CHAPTER 1 - GENERAL INFORMATION 100. APPLICATION 6. Chassis beams 10” deep for 12’ and 14’ nominal unit widths, and 12” 100-1. GENERAL. Manufactured homes, as deep for 16’ nominal unit width. addressed by this handbook, are manufactured in accordance with 24 CFR Chapter XX, Part 7. Roof slope varies from a minimum 3280, Manufactured Home Construction and 1/2:12 to a maximum 4.4:12 (20°). Safety Standards (MHCSS), and are sited on a permanent foundation in accordance with 8. Set on permanent foundation of Handbook 4145.1, REV-2, Change 1, Feb. 14, piers, or of continuous, cast-in- 1992, Architectural Processing and Inspections place concrete, concrete-block ma- for Home Mortgage Insurance, paragraph 3-4. sonry, all-weather wood, or other approved systems. A. Description of Manufactured Unit. Designs and approval for foundations in this 9. Double width units are assumed manual are based on the following assumptions connected to behave structurally as about the manufactured home: a single box. 1. Transportable in one or more sec- B. Chassis Removal. The chassis of a tions. manufactured home, under the Federal Manu- factured Housing and Construction safety 2. Between 11'-4" and 16'-0" in width Standards, is not permitted to be removed. Ac- in transport mode. cordingly, foundations in this manual are de- signed for manufactured homes that DO NOT 3. Minimum 400 sf. in area for a sin- HAVE THEIR CHASSIS REMOVED. gle section unit. C. Definition of Permanent Founda- 4. Exterior wall height of 7'-6" or 8'-0" tion. Permanent foundations must be con- from top of wall to foundation. structed of durable materials; i.e. concrete, mortared masonry, or treated wood - and be 5. Built on permanent chassis with site-built. It shall have attachment points to an- minimum distance between main chor and stabilize the manufactured home to chassis beams of: transfer all loads, herein defined, to the under- lying soil or rock. The permanent foundations Mfg. Home Width Beam Spacing shall be structurally developed in accordance 12' nom. 6'-3" with this document or be structurally designed 14' nom. 6'-10" by a licensed professional engineer for the fol- 16' nom. 8'-0" lowing: Note: Smaller beam spacing will require 1. Vertical stability: design by a professional engineer. 1 - 1 a. Rated anchorage capacity to Chassis: The structural system running prevent uplift and overturning beneath the manufactured home. Example: Pair due to wind or seismic forces, of steel beams. whichever controls. Screw-in soil anchors are not considered a Exterior Foundation Wall: Founda- permanent anchorage. tion walls placed directly below the exterior perimeter walls of the unit. These walls may, or b. Footing size to prevent over- may not, be structurally used as bearing walls loading the soil-bearing capacity under gravity loads, and/or used as shear walls and avoids soil settlement. under horizontal loads. If these walls are not Footing shall be reinforced con- used structurally they are called non-bearing crete to be considered perma- walls or skirt walls. nent. Exterior Piers: Piers inside the exte- c. Base of footing below maxi- rior walls, needed to support the chassis beams mum frost-penetration depth. nearest the longitudinal foundation walls. d. Encloses a basement of crawl Foundation Types: space with a continuous wall (whether bearing or non- Type C: Foundation system supported bearing) that separates the and anchored at chassis only, to equally spaced basement of crawl space from piers. the backfill, and keeps out ver- min and water. Type E: Foundation system supported at chassis and exterior wall but anchored for 2. Lateral stability. Rated anchorage uplift and overturning at exterior wall only. capacity to prevent sliding due to wind or seismic forces, whichever Type I: Foundation system supported controls, in the transverse and lon- at chassis and exterior wall but anchored for gitudinal directions. uplift and overturning at exterior piers only. 100-2. DEFINITIONS. These are terms Interior Piers: Piers nearest the mar- used throughout the Handbook and the Design riage wall and supporting the chassis in multi- Worksheet. Additional terms are used in Ap- section units. pendix D, where the derivation of equations is shown. These terms are defined in Appen- Longitudinal Foundation Walls: Two dix D, and illustrated in Figure 6-2. walls beneath the long dimension of the unit (in its transport mode) which are structurally Anchorage: Connection between su- used as foundation shear walls that resist ap- perstructure and foundation, by means of plied wind or seismic forces from the super- welds, bolts, and various light gage metal structure’s shear walls in the longitudinal di- plates. Anchorage does not refer to any type of rection. soil anchor. 1 - 2 Longitudinal Direction: Direction of horizontal wind or seismic forces applied par- allel to long dimension of unit. See Figure 1-1. 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. Marriage Wall Piers: Piers placed be- neath a continuous marriage wall in multi- Figure 1 - 1 section homes are assumed to be equally spaced. Piers are also placed at the ends of Av: Vertical anchorage force require- openings, beneath the posts that transfer con- ment for the unit; (Pier load in lbs. or wall load centrated loads from the roof. in lbs./LF). Example; Anchorage force to pre- vent uplift and overturning in the transverse Superstructure Shear walls: Vertical direction of applied wind or seismic forces. elements (usually walls) of the superstructure’s lateral load resistance system. These vertical Ah: Horizontal anchorage force re- elements structurally transfer horizontal wind quirement (lbs./ft.). Example; Anchorage force or seimsic forces, applied to the roof and floor to keep unit from sliding in the transverse and planes of the unit, to the foundation system. longitudinal directions of applied wind or seismic forces. Transverse Foundation Walls: Walls across the short dimension of the unit which Aftg: Foundation footing size for the are structurally designed to function as founda- isolated unit pier spread footing area (sq. ft.) & tion shear walls that resist horizontal applied continuous wall footing width (ft.). wind or seismic forces from the superstruc- ture’s shear walls in the transverse direction. hn: The height of the manufactured unit exterior wall. Transverse Direction: Direction of horizontal wind or seismic forces applied per- hp: The depth at which a pier footing pendicular to long dimension of unit. See Fig- must be placed to prevent it from pulling out of ure 1-1. the soil (ft.). Aa: The seismic coefficient represent- hw: The depth at which a continuous ing the effective peak acceleration as deter- foundation wall must be placed to prevent it mined by the seismic map 1. from pulling out of the soil (ft.). Av: The seismic coefficient represent- L: Length of manufactured home (ft.). ing the effective peak velocity-related accelera- tion as determined by the seismic map 2. W: Actual self (dead load) weight of the unit (lbs.). 1 - 3 w: The distributed weight of the unit existing anchorages and footings shall meet the (lbs./ft). W/L = w; therefore weight per foot of intent of the definition of permanent foundation length. stated herein. Wt: Actual measured width of the unit 101-3. RESPONSIBILITY. This handbook (ft.) between superstructure walls, excluding does not relieve the installer of responsibility roof projections. A single-section unit has one for compliance with local ordinances, codes, width measurement (Wt). A double-section and regulations established by authorities hav- unit is composed of 2 single-section widths ing jurisdiction. (2Wt). 101-4. OTHER FOUNDATION DESIGNS. 100-3. LICENSED PROFESSIONALS. Manufacturers of home designs not covered by Those using this handbook are referred to using this handbook or recommending a foundation licensed professionals when design considera- system not included in this handbook shall tions require additional information or when a submit drawings and structural calculations particular site, foundation system, or super- prepared and sealed by a licensed professional structure (manufactured home) falls outside the to the owner. design assumptions and parameters of the handbook. As used herein, the term Geotech- 102. REFERENCED STANDARDS nical Engineer is a professional engineer regis- tered under the appropriate laws of the State to 102-1. CODES GOVERNING SUBSUR- practice in the field of Geotechnical Engineer- FACE INVESTIGATION ing. The term Structural Engineer is a profes- sional or structural engineer registered under A. HUD Minimum Property Standards the appropriate laws of the State to practice in for Housing 1994 Ed. Handbook 4910.1; Fi- the field of Structural Engineering . And the nal Rule-24 CFR Part 200.926 contain provi- term Architect is a professional architect regis- sions that apply to permanent foundation in- tered under the appropriate laws of the State to stallations recommended in this handbook. practice Architecture. B. Engineering Report. If adverse site 101. LOCAL CODES AND STAN- conditions are discovered, specific recommen- dations by a Geotechnical Engineer shall be DARDS included with the Design Worksheet (Appen- 101-1. NEW CONSTRUCTION. This dix F). handbook has been developed for use at all 102-2. CODES GOVERNING BUILD- new permanent manufactured home sites, INGS AND SITES communities, and set-ups. A. Seismic, Wind and Snow Loads for 101-2. EXISTING CONSTRUCTION. The each type of structure were computed based on practices recommended in the Handbook are ASCE 7-93: Minimum Design Loads for Build- not intended to be applied retroactively to ex- ings and Other Structures. Minimum wind and isting sites unless the authority in the jurisdic- minimum roof live load were based on MPS tion considers such application essential for safety and health of occupants.