18E.70.040 Flood Hazard Area Standards

18E.70.040 Flood Hazard Area Standards.

1. New construction done by or for Pierce County, such as bridges, roads, flood control works, revetments, retaining walls, drainage structures, sewer or water lines, parks, public facility or other development necessary to promote the public's health, safety, and welfare shall be allowed in a flood hazard area when:

a. The project is prepared under the responsible charge of and is signed and dated by a registered professional engineer in the State of Washington. The project shall be designed so the project does not result in any increase in flood levels during the occurrence of the base flood discharge (zero-rise) or obstruct the floodway or cause an adverse impact to critical fish or wildlife habitat on adjacent, cross-channel, or upstream or downstream properties and will keep documentation on how the project meets these requirements; and

b. The improvements utilize appropriate flood hazard protection standards.

2. Repair and replacement of existing public and private utilities and associated development necessary to promote the public's health, safety, and welfare shall be allowed in a flood hazard area when:

a. The improvements utilize appropriate flood hazard protection standards; and

b. The project is prepared under the responsible charge of, and is signed and dated by, a registered professional engineer in the State of Washington. The project shall be designed so the project does not result in any increase in flood levels during the occurrence of the base flood discharge (zero-rise) or obstruct the floodway or cause an adverse impact to critical fish or wildlife habitat on adjacent, cross-channel, or upstream or downstream properties, and will keep documentation on how the project meets these requirements.

3. A Federal Emergency Management Agency (FEMA) elevation certificate shall be required for new construction, additions affixed to the side of a structure, and substantial improvements located within flood hazard areas. The County may approve alternative documentation that verifies compliance for development determined to be above the BFE and not shown on the FEMA map as Zone A or V. The most current version of the FEMA elevation certificate must be completed by a professional land surveyor, currently licensed in the State of Washington, and kept on file with the Pierce County Planning and Public Works Department. Additional certifications will be required and retained for V Zone construction, engineered flood openings and floodproofing.

4. Agricultural chemicals, fertilizers, pesticides, and similar hazardous materials that may contaminate surface and groundwater in the event of flood inundation shall not be stored in agricultural accessory structures except as otherwise provided within PCC 18E.70.040.B and C below¹.

5. Plat notes for the Puyallup, Carbon, Nisqually, Greenwater, and White Rivers and Creeks and for other Flood Hazard Areas as well, shall be placed on the face of any final plat (includes commercial, industrial, single family, and multi-family residential), short plat, large lot, or binding site plan documents which lie in these areas. The plat notes shall be per PCC 18E.10.140 – Appendix B, Title and Plat Notification/Plat Notes.

B. Floodways. Any development, encroachment, filling, clearing, grading, new construction, and substantial improvement shall be prohibited within the floodway, except as follows:

1. When located in a floodway only designated as a floodway because it is in a Channel Migration Zone and when in conformance with PCC 18E.20.040, Nonconforming Uses.

2. Structures that do not require a building permit and that do not have any associated fill.

3. Agricultural activities as follows:

a. Agricultural activities that do not require the installation of structures and that do not have any associated fill;

b. Agricultural structures that do not require a building permit and have no associated fill;

c. The storage and manufacture of compost outside the FEMA mapped floodway on land meeting the definition of farm or agricultural land pursuant to RCW 84.34.020; provided that the compost is manufactured from feedstock produced on-site. The composting operation shall meet the requirements of WAC 173-350-220 and the maximum volume of composting material on site at any one-time shall be limited to 25 cubic yards. Compost and composting material meeting the requirements of this subsection shall not be considered fill; and

d. The import and application of compost for purposes of soil amendment on land meeting the definition of farm or agricultural land pursuant to RCW 84.34.020 and located outside the FEMA mapped floodway. The maximum amount of compost imported to a site shall not exceed 20 cubic yards per acre per year. Compost imported to a site shall be applied within 180 days and not more than one year's supply of compost shall be present on site. The import and application of compost consistent with the requirements of this subsection shall not be considered fill.

4. In the event that construction, reconstruction, or replacement in a floodway is allowed, the construction must comply with the standards of PCC 18E.70.040 C.

5. Repairs of an existing structure within the footprint of the existing structure provided the repairs are not substantial improvements.

6. Repair, reconstruction, and replacement of substantially damaged residential structures in accordance with WAC 173-158-076, as amended, when recommended by the Department of Ecology and constructed to the standards set forth within PCC 18E.70.040 C.

7. Repair, reconstruction, replacement, and improvements to existing farmhouses pursuant to WAC 173-158-075, as amended, within an Agricultural Resource Lands (ARL) or Rural Farm (RF) zone when in compliance with the following standards:

a. The new farmhouse is a replacement for an existing farmhouse on the same farm site;

b. There is no potential safe building site for a replacement farmhouse on the same farm site outside the designated floodway or the location requires close proximity to other structures in the farm operation in order to maintain the integrity and operational viability of the farm; in no case shall a replacement be located into an area with higher flood hazards in terms of depths, velocities and erosion;

c. Repairs, reconstruction, or improvements to a farmhouse shall not increase the total square footage of encroachment of the existing farmhouse;

d. A replacement farmhouse shall not exceed the total square footage of encroachment of the structure it is replacing;

e. A farmhouse being replaced shall be removed, in its entirety, including foundation, from the floodway within ninety days after occupancy of a new farmhouse;

f. For substantial improvements, and replacement farmhouses, the construction shall comply with the standards set forth in PCC 18E.70.040 C.;

g. New and replacement water supply systems are designed to eliminate or minimize infiltration of flood waters into the system;

h. New and replacement sanitary sewerage systems are designed and located to eliminate or minimize infiltration of flood water into the system and discharge from the system into the flood waters; and

i. All other utilities and connections to public utilities are designed, constructed, and located to eliminate or minimize flood damage.

8. Repairs, reconstruction, replacement, or improvements to existing non-residential agricultural structures as follows:

a. The non-residential agricultural structure is a replacement for an existing structure on the same farm site and the use of the structure must be limited to agricultural purposes only;

b. There is no potential safe building site for a replacement non-residential agricultural structure on the same farm site outside the designated floodway or the location requires close proximity to other structures in the farm operation in order to maintain the integrity and operational viability of the farm; in no case shall a replacement be located into an area with higher flood hazards in terms of depths, velocities and erosion;

c. An agricultural structure larger than 576 square feet must build the lowest floor to the standards of subsection C.7 of this Section or receive a variance. Agricultural structures that are smaller can be built at grade but must be built, repaired, or reconstructed with flood-resistant materials for the exterior and interior building components and elements (i.e., foundation, wall framing, exterior and interior finishes, flooring, etc.) for all parts of the building below the BFE;

d. The agricultural structure must be adequately anchored to prevent flotation, collapse, or lateral movement of the structure. All of the building's structural components must be capable of resisting specific flood-related forces including hydrostatic, buoyancy, hydrodynamic and debris impact forces;

e. The agricultural structure must meet the NFIP openings requirement. NFIP requires that enclosure walls or foundations walls, subject to the 1 percent recurrence interval flood, contain openings that will permit the automatic entry and exit of floodwaters;

f. Any mechanical, electrical, or other utility equipment must be located at or above the lowest floor per subsection C of this Section or floodproofed so that they are contained within a watertight, floodproofed enclosure that is capable of resisting damage during flood conditions;

g. An agricultural structure being replaced shall be removed, in its entirety, including foundation, from the floodway within 90 days of final inspection of the structure by Pierce County;

h. New and replacement water supply systems are designed to eliminate or minimize infiltration of flood waters into the system;

i. New and replacement on-site sewerage systems are designed and located to eliminate or minimize infiltration of flood water into the system and discharge from the system into the flood waters;

j. All other utilities and connections to public utilities are designed, constructed, and located to eliminate or minimize flood damage;

k. Storage of agricultural chemicals, fertilizers, pesticides, and similar hazardous materials shall be permitted only where no other on-site storage alternative outside the floodplain exists and the building permit is accompanied by a written description of how on-site storage procedures will prevent the release of agricultural chemicals during a flood event; and

l. The repair, reconstruction, replacement, or improvement of the non-residential agricultural structures shall not exceed the square footage of the structure being repaired or replaced except where through an approved zero-rise analysis the applicant has shown it will not result in an increase in flood elevations.

9. Construction of new non-residential agricultural structures are allowed in the Lower Puyallup River area, downstream of River Mile 6, under the criteria set forth in subsection B.8 of this Section.

10. Park and recreational uses and facilities that do not require the installation of structures and that do not have any associated fill.

11. For existing park and recreational property uses, existing park and recreation structures and facilities may be substantially improved provided they are located outside of the FEMA mapped floodway and comply with the following conditions:

a. The repair, reconstruction, replacement, and improvement of the existing structure and facility complies with the elevation requirements set forth in subsection C of this Section.

b. The repair, reconstruction, replacement, and improvement of the existing structure and facility shall not increase the total square footage of encroachment of the existing structure and facility.

c. Any fill material used to elevate the structure(s) shall provide compensatory storage per subsection C.4.a of this Section. Backfill material within a stem wall crawlspace foundation does not apply to the compensatory storage requirement.

d. The existing access to the site shall not be required to be elevated to 1.0 feet above the BFE, as outlined in subsection C.3 of this Section.

e. The repair, reconstruction, replacement, and improvement of the existing structure and facility will not result in an increase in flood elevations.

12. Individual recreational vehicles which are licensed and ready for highway use, not permanently attached to the site, and occupy the site for fewer than 180 consecutive days. Vehicles may return to the same site after demonstrating road readiness.

13. Habitat enhancement/stream restoration activities are permitted subject to the provisions outlined in subsection D of this Section.

14. Rehabilitation, reconstruction, or an upper story addition to an existing structure that does not exceed the limits for a substantial improvement.

15. Private bridges may be allowed to cross the floodway provided that the structure meets the requirements contained in PCC 18E.70.030 and the following:

a. The lowest structural member of a private bridge proposed to cross the floodway portion of any of the rivers listed in PCC 18E.70.020.B.4 shall be a minimum of 6 feet above the base flood elevation.

b. The lowest structural member of a private bridge proposed to cross the floodway portion of any other watercourse shall be a minimum of 1 foot above the base flood elevation.

C. Flood Fringe Areas. All activities allowed in subsection B of this Section shall be permitted in a flood fringe area. Any other proposed development, encroachments, filling, clearing or grading, new construction, and substantial improvements are prohibited in a flood fringe area except as follows:

1. Structures that do not require a building permit and that do not have any associated fill are permitted.

2. All other regulated activities shall only be allowed when the proposed development is located on an existing lot of record that was created prior to March 1, 2005. Applicants shall demonstrate there are no other feasible alternatives that would allow the proposed development to occur completely outside the flood hazard area. At a minimum, the following shall be demonstrated:

a. The development cannot be located outside the flood hazard area due to topographic constraints of the parcel or size and/or location of the parcel in relation to the limits of the flood hazard area and a building setback variance has been reviewed, analyzed, and rejected as a feasible alternative to encroachment into the flood hazard area; and

b. The proposed development shall not cause an adverse impact to adjacent, cross-channel, or upstream or downstream properties.

a. Access including, but not limited to, roads, bridges, driveways, emergency vehicle access, and other access routes and easements, where allowed, shall be constructed and armored based on the standards in PCC 18E.70.040 C.4. and elevated a minimum of 1 foot above the base flood elevation. Provided, however, that the requirement to elevate the access may be waived in whole or part by the PPW Department whenever it is determined that the roadway to which the access connects is located at an elevation that would make the roadway impassible during the base flood and no plan for elevating the roadway exists.

b. Parking lots shall be elevated to a minimum of one-half foot below the base flood elevation.

4. Grading and Filling. When development is permitted under this subsection, it shall be designed to a zero-rise standard as set forth in PCC 18E.70.030.E and PCC 18E.70.050 – Appendix A. Any filling, grading, or clearing associated with the permitted development shall not increase flood hazards, water velocities, or flood elevations. In addition to meeting the requirements for zero-rise, all permitted development must also meet the following requirements:

a. Compensatory Storage. New excavated storage volume shall be equivalent to the flood storage capacity eliminated by filling or grading within the flood fringe. Equivalent shall mean that the storage removed shall be replaced by equal live storage volume between corresponding 1-foot contour intervals that are hydraulically connected to the floodplain through their entire depth (refer to Figure 18E.70-13 in Chapter 18E.120 PCC). The compensatory storage requirement may be waived for pre-existing lots where compensatory storage is not available and filling or grading is limited to either elevating the interior building crawl space (see Figure 18E.70-14) or providing positive drainage from the structure in accordance with IBC standards.

The requirement for compensatory storage may be waived at the discretion of a Pierce County Certified Floodplain Manager in flood hazard areas where the source of flooding is from Puget Sound or when all of the following conditions exist:

(1) The flood hazard area is the result of emergent groundwater;

(2) Groundwater flooding is isolated in porous soils; and

(3) No surface flow component contributes to flooding.

b. Flow Conveyance. New excavated conveyance areas shall be equivalent to existing conveyance within the flood fringe. Equivalent shall mean a mechanism for transporting water from one point to another using an open channel system.

c. Erosion Protection. Development shall be protected from flow velocities greater than 2 feet per second through the use of bio-engineering methods or, when bio-engineering methods have been deemed insufficient to protect development, then hard armoring may be utilized. All erosion protection shall extend 1 to 3 feet, depending on development requirements, above the base flood elevation and shall be covered with topsoil and planted with native vegetation. (See Figure 18E.70-14 in Chapter 18E.120 PCC.)

a. New construction, additions affixed to the side of an existing structure, and substantial improvement of hazardous facilities and special occupancy structures are prohibited.

b. New construction of an essential facility, reconstruction of an existing essential facility, or additions to an existing essential facility that exceed the threshold for substantial improvement shall be permitted when no feasible alternative site is available outside the flood hazard area. Such regulated activities are subject to the following:

(1) Essential facilities with a slab-on-grade or crawlspace shall have the lowest floor and any utilities and ductwork elevated a minimum of 3 feet above base flood elevation. (See Figure 18E.70-14 in Chapter 18E.120 PCC.)

(2) Essential facilities elevated by piers or pilings shall have the bottom of the lowest horizontal structural member and any utilities and ductwork elevated a minimum of 3 feet above the base flood elevation and must be designed by a professional structural engineer. (See Figure 18E.70-15 in Chapter 18E.120 PCC.)

(3) Essential facilities shall be armored based on the standards in subsection C.4 of this Section. Flood resistant materials, construction methods and practices shall be used in construction of such facilities.

(4) Adequate containment and sealing measures must be taken to insure that toxic or explosive substances will not be displaced or released into floodwaters.

6. Structures. Single-family, two-family, multi-family, mobile/manufactured homes, commercial, and industrial structures, etc., except for critical facilities as set forth in subsection C.5 of this Section, shall be allowed subject to the following standards:

a. New construction, additions affixed to the side of an existing structure, and substantial improvement of any structure shall have the lowest floor elevated a minimum of 1 foot above base flood elevation when constructed with a crawlspace or a minimum of 2 feet above the base flood elevation when constructed using a slab on grade construction, except as provided in PCC 18E.70.040 C.6.c. and d. below. (See Figure 18E.70-14 in Chapter 18E.120 PCC.) Flood resistant materials, construction methods and practices shall be used.

b. New construction, additions affixed to the side of an existing structure, and substantial improvement of any structure elevated by piers or pilings shall have the bottom of the lowest horizontal structural member elevated a minimum of 2 feet above the base flood elevation, except as provided in subsections 18E.70.040 C.6.c. and d. below, and must be designed by a professional structural engineer. Areas below the lowest horizontal structural member shall not be enclosed and shall remain free of obstructions. Flood resistant materials, construction methods and practices shall be used. Fully enclosed areas below the lowest horizontal structural member are prohibited. Screens, louvers, or other coverings or devices are allowed if they do not restrict the entry and exit of flood waters. Skirting for mobile homes is allowed where the material is not rigid and is easily collapsed or removed by floodwaters.

c. New construction of minor residential detached accessory structures and substantial improvement of minor residential detached accessory structures including, but not limited to, storage buildings, detached garages, sheds, and small pole buildings, together with attendant utility facilities may as an alternative to the provisions of PCC 18E.70.040 C.6.a. and b. be flood proofed when compliant with the following:

(1) The structure must have a low potential for structural flood damage and shall not exceed 576 square feet in size;

(2) Be designed and oriented to allow the free passage of floodwaters through the structure in a manner affording minimum flood damage;

(3) Not be used for human habitation;

(4) Shall not have internal plumbing nor be connected to sanitary sewage/on-site septic facility;

(5) Include adequate hydrostatic flood openings;

(6) Use flood resistant materials below the flood protection elevation (minimum elevation required per foundation type as set forth in PCC 18E.70.040 C.6.a. and b. above);

(7) Must offer minimum resistance to the flow of floodwater;

(8) Must be anchored to prevent flotation, collapse or lateral movement; and

(9) All utilities must comply with the standards set forth in subsection 18E.70.040 C.9.e.

d. New commercial, industrial, or other non-residential structures and substantial improvements of such structures shall elevate the lowest floor to the flood protection elevation (minimum elevation required per foundation type as set forth in subsections C.6.a and C.6.b of this Section) or meet the following standards:

(1) Dry flood-proof the structure to the flood protection elevation to meet the following standards:

(a) The applicant shall provide certification by a civil or structural engineer that the dry flood-proofing methods are adequate to withstand the flood depths, pressures, velocities, impacts, uplift forces, and other factors associated with the base flood. After construction, the engineer shall certify that the permitted work conforms to the approved plans and specifications; and

(b) Approved building permits for dry flood-proofed non-residential structures shall contain a statement notifying applicants that flood insurance premiums are based upon rates for structures that are 1 foot below the BFE;

(2) Use materials and methods that are resistant to and minimize flood damage;

(3) Dry flood-proof all electrical, heating, ventilation, plumbing, air conditioning equipment, and other utility and service facilities to, or elevated above, the flood protection elevation.

e. A written notice regarding the use of flood proofing, in a form approved by the Department of Planning and Public Works, shall be recorded with the title of the property. The notice shall:

(1) Disclose that the structure is located in a flood hazard area and portions of the structure are below the base flood elevation;

(2) Disclose that flood proofing has been utilized and detailed instructions of how to operate and maintain all flood-proofing design features;

(3) Include a diagram identifying the flood proofed spaces; and

(4) Disclose that the use of flood proofing in lieu of elevating a structure to the flood protection elevation may result in increased flood insurance premiums.

f. The property owner shall be responsible for notifying future owners of the use of flood proofing and associated risks and limitations.

a. Storage of agricultural chemicals, fertilizers, pesticides, and similar hazardous materials shall be permitted only where no other on-site storage alternative outside the floodplain exists and the building permit is accompanied by a written description of how on-site storage procedures will prevent the release of agricultural chemicals during a flood event.

b. The lowest floor in an agricultural accessory structure shall be located at the base flood elevation or higher provided that the structure is designed to automatically equalize hydrostatic flood forces on exterior walls by allowing for the entry and exit of floodwaters. Designs for meeting this requirement must either be certified by a professional engineer in the State of Washington or must meet or exceed the following minimum criteria:

(1) A minimum of two openings having a total net area of not less than one square inch for every square foot of enclosed area subject to flooding shall be provided;

(2) The bottom of all openings shall be no higher than 1 foot above grade; and

(3) Openings may be equipped with screens, louvers, or other covering or devices provided that they permit the automatic entry and exit of floodwaters.

8. Livestock Flood Sanctuaries. Livestock flood sanctuaries pursuant to RCW 86.16.190, as amended, shall be allowed when in compliance with the following minimum criteria:

a. The livestock sanctuary is accessory to a farming operation located within an Agricultural Resource Lands (ARL), Rural Separator (RSep), Rural 10 (R10), or Rural Farm (RF) zone and located on the same site as the farming operation;

b. The keeping of livestock is a component of the farming operation;

c. There is no other suitable holding area on the site outside the floodplain to which the livestock have access;

d. The livestock flood sanctuary complies with the compensatory storage requirements set forth within subsection C.4.a of this Section;

e. The livestock sanctuary will not result in an increase in flood elevations;

f. The livestock sanctuary is located in the area least subject to risk from floodwaters; and

g. Structures shall not be erected or placed upon a livestock flood sanctuary. A notice in a form approved by the Planning and Public Works Department shall be recorded with the title indicating the limits of the livestock flood sanctuary and acknowledging the prohibition of structures.

a. Construction of a basement is prohibited.

b. Crawl spaces shall meet Pierce County Building Code requirements. Crawl spaces shall either be backfilled with clean earth material and have a finished grade within the crawl space that is at least 1 foot above the base flood elevation and the following:

(1) The building must be designed and adequately anchored to resist floatation, collapse, and lateral movement of the structure resulting from hydrodynamic and hydrostatic loads, including the effects of buoyance.

(2) The height of the crawlspace, measured from the interior grade of the crawlspace to the next higher floor must not exceed 5 feet at any point.

(3) Provide a minimum of two openings on each of two opposite side walls in the direction of flow, with each of these walls having a total open area of not less than one square inch for every square foot of enclosed area subject to flooding;

(4) Design the bottom of all openings to be no higher than 1 foot above grade, the higher of the interior or exterior grade; and

(5) Screens, louvers, or other coverings or devices are allowed if they do not restrict entry and exit of flood waters.

c. Flood proofing in lieu of elevating the structure is prohibited, except for non-residential structures and residential accessory structures as set forth in PCC 18E.70.040 C.6.c and d.

d. All single-family, two-family, multi-family, mobile/manufactured homes, commercial, and industrial structures shall be placed on standard concrete stem wall/footing foundations or piles, piers, or column foundations as designed in accordance with Figures 18E.70-14 or 18E.70-15 in Chapter 18E.120 PCC. Structures shall also be anchored to the foundation to resist floatation, collapse, and lateral movement.

e. Electrical, heating, ventilation, plumbing, air-conditioning equipment, other service facilities, and associated ductwork shall be elevated to at least the minimum required lowest floor elevation; however, the Department may approve a lesser minimum distance above base flood elevation provided that the systems are designed to prevent floodwater from entering or accumulating within the components. (See Figure 18E.70-15 in Chapter 18E.120 PCC.)

a. New and replacement public water sources (i.e., wells and water supply lines) and public sanitary sewage conveyance systems are allowed. These systems shall be designed to withstand scour resulting from flow velocity, minimize or eliminate infiltration of floodwaters into the systems, and minimize or eliminate discharge from the systems into floodwaters.

b. All replacement wells and new or replacement on-site sewage systems (OSS) shall be designed to minimize or eliminate impairment to them or contamination from/to them during flooding (i.e., infiltration of floodwaters into or discharge out of the systems). They shall not be located in groundwater, pothole or no-outlet floodplains.

c. All new individual wells shall be prohibited. Conveyance systems from a structure to a well or OSS located outside of the flood hazard area shall be allowed provided these systems are designed to meet the standards in subsection C.3 of this Section.

D. Alteration of Watercourses. Any alteration of a watercourse shall comply with the following standards:

1. Pierce County will notify adjacent communities and the Washington State Department of Ecology prior to any alteration or relocation of a watercourse proposed by the applicant and submit evidence of such notification to the Federal Insurance Administration.

2. Pierce County shall require that maintenance be provided within the altered or relocated portion of said watercourse, so that the flood-carrying capacity is not diminished. Therefore, if the maintenance program calls for future cutting of planted native vegetation used in performing the alteration, the system shall be oversized at the time of construction to compensate for said vegetation growth or any other natural factor that may need future maintenance.

3. The project engineer shall design the watercourse alteration so the activity does not increase the water surface elevation (zero-rise); decrease the capacity, storage, and conveyance of the watercourse; nor cause an adverse impact to adjacent, cross-channel, or upstream or downstream properties. Pierce County has the discretion to determine if potential impacts may be insignificant or not applicable.

E. Coastal Flood Hazard Areas and Coastal Flood Fringe Areas. Any proposed development, encroachments, filling, clearing, grading, new construction, and substantial improvements within a coastal flood hazard area or coastal flood fringe area shall be subject to the following standards:

a. Roads, bridges, driveways, emergency vehicle access, and access routes and easements, where allowed, shall be constructed and armored based on the standards in PCC 18E.70.040 C.3. and elevated a minimum of 1 foot above the base flood elevation.

b. Parking lots shall be elevated to a minimum of one-half foot above the base flood elevation.

c. Private bridges may be allowed to cross Puget Sound marine waters subject to all Federal, State and local requirements.

2. Grading and Filling. All permitted development must also meet the following requirements:

a. The use of fill for structural support of buildings is prohibited.

b. Man-made alteration of sandbars or spits shall be prohibited.

3. Structures. Single-family, two-family, multi-family, mobile/manufactured homes, commercial, and industrial structures shall be allowed subject to the following standards:

a. Electrical, heating, ventilation, plumbing, air-conditioning equipment, and other service facilities and associated ductwork shall be elevated a minimum of 2 feet above base flood elevation. (See Figure 18E.70-16 in Chapter 18E.120 PCC.)

b. New construction, additions affixed to the side of an existing structure, and substantial improvement of any structure located seaward of a line 2 feet above the base flood elevation may be allowed when elevated by piers or pilings provided:

(1) The bottom of the lowest horizontal structural member is elevated a minimum of 2 feet above the base flood elevation.

(2) The structure must be designed by a professional structural engineer.

(3) Areas below the lowest horizontal structural member shall not be enclosed and shall remain free of obstructions.

(4) Structures shall be anchored to the foundation to resist floatation, collapse, and lateral movement due to the effects of wind and water loads acting simultaneously on all building components. Flood resistant materials, construction methods and practices shall be used. Water loading values used shall be those associated with the base flood. Wind loading values used shall be those required by the Pierce County Building Code.

(5) All new construction shall be located landward of a contour line delineated at elevation 9.5 feet, NAVD 1988. (Note: The 9.5 feet elevation approximates mean high tide, where mean high tide varies from 8.0 to 9.25 NAVD 1988 along Pierce County Puget Sound Marine Waters.)

c. New construction, additions affixed to the side of an existing structure, and substantial improvement of any structure located outside of a mapped V Zone and in the coastal flood fringe area may be allowed when elevated on a stem wall foundation provided (Figure 18E.70-16):

(1) The footing of the stem wall is placed on existing subgrade and per Figure 18E.70-14.

(2) The crawlspace is backfilled to an elevation that is 2 feet above the base flood elevation.

d. New construction, additions affixed to the side of an existing structure, and substantial improvement of any structure located outside of a mapped V Zone and in the coastal flood fringe area, may be allowed when elevated on a slab on grade with a stem wall foundation provided:

(1) The footing of the stem wall is placed on existing subgrade and any fill in front of the stem wall is placed per Figure 18E.70-14.

(2) The slab is poured to an elevation that is a minimum of 3 feet above the base flood elevation.

e. New construction of minor residential accessory boat storage structures and substantial improvement of minor residential accessory boat storage structures located outside of a V zone may, as an alternative to the provisions of subsection E.3.b of this Section, be flood-proofed when compliant with the following:

(1) The structure must have a low potential for structural flood damage and shall not exceed 576 square feet in size;

(2) Be designed and oriented to allow the free passage of floodwaters through the structure in a manner affording minimum flood damage;

(3) Not be used for human habitation;

(4) Shall not have internal plumbing nor be connected to sanitary sewage/on-site septic facilities;

(5) Include adequate hydrostatic flood openings;

(6) Use flood resistant materials below the flood protection elevation;

(7) Must offer minimum resistance to the flow of floodwater;

(8) Must be anchored to prevent flotation, collapse or lateral movement;

(9) All utilities must comply with the standards set forth in subsection C.9.e of this Section;

(10) New construction shall be located landward of a contour line delineated at elevation 10.5 feet, NAVD 1988;

(11) Substantial improvement of existing structures, including those located over water, shall ensure that the bottom of the lowest horizontal structural member is located above elevation 10.5 feet, NAVD 1988, or the pre-substantial improvement elevation, whichever is greater;

(12) No expansion of a building footprint over water shall occur;

(13) The structure is compliant with the requirements of Title 20 PCC; and

(14) Boat storage structures and similar storage structures which exceed any of the standards set forth in subsections (1) through (11) above, shall be subject to the requirements set forth in subsections E.3.a and E.3.b of this Section.

f. Adequate containment and sealing measures must be taken to insure that toxic or explosive substances will not be displaced or released into Puget Sound marine waters.

g. Rehabilitation, reconstruction, or an upper story addition to an existing structure that does not exceed the limits for a substantial improvement shall be allowed.

b. All new or replacement individual wells and on-site sewage systems (OSS) shall be subject to the Tacoma-Pierce County Health Department regulations.