APPENDIX D\
DERIVATION OF FOUNDATION DESIGN

**D-100. CONDITIONS AFFECTING DESIGN.** Values for the Foundation Design
Load Tables have been derived based on major foundation design factors,
foundation design criteria, and design assumptions.

**D-100.1 MAJOR FOUNDATION DESIGN FACTORS** determine the
appropriateness of foundations for manufactured homes:

**A. Soil and site conditions.**

1\. Soil types

2\. Bearing capacities

3\. Drainage

4\. Slopes

**B. Load Conditions and Combinations.** Various combinations of (1)
through (5) with appropriate factors:

1\. Dead loads

2\. Occupancy live loads

3\. Wind loads

4\. Snow loads / Minimum roof live loads

5\. Seismic loads

**C. Foundation Design and Capacity.**

1\. Footing depth

2\. Footing size

3\. Reinforcing

4\. Materials

**D. Connection Compatibility with Manufactured Home.** Adequate
capacity plus a safety factor is required to transfer forces from the
manufactured house to the foundation without failure.

**D-100.2 CRITERIA FOR FOUNDATION DESIGN** for manufactured homes must
meet the following:

**A. Assumptions** made in foundation system design must be compatible
with the design of the housing unit and actual site conditions.

**B. Stress Limitations.** The design must sustain all loads within
stress limitations of connection systems.

**C. Acceptable Foundation Design** must provide for the Permanent
Foundation criteria as specified in Section 100-1.C.

**D-100.3 DESIGN ASSUMPTIONS**

**A. Values Included In Appendix B & C.** The foundation tables in
Appendices B & C are based on a number of design assumptions:

1\. Building width is discussed in terms of minimum chassis beam spacing
in Chapter 1: 100-1.A.5 and again in Chapter 6: 600-2.A.1. for
comparison of nominal and range of actual width, and then is illustrated
in Figure 6-1. It is clear that many actual widths are possible. The
following actual widths and projections (dc) were used in the Tables of
Appendix B:

+------------------+---------------------------+----------------------+
| Wt               | Wt                        | dc                   |
|                  |                           |                      |
| (nominal)        | (actual)                  |                      |
+------------------+---------------------------+----------------------+
| 12'              | 11'-8"(11.67')            | 32.25"(2.69')        |
+------------------+---------------------------+----------------------+
| 14'              | 13'-8"(13.67')            | 41"(3.42')           |
+------------------+---------------------------+----------------------+
| 16'              | 15'-6"(15.5')             | 45.25"(3.77')        |
+------------------+---------------------------+----------------------+

2\. The Overturning (Av) and Sliding (Ah) Tables in Appendix B assume
hn=8.0 feet and assume a chassis beam depth of 10" (0.833 ft).

3\. The manufactured home is located on a flat, open site with no
protection from the wind.

4\. Wind force on the manufactured home, instead of seismic force, is
the controlling factor for the foundation overturning anchorage design
in the transverse direction. Seismic forces or wind force may control
sliding anchorage in the transverse or longitudinal direction.

5\. Uplift, overturning, and sliding caused by wind or seismic forces
acting on the manufactured home are transferred to the foundation by the
structural integrity of the manufactured home.

6\. The manufactured home unit, single or multi-width, is assumed to be
a box with flexible floor and roof diaphragms. End walls and selected
interior shear walls were assumed to transfer lateral forces based on
tributary area methodology. The unit's shear wall locations must closely
coincide with the foundation shear walls or vertical X-bracing planes. A
structural engineer shall design the system if deviations from these
assumptions exist.

7\. Multi-section units are assumed to be connected at the marriage wall
to act as a single box for overturning consideration, and do not act
separately as illustrated in Figure D‑1. This is particularly necessary
in high seismic locations.

**B. List of Variables.** These variables are used throughout Appendix
D.

**[Aa]{.underline}** Seismic coefficient representing effective peak
acceleration

**Ah** Required horizontal anchorage (lbs. or lbs./LF)

**Av** Required vertical anchorage (lbs. or lbs./LF)

**[Av]{.underline}** Seismic coefficient representing effective peak
velocity related acceleration

**Ce** Exposure factor (See ASCE 7‑93)

**Ct** Thermal factor (See ASCE 7‑93)

**Cp** External wall or roof pressure coefficient (See ASCE 7‑93)

**Cs** Roof slope factor (See ASCE 7‑93)

**[Cs]{.underline}** Seismic design coefficient (See ASCE 7‑93)

**dc** Distance from perimeter of structure to chassis beam line.

**DL** Total dead load of structure for each foot of length

**Fr** Force resisting sliding

**Fsl** Sliding force (lbs.)

**GCpi** Internal wall or ceiling pressure coefficient (See ASCE 7‑93)

**Gh** Gust response factor (See ASCE 7‑93)

**hn** Height of the exterior wall acted on by lateral wind pressure

**I** Importance factor (See ASCE 7‑93)

**Kz** Velocity pressure exposure coefficient (See ASCE 7‑93)

**LL** Live load

**Mo** Overturning moment of structure

**Mr** Moment resisting overturning

**p** Design wind pressure

**Pf** Design roof snow load (See ASCE 7‑93)

**Pg** Ground snow load (See ASCE 7‑93)

**Sp** or Spacing: Spacing of foundation elements in the longitudinal
direction.

**V** Basic wind speed (See ASCE 7‑93)

**Wt** Width of structure (or 1/2 the total width of a multi-section
unit)

**D-200. LOAD CONDITIONS INCLUDED IN FOUNDATION DESIGN.** The following
load conditions have been used as assumptions in design of the
foundation systems in this handbook. This information is important for
engineers who may be designing connection details or modifying
foundations designs. All Design Loads are based on ASCE 7‑93, except as
noted otherwise.

**D-200.1 DEAD LOAD DESIGN FACTORS.** Dead loads consist of the material
weight of the manufactured home without furnishings or occupants. Dead
load includes the weight of the roof, floor, walls, and chassis, and may
include permanent attachments such as cabinets and attached appliances.

**A. Dead Load Categories.** Dead loads were grouped into two
categories: heavy and light. The heaviest combinations of dead loads
were used for the computation of footing areas, and the determination of
inertia forces for the computation of sliding and overturning due to
seismic activity. Heavier loads generate the largest inertia forces and
produce the largest footings. The lightest combinations of dead loads
were used for the computation of horizontal and vertical anchorage due
to wind. Lighter loads offer less resistance to overturning and sliding
and thus require greater anchorage. The following dead loads in Table
D‑1 have been included in the calculations for the

Foundation Design Load Tables on the next page.

**B. Dead Load Equations** for use in computing the required vertical
and horizontal anchorage to resist overturning and sliding are listed
below by type. The equations are for the total Dead Load per foot of
Manufactured Home length. Figure D‑2 illustrates the individual
component loads and the total dead load situated at the geometric
centroid of the unit.

**Lightest combination of loads:**

SINGLE-SECTION TYPES C, E, & I

DL = (34.5)2 + (6 + 8.6)Wt + 9 × 2\
(walls)+(floor+roof)+(chassis beams)

> DL = 87 + (14.6)Wt

MULTI-SECTION TYPES C, E, & I

DL = (34.5)2 + (26.25)2 +\
2(6 + 8.6)Wt + 9 × 4\
(ext. walls) + (marriage wall) +\
(floor + roof) + (chassis beams)

> DL = 157.5 + (29.2)Wt

**Heaviest combination of loads:**

SINGLE-SECTION TYPES C, E, & I

DL = (44.25)2 + (13 + 9.7)Wt + 9 × 2\
(walls) + (floor + roof) +\
(chassis beams)

> DL = 106.5 + (22.7)Wt

MULTI-SECTION TYPES C, E, & I

DL = (44.25)2 + (26.25)2 +\
2(13 + 9.7)Wt + 9 × 4\
(ext. walls) + (marriage wall) +\
(floor + roof) + (chassis beams)

> DL = 177 + (45.4)Wt

  ------------ ---------------- ---------- ---------- ----------- -----------
  TABLE D-1\                                                      
  DEAD LOAD ON                                                    
  FOUNDATION                                                      

  LOCATION     ITEM             HEAVY\     LIGHT\     HEAVY\      LIGHT\
                                (psf)      (psf)      (plf of     (plf of
                                                      length)     length)

  EXTERIOR     7/16\" siding    1.4                               

  WALL         .019 aluminum               0.1                    

               2 x 4 studs @    1.5        1.5                    
               16\"o.c.                                           

               3 1/2\"          1.0        1.0                    
               fiberglass                                         
               insulation                                         

               1/2\" gypsum     2.0        2.0                    

               **SUM =**        **5.9**    **4.6**                

  **TOTAL**    **7\'-6\" WALL**                       **44.25**   **34.5**

  FLOOR        carpet & pad     1.0                               

               1/16" vinyl                 0.7                    

               5/8\" plywood    1.7        1.7                    

               2 x 10 joist @   2.6                               
               16\"o.c.                                           

               2 x 6 joist @               1.4                    
               16\"o.c.                                           

               11\" fiberglass  2.2                               
               insulation                                         

               5 1/2\"                     1.2                    
               fiberglass                                         
               insulation                                         

               mechanical       2.0        1.0                    

               misc. partitions 3.5        0.0                    

               **SUM =**        **13.0     **6.0 \*** **13 × Wt + **6 × Wt +
                                \***                  9**         9**

               \* plus 9 plf                                      
               for each                                           
               manufactured                                       
               home beam                                          

  ROOF         asphalt shingles 2.5                               
               with felt                                          

               3/8\" plywood    1.1                               

               20 ga. steel                2.5                    

               2 x 3 truss      1.5        1.5                    

               9 1/2\"          2.6        2.6                    
               fiberglass                                         
               insulation                                         

               1/2\" gypsum     2.0        2.0                    
               ceiling                                            

               **SUM =**        **9.7**    **8.6**    **9.7 ×     **8.6 ×
                                                      Wt**        Wt**

  MARRIAGE     2x4 studs @ 16\" 1.5        1.5                    

  WALL         1/2\" gypsum     2.0        2.0                    
               (one side)                                         

               **SUM =**        **3.5**    **3.5**                

  **TOTAL**    **7\'-6\" WALL**                       **26.25**   **26.25**
  ------------ ---------------- ---------- ---------- ----------- -----------

**D-200.2 LIVE LOAD DESIGN FACTORS**

**A. Description.** Design live loads consist of the weight of all
moving and variable loads (from use and occupancy) that may act on the
manufactured home including loads on floors, operational loads on roofs
and ceilings, or snow loads, but do not include wind, earthquake or dead
loads. All live loads are assumed to be uniformly distributed and roof
live loads are horizontally projected on sloped surfaces. The design
live loads specified herein for the floor and attic are the minimums
recommended by the ASCE standard. The design live loads specified herein
for the roof are the minimum recommended by the *Minimum Property
Standard*, HUD Handbook 4910.1, 1994 Edition. The roof live load used
for the design of the foundation system should be the greater of the
appropriate value indicated in the Data Plate shown here or as obtained
from the ASCE 7-93 for snow load.

**B. Design Assumptions.** The following values for live loads were used
in the engineering calculations and are included in the tables. They are
provided here as background information only. The field inspector will
not need to calculate live loads under normal circumstances. See box of
live loads.

**D-200.3 SNOW LOAD DESIGN FACTORS**

**A. Ground Snow Load.** The ground snow load values (Pg) to be used in
the design of the manufactured home are found in Appendix H. The ground
snow load is converted to a roof snow load to account for wind and
thermal factors (see Figure D‑3). The value (Pg) modified by snow load
design factors has been included in the derived values for the
Foundation Design Load Tables. The following assumptions were made to
find Pf, the horizontally projected uniformly distributed design roof
snow load:

**B. Design Assumptions.**

Basic Snow Load Equation:\
Pf = 0.7 × Ce × Ct × I × Pg

Where:

1\. Ground snow load (Pg) from the Ground Snow Load maps on pages H‑11,
H‑12 and H‑13.

2\. Importance factor I = 1.0 (residential buildings)

3\. Exposure factor Ce = 1.0 (locations where snow removal cannot be
relied on to reduce snow loads)

4\. Thermal factor Ct = 1.0 (heated structures)

5\. Slope factor Cs = 1.0 (4/12 slope or less)

6\. Flat roof factor = 0.7 (contiguous U.S.; Use 0.6 in Alaska.)

Therefore, the Required Effective Footing Area Tables are based on:

Pf = 0.7 × Pg (Roof snow load)

**C. Drifted Snow.** At locations where the manufactured home is
adjacent to a higher structure, drifted snow loads MUST be calculated in
accordance with ASCE 7‑93. An average value including the drifted load
may be used with the Foundation Design Load Tables.

**D-200.4 WIND LOAD DESIGN FACTORS.**

**A. Model for Analysis.** The methodology for resistance of the box to
uplift, overturning and sliding utilizes equations for Main Wind-Force
Resisting Systems as defined in ASCE 7‑93.

**B. Basic Wind Speed.** The basic wind speed map is found on page H‑14.
Wind factors have been included in the derived values for the Foundation
Design Load Tables of Appendix B.

**C. Design Assumptions.**

1\. To convert mile per hour (MPH) wind speed to a basic wind velocity
pressure (q) in pounds per square feet (psf) use the following equation
from ASCE 7‑93:

q = 0.00256 × Kz × (V x I )^2^

where:

a\. Mean roof height is assumed to be less than or equal to 15 feet from
grade.

b\. Basic Wind Speed (V) is from the isobar map on page H‑14 for the
unit's geographic location.

c\. Velocity Pressure Coefficient (Kz) is based on Exposure C: open
terrain with scattered obstructions having heights generally less than
30 feet. This Category includes flat open country and grasslands. For
these conditions, including item (a) above, Kz = 0.8.

d\. Importance Category I (residential) for inland sites, sets I = 1.0,
while for coastal sites (hurricane oceanline) I = 1.05. Linear
interpolation can be utilized for sites between the oceanline and 100
miles inland; however, this was not done for the tables of Appendix B.
Thus, only the above two values have been included.

2\. Velocity pressure (q) is applied to surfaces, i.e. walls and roof
planes, to generate design wind pressures (p) for Main Wind-Force
Resisting Systems. Design wind pressures (p) are based on external and
internal effects utilizing the following equation from ASCE 7‑93:

p = q × Gh × Cp - q × (± GCpi)

> (external) - (internal)

where:

a\. The Gust Response Factor (Gh) is assumed to be based on Exposure C
(see section D‑200.4.C.1.c). The Minimum Property Standard (MPS) permits
use of Exposure C regardless of whether the site is inland or coastal.
Thus, for units of assumed mean height less than or equal to 15 feet, Gh
= 1.32.

b\. External Roof and Wall Pressure Coefficients (Cp) vary on the
windward roof surface based on the structural issue being analyzed.
Figure D‑4 illustrates the various (Cp) values for the transverse and
longitudinal directions. A roof slope of 10 to 15 degrees ( 2 in 12 to 3
in 12) produces 2 possible situations: (+0.2) pressure and (‑0.9)
suction. The value (‑0.9) was selected to produce maximum suction for
uplift and overturning while (+0.2) was selected to maximize sliding.
Note that (+) means pressure on the external surface, while (‑) means
suction on the external surface. For the leeward wall in the
longitudinal direction the proportions of the unit (L/Wt) are important
to establishing the proper exterior (Cp) value. Single-section units,
regardless of the combination of width or length, has a ratio L/Wt ≥
4.0; therefore, Cp = -0.2. For multi-section units An average proportion
of unit (28' x 70', or 32' x 80') was assumed. Thus, the L/Wt ratio was
2.5 and by interpolation Cp = -0.275. Single or multi-section units have
a Wt/L ratio, which is ≤ 1.0 for all proportions of units. Thus, the
leeward value for Cp = -0.5 in the transverse direction.

c\. Internal Roof and Wall Pressure Coefficients assume a uniform
distribution of openings on all surfaces, thus GCpi = ±0.25. Figure D‑5
illustrates the pressures and suctions used for various structural
considerations. Note that the walls receive offsetting values that
cancel any internal effect; therefore, only the roof (GCpi) values are
utilized for the calculation of overturning and sliding in the
transverse direction. Internal roof Pressures are not utilized in the
longitudinal direction.

d\. Wind pressures and suctions are typically treated as uniformly
distributed and typically applied perpendicular to the orientation of
any planar surface. This usually requires the calculation of horizontal
and vertical components when wind is applied to sloping surfaces, in
this case only roof planes. Figure D‑6 illustrates that by the use of
trigonometry the resultant force (P) on any sloping surface has
components (P~V~) and (P~H~), which can be arrived at as shown. Note
that for the vertical components (P~V~) it is possible to merely
multiply the pressure (p) by the horizontal length of the slope (Wt/2)
for single section units or by (Wt) for multi-section units. This
approach simplifies the sample calculations provided in section D‑300
for uplift, overturning and sliding in the transverse direction.

**D-200.5 SEISMIC LOAD FACTORS.**

**A. Seismic Versus Wind Forces.** It has been stated in Chapters 4 and
6 that seismic forces did not control over wind forces in the
computations for consideration of overturning in the transverse
direction; however, seismic forces did sometimes control over wind for
certain situations of sliding in the transverse and longitudinal
direction. This is particularly true in the longitudinal direction
because only the end wall elevations are exposed to the wind, producing
small applied horizontal forces. Seismic inertia forces are a function
of mass that is the same in both directions, which may be larger than
the wind forces in particular when the geographic region is also a high
snow region.

**B. Dead Loads.** The model assumes use of the "heavy" dead load values
for roof, floor and wall components from Table D‑1. It is assumed that
the weight of the exterior walls and the weight of the marriage wall
(for multi-section units only) are distributed half to the roof plane
and half to the floor plane. The marriage wall was assumed continuous,
without any large openings to maximize the dead load. This distribution
of the dead load is illustrated in Figure D‑7 to arrive at inertia
forces (Fxr) and (Fxf). The weight of the end walls was included in the
total mass of the unit and distributed to the roof and floor as shown in
Figure D-7 and defined by the equations below:

1\. Areas at each end of a Single-Section unit:

$A_{r} = \frac{\text{Wt}´a}{2} + \frac{\text{hn}}{2}´\text{Wt}$

$A_{f} = \text{Wt}´\frac{\text{hn}}{2}$

2\. Areas at each end of a Multi-Section unit:

$A_{r} = \text{Wt}´a + 2´\text{Wt}´\frac{\text{hn}}{2}$

$A_{f} = 2´\text{Wt}´\frac{\text{hn}}{2}$

3\. These areas are multiplied by the heavy wall weight of 5.9 psf
resulting in total roof and floor load additions respectively for Single
or Multi-Section units as follows:

$W_{\text{endroof}} = 2´5\text{.}9´A_{r}$

$W_{\text{endfloor}} = 2´5\text{.}9´A_{f}$

The above loads are in pounds and are smeared into the unit's dead load
for overturning by using an average length of 60 feet, while for sliding
they are smeared into the unit's dead load by dividing by "L". See
Section D‑200.5.E.7.a for further clarification.

**C. Snow Loads.** When the flat roof snow load (Pf) is less than 30
psf, the snow load to be attributed to the mass at the roof plane shall
be zero. Where siting and snow duration and conditions warrant, and roof
snow load is equal to or exceeds 30 psf , the snow load shall be added
to the mass of the roof plane. The local authority may permit a
reduction in snow load by as much as 80%. See Figure D‑7. Note that roof
snow load (Pf) has been previously defined as 70% of the ground snow
load (Pg) in section D‑200.3B.

**D. Miscellaneous Loads.** No consideration of partial occupancy live
load was included in the mass of the floor plane; however, mechanical
and partition load was included in the floor plane.

**E. Seismic Analysis Method.** The Equivalent Lateral Force Procedure
(ELF) was assumed for manufactured housing units, as defined by ASCE
7‑93. No plan or elevation irregularities were assumed, Thus, the
manufactured home superstructure was assumed to be a simple rectangular
box with proportions of length to width not exceeding 5 to 1.

1\. The Fundamental Period (T): the manufactured home is assumed to have
the same period in either direction, transverse or longitudinal,
determined from the following equation:

T = Ct x h^3/4^

where:

a\. Ct = 0.02 for the category of: all other buildings.

b\. the height from bottom of footing to the mean roof height (h) has
been assumed as 13.5 feet.

c\. Thus: T = 0.14 seconds.

2\. Site Coefficient (S): the site has been selected for the most
significant soil classification, thus S = 2.0.

3\. The Response Modification Coefficient (R): the structure has been
selected as a bearing wall system with light frame walls with shear
panels. Thus, R = 6.5.

4\. Effective peak velocity-related acceleration coefficient
([A]{.underline}v): is selected for the geographic location based on the
map H‑16 in Appendix H.

5\. The Seismic Design Coefficient ([C]{.underline}s) is determined by
the following equation:

> $$\underline{\text{Cs}} = \frac{1\text{.}2´\underline{\text{Av}}´S}{R´T^{2/3}}$$

Insertion of all the above values in the equation for ([C]{.underline}s)
leads to the results tabulated below:

[A]{.underline}v [C]{.underline}s

0.15 0.204

0.2 0.273

0.3 0.409

0.4 0.546

6\. But ([C]{.underline}s) need not exceed the following equation:

> $$\underline{\text{Cs}} = \frac{2\text{.}5´\underline{\text{Aa}}}{R}$$

where:

a\. Effective peak acceleration coefficient ([A]{.underline}a): selected
for the geographic location based on map H‑15 in Appendix H.

b\. The results are tabulated below:

[Aa]{.underline} [Cs]{.underline}

0.15 0.058

0.2 0.077

0.3 0.115

0.4 0.154

c\. The values for ([Cs]{.underline}) are definitely smaller in item
(6.b) above rather than in item (5.a), thus [Cs]{.underline} is based on
the equation in item (6). Thus, for this Manual assuming
[Aa]{.underline} = [Av]{.underline}:

> $$\underline{\text{Cs}} = \frac{2\text{.}5´\underline{\text{Aa}}}{R}$$

7\. The basic equation for base shear (V~B~), using the (ELF) method,
is:

V~B~ = [Cs]{.underline} × W

where:

a\. The total weight (W) is the summation of the roof plane mass and the
floor plane mass, including snow as applicable, as a function of unit
length. It is advantageous to keep the roof and floor loads separated
for calculation ease and kept in units of lbs/ft of unit length as
follows:

For a [Single-Section Unit]{.underline}:

$$w_{\text{roof}} = 9\text{.}7´\text{Wt} + \text{44}\text{.}\text{25} + \frac{W_{\text{endroof}}}{L} + {\% P}_{f}´\text{Wt}$$

$$w_{\text{floor}} = \text{13}\text{.}0´\text{Wt} + \text{44}\text{.}\text{25} + \text{18} + \frac{W_{\text{endfloor}}}{L}$$

For a [Multi-Section Unit]{.underline}:

$$\begin{array}{r}
w_{\text{roof}} = \text{19}\text{.}4´\text{Wt} + \text{44}\text{.}\text{25} + \text{26}\text{.}\text{25} + \frac{W_{\text{endroof}}}{L} + \\
2´\text{\%P}_{f}´Wt
\end{array}$$

$$w_{\text{floor}} = \text{26}\text{.}0´\text{Wt} + \text{36} + \text{44}\text{.}\text{25} + \text{26}\text{.}\text{25} + \frac{W_{\text{endfloor}}}{L}$$

**Note:** For overturning calculations, where (L) does not enter the
equations, use L=60 ft as an average length to smear the end wall load.
For Sliding (L) is always required and the end wall weight is smearing
over the real length (L).

Where for either the Single or Multi-Section unit, the total dead load
per foot of length of the unit becomes:

$W = w_{\text{roof}} + w_{\text{floor}}$

b\. The seismic coefficient ([Cs]{.underline}) is based on equation in
item (6.b).

8\. The base shear (V~B~) is then distributed vertically as inertia
forces (F~xr~ and F~xf~) to the floor and roof levels according to the
mass that exists at each level (see Figure D‑7), based on the following
generic equation:

F~x~ = C~vx~ × V~B~

where also generically:

$C_{\text{vx}} = \frac{w_{x}´h_{x}}{\sum_{\text{i=1}}^{n}\left( w_{i}´h_{i} \right)}$

a\. The weight and height at each respective level is subscripted with
an (x) while the sum of the product of each level's weight and height
are generically subscripted with an (I). The uppermost level of the
building (n) is in this case the roof. For a one story manufactured
home, there will only be two levels, w~roof~ and w~floor~ reducing to
two expressions substituting Single or Multi-Section unit values as
follows:

$C_{\text{roof}} = \frac{w_{\text{roof}}´h_{r}}{w_{\text{roof}}´h_{r} + w_{\text{floor}}´h_{f}}$

$C_{\text{floor}} = \frac{w_{\text{floor}}´h_{f}}{w_{\text{roof}}´h_{r} + w_{\text{floor}}´h_{f}}$

Thus, the inertia forces in lbs/ft of unit length at the two respective
levels becomes:

$F_{\text{xr}} = C_{\text{roof}}´V_{B}$ and,

$F_{\text{xf}} = C_{\text{floor}}´V_{B}$

b\. Sample spreadsheet output for two cases (snow Pg = 0 psf and snow
Pg = 100 psf) indicates the range of (F~xr~) and (F~xf~) values at the
roof and floor levels respectively for a single section unit. These
examples include the 12, 14 and 16 nominal width units and are labeled
as Tables D‑2 and D‑3. Note: nominal , rather than actual unit width
(Wt) were used in the dead load calculations for conservatism.

9\. The forces (F~xr~ and F~xf~) were applied to the manufactured home
unit as illustrated in Figure D‑7 and used for transverse and
longitudinal overturning and sliding calculations for comparison to the
wind forces. The forces that produced the largest required resistance
values were used in the Foundation Design Load Tables - Appendix B.
Values that are grayed in the Tables of Appendix B are controlled by
seismic inertia forces.

**D-300. SAMPLE EQUATIONS USED FOR FOUNDATION DESIGN LOAD TABLE
VALUES.**

**D-300.1 Required Effective Footing Area.** Refer to Figures D‑8(A&B)
and D‑9(A&B) for the free-body diagrams illustrating the applied gravity
loads on the superstructure and on the foundation for a Type **C** and
Type **E** or **I** single-section unit, and a Type **C** multi-section
unit with consideration of a continuous marriage wall and a marriage
wall with a large opening. Note that the "heavy" dead loads are used
from Table D‑1. For allowable stress design methodology, the load
combination from ASCE 7‑93 is: DL(heavy) + LL(occupancy) + LL(attic) +
SL(or min. roof LL).

  --------------------------- ----------------- -------- ---------- ---------- ---------------- --------- ------- -------
  **[Seismic]{.underline}**                                                                                       

  Smax=                       2                          R=         6.5                         hn=       11.0    ft

  Exposure Group I                                                  Ct=        0.02                               

  Seismic Performance A to D                                                   Assume no plan                     
                                                                               or elevation                       
                                                                               irregularities                     

  Equivalent Lateral Force                                                                                        
  Procedure                                                                                                       

  Period:                     Ta=Ct(hn)\^3/4=                       0.120802                                      

                              Tmax=Ta\*Ca                           Ca=        1.5              (1.5 max          
                                                                                                for               
                                                                                                Av=.15)           

                                                         Tmax=      0.181203                                      

  Cs max=2.5\*Aa/R                                       Aa         Cs max                                        

                                                0.15     0.057692                                                 

                                                0.20     0.076923                                                 

                                                0.30     0.115385                                                 

                                                0.40     0.153846                                                 

  Snow Load: Pg=                                         0          psf        Pf=              0         psf     

                                                Wt                                                                

  DL                          12.0              14.0     16.0                                                     

  roof                        160.65            180.05   199.45                                                   

  floor                       218.25            244.25   270.25                                                   

  total                       378.90            424.30   469.70                                                   

                                                                                                                  

  **Width 12 ft**                                                   Vbase=     21.86            29.15     43.72   58.29

                                                                               Fx=Cvx\*Vbase                      

                                                                               Aa                                 

                              w                 h        w\*h       Cvx        0.15             0.2       0.3     0.4

  roof                        160.65            11.0     1767.15    0.729654   15.95            21.27     31.90   42.53

  floor                       218.25            3.0      654.75     0.270346   5.91             7.88      11.82   15.76

  sum                         378.90                     2421.90    1.0        21.86            29.15     43.72   58.29

                                                                                                                  

  **Width 14 ft**                                                   Vbase=     24.48            32.64     48.96   65.28

                                                                               Fx=Cvx\*Vbase                      

                                                                               Aa                                 

                              w                 h        w\*h       Cvx        0.15             0.2       0.3     0.4

  roof                        180.05            11.0     1980.55    0.729941   17.87            23.82     35.74   47.65

  floor                       244.25            3.0      732.75     0.270059   6.61             8.81      13.22   17.63

  sum                         424.30                     2713.30    1.0        24.48            32.64     48.96   65.28

                                                                                                                  

  **Width 16 ft**                                                   Vbase=     27.10            36.13     54.20   72.26

                                                                               Fx=Cvx\*Vbase                      

                                                                               Aa                                 

                              w                 h        w\*h       Cvx        0.15             0.2       0.3     0.4

  roof                        199.45            11.0     2193.95    0.730173   19.79            26.38     39.57   52.76

  floor                       270.25            3.0      810.75     0.269827   7.31             9.75      14.62   19.50

  sum                         469.70                     3004.70    1.0        27.10            36.13     54.20   72.26
  --------------------------- ----------------- -------- ---------- ---------- ---------------- --------- ------- -------

Seismic Forces - Ground Snow \< 30 psf

*Table D - 2*

  --------------------------- ----------------- --------- ---------- ---------- ---------------- --------- -------- --------
  **[Seismic]{.underline}**                                                                                         

  Smax=                       2                           R=         6.5                         hn=       11.0     ft

  Exposure Group I                                                   Ct=        0.02                                

  Seismic Performance A to D                                                    Assume no plan                      
                                                                                or elevation                        
                                                                                irregularities                      

  Equivalent Lateral Force                                                                                          
  Procedure                                                                                                         

  Period:                     Ta=Ct(hn)\^3/4=                        0.120802                                       

                              Tmax=Ta\*Ca                            Ca=        1.5              (1.5 max           
                                                                                                 for                
                                                                                                 Av=.15)            

                                                          Tmax=      0.181203                                       

  Cs max=2.5\*Aa/R                                        Aa         Cs max                                         

                                                0.15      0.057692                                                  

                                                0.20      0.076923                                                  

                                                0.30      0.115385                                                  

                                                0.40      0.153846                                                  

  Snow Load: Pg=                                          100        psf        Pf=              70        psf      

                                                Wt                                                                  

  DL                          12.0              14.0      16.0                                                      

  roof                        1000.65           1160.05   1319.45                                                   

  floor                       218.25            244.25    270.25                                                    

  total                       1218.90           1404.30   1589.70                                                   

                                                                                                                    

  **Width 12 ft**                                                    Vbase=     70.32            93.76     140.64   187.52

                                                                                Fx=Cvx\*Vbase                       

                                                                                Aa                                  

                              w                 h         w\*h       Cvx        0.15             0.2       0.3      0.4

  roof                        1000.65           11.0      11007.15   0.943856   66.37            88.50     132.75   176.99

  floor                       218.25            3.0       654.75     0.056144   3.95             5.26      7.90     10.53

  sum                         1218.90                     11661.90   1.0        70.32            93.76     140.64   187.52

                                                                                                                    

  **Width 14 ft**                                                    Vbase=     81.02            108.02    162.03   216.05

                                                                                Fx=Cvx\*Vbase                       

                                                                                Aa                                  

                              w                 h         w\*h       Cvx        0.15             0.2       0.3      0.4

  roof                        1160.05           11.0      12760.55   0.945695   76.62            102.16    153.24   204.31

  floor                       244.25            3.0       732.75     0.054305   4.40             5.87      8.80     11.73

  sum                         1404.30                     13493.30   1.0        81.02            108.02    162.03   216.05

                                                                                                                    

  **Width 16 ft**                                                    Vbase=     91.71            122.28    183.43   244.57

                                                                                Fx=Cvx\*Vbase                       

                                                                                Aa                                  

                              w                 h         w\*h       Cvx        0.15             0.2       0.3      0.4

  roof                        1319.45           11.0      14513.95   0.947095   86.86            115.82    173.72   231.63

  floor                       270.25            3.0       810.75     0.052905   4.85             6.47      9.70     12.94

  sum                         1589.70                     15324.70   1.0        91.71            122.28    183.43   244.57
  --------------------------- ----------------- --------- ---------- ---------- ---------------- --------- -------- --------

Seismic Forces - Ground Snow 100 psf

***Table D - 3***