CHAPTER 1 - GENERAL INFORMATION

**100. APPLICATION**

**100-1. GENERAL.** Manufactured homes, as addressed by this handbook,
are manufactured in accordance with 24 CFR Chapter XX, Part 3280,
*Manufactured Home Construction and Safety Standards* (MHCSS), and are
sited on a permanent foundation in accordance with *Handbook 4145.1,
REV-2, Change 1, Feb. 14, 1992*, Architectural Processing and
Inspections for Home Mortgage Insurance, paragraph 3-4.

**A. Description of Manufactured Unit.** Designs and approval for
foundations in this manual are based on the following assumptions about
the manufactured home:

1\. Transportable in one or more sections.

2\. Between 11\'-4\" and 16\'-0\" in width in transport mode.

3\. Minimum 400 sf. in area for a single section unit.

4\. Exterior wall height of 7\'-6\" or 8\'-0\" from top of wall to
foundation.

5\. Built on permanent chassis with minimum distance between main
chassis beams of:

  --------------------------------------- -------------------------------
  Mfg. Home Width                         Beam Spacing

  12\' nom.                               6\'-3\"

  14\' nom.                               6\'-10\"

  16\' nom.                               8\'-0\"
  --------------------------------------- -------------------------------

**Note**: Smaller beam spacing will require design by a professional
engineer.

6\. Chassis beams 10" deep for 12' and 14' nominal unit widths, and 12"
deep for 16' nominal unit width.

7\. Roof slope varies from a minimum 1/2:12 to a maximum 4.4:12 (20°).

8\. Set on permanent foundation of piers, or of continuous,
cast-in-place concrete, concrete-block masonry, all-weather wood, or
other approved systems.

9\. Double width units are assumed connected to behave structurally as a
single box.

**B. Chassis Removal.** The chassis of a manufactured home, under the
*Federal Manufactured Housing and Construction safety Standards*, is not
permitted to be removed. Accordingly, foundations in this manual are
designed for manufactured homes that DO NOT HAVE THEIR CHASSIS REMOVED.

**C. Definition of Permanent Foundation.** Permanent foundations must be
constructed of durable materials; i.e. concrete, mortared masonry, or
treated wood - and be site-built. It shall have attachment points to
anchor and stabilize the manufactured home to transfer all loads, herein
defined, to the underlying soil or rock. The permanent foundations shall
be structurally developed in accordance with this document or be
structurally designed by a licensed professional engineer for the
following:

1\. Vertical stability:

a\. Rated anchorage capacity to prevent uplift and overturning due to
wind or seismic forces, whichever controls. Screw-in soil anchors are
[not]{.underline} considered a permanent anchorage.

b\. Footing size to prevent overloading the soil-bearing capacity and
avoids soil settlement. Footing shall be reinforced concrete to be
considered permanent.

c\. Base of footing below maximum frost-penetration depth.

d\. Encloses a basement of crawl space with a continuous wall (whether
bearing or non-bearing) that separates the basement of crawl space from
the backfill, and keeps out vermin and water.

2\. Lateral stability. Rated anchorage capacity to prevent sliding due
to wind or seismic forces, whichever controls, in the transverse and
longitudinal directions.

**100-2. DEFINITIONS.** These are terms used throughout the Handbook and
the Design Worksheet. Additional terms are used in Appendix D, where the
derivation of equations is shown. These terms are defined in Appendix D,
and illustrated in Figure 6-2.

::: Definition
***Anchorage:*** Connection between superstructure and foundation, by
means of welds, bolts, and various light gage metal plates. Anchorage
does not refer to any type of soil anchor.
:::

::: Definition
***Chassis:*** The structural system running beneath the manufactured
home. Example: Pair of steel beams.
:::

::: Definition
***Exterior Foundation Wall:*** Foundation walls placed directly below
the exterior perimeter walls of the unit. These walls may, or may not,
be structurally used as bearing walls under gravity loads, and/or used
as shear walls under horizontal loads. If these walls are not used
structurally they are called non-bearing walls or skirt walls.
:::

::: Definition
***Exterior Piers:*** Piers inside the exterior walls, needed to support
the chassis beams nearest the longitudinal foundation walls.
:::

::: Definition
***Foundation Types:***
:::

::: Definition
***Type C:*** Foundation system supported and anchored at chassis only,
to equally spaced piers.
:::

::: Definition
***Type E:*** Foundation system supported at chassis and exterior wall
but anchored for uplift and overturning at exterior wall only.
:::

::: Definition
***Type I:*** Foundation system supported at chassis and exterior wall
but anchored for uplift and overturning at exterior piers only.
:::

::: Definition
***Interior Piers:*** Piers nearest the marriage wall and supporting the
chassis in multi-section units.
:::

::: Definition
***Longitudinal Foundation Walls:*** Two walls beneath the long
dimension of the unit (in its transport mode) which are structurally
used as foundation shear walls that resist applied wind or seismic
forces from the superstructure's shear walls in the longitudinal
direction.
:::

::: Definition
***Longitudinal Direction:*** Direction of horizontal wind or seismic
forces applied parallel to long dimension of unit. See Figure 1-1.
:::

::: Definition
***Marriage Wall:*** The wall where two single-section units are
structurally joined to form a multi-section unit. The marriage wall may
contain openings that permit interior spaces to expand to two units
wide.
:::

::: Definition
***Marriage Wall Piers:*** Piers placed beneath a continuous marriage
wall in multi-section homes are assumed to be equally spaced. Piers are
also placed at the ends of openings, beneath the posts that transfer
concentrated loads from the roof.
:::

::: Definition
***Superstructure Shear walls**:* Vertical elements (usually walls) of
the superstructure's lateral load resistance system. These vertical
elements structurally transfer horizontal wind or seimsic forces,
applied to the roof and floor planes of the unit, to the foundation
system.
:::

::: Definition
***Transverse Foundation Walls:*** Walls across the short dimension of
the unit which are structurally designed to function as foundation shear
walls that resist horizontal applied wind or seismic forces from the
superstructure's shear walls in the transverse direction.
:::

::: Definition
***Transverse Direction:*** Direction of horizontal wind or seismic
forces applied perpendicular to long dimension of unit. See Figure 1-1.
:::

::: Definition
***[Aa]{.underline}:*** The seismic coefficient representing the
effective peak acceleration as determined by the seismic map 1.
:::

::: Definition
***[Av]{.underline}:*** The seismic coefficient representing the
effective peak velocity-related acceleration as determined by the
seismic map 2.
:::

![](media/image1.emf)

Figure 1 -

::: Definition
***Av:*** Vertical anchorage force requirement for the unit; (Pier load
in lbs. or wall load in lbs./LF). Example; Anchorage force to prevent
uplift and overturning in the transverse direction of applied wind or
seismic forces.
:::

::: Definition
***Ah:*** Horizontal anchorage force requirement (lbs./ft.). Example;
Anchorage force to keep unit from sliding in the transverse and
longitudinal directions of applied wind or seismic forces.
:::

::: Definition
***Aftg:*** Foundation footing size for the isolated unit pier spread
footing area (sq. ft.) & continuous wall footing width (ft.).
:::

::: Definition
***hn:*** The height of the manufactured unit exterior wall.
:::

::: Definition
***hp:*** The depth at which a pier footing must be placed to prevent it
from pulling out of the soil (ft.).
:::

::: Definition
***hw:*** The depth at which a continuous foundation wall must be placed
to prevent it from pulling out of the soil (ft.).
:::

::: Definition
***L:*** Length of manufactured home (ft.).
:::

::: Definition
***W:*** Actual self (dead load) weight of the unit (lbs.).
:::

::: Definition
***w:*** The distributed weight of the unit (lbs./ft). W/L = w;
therefore weight per foot of length.
:::

::: Definition
***Wt:*** Actual measured width of the unit (ft.) between superstructure
walls, excluding roof projections. A single-section unit has one width
measurement (Wt). A double-section unit is composed of 2 single-section
widths (2Wt).
:::

**100-3. LICENSED PROFESSIONALS.** Those using this handbook are
referred to using licensed professionals when design considerations
require additional information or when a particular site, foundation
system, or superstructure (manufactured home) falls outside the design
assumptions and parameters of the handbook. As used herein, the term
Geotechnical Engineer is a professional engineer registered under the
appropriate laws of the State to practice in the field of Geotechnical
Engineering. The term Structural Engineer is a professional or
structural engineer registered under the appropriate laws of the State
to practice in the field of Structural Engineering . And the term
Architect is a professional architect registered under the appropriate
laws of the State to practice Architecture.

**101. LOCAL CODES AND STANDARDS**

**101-1. NEW CONSTRUCTION.** This handbook has been developed for use at
all new permanent manufactured home sites, communities, and set-ups.

**101-2. EXISTING CONSTRUCTION.** The practices recommended in the
Handbook are not intended to be applied retroactively to existing sites
unless the authority in the jurisdiction considers such application
essential for safety and health of occupants. Upgrade of existing
anchorages and footings shall meet the intent of the definition of
permanent foundation stated herein.

**101-3. RESPONSIBILITY.** This handbook does not relieve the installer
of responsibility for compliance with local ordinances, codes, and
regulations established by authorities having jurisdiction.

**101-4. OTHER FOUNDATION DESIGNS.** Manufacturers of home designs not
covered by this handbook or recommending a foundation system not
included in this handbook shall submit drawings and structural
calculations prepared and sealed by a licensed professional to the
owner.

**102. REFERENCED STANDARDS**

**102-1. CODES GOVERNING SUBSURFACE INVESTIGATION**

**A. HUD *Minimum Property Standards for Housing 1994 Ed.* Handbook
4910.1;** Final Rule-24 CFR Part 200.926 contain provisions that apply
to permanent foundation installations recommended in this handbook.

**B. Engineering Report.** If adverse site conditions are discovered,
specific recommendations by a Geotechnical Engineer shall be included
with the Design Worksheet (Appendix F).

**102-2. CODES GOVERNING BUILDINGS AND SITES**

**A. Seismic, Wind and Snow Loads** for each type of structure were
computed based on ASCE 7-93: *Minimum Design Loads for Buildings and
Other Structures*. Minimum wind and minimum roof live load were based on
*MPS* HUD Document 4910.1, Appendix K, art. 200.926e (a) & (c).

**B. Grading, Drainage and Fill.** The HUD *Land-Planning Data Sheet*s
(79g), Handbooks 4140.3 and 4145.1, should be used for grading, drainage
and fill specifications.

**C. Manufactured Homes on Elevated Foundations** should follow
standards in *Manufactured Home Installation in Flood Hazard Areas, FEMA
85/September 1985*.

**D. Additions to CABO *One and Two Family Dwelling Code, 1992 Ed*.
(including 1993 Amendments)** that apply to construction in this manual
are found in CABO, Appendix C \-- Section C‑101, C‑102, C‑201, C‑301,
C‑302, C‑303, C‑304, C‑305, C‑306, C‑307, C‑401, C‑501, C‑502, C‑503,
C‑504, C‑505, C‑506, C‑507, C‑600, C‑601, C‑602, C‑603, C‑604, C‑605.

**E. Rural Housing Service (RHS) Formerly Rural Housing and Community
Development Service, formerly Farmers Home Administration (FmHA).**
Provisions for the approval of direct loans for manufactured homes on
permanent foundations are contained in Subpart A of Part 1944: Section
502 Rural Housing Loan Policies and Authorizations and for guaranteed
loans in Subpart D of Part 1980: Rural Housing Loans. The provisions for
acceptable site development, installation and set-up are contained in
Subpart A of Part 1924 Exhibit J: Manufactured Home Sites, Rental
Projects and Subdivisions. These Agency instructions are available in
any RHS field office.

**F. Superstructure HUD Code *- Federal Manufactured Home Construction
and Safety Standards Oct. 25, 1994*.** The structural design of the
superstructure of the manufactured home has been assumed to be in
conformance with HUD Code Section 3280.305 and .306 (a)(2) which
anticipates the manufactured unit to make provision for the support and
anchoring system forces required by this document.

**103. GENERAL PROCEDURE**

**103-1. SUBMISSIONS.** Three worksheets must be filled out before
evaluation of the foundation system can begin, the \"Owner's Site
Acceptability Worksheet and Manufacturer\'s Worksheet\" in Appendix E,
and the \"Design Worksheet\" in Appendix F. Refer to Table i - 1 in the
Introductory Comments, which indicates requirements and submissions.

**103-2. BEGINNING THE APPROVAL PROCESS.** If the worksheets in
Appendices E and F have been filled out, the approval process can begin.
See Chapter 2, \"Site Acceptability Criteria\" and the Design Worksheet,
Appendix F. Persons using the handbook should fill out the Design
Worksheets while progressing through the chapters in the Handbook.
Questions on the Design Worksheet are tied to sections of the Handbook
and the section numbers are noted on the Worksheet.