A. Materials
approved for footings must
provide equal load-bearing capacity and resistance to decay, as required by
this section.Footings must be placed on undisturbed soil or fill compacted to
90 percent of maximum relative density.A
footing must support every
pier.Footings are to be either:
1.
Concrete
a. Four inch nominal
precast concrete pads meeting or exceeding ASTM C 90-02a, Standard
Specification for Loadbearing Concrete Masonry Units (incorporated by
reference), without reinforcement, with at least a 28-day compressive strength
of 1,200 pounds per square inch (psi); or
b. Six inch nominal poured-in-place concrete
pads, slabs, or ribbons with at least a 28-day compressive strength of 3,000
pounds per square inch (psi).Site-specific soil conditions or design load
requirements may also require the use of reinforcing steel in cast-in-place
concrete footings.
2.
Pressure-treated permanent wood
a. Pressure-treated wood footings must
consist of a minimum of two layers of nominal 2-inch thick pressure treated
wood, a single layer of nominal 3/4-inch thick, pressure-treated plywood with a
maximum size of 16 inches by 16 inches, or at least two layers of 3/4-inch
thick, pressure-treated plywood for sizes greater than 16 inches by 16 inches.
Plywood used for this purpose is to be rated exposure 1 or exterior sheathing,
in accordance with PS1-95, Construction and Industrial Plywood (incorporated by
reference).
b. Pressure-treated
lumber is to be treated with a water-borne adhesive, in accordance with AWPA
Standard U1-04 (incorporated by reference) for Use Category 4B ground contact
applications.
c. Cut ends of
pressure treated lumber must be field-treated, in accordance with AWPA Standard
M4-02 (incorporated by reference).
3.
ABS footing pads
a. ABS footing pads are permitted provided
they are installed in accordance with the pad manufacturer installation
instructions and certified for use in the soil classification at the
site.
b. ABS footing pads must be
listed or labeled for the required load capacity.
4.
Other materials
Footings may be of other materials than those identified
in this section, provided they are listed for such use and meet all other
applicable requirements of this subchapter.
B.
Placement in Freezing
Climates
Footings placed in freezing climates must be designed using
methods and practices that prevent the effects of frost heave by one of the
following methods:
1.
Conventional footings
Conventional footings must be placed below the frost line
depth for the site unless an insulated foundation or monolithic slab is used
(refer to Subchapter D, Section XII(B)(2) and Subchapter D, Section XII(B)(3)
).When the frost line depth is not available from the LAHJ, a registered
professional engineer, registered architect, or registered geologist must be
consulted to determine the required frost line depth for the manufactured home
site.This is not subject to the provisions in Subchapter A, Section
II(C) that also
require review by the manufacturer and approval by its DAPIA for any variations
to the manufacturer's installation instructions for support and
anchoring.
2.
Monolithic slab systems
A monolithic slab is permitted above the frost line when
all relevant site-specific conditions, including soil characteristics, site
preparation, ventilation, and insulative properties of the under floor
enclosure are considered and anchorage requirements are accommodated as set out
in Subchapter E, Section
I. The monolithic slab system must
be designed by a registered professional engineer or registered
architect:
a. In accordance with
acceptable engineering practice to prevent the effects of frost heave;
or
b. In accordance with SEI/ASCE
32-01 (incorporated by reference).
3.
Insulated foundations
An insulated foundation is permitted above the frost line,
when all relevant site-specific conditions, including soil characteristics,
site preparation, ventilation, and insulative properties of the under the floor
enclosure, are considered, and the foundation is designed by a registered
professional engineer or registered architect:
a. In accordance with acceptable engineering
practice to prevent the effects of frost heave; or
b. In accordance with SEI/ASCE 32-01
(incorporated by reference).
C.
Sizing of footings
The sizing and layout of footings depends on the
load-bearing capacity of the soil, footings, and the piers.-See Subchapter C,
Sections
II and
III, and Table to Subchapter D,
Section XII.
Figure A to Subchapter D, Section XII -
Footings
Typical Blocking Diagram for Single Section
Homes
Notes to Figure A:
Click here to view
Image
1. Refer to Table 1
to Subchapter D, Section
III for
pier and
footing
requirements when frame blocking only is used.
2. In addition to blocking required by
Subchapter D, Section
XI, see Table 2 to Subchapter D,
Section
III for maximum perimeter blocking
loads.
3. End piers under main
I-beams may be set back a maximum of 24 inches, as measure from the outside
edge of the floor to the center of the pier.
4. Place piers on both sides of sidewall
exterior doors, patio doors, and sliding glass doors; under porch posts,
factory-installed fireplaces, and fireplace stoves; under jamb studs at
multiple window openings; and at any other sidewall openings 48 inches or
greater in width. For roof loads of 40 psf or greater, a professional engineer
or registered architect must determine the maximum sidewall opening permitted
without perimeter supports. See Subchapter D, Section
VII and Subchapter D, Section
XI for additional requirements for
locating perimeter supports.
Figure B to Subchapter D, Section XII -
Footings
Typical Blocking Diagram for Multi-section
Homes
Notes to Figure B:
Click here to view
Image
1. Refer to
Table 1 to Subchapter D, Section
III for
pier and
footing
requirements when frame blocking only is used.
2. In addition to blocking required by
Subchapter D, Section
XI, see Tables 2 and 3 to
Subchapter D, Section
III for maximum perimeter blocking
loads.
3. End piers under main
I-beams may be set back a maximum of 24 inches, as measured from the outside
edge of the floor to center of the pier.
4. Place piers on both sides of sidewall
exterior doors, patio doors, and sliding glass doors; under porch posts,
factory-installed fireplaces, and fireplace stoves; under jamb studs at
multiple window openings; and at any other sidewall openings 48 inches or
greater in width.For roof loads of 40 psf or greater, a professional engineer
or registered architect must determine the maximum sidewall opening permitted
without perimeter supports or mating wall opening permitted without
pier or
other supports. See Subchapter D, Section
VII and Subchapter D, Section
XI for additional requirements for
locating perimeter supports.
5.
When an end pier under the mate-line also serves as a column pier, it may be
set back a maximum of 6 inches, as measured from the inside edge of the
exterior wall to the center of the pier.
Table to Subchapter D, Section XII - Footings
The Size & Capacity for Unreinforced
Cast-in-Place Footings
|
Soil
capacity (psf)
|
Minimum footing
Size (in.)
|
8 in. x 16 in. pier
|
16 in. x 16 in. pier
|
|
Maximum
footing capacity (lbs)
|
Unreinforced cast-in-place minimum thickness
(in.)
|
Maximum
footing capacity (lbs)
|
Unreinforced cast-in-place minimum thickness
(in.)
|
|
1,000
|
16 x 16
|
1,600
|
6
|
1,600
|
6
|
|
20 x 20
|
2,600
|
6
|
2,600
|
6
|
|
24 x 24
|
3,700
|
6
|
3,700
|
6
|
|
30 x 30
|
5,600
|
8
|
5,800
|
6
|
|
36 x 36
|
7,900
|
10
|
8,100
|
8
|
|
42 x 42
|
4 10,700
|
10
|
10,700
|
10
|
|
48 x 48
|
4 13,100
|
12
|
13,600
|
10
|
|
1,500
|
16 x 16
|
2,500
|
6
|
2,500
|
6
|
|
20 x 20
|
4,000
|
6
|
4,000
|
6
|
|
24 x 24
|
5,600
|
8
|
5,700
|
6
|
|
30 x 30
|
4 8,500
|
10
|
8,900
|
8
|
|
36 x 36
|
4 12,400
|
10
|
12,600
|
8
|
|
42 x 42
|
4 16,500
|
12
|
416,800
|
10
|
|
48 x 48
|
4 21,200
|
14
|
421,600
|
12
|
|
2,000
|
16 x 16
|
3,400
|
6
|
3,400
|
6
|
|
20 x 20
|
5,300
|
6
|
5,300
|
6
|
|
24 x 24
|
7,600
|
8
|
7,700
|
6
|
|
30 x 30
|
4 11,700
|
10
|
11,900
|
8
|
|
36 x 36
|
4 16,700
|
15
|
4 16,900
|
10
|
|
42 x 42
|
4 21,700
|
18
|
4 22,700
|
12
|
|
2,500
|
16 x 16
|
4,300
|
6
|
4,300
|
6
|
|
20 x 20
|
6,700
|
6
|
6,700
|
6
|
|
24 x 24
|
4 9,600
|
8
|
9,700
|
6
|
|
30 x 30
|
4 14,800
|
10
|
15,000
|
8
|
|
36 x 36
|
4 20,700
|
12
|
4 21,400
|
10
|
|
3,000
|
16 x 16
|
5,200
|
6
|
5,200
|
6
|
|
20 x 20
|
8,100
|
8
|
8,100
|
6
|
|
24 x 24
|
4 11,500
|
10
|
11,700
|
6
|
|
30 x 30
|
4 17,800
|
12
|
4 18,100
|
8
|
|
36 x 36
|
4 25,400
|
14
|
4 25,900
|
10
|
|
4,000
|
16 x 16
|
7,000
|
6
|
7,000
|
6
|
|
20 x 20
|
4 10,800
|
8
|
10,900
|
6
|
|
24 x 24
|
4 15,500
|
10
|
15,600
|
8
|
|
30 x 30
|
4 23,300
|
12
|
4 24,200
|
10
|
Notes to Table:
1. The footing sizes shown are for square
pads and are based on the area (in.2), shear and
bending required for the loads shown. Other configurations, such as rectangular
or circular configurations, can be used, provided the area and depth is equal
to or greater than the area and depth of the square footing shown in the table,
and the distance from the edge of the pier to the edge of the footing is not
less than the thickness of the footing.
2. The 6 inch cast-in-place values can be
used for 4 inch unreinforced precast concrete footings.
3. The capacity values listed have been
reduced by the dead load of the concrete footing.
4. Concrete block piers must not exceed their
design capacity of 8,000 lbs for 8" x 16" single stack block and 16,000 lbs for
16" x 16" double stack block.
5. A
registered professional engineer or registered architect must prepare the
design, if the design loads exceed the capacity for single or double stack
concrete block piers shown in footnote 4.
