Section 321.15. Footings.

 

(1)   General.

(a) The dwelling and attached structures, such as decks and garages, shall be supported on a structural system designed to transmit and safely distribute the loads to the soil.

(b) The loads for determining the footing size shall include the weight of the live load, roof, walls, floors, pier or column, plus the weight of the structural system and the soil over the footing.

(c) Footings shall be sized to not exceed the allowable material stresses.

(d) The bearing area shall be at least equal to the area required to transfer the loads to the supporting soil without exceeding the bearing capacity of the soil.

(e)

1. Structures supported on floating slabs or similar shallow foundations may not be physically attached to structures that are supported by footings that extend below the frost line unless an isolation joint is used between the structures, except as provided in subd. 2. This isolation shall extend for the full height of the structure.

2. Exterior ramps are not required to comply with subd. 1.

(2)   Size and type. Unless designed by structural analysis, unreinforced concrete footings shall comply with the following requirements:

(a) Continuous footings. The minimum width of the footing on each side of the foundation wall shall measure at least 4 inches wider than the wall. The footing depth shall be at least 8 inches nominal. Footing placed in unstable soil shall be formed. Lintels may be used in place of continuous footings when there is a change in footing elevation.

(b) Column or pier footing.

1. The minimum width and length of column or pier footings shall measure at least 2 feet by 2 feet.

2. The minimum depth of column or pier footings shall measure at least 12 inches nominal.

(c) Trench footings. Footings poured integrally with the wall may be used when soil conditions permit. The minimum width shall be at least 8 inches nominal.

(d) Chimney and fireplace footings. Footing for chimneys or fireplaces shall extend at least 4 inches on each side of the chimney or fireplace. The minimum depth shall measure at least 12 inches nominal.

(e) Floating slabs. Any dwelling supported on a floating slab on grade shall be designed through structural analysis.

(f) Deck footings. Decks attached to dwellings and detached decks which serve an exit shall be supported on a structural system designed to transmit and safely distribute the loads to the soil. Footings shall be sized to not exceed the allowable material stresses. The bearing area shall be at least equal to the area required to transfer the loads to the supporting soil without exceeding the bearing values of the soil.

(3)   Soil-bearing capacity. No footing or foundation shall be placed on soil with a bearing capacity of less than 2,000 pounds per square foot unless the footing or foundation has been designed through structural analysis. The soil-bearing values of common soils may be determined through soil identification.

(a) Minimum soil-bearing values. If the soil located directly under a footing or foundation overlies a layer of soil having a smaller allowable bearing value, the smaller soil-bearing value shall be used.

(b) Unprepared fill material, organic material. No footing or foundation shall be placed upon unprepared fill material, organic soil, alluvial soil or mud unless the load will be supported. When requested, soil data shall be provided.

Cr. Register, November, 1979, No. 287 , eff. 6-1-80; am. (1) (a), Register, January, 1989, No. 397 , eff. 2-1-89; cr. (1) (f), Register, March, 1992, No. 435 , eff. 4-1-92; am. (1) (e), Register, November, 1995, No. 479 , eff. 12-1-95; am. (1) (e), Register, March, 2001, No. 543 , eff. 4-1-01; CR 08-043 : renum. (intro.), (1) and (2) to be (1), (2) and (3) and am. (1), (2) (b) and (e), cr. (1) (e) Register March 2009 No. 639 , eff. 4-1-09; CR 15-041 : renum. (1) (e) to (1) (e) 1. and am., cr. (1) (e) 2. Register December 2015 No. 720 , eff. 1-1-16.

Note

Unstable soil includes soils that are unable to support themselves at a 90 degree angle for the full depth of the footing. Microsoft Windows NT 6.1.7601 Service Pack 1 The department will accept the soil-bearing values for the types of soil listed in the following table: - See PDF for table Microsoft Windows NT 6.1.7601 Service Pack 1 The decomposition of organic material in landfill sites established for the disposal of organic wastes may produce odorous, toxic and explosive concentrations of gas which may seep into buildings through storm sewers and similar underground utilities unless provisions are taken to release the gases to the atmosphere. Microsoft Windows NT 6.1.7601 Service Pack 1