Chapter 15.12
EXCAVATION AND GRADING

Sections:

15.12.010    Excavation and grading.

15.12.010 Excavation and grading.

Section(s) 1804 of the International Building Code in this chapter are amended in accordance pursuant to the authority provided in RCW 19.27.040 to read as follows:

Section 1804.1 of the IBC Excavation near foundations.

Excavation for any purpose shall not reduce vertical or lateral support for any foundation or adjacent foundation without first underpinning or protecting the foundation against detrimental lateral or vertical movement, or both.

Section 1804.2 Underpinning.

Where underpinning is chosen to provide the protection or support of adjacent structures, the underpinning system shall be designed and installed in accordance with Chapters 18 and 33 of International Building Code.

Section 1804.2.1 Underpinning sequencing.

Underpinning shall be installed in a sequential manner that protects the neighboring structure and the working construction site. The sequence of installation shall be identified in the approved construction documents.

Section 1804.3 Placement of backfill.

The excavation outside the foundation shall be backfilled with soil that is free of organic material, construction debris, cobbles, and boulders or with a controlled low-strength material (CLSM). The backfill shall be placed in lifts and compacted in a manner that does not damage the foundation or the waterproofing or dam proofing material.

1.    Exception: CLSM need not be compacted.

Section 1804.4 Site grading.

The ground immediately adjacent to the foundation shall be sloped away from the building at a slope of not less than one-unit vertical in 20 units horizontal (5-percent slope) for a minimum distance of 10 feet (3048 mm) measured perpendicular to the face of the wall. If physical obstructions or lot lines prohibit 10 feet (3048 mm) of horizontal distance, a 5-percent slope shall be provided to an approved alternative method of diverting water away from the foundation. Swales used for this purpose shall be sloped not less than 2-percent in areas located within 10 feet (3048 mm) of the building foundation. Impervious surfaces within 10 feet (3048 mm) of the building foundation shall be sloped not less than 2-percent away from the building.

1.    Exceptions:

a.    Where climatic or soil conditions warrant, the slope of the ground away from the building foundation shall be permitted to be reduced to not less than one-unit vertical in 48 units horizontal (2-percent slope).

b.    Impervious surfaces shall be permitted to be sloped less than 2-percent where the surface is a door landing or ramp that is required to comply with Section 1010.1.5, 1012.3 or 1012.6.1 of the International Building Code.

c.    The procedure used to establish the final ground level adjacent to the foundation shall account for additional settlements of the backfill.

1804.5 Grading and fill in flood hazard areas.

A.    In flood hazard areas established in Section 1612.3 of the International Building Code, grading or fill, or both, shall not be approved: See Chapter 15.16 for additional provisions.

1.    Unless such fill is allowed in accordance with Chapter 15.16 and placed, compacted, and sloped to minimize shifting, slumping, and erosion during the rise and fall of floodwater and, as applicable, wave action.

2.    In floodways, unless allowed in accordance with Chapter 15.16 and it has been demonstrated through hydrologic and hydraulic analyses performed by a registered design professional in accordance with standard engineering practice that the proposed grading or fill, or both, will not result in any increase in flood levels during the occurrence of the design flood.

3.    In coastal high-hazard areas, unless allowed in accordance with Chapter 15.16 and such fill is conducted or placed to avoid diversion of water and waves toward any building or structure.

4.    Where design flood elevations are specified but floodways have not been designated, unless allowed in accordance with Chapter 15.16 and it has been demonstrated that the cumulative effect of the proposed flood hazard area encroachment, when combined with all other existing and anticipated flood hazard area encroachment, will not increase the design flood elevation more than one (1) foot (305 mm) at any point.

Section 1804.6 Compacted fill material.

Where shallow foundations will bear on compacted fill material, the compacted fill shall comply with the provisions of an approved geotechnical report, as set forth in Section 1803 of the International Building Code.

Exception: Compacted fill material 12 inches (305 mm) in depth or less need not comply with an approved report, provided that the in-place dry density is not less than 90 percent of the maximum dry density at optimum moisture content determined in accordance with ASTM D1557. The compaction shall be verified by special inspection in accordance with Section 1705.6 of the International Building Code.

Section 1804.7 Controlled low-strength material (CLSM).

Where shallow foundations will bear on controlled low-strength material (CLSM), the CLSM shall comply with the provisions of an approved geotechnical report, as set forth in Section 1803 of the International Building Code.

(Ord. O-03-21 § 4)