Ala. Admin. Code r. 535-X-13 § 535-X-13-.06

(1) Pier foundations shall be installed directly under the main frame of the home or building. The piers shall not be further apart than six (6) feet on center when using a minimum pier foundation of a 16” x 16” x 4” concrete pad or equivalent in the minimum soil bearing capacity of 2000 lbs. PSF. Piers shall be no more than two feet from each end of the frame.

(2) The minimum pier foundation shall be a 16" X 16" X 4" concrete pad, precast or poured in place concrete slab. All grass and organic material must be removed and the pier foundation placed on stable soil. The minimum soil bearing capacity for the minimum pier foundation is 2000 lbs. If the actual soil’s bearing capacity is greater than 2000 lbs., an assumed value of 2,000 lbs. must be used to determine pier spacing. In a soil bearing capacity below these values, the pier foundations must be increased in size according to the bearing load and the soil bearing capacity of the soil. Two (2) 8" X 16" X 4" concrete pads are considered minimum. All debris, grass, grass sod and other foreign material that would be under the footers must be removed before footings or pier foundations are installed. Pier footing must not be placed on a mound. If the space under the home is to be enclosed with skirting or other material, the skirting shall be vented, and a ground vapor retarder of 6 mil rated polyethylene sheeting or equivalent should be installed. Venting shall be provided for the crawl space at the minimum required by the latest publication of NCSBCS/ANSI A225.1. The vapor barrier should cover the entire area under the home and overlap at least 12 inches at all joints. All decayable material, such as grass, roots, twigs, and wood scraps shall be removed from beneath the home.

(3) Piers may be manufactured load-bearing supports or devices and must be approved for the loads and use intended, or piers shall be constructed of regular 8" X 8" X 16" concrete blocks, with open cells in a vertical position when placed upon the pier foundation. A 2" x 8" X 16" treated wood or hardwood plate or a concrete cap shall be placed on top of the pier to serve as a pier cap. A true 1” thick hardwood plate is optional. All piers must have a full size cap covering the pier. Additional full size plates not less than (1" X 8" X 16") may be used; but, the additional plates shall not exceed 4" in total height. The frame may be cushioned with treated wood, hardwood, or other Commission approved shims (wedges) and the shims shall not occupy more than 1" of vertical space between the top plate and main frame. One shim at least 4” x 6” nominal is to be placed on each side of the main frame on single tiered piers. Two shims are to be placed on each side of the main frame on double tiered piers. Shims must be used in pairs and driven tight. Concrete block piers are to be placed perpendicular to the main I beam or frame.

(4) All piers over 32" (over four 8” x 8” x 16” concrete blocks) in height shall be double tiered with the blocks interlocked.

(5) A minimum of 12" clearance shall be maintained from beneath the main frame or I beam to the top of the soil's surface.

(6) The maximum pier height shall be no more than 60 inches unless designed and approved by a registered engineer or a higher height/different design is required by the National Flood Insurance Program (NFIP) floodplain management criteria.

(7) Exterior sidewall/marriage wall blocking - In addition to providing piers for supporting the frame, piers are also required to support the special roof loads. The support piers are required at all marriage wall and sidewall openings 48" and greater in width. These piers are to be placed at each side of each opening. The most commonly occurring openings are sliding glass doors and full bay windows. Typical marriage wall openings are cathedral openings and passageway openings which are 48" and larger. Recessed walls are considered sidewall openings. Each ridge beam column shall be supported by piers under the marriage wall. Piers shall be placed under heavy loads such as masonry-faced fireplaces, etc. Marriage walls shall have piers at each end of the home. Exterior door openings shall have piers or an approved support device on each side.

(8) Marriage wall piers shall be constructed to the same requirements as all other pier requirements.

(9) Perimeter pier foundations are required to be 8" X 16" X 4" concrete pads. Perimeter piers shall be single tiered and placed parallel to the sidewall.

(10) To assure that the manufacturer's warranty remains valid, all new homes and buildings must be blocked according to the manufacturer's installation manual.

(11) All new manufactured homes or manufactured buildings shall be installed in accordance with the manufacturer’s installation instructions. Effective October 20, 2008, the Manufacturer’s Installation Instructions must meet or exceed the minimum requirements of the HUD Model Manufactured Home Installation Standards. Manufacturers may provide training to the installers of their homes to include lagging, sealing, and complete trim out. Paragraphs 1-9 shall apply to all used homes and buildings when the manufacturer’s installation instructions are not available. It is the installer's responsibility to ascertain for himself which homes may be installed according to the State's minimum blocking standards.