APPENDIX C\
FOUNDATION CAPACITIES TABLES

**C-100. USE OF FOUNDATION CAPACITIES TABLES.**

**C-100.1. GENERAL.** The Foundation Capacities Tables provide
foundation design capacities and dimensions for three conditions of
foundation design.

**A. Withdrawal Resistance.** The ability of a foundation wall or pier
plus its respective footing to resist uplift and overturning. See Tables
C‑­1 & C‑­2.

**B. Vertical Anchor Capacity.** The required size and spacing of
anchors to tie the superstructure to the foundation to meet the required
uplift or overturning in the transverse direction. See Tables C‑­3 & C‑­4
(a & b).

**C. Horizontal Anchor Capacity.** The required size and spacing of
anchors to tie the superstructure to the foundation to resist sliding in
the transverse and longitudinal directions - Horizontal Anchor Capacity
Table, Table C‑­5.

**C-100.2. CONNECTIONS** of the foundation to the manufactured home is
dependent on the rated capacity of the manufacturer\'s connection
designs.

**C-200. WITHDRAWAL RESISTANCE CAPACITY TABLES.** There are two tables
providing the withdrawal resistance (uplift and overturning) for
different designs of foundation walls and piers on spread footings at
different depths.

**C-200.1. LONGITUDINAL FOUNDATION WALLS.** The \"Withdrawal Resistance
for Longitudinal Foundation Walls - Table C‑­1" is used for manufactured
homes anchored to longitudinal foundation walls, specifically system
type E. The table provides a footing width and depth below grade to
prevent uplift.

*Example*: Determine the withdrawal resistance of a 6" reinforced
concrete wall with a height (hw) of 3'- 4" and with a 6"x16" footing.
Repeat for a 6"CMU wall grouted solid, then grouted at 48" o.c., and
lastly for an all-weather wood foundation.

Solution: Start with the concrete wall: wall weight: (0.5')×(3.33')×150
pcf = 250 plf; reinforced concrete footing weight:
(6"×16"÷144in.sq./sq.ft.)×150pcf = 100 plf; rectangular soil wedge wt:
(3.33'-1')×((16"× 6")÷(2"×12"))×120pcf = 116 plf. The total withdrawal
resistance is the sum of the wall, footing and soil block weight, which
is 250+100+116 = 466 plf. This matches the tabled value. The solid
grouted CMU wall: wall wt.: (3.33')× (63 psf) = 210 plf, 16" footing and
5" soil wedge calculations are the same as above. The total withdrawal
is the sum = 210 + 100 + 116 = 426 plf, just as found in the Table. The
partially grouted CMU wall: wall wt.: (3.33)×(45psf) = 150 plf, 16"
footing and 5" soil wedge are the same. The total withdrawal is the sum
= 150+100+116 = 366 plf, just as found in the table. Lastly, for the
all-weather wood foundation: wood stud wall wt.: 2"x6" plate = 2.1 plf;
(3)-2"x4" plates = 3×1.3 plf = 3.9 plf; 2"x4"@ 16" o.c. = 1.0 psf ×
3.33' = 3.33plf; 1/2"plywood = 1.5psf × 3.33' = 5.0 plf. Wood sum =
2.1+3.9+3.33+5.0 = 14.3 plf; footing weight is the same as caculated
before. Soil weight is based on a 6" wide wedge:
(3.33')×(16-4)÷(2×12)×pcf = 140 plf. Total withdrawal = 14.3+100+140 =
254 plf, just as in the Table.

**C-200.2. PIER FOUNDATIONS.** The \"Withdrawal Resistance for Piers -
Table C‑­2" is used for manufactured homes anchored to piers;
specifically system Types **C**, **I**, and Type **E** when interior
piers are used for anchorage. This table also applies to the concrete
tie-down block for type **C1** foundations.

*Example*: Determine the withdrawal resistance of a 3 foot square
footing with an 8"x16" solid grouted CMU pier of a height (hp) of 3'-4".
Grade exists 12 inches down from the top of the pier.

Solution: Assume the following material weights: 8"CMU = 84 psf; soil =
120 pcf; and concrete = 150 pcf. Pier weight = (84psf) × (16/12) ×
(3.33') = 373 lbs.$$Footing weight = (150pcf)×(8/12)×(3'×3') = 900 lbs.
Assume footing perimeter creates a conservative shear plane. Soil above
footing also counted to resist withdrawal. Soil Weight =
(120pcf)×(3.33'-1')×(3^2^ - (8)×(16)/144) = 2267 lbs. Total withdrawal
resistance is the sum of the pier + footing + soil = 3541 lbs. This
magnitude matches the value found in the Table C-2.$$

**C-200.3. FOOTING DEPTH.** The bottom of the footings must be below the
maximum frost depth for the area where the home is located.

*Example*: The average depth of frost penetration is 35 inches. Assume
that the required footing depth to resist withdrawal (Av) is hw = 2
feet. The depth of the base of the footing is 24\"-12\"+6\"=18\". This
is less than 35\". The depth of hw must be increased to 41\" in order
for the base of the footing to be at 35\"\--the required depth to
prevent frost damage & also satisfy withdrawal requirements
(41\"-12\"+6\"=35\").

**C-300. VERTICAL ANCHOR CAPACITY TABLES** provide the required anchor
and reinforcing size and spacing to tie the superstructure to the
foundation wall or piers. As in section C-200.1 above, there are two
Vertical Anchorage Capacity Tables, one for longitudinal foundation
walls and one for piers.

**C-300.1. PIERS.** The "Vertical Anchor Capacity for Piers - Table C‑­3"
is used for manufactured homes anchored to piers to prevent uplift
specifically system Types **C**, **I**, and Type **E** when interior
piers are used for anchorage (multi-section E\'s).

*Example*: Anchor bolts are assumed to be made from A36 rod stock and of
embedment length sufficient to fully develop the allowable tensile
capacity (0.6×F~y~) of the diameter of rod used. A 1/2"diameter anchor
bolt has the following capacity: (0.6×36,000psi)×(π × 0.5^2^/4) = 4,240
psi, as noted in the Table. The capacity of any substituted grade of
steel can easily be calculated if the yield point and diameter are
known.

**C-300.2. LONGITUDINAL CONCRETE/MASONRY FOUNDATION WALLS.** The
"Vertical Anchorage Capacity for Longitudinal Foundation Walls - Table
C‑­4A" is used for manufactured homes anchored to a continuous Reinforced
concrete or reinforced concrete masonry foundation wall, specifically
system Type **E**.

*Example*: Determine the anchorage capacity per foot of foundation wall
if 1/2" diameter anchor bolts are spaced 3'-4" o.c. and attach to a
continuous treated wood mud sill 1-1/2" thick. Standard washers are used
under the nut and bear into the mud sill perpendicular to grain.

Solution: Determine the bearing area of a standard washer with O.D. =
1.375" and I.D. = 0.5625": A~brg~ = π × (1.375^2^ - 0.5625^2^) ÷ 4 =
1.237 ^sq.\ in.^ . The capacity in bearing multiplied by a bearing area
factor C~b~ = 1.25. Thus, the bearing capacity = 1.237 × 1.25 × 565 psi
= 873 lbs./ bolt. The capacity for a given spacing of bolts is found by
division of that spacing. Thus, for a 3'-4" bolt spacing: 873 ÷ 3.33' =
262 plf, which is the same as in the Table.

Use of an oversized washer (for a 5/8" dia. bolt) produces a larger
capacity per bolt. The O.D. = 1.75" and the I.D. = 0.6875", thus the net
bearing area : A~brg~ = π × (1.75^2^ - 0.6875^2^) ÷ 4 = 2.03^sq.\ in.^.
The vertical anchor capacity at the same same spacing = 2.03 × 1.25 ×
565 psi ÷ 3.33' = 431 plf, which is the same as in the Table.

**C-300.3. LONGITUDINAL TREATED WOOD FOUNDATION WALLS.** The "Vertical
Anchorage Capacity for Longitudinal Foundation Walls - Table C‑­4B" is
used for manufactured homes anchored to a continuous treated wood
foundation wall, specifically system Type **E**. Vertical anchorage
capacities are based on the use of standard washers over 1/2" dia.
bolts. Plywood thickness, nail size and spacing are selected so as to
provide equal or greater capacity than the standard washer in bearing.
The APA Plywood Diaphragm Guide was used to select plywood, and nailing
requirements for the Table.

*Example:* A 1/2" dia. bolt spaced at 3'-4" o.c. provides a vertical
anchor capacity of 262 lbs./ft. This is the same capacity as found in
Table C-4A for a standard washer in bearing, and its calculation is
illustrated above. The APA Table - *Recommended Shear for Horizontal APA
Panel Diaphrapms* requires for a shear of 320 plf \> 262 plf: 8d COM
nails @ 4" o.c. and uses 3/8" APA rated sheathing.

**C-400. HORIZONTAL ANCHOR CAPACITY TABLES FOR TRANSVERSE AND
LONGITUDINAL FOUNDATION WALLS** (Table C‑­5A & C-5B) are used for all
types of manufactured homes: homes on continuous foundations - Type
**E**; homes on piers - Types **C** and **I**.

**C-400.1. ASSUMPTIONS.** Along with the notes at the bottom of the
tables the following assumptions are made:

**A.** The horizontal sliding forces are resisted totally by transverse
foundation shear walls in the transverse direction and by longitudinal
foundation shear walls in the longitudinal direction. An appropriate
number of vertical X-bracing planes can be substituted for shear walls
to resist sliding in the transverse or longitudinal direction. See
sections 602‑­5.G and 602‑­6.F.

**B.** The roof/ceiling and floor of the superstructure are adequate as
diaphragms, transferring wind load to the transverse and longitudinal
foundation shear walls.

**C.** A home supported by piers does not provide adequate horizontal
sliding resistance unless the piers and footings have been engineered to
withstand lateral loads.

**C-400.2. TABLES FOR HORIZONTAL ANCHOR CAPACITY.** There are two Tables
(C‑­5A & C-5B) for the Horizontal Anchor Capacity for Transverse or
Longitudinal Walls.

**A. Concrete or Masonry Walls.** Table C-5A is based on the capacity of
the anchor bolt in a properly designed concrete or masonry foundation
system. Horizontal shear capacity for a specific spacing of anchor bolts
is based on bearing of the anchor bolt against concrete or grout: F~brg~
= 0.35 × f~c~' = 0.35 × 2500psi = 875psi.

*Example:* Horizontal capacity per anchor bolt bearing = 875 psi × 1/2"
dia. × 4" min. embed. = 1750 lb/bolt, rounded to 1800 lb/bolt. (Note:
shear of the bolt did not control since it calculated to be 2830
lb/bolt, assuming A36 rod stock). Thus for 3 foot spacing: 1800 ÷ 3' =
600 plf, as shown in the Table.

**B. Wood Foundation Walls.** Table C-5B is based on the capacity of the
anchor connection to a treated wood wall which is attached to a concrete
footing. Horizontal shear capacity is controlled by bearing of wood
parallel to grain against the anchor bolt, and then the spacing of those
bolts. A 1600 psi end grain bearing allowable stress was assumed, since
it would cover most typical species. Thus, the capacity per bolt = 1/2"
dia. × 1.5" × 1600 psi = 1200 lb. The APA Plywood Diaphragm Guide was
used to select plywood, and nailing requirements for the Table.

*Example:* For a 1/2" dia. bolt spaced at 3'- 4", the horizontal
capacity is: 1200 lb. ÷ 3.33' = 360 plf as shown in the Table. The APA
Table - *Recommended Shear for Horizontal APA Panel Diaphrapms* requires
for a shear of 360 plf: 8d COM nails @ 4" o.c. and uses 15/32" APA rated
sheathing, just as shown in the Table.

**C. Anchorage For Diagonal Steel Members To Complete Transverse
Foundation Walls Used As Shear Walls.** The number of anchor bolts
required to anchor the diagonal steel members to the foundation wall can
be found by dividing the capacity value for a bolt spaced at 12 inches
into the required Ah.

Table C-1\
Withdrawal Resistance^1\
^Longitudinal Continuous Foundations^2,\ 3^\
(In pounds per linear foot of wall)

![](media/image1.emf)

  ----------------------------------------------------------------------------------------------
  hw        Reinforced\           Masonry-\           Masonry-\           All-Weather\   
            Concrete              Fully               Grouted @\          Wood w/\       
                                  Grouted\            48" o.c.            Conc. Footing  
                                  6" CMU                                                 
  --------- ------------- ------- ----------- ------- ----------- ------- -------------- -------
            Footing Width         Footing             Footing             Footing Width  
                                  Width               Width                              

            12"           16"     12"         16"     12"         16"     12"            16"

  2'-0"     255           300     231         276     195         240     126            171

  2'-8"     325           383     293         351     245         303     154            212

  3'-4"     395           466     355         426     295         366     182            254

  4'-0"     465           550     417         502     345         430     211            296

  4'-8"     535           633     479         577     395         493     240            337
  ----------------------------------------------------------------------------------------------

^1^ Potential resistance to withdrawal is the maximum uplift resistance
which can be provided by the foundations shown. It is computed by adding
the weights of building materials and soil over the top of the footing,
plus the footing weight. To fully develop this potential, adequate
connections to the footing and superstructure must be provided. Material
weights used: concrete (nlwt) = 150 psf; 6"solid grouted CMU = 63 psf;
6" CMU grouted @ 48"o.c. = 45psf; grout wt assumed = 140 pcf; CMU units
nlwt; wood = 35 pcf; soil = 120 pcf.

^2^ Foundations must be designed for bearing pressure, gravity loads,
and uplift loads in addition to meeting the anchorage requirements
tabulated in the Foundation Design Tables.

^3^ Values shown in this table could be increased by widening the
footing, provided the system is designed for the increased load, or by a
more detailed analysis of the shearing strength of the soil overburden.

Table C-2\
Withdrawal^1^ Resistance For Piers^2,\ 3^\
(In pounds per pier)

  ---------------- ------------- ------------- ------------- -------------
  Hp               Width of                                  
                   Square                                    
                   Footing: Wf                               

  Depth            1'-0"^4^      2'-0"         3'-0"         4'-0"^4^

  2'-0"            279           997           2097          3755

  2'-8"            361           1322          2824          5049

  3'-4"            442           1643          3541          6325

  4'-0"            525           1967          4267          7617

  4'-8"            607           2292          4994          8911
  ---------------- ------------- ------------- ------------- -------------

^1^ Potential resistance to withdrawal is the maximum uplift resistance
which can be provided by the foundations shown. It is computed by adding
the weights of building materials and soil over the top of the footing,
plus the footing weight. To fully develop this potential, adequate
connections to the footing and superstructure must be provided. Material
weights used: concrete (nlwt) = 150 psf; nlwt 8"CMU = 84 psf grouted
solid; grout (nlwt) = 140 pcf; soil = 120 pcf.

^2^ Foundations must be designed for lateral soil pressure, bearing
pressure, gravity loads, and uplift loads, in addition to meeting the
anchorage requirements tabulated in the Foundation Design Tables. The
bottom of the footing must also be below the maximum depth of frost
penetration.

^3^ Values shown in this table could be increased by widening the
footing, providing the wall system is designed for the increased load,
or by a more detailed analysis of the shear strength of the soil
overburden.

^4^ Assumes 8" x 8" pier for the 1'-0" square footing, and 16" x 16"
pier for the 4'-0" square footing.

Table C-3\
Vertical Anchor Capacity For Piers^1,\ 2^\
(In pounds)

  ------------------------------------------------------------------------
  Anchor               Capacity Per Number Of    
                       Bolts                     
  -------------------- ------------------------- -------------------------
  Bolt Dia.            1                         2

  1/2"                 4240                      8480

  5/8"                 6620                      13240
  ------------------------------------------------------------------------

Table C-3A

^1^ The vertical anchor capacity is based upon the working capacity of
ASTM A-36 rod stock anchor bolts in 2500 psi concrete or grout. To fully
develop this capacity, anchor bolts must be properly lapped with the
pier's vertical reinforcement.

^2^ The capacity is based on f~c~ = 2500 psi; F~y~ = 36,000 psi.

Table C-4A\
Vertical Anchor Capacity For Longitudinal Foundation Wall^1^\
(In pounds per linear foot of wall)

![](media/image6.emf)

^1^ Compare with required Av for Type E units.

^2^ Values are based on vertical capacity per foot of wall.

^3^ Assuming 1 1/2" thick sill plate, 3/4" edge distance for wood or
composite nailer plates or 20 diameter end distance for plywood
sheathing; APA rated, properly seasoned wood; Group III woods, not
permanently loaded, and a 25% length of bearing factor increase.

^4^ It is assumed that a reinforcing bar of the same diameter and
spacing as the anchor is adequately embedded in the footing and lapped
with the anchor.

^5^ Spacing and capacity is based on allowable compression of wood
perpendicular to grain for F~c~ = 565 psi and washer as define below:

Standard washer: 1 3/8" O.D. and 0.5625" I.D. washer (for 1/2" φ bolt)

Over-sized washer: 1 3/4" O.D. and 0.6875" I.D. washer (for 5/8" φ bolt)
placed under the standard washer.

Table C-4B\
Vertical Anchor Capacity For Longitudinal Foundation Wall^1,\ 2^\
(In pounds per linear foot of wall)

![](media/image9.emf)

> \*\*\* For required Av greater than 437 lbs./ft., consider using a
> different foundation material or utilize an engineered design with a
> higher capacity.

^1^ Compare with required Av for Type E units.

^2^ In the case of a treated wood foundation wall, the wood wall and its
connections must be designed to transfer the anchor load to a concrete
footing. This table does not apply to treated wood foundation walls on
gravel bases.

^3^ Values are based on vertical capacity per foot of wall.

^4^ Assuming 1 1/2" thick sill plate, 3/4" edge distance for wood or
composite nailer plates or 20 diameter end distance for plywood
sheathing; APA rated, properly seasoned wood; Group III woods, not
permanently loaded, and a 25% length of bearing factor increase.

^5^ Nailing schedule in this table is intended to secure the
superstructure to the foundation only, and not to provide required edge
fastening for plywood siding or sheathing.

^6^ Spacing and capacity is based on allowable compression of wood
perpendicular to grain for F~c~ = 565 psi and standard washer = 1 3/8"
O.D. and 9/16" I.D. washer (for 1/2" φ bolt).

Table C-5A\
Horizontal Anchor Capacity For Transverse or Longitudinal Shear
Walls^1^\
(In pounds per foot of wall)

Concrete or Masonry

\*\*\* For required Ah greater than 1800 lbs./ft., consider using an
engineered design with a higher capacity.

Table C-5B

Treated Wood

+-----------+----------------+----------------+-----------+-----------+
| H         | Required       | Min.           | Required  |           |
| orizontal | Nailing^3,\ 4^ | Plywood^4^     | Anchorage |           |
+-----------+----------------+----------------+-----------+-----------+
| Ca        | (Edge Spacing, | Nailer         | Anchor    | Bolt      |
| pacity^2^ | in.)           | Thickness      | Bolt      | S         |
|           |                |                | Diameter  | pacing^7^ |
| lbs./ft.  |                |                |           |           |
+-----------+----------------+----------------+-----------+-----------+
| 300       | 8d @ 4" o.c.   | 7/16"          | 1/2"      | 4'-0"     |
|           |                |                |           | max.      |
+-----------+----------------+----------------+-----------+-----------+
| 360       | 8d @ 4" o.c.   | 15/32"         |           | 3'-4"     |
+-----------+----------------+----------------+-----------+-----------+
| 449       | 10d @ 4" o.c.  | 15/32"         |           | 2'-8"     |
+-----------+----------------+----------------+-----------+-----------+
| 600       | 10d @ 3" o.c.  | 19/32"         |           | 2'-0"     |
+-----------+----------------+----------------+-----------+-----------+

^1^ Compare capacity with required Ah in transverse or longitudinal
direction.

^2^ Values are based on horizontal load per foot of wall. Select Ah for
pier spacing of 4 feet for use with this table.

^3^ Assuming 1 1/2" thick sill plate, 3/4" edge distance for wood or
composite nailer plates or 20 diameter end distance for plywood
sheathing; APA rated, properly seasoned wood; Group III woods, not
permanently loaded.

^4^ Nailing schedule in this table is intended to secure the
superstructure to the foundation only, and not to provide required edge
fastening for plywood siding or sheathing.

^5^ It is assumed that a reinforcing bar of the same diameter as the
anchor is adequately embedded in the footing and lapped with the anchor.
In the case of a treated wood foundation wall, the wood wall and its
connections must be designed to transfer the anchor load to a concrete
footing. This table does not apply to treated wood foundation walls on
gravel bases.

^6^ Spacing based on bearing capacity of bolt against concrete/grout.

^7^ Spacing based on capacity of anchor bolt in bearing against the wood
plate. (see also #5.)