Current through Register Vol. 48, No. 12, March 22, 2024
Each manufactured home shall be installed on a support system
capable of supporting a total of 80 pounds per square foot.
a) Footings. Footings must be placed on
level, firm, undisturbed soil or compacted or controlled fill that is free of
grass and organic materials, compacted to a minimum load bearing capacity of
2,000 pounds per square foot. Pre-owned homes for which the manufacturer of the
home is no longer in business or for which the installation instructions are
not available may be placed on an existing footing system if the system meets
the requirements of this Section.
1) Area. The
area in square inches of the footings is based on the width of the home, the
roof design loads, the soil load-bearing capacity and the intended spacing of
the piers. (See 870.Tables A-G.)
2)
Types. Footings may consist of the following:
A) Individual pier footings consisting of
precast or poured-in-place individual pier footing concrete at least 31/2
inches thick with a 28-day compressive strength of 3,000 pounds per square
inch.
B) Concrete runners a minimum
of 31/2 inches thick under each I-beam or perpendicular to the I-beams at no
more than 8 foot intervals.
C)
Concrete pads a minimum of 31/2 inches thick the approximate dimension of the
home.
D) Pressure treated wood
having a 0.60 retention in accordance with the AWPA C22-03 Standard.
E) Acrylonitrile butadiene styrene (ABS)
footing pads in accordance with pad manufacturer installation instructions and
listed for the required load capacity and type of installation. Support devices
and piers must not overlap the footings.
F) A support system approved by a licensed
professional engineer.
b) Piers. Piers or load-bearing supports or
devices shall be designed and constructed to transmit the vertical live and
dead loads to the foundation below. In order to properly support the home, the
piers must be of the proper type, size, location and spacing. Piers shall be
installed directly under the main frames of the home. Piers shall be no more
than two feet from each end of the frame and adequately spaced. (See 870.Tables
A-G.) Piers may be concrete blocks or adjustable metal or concrete devices
approved and listed for the required load capacities. Load bearing supports or
devices shall be listed and labeled, or shall be designed by a licensed
professional engineer in Illinois, and shall be approved for the use intended,
prior to installation.
1) Types. Non-mortared
concrete blocks conforming to ASTM C 90-96 Type N with a nominal size of 8
inches by 8 inches by 16 inches shall be installed with the 16 inch dimension
perpendicular to the main frame (I-beam), the open cells vertical, stacked
level. A 2 or 4 inch thick 8 inch by 16 inch solid concrete cap block that
conforms to ASTM C 90-96 Type N shall be placed on the top of each stack. The
vertical load shall not exceed 8,000 pounds per single stack and 14,000 pounds
for a double stack. The blocks must be stacked on a solid base pad in
accordance with the soil bearing capacity. As many as 2 wood plates not
exceeding 3 inches in combined thickness and 2 shims not exceeding 1 inch total
thickness must be used to fill any gap between the concrete cap and main frame.
Hardwood shims must be a minimum of 3 inches wide and 6 inches long fitted
tight between cap or wood plate and main frame.
2) Clearance and Height. A minimum clearance
of 12 inches must be provided between the ground and the bottom of the frame.
If piers exceed 36 inches in height, they shall be double blocked. If the
height exceeds 80 inches, the pier must be double blocked and mortared with
rebar. If the home is placed in an area subject to flooding, a licensed
professional engineer in Illinois shall design a support and anchoring system
that will resist flood forces. The Federal Emergency Management Agency has
information that may assist in the design.
3) Load-Bearing Openings. In addition to the
piers under the main I-beams of the home, piers must be placed under openings
in the perimeter walls and center-mating wall openings greater than 4 feet.
(See 870.Tables E-G.)
4) Elevated
Manufactured Homes. When more than 1/4 of the area of a home is installed so
that the bottom of the main frame is more than 7 feet above ground level, the
home support system shall be designed by a licensed professional engineer in
Illinois and installation shall be approved by the Department prior to the
installation.