The provisions of this chapter shall control the design and construction of the foundation and foundation spaces for buildings. In addition to the provisions of this chapter, the design and construction of foundations in flood hazard areas as established by Table R301.2(1) shall meet the provisions of Section R322. Wood foundations shall be designed and installed in accordance with AWC PWF.
Exception: The provisions of this chapter shall be permitted to be used for wood foundations only in the following situations:
1.In buildings that have no more than two floors and a roof.
2.Where interior basement and foundation walls are constructed at intervals not exceeding 50 feet (15 240 mm).
Wood foundations in Seismic Design Category D0, D1 or D2 shall be designed in accordance with accepted engineering practice.
Foundation construction shall be capable of accommodating all loads in accordance with Section R301 and of transmitting the resulting loads to the supporting soil. Fill soils that support footings and foundations shall be designed, installed and tested in accordance with accepted engineering practice. Gravel fill used as footings for wood and precast concrete foundations shall comply with Section R403.
Surface drainage shall be diverted to a storm sewer conveyance or other approved point of collection that does not create a hazard. Lots shall be graded to drain surface water away from foundation walls. The grade shall fall a minimum of 6 inches (152 mm) within the first 10 feet (3048 mm).
Exception: Where lot lines, walls, slopes or other physical barriers prohibit 6 inches (152 mm) of fall within 10 feet (3048 mm), drains or swales shall be constructed to ensure drainage away from the structure. Impervious surfaces within 10 feet (3048 mm) of the building foundation shall be sloped a minimum of 2 percent away from the building.
Where quantifiable data created by accepted soil science methodologies indicate expansive, compressible, shifting or other questionable soil characteristics are likely to be present, the building official shall determine whether to require a soil test to determine the soil’s characteristics at a particular location. This test shall be done by an approved agency using an approved method.
In lieu of a complete geotechnical evaluation, the load-bearing values in Table R401.4.1 shall be assumed.
PRESUMPTIVE LOAD-BEARING VALUES OF FOUNDATION MATERIALSa
|CLASS OF MATERIAL||LOAD-BEARING PRESSURE (pounds per square foot)|
|Sedimentary and foliated rock||4,000|
|Sandy gravel and/or gravel (GW and GP)||3,000|
|Sand, silty sand, clayey sand, silty gravel and clayey gravel (SW, SP, SM, SC, GM and GC)||2,000|
|Clay, sandy, silty clay, clayey silt, silt and sandy siltclay (CL, ML, MH and CH)||1,500b|
For SI: 1 pound per square foot = 0.0479 kPa.
a.Where soil tests are required by Section R401.4, the allowable bearing capacities of the soil shall be part of the recommendations.
b.Where the building official determines that in-place soils with an allowable bearing capacity of less than 1,500 psf are likely to be present at the site, the allowable bearing capacity shall be determined by a soils investigation.
Instead of a complete geotechnical evaluation, where top or subsoils are compressible or shifting, they shall be removed to a depth and width sufficient to ensure stable moisture content in each active zone and shall not be used as fill or stabilized within each active zone by chemical, dewatering or presaturation.