 1805.3

Footings on or adjacent to slopes. The placement of
buildings and structures on or adjacent to slopes steeper than
one unit vertical in three units horizontal (33.3-percent slope)
shall conform to Sections 1805.3.1 through 1805.3.5.

Building clearance from ascending slopes. In
general, buildings below slopes shall be set a sufficient distance
from the slope to provide protection from slope drainage,
erosion and shallow failures. Except as provided for in
Section 1805.3.5 and Figure 1805.3.1, the following criteria
will be assumed to provide this protection. Where the existing
slope is steeper than one unit vertical in one unit horizontal
(100-percent slope), the toe of the slope shall be
assumed to be at the intersection of a horizontal plane drawn
from the top of the foundation and a plane drawn tangent to
the slope at an angle of 45 degrees (0.79 rad) to the horizontal.
Where a retaining wall is constructed at the toe of the
slope, the height of the slope shall be measured from the top
of the wall to the top of the slope.

Footing setback from descending slope surface.
Footings on or adjacent to slope surfaces shall be
founded in firm material with an embedment and set back
from the slope surface sufficient to provide vertical and lateral
support for the footingwithout detrimental settlement.
Except as provided for in Section 1805.3.5 and Figure
1805.3.1, the following setback is deemed adequate to
meet the criteria. Where the slope is steeper than 1 unit vertical
in 1 unit horizontal (100-percent slope), the required
setback shall be measured from an imaginary plane 45
degrees (0.79 rad) to the horizontal, projected upward
from the toe of the slope.

Pools. The setback between pools regulated by
this code and slopes shall be equal to one-half the building
footing setback distance required by this section. That portion
of the pool wall within a horizontal distance of 7 feet
(2134 mm) from the top of the slope shall be capable of supporting
the water in the pool without soil support.

346 2006 INTERNATIONAL BUILDING CODE
SOILS AND FOUNDATIONS

Foundation elevation. On graded sites, the top of
any exterior foundation shall extend above the elevation of
the street gutter at point of discharge or the inlet of an
approved drainage device a minimum of 12 inches (305
mm) plus 2 percent. Alternate elevations are permitted subject
to the approval of the building official, provided it can
be demonstrated that required drainage to the point of discharge
and away from the structure is provided at all locations
on the site.

Alternate setback and clearance. Alternate setbacks
and clearances are permitted, subject to the approval of
the building official. The building official is permitted to
require an investigation and recommendation of a registered
design professional to demonstrate that the intent of this section
has been satisfied. Such an investigation shall include
consideration of material, height of slope, slope gradient,
load intensity and erosion characteristics of slope material.

International Building Code 1805.3.1

International Building Code 1805.3.2

International Building Code 1805.3.3

346 2006 INTERNATIONAL BUILDING CODE
SOILS AND FOUNDATIONS

International Building Code 1805.3.4

International Building Code 1805.3.5

International Building Code 1805.4

Footings. Footings shall be designed and constructed
in accordance with Sections 1805.4.1 through 1805.4.6.

Design. Footings shall be so designed that the
allowable bearing capacity of the soil is not exceeded, and
that differential settlement is minimized. The minimum
width of footings shall be 12 inches (305 mm).
Footings in areas with expansive soils shall be designed
in accordance with the provisions of Section 1805.8.

Design loads. Footings shall be designed for
the most unfavorable effects due to the combinations of
loads specified in Section 1605.2 or 1605.3. The dead
load is permitted to include the weight of foundations,
footings and overlying fill. Reduced live loads, as specified
in Sections 1607.9 and 1607.11, are permitted to be
used in the design of footings.

Vibratory loads. Where machinery operations
or other vibrations are transmitted through the
foundation, consideration shall be given in the footing
design to prevent detrimental disturbances of the soil.

Concrete footings. The design, materials and construction
of concrete footings shall comply with Sections
1805.4.2.1 through 1805.4.2.6 and the provisions of Chapter
19.
Exception: Where a specific design is not provided, concrete
footings supporting walls of light-frame construction
are permitted to be designed in accordance with
Table 1805.4.2.
2006 INTERNATIONAL BUILDING CODE 347
SOILS AND FOUNDATIONS
For SI: 1 foot = 304.8 mm.
FIGURE 1805.3.1
FOUNDATION CLEARANCES FROM SLOPES

Concrete strength. Concrete in footings
shall have a specified compressive strength (f c) of not
less than 2,500 pounds per square inch (psi) (17 237 kPa)
at 28 days.

Footing seismic ties.Where a structure is
assigned to Seismic Design Category D, E or F in accordance
with Section 1613, individual spread footings
founded on soil defined in Section 1613.5.2 as Site Class
E or F shall be interconnected by ties. Ties shall be capable
of carrying, in tension or compression, a force equal
to the product of the larger footing load times the seismic
coefficient, SDS ,divided by 10 unless it is demonstrated
that equivalent restraint is provided by reinforced concrete
beams within slabs on grade or reinforced concrete
slabs on grade.

Plain concrete footings. The edge thickness
of plain concrete footings supporting walls of other than
light-frame construction shall not be less than 8 inches
(203 mm) where placed on soil.
Exception: For plain concrete footings supporting
Group R-3 occupancies, the edge thickness is permitted
to be 6 inches (152 mm), provided that the footing
does not extend beyond a distance greater than the
thickness of the footing on either side of the supported
wall.

Placement of concrete. Concrete footings
shall not be placed through water unless a tremie or other
method approved by the building official is used. Where
placed under or in the presence of water, the concrete
shall be deposited by approved means to ensure minimum
segregation of the mix and negligible turbulence of
the water.

Protection of concrete. Concrete footings
shall be protected from freezing during depositing and for
a period of not less than five days thereafter. Water shall
not be allowed to flow through the deposited concrete.

Forming of concrete. Concrete footings are
permitted to be cast against the earth where, in the opinion
of the building official, soil conditions do not require
forming. Where forming is required, it shall be in accordance
with Chapter 6 of ACI 318.

Masonry-unit footings. The design, materials
and construction of masonry-unit footings shall comply
with Sections 1805.4.3.1 and 1805.4.3.2, and the provisions
of Chapter 21.
Exception: Where a specific design is not provided,
masonry-unit footings supporting walls of light-frame
construction are permitted to be designed in accordance
with Table 1805.4.2.

Dimensions. Masonry-unit footings shall be
laid in Type M or S mortar complying with Section
2103.8 and the depth shall not be less than twice the projection
beyond the wall, pier or column. The width shall
not be less than 8 inches (203 mm) wider than the wall
supported thereon.

Offsets. The maximum offset of each course
in brick foundation walls stepped up from the footings
shall be 1.5 inches (38 mm) where laid in single courses,
and 3 inches (76 mm) where laid in double courses.

Steel grillage footings. Grillage footings of structural
steel shapes shall be separated with approved steel
spacers and be entirely encased in concrete with at least 6
inches (152 mm) on the bottom and at least 4 inches (102
mm) at all other points. The spaces between the shapes shall
be completely filled with concrete or cement grout.

Timber footings. Timber footings are permitted
for buildings of Type V construction and as otherwise
approved by the building official. Such footings shall be
treated in accordance with AWPA U1 (Commodity Specification
A, Use Category 4B). Treated timbers are not
required where placed entirely belowpermanentwater level
or where used as capping for wood piles that project above
the water level over submerged or marsh lands. The compressive
stresses perpendicular to the grain in untreated timber
footings supported upon treated piles shall not exceed
70 percent of the allowable stresses for the species and grade
of timber as specified in the AF&PA NDS.

Wood foundations. Wood foundation systems
shall be designed and installed in accordance with AF&PA
Technical Report No. 7. Lumber and plywood shall be
treated in accordance with AWPA U1 (Commodity Specification
A, Use Category 4B and Section 5.2) and shall be
identified in accordance with Section 2303.1.8.1.

International Building Code 1805.4.1

International Building Code 1805.4.1.1

International Building Code 1805.4.1.2

International Building Code 1805.4.2

Concrete strength. Concrete in footings
shall have a specified compressive strength (f c) of not
less than 2,500 pounds per square inch (psi) (17 237 kPa)
at 28 days.

International Building Code 1805.4.2.1

Concrete strength. Concrete in footings
shall have a specified compressive strength (f c) of not
less than 2,500 pounds per square inch (psi) (17 237 kPa)
at 28 days.

International Building Code 1805.4.2.2

International Building Code 1805.4.2.3

International Building Code 1805.4.2.4

International Building Code 1805.4.2.5

International Building Code 1805.4.2.6

International Building Code 1805.4.3

International Building Code 1805.4.3.1

International Building Code 1805.4.3.2

International Building Code 1805.4.4

International Building Code 1805.4.5

International Building Code 1805.4.6

International Building Code 1805.5

Foundation walls. Concrete and masonry foundation
walls shall be designed in accordance with Chapter 19 or 21,
respectively. Foundation walls that are laterally supported at
the top and bottom and within the parameters of Tables
1805.5(1) through 1805.5(5) are permitted to be designed and
constructed in accordance with Sections 1805.5.1 through
1805.5.5.

Foundation wall thickness. The minimum thickness
of concrete and masonry foundationwalls shall comply
with Sections 1805.5.1.1 through 1805.5.1.3.

Thickness at top of foundation wall. The
thickness of foundation walls shall not be less than the
thickness of the wall supported, except that foundation
walls of at least 8-inch (203 mm) nominal width are permitted
to support brick-veneered frame walls and
10-inch-wide (254 mm) cavity walls provided the
requirements of Section 1805.5.1.2 are met. Corbeling
of masonry shall be in accordance with Section 2104.2.
Where an 8-inch (203 mm) wall is corbeled, the top corbel
shall not extend higher than the bottom of the floor
framing and shall be a full course of headers at least 6
inches (152 mm) in length or the top course bed joint
shall be tied to the vertical wall projection. The tie shall
be W2.8 (4.8 mm) and spaced at a maximum horizontal
distance of 36 inches (914 mm); the hollowspace behind
the corbelled masonry shall be filled with mortar or
grout.
348 2006 INTERNATIONAL BUILDING CODE
SOILS AND FOUNDATIONS
2006 INTERNATIONAL BUILDING CODE 349
SOILS AND FOUNDATIONS

Thickness based on soil loads, unbalanced
backfill height and wall height. The thickness of foundation
walls shall comply with the requirements of Table
1805.5(5) for concrete walls, Table 1805.5(1) for plain
masonry walls or Table 1805.5(2), 1805.5(3) or
1805.5(4) for masonry walls with reinforcement. When
using the tables, masonry shall be laid in running bond
and the mortar shall be Type M or S.
Unbalanced backfill height is the difference in height
between the exterior finish ground level and the lower of
the top of the concrete footing that supports the foundation
wall or the interior finish ground level. Where an
interior concrete slab on grade is provided and is in contact
with the interior surface of the foundation wall, the
unbalanced backfill height is permitted to be measured
from the exterior finish ground level to the top of the interior
concrete slab.

Rubble stone. Foundation walls of rough or
random rubble stone shall not be less than 16 inches (406
mm) thick. Rubble stone shall not be used for foundations
for structures in Seismic Design Category C, D, E or F.

Foundation wall materials. Concrete foundation
walls constructed in accordance with Table 1805.5(5) shall
comply with Section 1805.5.2.1. Masonry foundation walls
constructed in accordance with Table 1805.5(1), 1805.5(2),
1805.5(3) or 1805.5(4) shall comply with Section
1805.5.2.2.

Concrete foundation walls. Concrete foundation
walls shall comply with the following:
1. The size and spacing of vertical reinforcement
shown in Table 1805.5(5) is based on the use of
reinforcement with a minimum yield strength of
60,000 psi (414 MPa). Vertical reinforcement with
a minimum yield strength of 40,000 psi (276 MPa)
or 50,000 psi (345 MPa) is permitted, provided the
same size bar is used and the spacing shown in the
table is reduced by multiplying the spacing by 0.67
or 0.83, respectively.
2. Vertical reinforcement, when required, shall be
placed nearest the inside face of the wall a distance,
d, from the outside face (soil side) of the
wall. The distance, d, is equal to the wall thickness,
t, minus 1.25 inches (32 mm) plus one-half the bar
diameter, db [d = t # (1.25 + db/2)]. The reinforcement
shall be placed within a tolerance of # 3/8 inch
(9.5 mm) where d is less than or equal to 8 inches
(203 mm) or#1/2 inch (2.7 mm) where d is greater
than 8 inches (203 mm).
3. In lieu of the reinforcement shown in Table
1805.5(5), smaller reinforcing bar sizes with
closer spacings that provide an equivalent
cross-sectional area of reinforcement per unit
length of wall are permitted.
4. Concrete cover for reinforcement measured from
the inside face of the wall shall not be less than 3/4
inch (19.1 mm). Concrete cover for reinforcement
measured from the outside face of the wall shall
not be less than 1.5 inches (38 mm) for No. 5 bars
and smaller and not less than 2 inches (51 mm) for
larger bars.
5. Concrete shall have a specified compressive
strength, fc , of not less than 2,500 psi (17.2 MPa)
at 28 days.
6. The unfactored axial load per linear foot of wall
shall not exceed 1.2 tfc , where t is the specified
wall thickness in inches.

Masonry foundation walls. Masonry foundation
walls shall comply with the following:
1. Vertical reinforcement shall have a minimum
yield strength of 60,000 psi (414 MPa).
2. The specified location of the reinforcement shall
equal or exceed the effective depth distance, d,
noted in Tables 1805.5(2), 1805.5(3) and
1805.5(4) and shall be measured from the face of
the exterior (soil) side of the wall to the center of
the vertical reinforcement. The reinforcement
shall be placed within the tolerances specified in
ACI 530.1/ASCE 6/TMS 402, Article 3.4 B7 of
the specified location.
3. Grout shall comply with Section 2103.12.
4. Concrete masonry units shall comply with ASTM
C 90.
5. Clay masonry units shall comply with ASTM C
652 for hollow brick, except compliance with
ASTM C 62 or ASTM C 216 is permitted when
solid masonry units are installed in accordance
with Table 1805.5(1) for plain masonry.
6. Masonry units shall be installed with TypeMor S
mortar in accordance with Section 2103.8.
7. The unfactored axial load per linear foot of wall
shall not exceed 1.2 tf m where t is the specified
well thickness in inches and f m is the specified
compressive strength of masonry in pounds per
square inch.

Alternative foundation wall reinforcement. In
lieu of the reinforcement provisions for masonry foundation
walls in Table 1805.5(2), 1805.5(3) or 1805.5(4), alternative
reinforcing bar sizes and spacings having an equivalent
cross-sectional area of reinforcement per linear foot (mm)
of wall are permitted to be used, provided the spacing of
reinforcement does not exceed 72 inches (1829 mm) and
reinforcing bar sizes do not exceed No. 11.

Hollow masonry walls. At least 4 inches (102
mm) of solid masonry shall be provided at girder supports at
the top of hollow masonry unit foundation walls.

Seismic requirements. Tables 1805.5(1) through
1805.5(5) shall be subject to the following limitations in
Sections 1805.5.5.1 and 1805.5.5.2 based on the seismic
design category assigned to the structure as defined in Section
1613.

Seismic requirements for concrete foundation
walls. Concrete foundation walls designed using
354 2006 INTERNATIONAL BUILDING CODE
SOILS AND FOUNDATIONS
?
Table 1805.5(5) shall be subject to the following limitations:
1. Seismic Design CategoriesAand B. No additional
seismic requirements, except provide not less than
two No. 5 bars around window and door openings.
Such bars shall extend at least 24 inches (610 mm)
beyond the corners of the openings.
2. Seismic Design Categories C, D, E and F. Tables
shall not be used except as allowed for plain concrete
members in Section 1908.1.15.

Seismic requirements for masonry foundation
walls. Masonry foundation walls designed using
Tables 1805.5(1) through 1805.5(4) shall be subject to
the following limitations:
1. Seismic Design CategoriesAand B. No additional
seismic requirements.
2. Seismic Design Category C. A design using
Tables 1805.5(1) through 1805.5(4) is subject to
the seismic requirements of Section 2106.4.
3. Seismic Design Category D. A design using
Tables 1805.2(2) through 1805.5(4) is subject to
the seismic requirements of Section 2106.5.
4. Seismic Design Categories E and F. A design
using Tables 1805.2(2) through 1805.5(4) is subject
to the seismic requirements of Section 2106.6.

Foundation wall drainage. Foundation walls
shall be designed to support the weight of the full hydrostatic
pressure of undrained backfill unless a drainage system
is installed in accordance with Sections 1807.4.2 and
1807.4.3.

Pier and curtain wall foundations. Except in
Seismic Design Categories D, E and F, pier and curtain wall
foundations are permitted to be used to support light-frame
construction not more than two stories in height, provided
the following requirements are met:
1. All load-bearing walls shall be placed on continuous
concrete footings bonded integrally with the exterior
wall footings.
2. The minimum actual thickness of a load-bearing
masonry wall shall not be less than 4 inches (102 mm)
nominal or 3.625 inches (92 mm) actual thickness,
and shall be bonded integrally with piers spaced 6 feet
(1829 mm) on center (o.c.).
3. Piers shall be constructed in accordance with Chapter
21 and the following:
3.1. The unsupported height of the masonry piers
shall not exceed 10 times their least dimension.
3.2. Where structural clay tile or hollow concrete
masonry units are used for piers supporting
beams and girders, the cellular spaces shall be
filled solidly with concrete or Type M or S
mortar.
Exception: Unfilled hollow piers are permitted
where the unsupported height of the
pier is not more than four times its least
dimension.
3.3. Hollow piers shall be capped with 4 inches
(102 mm) of solid masonry or concrete or the
cavities of the top course shall be filled with
concrete or grout.
4. The maximum height of a 4-inch (102 mm)
load-bearing masonry foundation wall supporting
wood frame walls and floors shall not be more than 4
feet (1219 mm) in height.
5. The unbalanced fill for 4-inch (102 mm) foundation
walls shall not exceed 24 inches (610 mm) for solid
masonry, nor 12 inches (305 mm) for hollow
masonry.

International Building Code 1805.5.1

Foundation wall thickness. The minimum thickness
of concrete and masonry foundationwalls shall comply
with Sections 1805.5.1.1 through 1805.5.1.3.

International Building Code 1805.5.1.1

International Building Code 1805.5.1.2

International Building Code 1805.5.1.3

International Building Code 1805.5.2

International Building Code 1805.5.2.1

International Building Code 1805.5.2.2

International Building Code 1805.5.3

International Building Code 1805.5.4

Hollow masonry walls. At least 4 inches (102
mm) of solid masonry shall be provided at girder supports at
the top of hollow masonry unit foundation walls.

International Building Code 1805.5.5

International Building Code 1805.5.5.1

International Building Code 1805.5.5.2

International Building Code 1805.5.6

International Building Code 1805.5.7

International Building Code 1805.6

Foundation plate or sill bolting. Wood foundation
plates or sills shall be bolted or strapped to the foundation or
foundation wall as provided in Chapter 23.

International Building Code 1805.7

Designs employing lateral bearing. Designs to resist
both axial and lateral loads employing posts or poles as columns
embedded in earth or embedded in concrete footings in
the earth shall conform to the requirements of Sections
1805.7.1 through 1805.7.3.

Limitations. The design procedures outlined in
this section are subject to the following limitations:
1. The frictional resistance for structural walls and slabs
on silts and clays shall be limited to one-half of the
normal force imposed on the soil by the weight of the
footing or slab.
2. Posts embedded in earth shall not be used to provide
lateral support for structural or nonstructural materials
such as plaster, masonry or concrete unless bracing
is provided that develops the limited deflection
required.
Wood poles shall be treated in accordance with AWPA
U1 for sawn timber posts (Commodity Specification A, Use
Category 4B) and for round timber posts (Commodity
Specification B, Use Category 4B).

Design criteria. The depth to resist lateral loads
shall be determined by the design criteria established in Sections
1805.7.2.1 through 1805.7.2.3, or by other methods
approved by the building official.

Nonconstrained. The following formula
shall be used in determining the depth of embedment
required to resist lateral loads where no constraint is provided
at the ground surface, such as rigid floor or rigid
ground surface pavement, and where no lateral constraint
is provided above the ground surface, such as a
structural diaphragm.

Constrained. The following formula shall be
used to determine the depth of embedment required to
resist lateral loads where constraint is provided at the
ground surface, such as a rigid floor or pavement.

Vertical load. The resistance to vertical loads
shall be determined by the allowable soil-bearing pressure
set forth in Table 1804.2.

Backfill. The backfill in the annular space around
columns not embedded in poured footings shall be by one of
the following methods:
1. Backfill shall be of concrete with an ultimate strength
of 2,000 psi (13.8 MPa) at 28 days. The hole shall not
be less than 4 inches (102 mm) larger than the diameter
of the column at its bottom or 4 inches (102 mm)
larger than the diagonal dimension of a square or rectangular
column.
2. Backfill shall be of clean sand. The sand shall be thoroughly
compacted by tamping in layers not more than
8 inches (203 mm) in depth.
3. Backfill shall be of controlled low-strength material
(CLSM).

International Building Code 1805.7.1

International Building Code 1805.7.2

Vertical load. The resistance to vertical loads
shall be determined by the allowable soil-bearing pressure
set forth in Table 1804.2.

International Building Code 1805.7.2.1

International Building Code 1805.7.2.2

International Building Code 1805.7.2.3

Vertical load. The resistance to vertical loads
shall be determined by the allowable soil-bearing pressure
set forth in Table 1804.2.

International Building Code 1805.7.3

International Building Code 1805.8

Design for expansive soils. Footings or foundations for
buildings and structures founded on expansive soils shall be
designed in accordance with Section 1805.8.1 or 1805.8.2.
Footing or foundation design need not comply with Section
1805.8.1 or 1805.8.2 where the soil is removed in accordance
with Section 1805.8.3, nor where the building official approves
stabilization of the soil in accordance with Section 1805.8.4.

Foundations. Footings or foundations placed on
or within the active zone of expansive soils shall be designed
to resist differential volume changes and to prevent structural
damage to the supported structure. Deflection and
racking of the supported structure shall be limited to that
which will not interfere with the usability and serviceability
of the structure.
Foundations placed below where volume change occurs
or below expansive soil shall comply with the following
provisions:
1. Foundations extending into or penetrating expansive
soils shall be designed to prevent uplift of the supported
structure.
2. Foundations penetrating expansive soils shall be
designed to resist forces exerted on the foundation
due to soil volume changes or shall be isolated from
the expansive soil.

Slab-on-ground foundations. Moments, shears
and deflections for use in designing slab-on-ground, mat or
raft foundations on expansive soils shall be determined in
accordance with WRI/CRSI Design of Slab-on-Ground
Foundations or PTI Standard Requirements for Analysis of
Shallow Concrete Foundations on Expansive Soils. Using
the moments, shears and deflections determined above,
nonprestressed slabs-on-ground, mat or raft foundations on
expansive soils shall be designed in accordance with
WRI/CRSI Design of Slab-on-Ground Foundations and
post-tensioned slab-on-ground, mat or raft foundations on
expansive soils shall be designed in accordance with PTI
Standard Requirements for Design of Shallow
Post-Tensioned Concrete Foundations on Expansive Soils.
It shall be permitted to analyze and design such slabs by
other methods that account for soil-structure interaction, the
deformed shape of the soil support, the plate or stiffened
plate action of the slab as well as both center lift and edge lift
conditions. Such alternative methods shall be rational and
the basis for all aspects and parameters of the method shall
be available for peer review.

Removal of expansive soil. Where expansive soil
is removed in lieu of designing footings or foundations in
accordance with Section 1805.8.1 or 1805.8.2, the soil shall
be removed to a depth sufficient to ensure a constant moisture
content in the remaining soil. Fill material shall not contain
expansive soils and shall comply with Section 1803.5 or
1803.6.
Exception: Expansive soil need not be removed to the
depth of constant moisture, provided the confining pressure
in the expansive soil created by the fill and supported
structure exceeds the swell pressure.

Stabilization. Where the active zone of expansive
soils is stabilized in lieu of designing footings or foundations
in accordance with Section 1805.8.1 or 1805.8.2, the
soil shall be stabilized by chemical, dewatering,
presaturation or equivalent techniques.

International Building Code 1805.8.1

International Building Code 1805.8.2

International Building Code 1805.8.3

International Building Code 1805.8.4

International Building Code 1805.9

Seismic requirements. See Section 1908 for additional
requirements for footings and foundations of structures
assigned to Seismic Design Category C, D, E or F.
For structures assigned to Seismic Design Category D, E or
F, provisions of ACI 318, Sections 21.10.1 to 21.10.3, shall
apply when not in conflict with the provisions of Section 1805.
356 2006 INTERNATIONAL BUILDING CODE
SOILS AND FOUNDATIONS
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Concrete shall have a specified compressive strength of not less
than 3,000 psi (20.68 MPa) at 28 days.
Exceptions:
1. Group R or U occupancies of light-framed construction
and two stories or less in height are permitted
to use concrete with a specified
compressive strength of not less than 2,500 psi
(17.2 MPa) at 28 days.
2. Detached one- and two-family dwellings of
light-frame construction and two stories or less in
height are not required to comply with the provisions
of ACI 318, Sections 21.10.1 to 21.10.3.