Section 1809 Shallow Foundations
Except where otherwise protected from frost, foundations and other permanent supports of buildings and structures shall be protected from frost by one or more of the following methods:
- Extending below the frost line of the locality.
- Constructing in accordance with ASCE 32.
Erecting on solid rock.
Exception: Free-standing buildings meeting all of the following conditions shall not be required to be protected:
- Assigned to Risk Category I.
- Area of 600 square feet (56 m2) or less for light-frame construction or 400 square feet (37 m2) or less for other than light-frame construction.
- Eave height of 10 feet (3048 mm) or less.
Shallow foundations shall not bear on frozen soil unless such frozen condition is of a permanent character.
| NUMBER OF FLOORS SUPPORTED BY THE FOOTINGf |
WIDTH OF FOOTING (inches) |
THICKNESS OF FOOTING (inches) |
| 1 | 12 | 6 |
| 2 | 15 | 6 |
| 3 | 18 | 8g |
- Depth of footings shall be in accordance with Section 1809.4.
- The ground under the floor shall be permitted to be excavated to the elevation of the top of the footing.
- Interior stud-bearing walls shall be permitted to be supported by isolated footings. The footing width and length shall be twice the width shown in this table, and footings shall be spaced not more than 6 feet on center.
- See Section 1905 for additional requirements for concrete footings of structures assigned to Seismic Design Category C, D, E or F.
- For thickness of foundation walls, see Section 1807.1.6.
- Footings shall be permitted to support a roof in addition to the stipulated number of floors. Footings supporting roof only shall be as required for supporting one floor.
- Plain concrete footings for Group R-3 occupancies shall be permitted to be 6 inches thick.
The edge thickness of plain concrete footings supporting walls of other than light-frame construction shall be not less than 8 inches (203 mm) where placed on soil or rock.
Exception: For plain concrete footings supporting Group R-3 occupancies, the edge thickness is permitted to be 6 inches (152 mm), provided that the footing does not extend beyond a distance greater than the thickness of the footing on either side of the supported wall.
The design, materials and construction of masonry-unit footings shall comply with Sections 1809.9.1 and 1809.9.2, and the provisions of Chapter 21.
Exception: Where a specific design is not provided, masonry-unit footings supporting walls of light-frame construction shall be permitted to be designed in accordance with Table 1809.7.
Except in Seismic Design Categories D, E and F, pier and curtain wall foundations shall be permitted to be used to support light-frame construction not more than two stories above grade plane, provided that the following requirements are met:
- All load-bearing walls shall be placed on continuous concrete footings bonded integrally with the exterior wall footings.
- The minimum actual thickness of a load-bearing masonry wall shall be not less than 4 inches (102 mm) nominal or 35/8 inches (92 mm) actual thickness, and shall be bonded integrally with piers spaced 6 feet (1829 mm) on center (o.c.).
Piers shall be constructed in accordance with Chapter 21 and the following:
- 3.1. The unsupported height of the masonry piers shall not exceed 10 times their least dimension.
3.2. Where structural clay tile or hollow concrete masonry units are used for piers supporting beams and girders, the cellular spaces shall be filled solidly with concrete or Type M or S mortar.
Exception: Unfilled hollow piers shall be permitted where the unsupported height of the pier is not more than four times its least dimension.
- 3.3. Hollow piers shall be capped with 4 inches (102 mm) of solid masonry or concrete or the cavities of the top course shall be filled with concrete or grout.
- The maximum height of a 4-inch (102 mm) load-bearing masonry foundation wall supporting wood frame walls and floors shall not be more than 4 feet (1219 mm) in height.
- The unbalanced fill for 4-inch (102 mm) foundation walls shall not exceed 24 inches (610 mm) for solid masonry, nor 12 inches (305 mm) for hollow masonry.