Sections:
16-11.1 Applicability.
16-11.2 Definitions.
16-11.3 Floodproofing requirements in certain areas.
16-11.4 Floodproofing methods.
16-11.5 Structural requirements.
16-11.6 Violations--Penalty.
Sec. 16-11.1 Applicability.
(a) General. The provisions contained herein are applicable to the construction of all new
buildings and structures, relocation and major alterations, additions or reconstruction of existing buildings
within the flood hazard districts as delineated on the flood boundary and floodway
maps and flood insurance rate maps, and any amendments by the Federal Emergency
Management Agency, on file with the department of land utilization, City and County
of Honolulu.
These provisions shall also apply to developments adjacent to drainage facilities outside the
flood hazard district which are determined to be within a floodway area or
a flood fringe area in accordance with Section 21-9.10-9.
(b) Nonconforming Buildings. Any building or structure which was previously lawful prior to the
effective date of this article but which is not in conformity with this
article may be continued subject to the provisions of Section 21-9.10-12.
(c) Exemptions. The provisions contained herein shall not apply:
(1) To buildings and structures exempted from the flood hazard district provisions under Section
21-9.10-13;
(2) To buildings and structures which have been granted a flood hazard variance under
provisions of Section 21-9.10-11.
(Sec 16-7.1, R.O. 1978 (1983 Ed.); Sec. 16-5.1, R.O. 1978 (1987 Supp. to
1983 Ed.); Am. Ord. 90-57)
Sec. 16-11.2 Definitions.
For the purpose of this article, the following terms are defined in Chapter
21, Article 10:
Coastal high hazard district;
Flood elevation;
Flood fringe;
Flood hazard district;
Floodproof;
Floodway;
Regulatory flood. (Sec. 16-7.2, R.O. 1978 (1983 Ed.); Sec. 16-5.2, R.O. 1978 (1987
Supp. to 1983 Ed.); Am. Ord. 90-57)
Sec. 16-11.3 Floodproofing requirements in certain areas.
(a) General. Building permit applications for structures which are required to be floodproofed under
the provisions of Section 21-9.10 and this article shall be accompanied by a
statement of a registered professional engineer or architect that to the best of
such person's knowledge, information and belief, the floodproofing methods are adequate to resist
the flood depths, pressures, velocities, impact and uplift forces, and other factors associated
with the flood, including flood waters due to tsunamis in coastal high hazard
districts.
(b) Floodproofing of Buildings above Regulatory Flood Elevation. All buildings and structures which are
required to be elevated above the regulatory flood elevation shall be floodproofed by
building on natural terrain above the regulatory flood elevation on natural undisturbed ground
or by building on stilts or by building on fill (unless fill is
specifically prohibited by Section 21-9.10, in the particular flood hazard district) or by
other approved methods.
(c) Waterproofing of Buildings Below Regulatory Flood Elevation. Any building or portion thereof, not
used for human habitation, and which is permitted to be below the regulatory
flood elevation shall either have the space below the regulatory flood elevation free
of obstructions or shall be designed and constructed so that below the regulatory
flood elevation, the structure is watertight with walls substantially impermeable to the passage
of water and with structural components having the capability of resisting hydrostatic and
hydrodynamic loads and effects of buoyancy due to the regulatory flood. Compliance with
the waterproofing provisions of the "Flood-Proofing Regulations," pamphlet No. EP1165 2 314, published
for the Office of the Chief Engineers, U.S. Army, Washington, D.C., shall be
deemed to be in compliance with this section. Within coastal high hazard districts,
however, any usable enclosed space below the regulatory flood elevation shall be constructed
with breakaway walls intended to collapse under stress without jeopardizing the structural support
of the building. Areas enclosed by such breakaway walls shall not be used
for human habitation.
(Sec. 16-7.3, R.O. 1978 (1983 Ed.); Sec. 16-5.3 R.O. 1978 (1987 Supp. to
1983 Ed.); Am. Ord. 90-57)
Sec. 16-11.4 Floodproofing methods.
(a) Natural Terrain. The following shall be applicable to buildings on natural terrain:
(1) Foundation design shall take into consideration the effects of soil saturation on the
performance of the foundation.
(2) The effects of floodwaters on slope stability and erosion shall be investigated.
(3) All utility service lines shall be designed and constructed as provided in the
plumbing and electrical codes.
(b) Building on Stilts. Where a building is to be constructed so that the
lowest floor is to be elevated above the regulatory flood elevation, the building
may be supported on columnar type members, such as columns, piers and in
certain cases, walls. Clear spacing of support members, measured perpendicular to the general
direction of flood flow shall not be less than eight feet apart at
the closest point. The stilts shall, as far as practicable, be compact and
free from unnecessary appendages which would tend to trap or restrict free passage
of debris during a flood. Solid walls or walled-in columns are permissible if
oriented with the longest dimension of the member parallel to the flow. Stilts
shall be capable of resisting all applied loads as required by this code
and all applicable flood-related loads as required herein. Bracing, where used to provide
lateral stability, shall be of a type that causes the least obstruction to
the flow and the least potential for trapping floating debris. Foundation supports for
the stilts may be of any approved type capable of resisting all applied
loads, such as spread footings, mats, piles and similar types. In all cases,
the effect of submergence of the soil and additional floodwater-related loads shall be
recognized. The potential of surface scour around the stilts shall be recognized and
protective measures provided, as required.
(c) Building on Fill.
(1) Except in districts where fill is specifically prohibited as structural support for buildings
by Section 21-7.10, as amended, buildings may be constructed on fill material.
(2) The fill shall not adversely affect the capacity of the floodway or any
tributary or any other drainage facility or system, and shall be performed in
accordance with Chapter 14, ROH 1990, as amended.
(Sec. 16-7.4, R.O. 1978 (1983 Ed.); Sec. 16-5.4, R.O. 1978 (1987 Supp. to
1983 Ed.); Am. Ord. 90-57
Sec. 16-11.5 Structural requirements.
(a) General. All buildings and structures to be constructed under the provisions of this
article shall be capable of resisting all loads required under this chapter and,
in addition, all loads prescribed in this section.
(b) Stability.
(1) Overturning or Sliding. All buildings and structures to be constructed under the provisions
of this article shall be designed and constructed to provide a minimum factor
of safety of 1.50 against failure by sliding or overturning when subjected to
combined loads as specified in subsection (d) of this section.
(2) Flotation. All buildings and structures to be constructed under the provisions of this
article shall be designed and constructed to resist flotation from floodwater at the
regulatory flood elevation with a safety factor of 1.33.
(c) Loads. The following loads shall be considered in the design and construction of
buildings and structures subject to the provisions of this article:
(1) Hydrostatic loads;
(2) Hydrodynamic loads;
(3) Impact Loads. Assume concentrated load acting horizontally at the regulatory flood elevation or
at any point below it, equal to the impact force produced by a
1,000-pound mass traveling at the velocity of the flood water and acting on
a one-square-foot surface of the structure;
(4) Soil Loads. Consideration shall be given to loads or pressures resulting from soils
against or over the structure. Computation shall be in accordance with accepted engineering
practice with proper consideration for effect of water on the soil. Special consideration
shall be given in the design of structures when expansive soils are present;
(5) Tsunami. Structural design of buildings and structures subject to tsunamis shall be in
accordance with subsection (f) of this section.
(d) Combined Loads. All loads stipulated in this chapter and all flood-related loads specified
under subsection (c) of this section shall be applied on the structure and
on structural components, alone and in combination, in such manner that the combined
effect will result in maximum loads and stresses on the structure and members.
Application of these loads shall be as follows:
(1) Dead Loads. Use at full intensity.
(2) Live Loads. Use at reduced intensity as provided in this chapter for design
of columns, piers, walls, foundation, trusses, beams and flat slabs. Live loads on
floors at or below the regulatory flood elevation and particularly in basement slabs,
shall not be used if their omission results in greater loading or stresses
on such floors. Similarly, for storage tanks, pools and other similar structures designed
to contain and store materials, which may be full or empty when a
flood occurs, both conditions shall be investigated in combination with flood-related loads of
the containing structure being full or empty.
(3) Wind Load. Use at full intensity as required in this chapter on areas
of the building and structure above the regulatory flood elevation.
(4) Earthquake Load. Combined earthquake and flood-related loads need not be considered.
(e) Allowable Soil Pressures. Under flood conditions, the bearing capacity of submerged soils is
affected and reduced by the buoyancy effect of the water on the soil.
For foundations of buildings and structures covered by this article, the bearing capacity
of soils shall be evaluated by a recognized acceptable method. Expansive soils should
be investigated with special care. Soils which lose all bearing capacity when saturated,
or become "liquefied" shall not be used for supporting foundations.
(f) Coastal Flood Water Design.*
(1) Buildings or structures shall be designed to resist the effects of coastal floodwaters
due to tsunamis. The regulatory flood elevation due to tsunamis is considered to
result from a non-bore condition, except where a bore condition is shown on
the flood insurance maps or in the flood study adopted for the county.
(2) Habitable space in building structures must be elevated above the regulatory flood elevation
by such means as posts, piles, piers or shear walls parallel to the
expected direction of flow of the tsunami wave. The forces and effects of
floodwaters on the structure shall be fully considered in the design.
(3) Allowable stresses (or load factors in the case of ultimate strength or limit
design) for the building materials used shall be the same as the building
code provides for wind or earthquake loads combined with gravity loads, i.e., treat
loads and stresses due to tsunamis in the same fashion as for earthquake
loadings.
(4) The main building structure shall be adequately anchored and connected to the elevating
substructure system to resist all lateral, uplift and downward forces. In wood construction,
toenailing is not allowed.
(5) Scour of soil from around individual piles and piers shall be provided for
in the design in the coastal flood hazard district. Shallow foundation types are
not permitted unless the natural supporting soils are protected on all sides against
scour by a shore protection structure, preferably a bulkhead. Shallow foundations may be
permitted beyond 300 feet from the shoreline, provided they are founded on natural
soil and at least two feet below the anticipated depth of scour, and
provided not more than three feet of scour is expected at the structure.
The table below gives estimated minimum depths of soil scour below existing grade
as a percentage of the depth (h) of water at the location.