18.92.070 GWP – Groundwater damage protection.
A. Purpose. This designation is intended to limit the construction of basements and structures below the natural elevation of the ground surface in order to minimize damage caused by elevated groundwater.
B. Regulations and Standards.
1. Any new construction or any additions to existing basements and structures below natural elevation of the ground surface is prohibited, except as permitted in this subsection. The placement of foundations, footings or crawlspaces below the natural elevation of the ground surface is permitted, except that crawlspaces shall not be used for mechanical combustion devices and electrical equipment or storage purposes of any kind below the surface of the natural elevation of the exterior ground surface.
2. Alternative Compliance. Any construction that is not otherwise in compliance with subsection (B)(1) of this section may be permitted if a sealed engineer’s report is submitted that contains the information in this subsection with a form required by the department. Upon submission of the required form and engineer’s report, the director will accept the alternative compliance document for filing with the department.
a. Foundation Stability. The report must:
i. Describe the building materials utilized in the construction of the structure below natural elevation.
ii. Certify that all supports and building structural components in contact with the ground are constructed with flood damage-resistant material.
iii. Certify that all metal components and fasteners within the structure below natural elevation are constructed with flood damage-resistant material and will not adversely react to wood preservative treatments used in the structure.
iv. Certify that wood components are preservative-treated to withstand anticipated environmental conditions.
v. Provide engineering analysis and calculations showing that the foundation is capable of withstanding anticipated horizontal hydrostatic and vertical buoyancy forces.
b. Electrical and Mechanical Equipment. The report must also:
i. List all electrical and mechanical equipment installed in the areas below natural elevation.
ii. Certify that electrical equipment has adequate electrical grounding and is suitable for installation in wet locations as defined by the most current version of the National Electrical Code.
iii. Certify that mechanical combustion devices and associated electrical equipment are not installed in areas below natural elevation.
iv. Certify that any other mechanical equipment is installed in a location to avoid groundwater flooding damage. (Ord. 2020-06 § 3, 2020; Ord. 2005-21 § 2, 2005; Ord. 94-088 § 2, 1995. 2004 Code § 18.48.070.)