HomeMy WebLinkAboutNotice PLANNER 6/16/2008
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RECEIVED
AFFIDAVIT OF SERVICE
JUN 162008
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By: 0 I '1J-.
STATE OF OREGON)
)ss'-
County of Lane )
I, Karen LaFleur, being first duly sworn, do hereby depose and say as foUciws: .
1. I state that I am a 'Program Technician for the Planning Division ofthe
Development Services Department, City of Springfield, Oreg'on.
2. I state that in my capacity as, Program Techn!cian, I {lrepared !Ind caused to I:!e
mailed copies of SM20013- a:::CrJ5 h~ cfl., .Da ~ -~ D~ .
(See attachment "A") on.k./1t, , 200lladdressed to (see . 1=>0'51
Attachment B"), by causing said letters to be placed in a U.S. mail box with
postage fully prepaid thereon.
l:t<6AVn, 1 a;t~
~JN LaFLEu~J ) .
STATE OF OREGON, County of Lane
~..lJLt.., / ft; , 2008. Personally appeared the above named Karen LaFleur, ,
\.Prqgram Technic,ian, who acknowledged the foregoing instrument to be their voluntary
'a:Ci. Before me: .
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OFFICIAL SEAL
DEYETIE KELLY
NOTARY PUBLIC, OREGON
COMMISSION NO, 420351
MY COMMISSION EXPIRES AUG, 15, 2011
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<g 1/5 /1/
My Commission Expires:
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Notice of Decision -Floodplain Overlay
Case Number: SHR2008-00005
Project Location: 2033 Inland Way
Application Submitted Date: June 5, 2008
Decision Issued Date: June 13, 2008
City of Springfield Staff: Steve Hopkins, Plarui.er
Owner: Gretchen Post, 2033 Inland Way, Springfield OR 97477
Representative: Shawn O'Hara, Pacific Key Contractors, 48 Irving Rd, Eugene OR 97404
Request: Type I review for replacement of a manufactured home at Assessors Map Number 18-
03-11-22, Lot 200. The site is within the floodplain of the Willarnette River, Zone AE as
identified on FEMA map, Firm Panel 41039Cl144F, dated June 2, 1999.
SDC 3.3-420 Development Standards
A. General Standards, In all areas of special flood hazard within the City and its
urbanizable area, the following standards apply:
1. Anchoring, All new construction, manufactured homes and substantial
improvements subject to less than 18 inches of flood water during a 100
year flood shall be anchored to prevent flotation, collapse or lateral
movement of the structure and shall be installed using methods and
practices . that minimize flood damage,' Anchoring methods for
manufactured homes may include, but are not limited to, use of
over-the-top or frame ties to ground anchors (Reference FEMA's
"Manufactured Home Installation in Flood Hazard Areas" guidebook for
additional techniques), If subject to 18 inches or more of flood water, or
located in the floodway, manufactured homes, apart from manufactured
homes in Mobile Home Parks and Subdivisions, shall be anchored to
prevent flotation or lateral movement and the design shall be certified by an
engineer or architect, Manufactured homes in an existing Mobile Home
Park or Subdivision' may use the ties to ground anchors and additional
techniques specified above,
B. Specific Standards. In all areas of special flood hazard within the City and its
urbanizable area where base flood elevation data has been provided as specified
in Sections 3,3-410A. and 8, or 3,3-4158.4" the following provisions are required:
1. Residential Construction, .
a.
New construction and substantial improvement of any residential
structure shall have the lowest floor, including basement, elevated
to 1 foot above the base flood elevation,
Fully enclosed areas below the lowest floor that are subject to
flooding are prohibited, or shall be designed to automatically
equalize hydrostatic flood forces on exterior walls by allowing for
b.
Post
Case No, DRC200B.()0005
:
1
the entry and exit of flood-waters, Designs for meeting this
requirement shall either be certified by an engineer or architect or
shall meet or exceed the following minimum criteria:
i. A minimum of two openinQs of equal size 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,
ii. The bottom of all openings shall be no higher than 1 foot
above grade.
iii. Openings shall be located to allow unrestricted cross-flow of
flood-waters through the enclosed area from one side to the
other.
iv. Openings may be equipped with screens, louvers, or other
coverings or devices if certified by an engineer or architect,
provided that they permit the automatic entry and exit of
flood-waters,
Findings: \
. The applicant will replace the existing single wide manufactured home with the same
size unit in the same location. :
. The applicant has provided an elevation certificate that demonstrates the base flood
elevation is 45' and the preconstruction elev~tiOli. of the site is 25 to 35 inches above
that elevation.
. The Oregon Manufactured Dwelling and Pa}k Specialty Code requires that
manufactured dwellings located in a flood hpard zone have a finished floor elevated
a minimum of 18 inches above the base flood elevation.
. The foundation needs to include openings to allow entry and exit of floodwaters.
Refer to SDC 3.3-420(B) and FEMA Bulletin 1-93,
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Post
Case No, DRGOO8.()0005
2
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Summary of Conditions:
1. Provide a FEMA Elevation Certificate completed by a certified engineer, surveyor or
architect, after placement of the manufactured home and before occupancy.
2. The finished floor elevation of the manufactured home shall be a minimum of 18 inches
above the base flood elevation.
3. In accordance with SDC 3.3-420(B) and FEMA Bulletin 1-93, include openings in the
foundation to allow entry and exit of floodwaters.
4. The applicant shall keep all records for mspection.
Questions: Please call Steve Hopkins in the Planning Division of the Development Services
Department at (541) 726-3649 if you have any questions regarding this process. .
~~~IIL
Steve Hopkins, AICP
Planner II
Development Services - Urban Planning Division
Post
Case No, DRaOO~0005
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1. If a porch is on only one side of a
multi-section manufactured dwelling, a
frame tie-down is required at the outside
corner;
2. If a full width porch is on two or more
sides of a multi-section manufactured
dwelling, frame tie-downs are required
at each outside corner;
3. If a full width porch is on a single
section manufactured dwelling, frame
tie-downs are required at each outside
corner (See Figure 3-2.3.3);
4. If a porch is located in the middle of a
manufactured dwelling sidewall area so
the roof is attached to the structure on at
least three sides, no tie-downs are.
required; and
5. If a porch is located between two
sections of a manufactured dwelling so
the roof is attached to the structure on at-
least three sides, no tie-downs are
required.
3-2.3.4 Wind Resistant Anchoring.,
When required by this section,
manufactured dwellings shall be
anchored by one of the following
methods:
(a) Installation of approved ground
anchors;
(b) Structural attachment to a foundation
wall or footing;
(c) Structural attachment to a basement
wall;
(d) Structural attachment to structural
skirting or;
(e) Structural attachment to a foundation
system capable of resisting the wind
forces when designed by an Oregon
professional engineer or architect and
approved by the authority having
jurisdiction.
~~rd Areas.
Manufactured dwellings may only be
located in hazardous areas according to
the following minimum requirements:
(a) When manufactured dwellings are to
be located in a flood hazard zone,
according to the Flood Insurance Rate
Map (FIRM), a FEMA Elevation
Certificate shall be submitted to the
authority having jurisdiction;
(b) Manufactured dwellings located in a
flood hazard zone shall have the
finished floor elevated a minimum of 18
inches (46 cm) above the Base Flood
Elevation, (BFE) as identified on the
FIRM. When the Base Flood Elevation
has not been established within a flood
hazard zone, the finished floor' shall be
elevated to the elevation established by
the Flood Plain Administrator. (see
Figure 3-2.4.1A):
1. Where a manufactured dwelling has a
ground level or pit set installation, the
manufactured dwelling stand shall be a
miniml,lm of one foot (305 mm) above
the BF;E unless openings are provided
per FEMA Technical Bulletin 1-93. (see
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Figur~ 3-2.4.1 B); .
2. Wh'ere a manufactured dwelling is
installed over a basement, the floor of
the basement, whether finished or
unfinished, shall be a minimum of one
foot (305 mm) above the BFE or
openings are provided per FEMA
Technical Bulletin 1-93. (see Figure 3-
2.4.1 C);
3. Manufactured dwelling electrical and
mechanical components and equipment
shall be elevated a minimum of one foot
(305 mm) above the BFE. Under-floor
crossover ducts are exempt from this
requirement; and
4. Plumbing openings below the
elevation of one foot (305 mm) above
the BFE shall be flood proofed and
equipped with backwater valves.
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3-2.4.2 Floodways. Floodways, as
identified on National Flood Insurance
Program (NFIP) maps, are generally
along the waterway's edge and carry
most of the floodwater. The water in a
floodway is often deeper and faster than
in the 'adjacent floodplain. Homes in
f100dways are subject to greater
damage and risk to the occupants than
homes in a floodplain; therefore, new
installations of manufactured dwellings
. in f100dways are prohibited.
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34
J.
. Lchnical
B tiiletin
1-93
Openings in Foundation Walls
, for Buildings Located in Special Flood Hazard Areas
in accordance with the
National Flood Insurance Program
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FEDERAL EMERGENCY MANAGEMENT AGENCY'
F.EC!ERAL I/I!~URANCE A~MINrSTRATION
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FIA-TB-l
(4/93) ,
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Key Word/Subject Inde~:
This index allows the user to quickly locate key words arid subjects in this Technical Bulle-
tin, The Technical Bulletin User's Guide (printed separa~ely) provides references to key
words and subjects throughout the Technical Bulletins, For definitions of selected terms,
refer to the Glossary at the end of this bulletin ;
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Key Word/Subject.
Page
3
,1
9.
4
4
2
7
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9
2
2
Basement, definition of
Foundations in A zones
Foundation openings in A zones, size, how to calculate
Garages, attached to residential buildings
Garage doors, to meet the openings requirement
Hydrostatic pressure,. automatically equalized.
Hydrostatic pressure, how to calculate
Openings for foundations in A zones i
Safety factor for foundation openings " " I
Substantial damage, foundation wall openings requirement
Substantial improvement, foundati'on wall openings requirement'
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'. . Any corriments onihe Technical Bulletins should be directed to:'.
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Offi~e of Loss Reduction
. Technical Standards Division
500 est., SW, Room 417'.
Washington, D,C. 20472 '
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Technical Bulletin 1-93 replaces Technical Bulletin 85-2 (draft)
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Kariagawa, by, Katsushika . Hokusai (1760:
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Graphic design based on the Japanese
1849), Asiatic collection, Mus.eum of Fine
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TECHNICAL BULLETIN 1-93.
Openings in Foundation Walls..
, Required for 'Buildings
Located in Special Flood Hazard Areas
in accordance with the
. National Flood Insurance Program
Introduction
An important objective of the National Flood Insurance Program (NFIP) is to protect buildings
constructed in floodplains from structural damage caused by flood forces, In support of this
'objective, the NFIP regulations inciude building design criteria that apply to new construction
and substantial improvements of existing buildings' in Special Flood Hazard Areas (SFHAs),
According to these criteria, residential buildings constructed in A zones (Zones A, AE, Al-A30,
AR, AO, and AH) ,?ust have their lowest floors at or above the base blood elevation (BFE),
Non-residential buildings constructed in A zones must either have their lowest floors at or above
the BFE or be dry floodproofed (made watertight) to or above the BFE Residential and non-
residential buildings whose lowest floors have been constructed at or above the BFE usually are
elevated on' piers, columns, piles, extended, foundation walls, .or fill, While the main portion of
such'a building is protected from the IOO-year and lesser"inagnifude floods, the foundation and
, any enclosures below the BFE used forparking, building acces,s,or limited storage will be .
exposed to flood forces. .' .', '
F or buildings constructed on' extended foundation walls or that have other enclo'sures below the
BFE; these flood forces include the hydrostatic pressure of floodwaters against the foundation or ,
enclosure walls, If the waIls are not designed to withstand hydrostatic pressure, they can be' .
weakened or can fail and the building damaged, Therefore, !he NFIP, regulations require that
foundation and enclosure. walls that are subject to the lOG-year flood contain operiings that will
permit the automatic entry imdexit of floodwaters, These',ope'nings allow floodwaters to reach ,.
equal levels on both sides of the walls, and ,thereby lessen 'the potential for damage from hydro- .
, static pressure. The requirelnent. for openings applies to' all new and substantially improved ' '
'. ' buildings in A zones, This Technical Bulletin explains the requirement for openings and pro-
. 'vi des guidance for,. designing and constructing foundation and .enclosure walls that irtclude the'.' .
'"'t required op~nin,.~s.. t' . '." ': . " .'. ',.:. ' ":,; . .:,..' '_ .
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Extended fo,;J.,dation and ericiosure walls below the BFE may also'be threatened by hydrody-, ....
'narnic forces resulting from velocity flows and debris impact. The requirement for openings is ' .
" intended to reduce flood damage associated with,hydrostatic not hydrodynamic forces, These, ,"" .
forces are described within this bulletin, and additional design guidance5s given for buildingsin
. , ,areas subject tovelopity noo~ flows, which may include deblis.,' " . ,.
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'. " for buildings' in V zones (Zones ,V, VE, imd VI-V30),more stringent design and construction
" " requirements have been established for the portions of the buildings below the BFE, For infor-,
. . . mation on V -zone design and construction requirements, refer to the NFIP regulations, the
T~chnicalBulletin series, and FEMA's"'Coastal Co!'struction Manuai,",' ..~' ... , .
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NFIP Regulations
The NFIP regulations require that all enclosures below the BFE in A zones be designed to allow
for the automatic equalization of hydrostatic forces during a flood event. Section60,3(c)(5) of
the NFIP regulations states that a community shall:
"Require, for all new construction and substantial improvements, that fully enclosed areas
below the lowest floor thai are usable solely for parking of vehicles, building access, or
storage in an area other than a basement and which a~e subject to flooding shall be de-
" signed to automatically equalize hydrostatic flood forces on exte~ior walls by allowing for
the entry and exit offloodwaters. Designs for meeting this requirement must either be
certified by a 'registered professional engineer or architect or meet or exceed the following
minimum criteria: 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 pro-
vided; The bottom of all openings shall be no higher !han one foot above grade. Openings
may be equipped with screens, 10livers, valves, or othe~ coverillgs or devices provided that
. they permit the automatic entry and eXit offloodwaters~'" ., . .'. .,.. ..,,'
As stated in the regulati~ns, ~uildings in A zones that 'are slbstantia;lydaIIlaged and/or subs tan-
tially improved must meet all the NFIP requirements for new construction,' including the,open-
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ings requirement. All design plans for substantial improvements to buildings in A zones must be
thoroughly reviewed by the conununity to ensure complian~e with the openings req,!irement. ,"
. Further information on substantial damage and substantial improvement maybe found in the
FEMA publication "Answers to Questions About Substantiklly Damaged Buildings:". , .
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It should be noted that Technical Bulletins provide guidance on the minimum requirements.
of the NFIP regulations. Community or State requirements that exceed those of. the NFIP
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take precedence, DeSign professionals should contact the 'community to determine whether
more restrictive local or State regulations apply to the building or site, in question, All .
applicable standards of the State or local building code must also be met for any building in a
flood hazard area, . . . ,
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Guidance for Non.Engine'ered,Foundation Openings.,.
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.', Each of the following four design criteria must be met for new and substantially improved A-zone
buildings that have enclosed areas below the BFE with openings not designed and certified,by a
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. design prof~ssional:. .... .'.. .
. I, There must be a minimum of two openings on different sides of each enclosed area. If a .
building has more than one enclosed area, each area must'have openings on exterior walls to
allow floodwater to dire~tJy ent~L:, ',' . .,.
.' 2, The total area of all ~penings mu~t be at least I'squ';e inch for each I square foot of enclosed
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3. The bottom of each opening can be no more than I foot above the adjacent grade,
4, Any louvers, screens, or other opeI!ing covers must not block or impede the automatic flow' of '
floodwaters into and out of the enclosed area.
Types of Buildings Affected
In all cases, any enclosed area below the BFE is subject to flood forces and must be equipped
with exterior wall openings in accordance with the NFIP regulations, either at the time of initial
construction or, if the building is being substantially improved, at the time of improvement. The
only exception to this requirement is floodproofed non-residential buildings that are engineered
and meet stringent watertight construction requirements. For further information on this topic,
refer to Technical Bulletin 3, "Non-Residential Floodproofing - Requirements and Certifica-
tion."
basement whose lowest floor (including
basement) is belo.'"', the BFJO, ' ..
, To m~ei the NFIP requiremenis, fill placed
,around,foundation walls must,be graded so , '
that the grade inside the enclosed area is equal
. to or higher than the adjacent grade outside the
building on at least one side of the building (as
illustrated in Figure 2), If the grade inside the
foundation walls is, above the BFE, openings
are not required, ,
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Buildings Elevated on Solid Foundation Walls
When a building -is elevated on solid foundation walls,
an enclosed area is often created below the lowest '
floor. All foundation enclosures below the BFE must '
have openings that meet NFIP criteria, Figure I
shows an example of a properly placed foundation
opening, As discussed previously, screens, louvers, or
other covers that allow floodwaters to flow freely into
the enclosed area may be placed over the openings to. '
keep out vermin and weather. '
Care must be taken when placing fill dirt around the
: outside of the foundation, The resulting enclosed area
may be considered a basement under the NFIP, A '
, basement is defined as any area of a building having a
floor (finished or unfini~hed) that is subgrade (below
grade) on all sides, The NFIP regulations do not
permit a residential building in an SFHA to have a
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Figure 2, Compliant Grading for a Walkout'
," Basament' "
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Figure 1, Opening for Solid Foundation Wall
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Buildings in Hazardous Velocity Areas
In coastal A zones, or in riverine A zones where flood velocities exceed 5 feet per second, fast-
flowing floodwaters can exert considerable pressure on solid foundation walls, This hydrody-:
namic pressure, as described in the following section, may destroy a building's foundation. In
such areas, foundations that allow floodwaters to flow freely beneath the building should be
considered, Foundations such as piles, piers, or columns will provide the appropriate level of
safety to a building located in a hazardous velocity area, if properly embedded and anchored,
See the discussion of hydrodynamic pressure for design guidance,
Buildings in A-zone floodplains with velocity floodwaters, may have breakaway walls con-
structed in areas below the BFE, Compliant foundation openings are required in breakaway
,walls in A zones, '
Buildings with Attached Garages
Any new or substantially improved residential building constructed in an A zone must have its
lowest floor at or above the BFE, Many of these buildings have struc,tu'rally attached garages
with floor slabs below the BFE, Because such a below-BFE attached garage is an enclosed area
below the BFE, openings are required' either in the exterior, walls of the garage or in the garage
, 'doors themselves in order'to meet the NFIP openings criteria (see Figure 3), Openings are
required because they prevent flood damage to the garage and subsequently to the structurally.
attached residence, Garage doors without openings specifically designed to allow for the free
flow of floodwaters do not meet the openings requirement. The human intervention necessary to
open garage doors when flooding threatens is not an acceptable means of meeting the openings
requirement. Gaps that may be present between the door segments and between the garage door
and the garage door jamb do not guarantee the automatic entry and exit of floodwaters, There-
fore, openings are required, either in the ,exterior walls of the enclosed area or in the garage doors'
, themselves, Openings in garage doors must either meet the non-engineered openings require- '
ments or be certified by a design professional. "
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Areo
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Figure 3. Compliant R~sidential
on Solid F~undation! Walls' With' Attached Garage
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Flood Insurance Implication
If a below- BFE attached garage does not have proper openings, the Elevation Certificate pre-
pared for the building must identify the elevation of the garage floor slab as the lowest floor
(reference level) of the building, This may result in flood insurance premiums significantly
higher than those that would have applied if the garage had proper openings,
Guidance for Engineered Openings
In situations where it is not feasible or desirable to meet the openings criteria stated previously, a
design professional (registered engineer or architect) may design and certify openings. This
section provides guidance'for such engineered designs. For openings not meeting all four re-
quirements for non-engineered openings listed on pages 2 and 3, certification by a registered
professional engineer or architect is required, Such certification must be submitted to, and kept
on file by, the community, These certifications must assure community officials that the open-
ings are designed in accordance with accepted standards of practice, A certification may be
affixed to the design drawings or submitted separately, It must include appropriate certification
language, and the name, title, address, signature, type of license, license number, and profes-
sional seal of the certifier. Figure 4 is an example of an acceptable certification, '
Proiect Name
1, . rio hereoy certify that the,opening(s) designed for installation in the
aforementioned building will alldw for the automatic equalizing of hydrostatic flood forces on exterior
walls by allowing for the automatic entry and exit of floodwater ,during floods up tei and including the
base (100,year) flood, ' '
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Sign~ture
Date
Title
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Type of l.icence
licence Number
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PROFESSIONAL SEAL,
Address
~ "Figure 4. ExampJ~ c:>f Openings Cert}fic:at~.
" , C~lculation of Flood .forces
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Floodwaters can impose both hydrostatic and hydrodynamic' forces o'n floodprone buildings.
'Hydrostatic pressure is the force that water at rest exerts on any submerged object, including a
floodprone building, Hydrostatic pressure is capable of collapsing, moving, and severely damag-
, ,ing mosftypes of buildings, In many floods, hydrostatic pressure is the most prevalent cause of
" 'damage. Hydrodynamic pressure is the force exerted on a vertical obstruction (foundation wall)
, by flowing water and debris. '
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, Hydrostatic pressure on an enclosed area above grade can be calculated'by multiplying the
specific weight of water (62.4 pounds per cubic foot) by the height of the water on the surface
being analyzed, The application of the force generated by hydrostatic pressure is always peIpen-
dicular (normal) to the surface,in question. In the case of a submerged object, this means that
hydrostatic forces act in two ways, First, the force will act laterally (see Figure 5), which can
result in collapse of walls or movemerit of the entire building off its foundation, Second, the
force will act vertically (the vertical force is also known as buoyancy, see Figure 6), which can
result in the building being lifted from its foundation or floor system,
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BFE
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F.= Resultant lateral farce
I due to -hydrostatic pressure
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p.::; Hydrostatic pressure at H .
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w ::; Specific weight of w~te~
H = Depth of floodwaters
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Figure 5. Lateral Hydrostatic Force and Pressure
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BFE
I Fb = Resultant vertical '
(buoyant)
force due to
hydrostatic pressure-
Wo i Specific weight of
waler
A : Area of horizontal
floor surface
H ::; Depth of floodwater
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Figure,G. Buoyancy Force
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To describe hydrostatic pressure in mor~ technical terms:
The hydrostatic pressure, P., at a specific location on a structure is:
p; wH
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",here:
Ph
,is the pressure in pounds per square foot
, ,
w is the specific weight of water, 62.4 pounds per cubic foot
H is the depth from the surface of the water to the location in
question (generally from BFE to bottom of foundation wall).
The lateral force resulting from hydrostatic pressure is:
The resultant lateral (horizontal) force against the surface is:
F.; Y,P.H ; Y,~H'
where: '
, Fh
is the lateral force in pounds per linear foot ~f surfac~,
Describing the hydrostatic vertical force (buoyancy) in more technical terms:
F;wAH
.
where:
, Fh
w
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II
A
H
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, is the total buoyant force in pounds ,
is ille spe,cific weight of water" 62.4 pounds per cubic foot
, is the area of the h~rizontal surface in sq~afe feet ,: "
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is the depth of the building below the flood level. ' ' ','
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As shown in the following table, hydrostatic pressure, whether it affects a building laterally or
vertically, increases rapidly as floodwater depths increase:
Height, H (in feet)
1,
2
3
4
250
5
6
7
437
8,
499
Pressure,P. (in pounds per square foot)
62
,125
187
312
374
Hydrodynamic pressure is exerted on all vertical surfaces of obstructions, such as building
foundations, by the impact of velocity water and debris. Depending upon site-specific flood
characteristics and the strength of the foundation, hydrodynamic pressure can overload and
destroy a building's foundation, The openings criteria are intended to equalize hydrostatic
pressure and are not intended to minimize hydrodynamic pressure on the foundation. Hydrody"
namic pressure must be considered in the design of any foundation system where velocity waters
or the potential for debris flow exists, If flood velocities are excessive (greater than 5 feet per
second), foundation systems other than solid foundation walls should be considered, so that
obstructions to damaging flood flows are minimized, Safe foundations in such locations'include
pile, post, column, and pier foundations. These types of foundation systems are appropriate for,
A zones in coastal environs subject to waves and velocity floodwaters, as well as in riverine
floodplains subject to velocity floodwaters (velocities greater than 5 feet per second) and areas
subject to debris flows and ice'floes, In areas with high-velocity floodwaters, it is advisable to
, construct any enclosures below the BFE using the breakaway wall specifications described in
FEMA's "Coastal Construction Manual." As stated previously, breakaway walls in A zones
, must have openings compliant with NFIP regulatory requirements so that hydrostatic pressures'
" are equalized during low-level flood events, '
Design Criteria for Engineered Openings
Engineered 'Openings that all~w floodwaters into an encl~s~e for the purpose' of equ'aiizing
, hydrostatic pressures shall be designed using the following criteria: "
, ,
: . The difference between the exterior and interior floodwater levels should not exceed I foot at ' '
any time during the flood event. Greater differences can result in excessive hydrostatic
pressures and structural damage to the enclosure walls. " "
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. The arrangement of the openings must be' capable" of equalizing ,the hydrostatic pressures
associated with the "worst-case" rate of rise of floodwaters. Historical flooding information
should be used to determine rate of rise, A rate 'of rise of 5 feet per hour was assumed in the ,
'development of tIle NFIP non-engineered openings design:criteria. .
, ,
.Because of the large amount of debris associated with flooding and because openings will
often be equipped with some form of vermin screen to meet applicable building codes, there
is a high probability that openings may be obstructed during a flood, For this reason, a
· substantial safety factor is needed. Standard engineering practice is to use a safety factor of 5, '
'in similar life/safety situations involving' potential strUcrirra!,'failure; therefore, a safety factor
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of 5 was incorporated into the calculations that follow. Openings on the sides of the building'
facing the primary direction of velocity flow will add an additional safety factor however,
such openings will tend tobe blocked with debris sooner than other openings,
.At least two openings must be included to provide for Ii safety factor' against debris blockage,
This safety factor is enhanced when openings are located on at least two different sides of the
enclosed, area, This will allow for more even filling and emptying of the enclosed area and
will also reduce the risk of debris being forced against an opening and blocking it.
The first step in determining the total net area required for openings js to calculate the flow rate
per square foot of enclosed area, which is based on the rate of rise of the floodwaters, The
assumed worst-case rate of rise is 5 feet per hour per square foot of area, or about 0,1, foot per
, minute, To convert this to gallons per minute per square foot of enclosed area, multiply by a
conversion factor of 7,5 gallons per cubic foot. The needed flow rate into the enclosure per
square foot of area is then (0, I foot per minute) times (7,5 gallons per cubic foo't), or 0,8 gallon
per minute per square foot of enclosed area, The second step is outlined below,
To determine the total.net area of the openings, A, needed to permit the above flow rate,
the formula is: '
Q = 38,OcA(P)3
Solving for area A and multiplying by a factor of safety:
A = 0' (FS)
38,0 Cp3 ,
where: A is the net area of openings required, in square inches,
, Q is the flow rate persquar~ foot, which is 0,8 gallon per minute,
,c' is the coefficient of discharge, which is assumed to b~ 0.2"
P is the pressure, which for one square foot of differential is '
62.4pounds per square foot, or 0.4 'pound per square inch
FS,
is the factor of safety, which is 5
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, " ',Therefore:
'A= 0,8 '(5),
, 38,0 x 0,2 x 0.6'
= about 1,0 square inch of opening per square foot of enclosed area,
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,_.The NFIP
'The NFIP was created by Congress in 1968 to provide federally backed flood insurance cover- '
age, because it was generally unavailable from private insurance companies, The NFIP is also.
intended to reduce futUre flood losses by identifying floodprone ,areas and ensuring that ne~ '
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development in these areas inadequately protected from flood damage, The NFIP is based on a'
'mutual agreement between the federal ,government and communities that have been identified as,
floodprone, FEMA, through the Federal Insurance Administration (FlA), makes flood insurance,
, available to community residents provided that the participating community adopts and enforces
adequate floodplain management regulations that meet ille minimum NFIP requirements, The
NFIP encourages communities to adopt floodplain management ordinances that exceed the
minimum NFIP criteria. Included in the NFIP requirements, found under Title 44 of the U.S,
Code of Federal Regulations, are minimum building design and construction standards for
buildings located in SFHAs, Through their floodplain management ordinances, communities
adopt the NFIP design performance standards for new and substantially improved buildings
located in floodprone areas identified on FIA' s Flood Insurance Rate Maps,
Technical Bulletins
This is one of a series of Technical Bulletins FEMA has produced to provide guidance concern-
ing the building performance standards of the NFIP, These standards are contained in Title 44 of
the U,S. Code of Federal Regulations at Section 60.3, The bulletins are intended for use prima- '
rily by State and local officials responsible for interpreting and enforcing NFIP regulations and
by members of the development community, such as design professionals and builders, New
bulletins, as well as updates of existing bulletins, are issued periodically, as necessary, The
bulletins do not create regulations; rather they provide specific guidance for complying with the
minimum requirements of existing NFIP regulations, Users of the Technical Bulletins who need
additional guidance concerning NFIP regulatory requirements should contact the Natural Haz- ,
ards Branch of the appropriate FEMA regional office, The "User's Guide to Technical Bulle-
, ,tins" lists the bulletins issued to date and provides a key word/subject index for the entire series.
Ordering Information
Copies of the TechIDcal Bulletins can be obtained from the appropriate FEMA regional office,
, Technical Bulletins can also be ordered from the FEMA publications warehouse. Use of FEMA
Form 60-8 will result in a more timely delivery from the warehouse - the form can be obtained
from FEMA regional offices and your state's Office of Emergency Management. Send publica-
"tion requests to FEMA Publications, P,O, Box 70274, Washington, D.C, 20024,
, ,
"
Further Information
. ..".
, The following publications provide further information concerning openings in foundation 'walls:
, ",1. ,"Answers to Questions About Substantially Dam~ged Buildings," FEMA, May 1991, FEMA-
213,.. '
"
2, ':Coastal Construction Manual," FEMA, February 1986, FEMA-55,
,3, "Colorado Floodproofing Manual," Colorado Department of Natural Resources, Water
Conservation Board, ()ctober 1983.
" 4,
. " ..( , . . .
"Design Manual for Retrofitting Flood-Prone Residential Structures," FEMA, September
1986, FEMA-I 14., ,,' ,,' ' "
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.
5, "Elevated Residential Structures," FEMA; May 1986,FEMA-54,
6, "Elevating Flood-Prone' Buildings': 'A Contractor's Guide," Illinois Department of Transpor-
tation, Division of Water Re'sources, 1985, '
7, "Flood Proofing Regulations," U,S: Army Corps of Engineers, March 1992, EP 1165:2-314"
8, "Flood Proofmg Systems and Techniques," U,S, Army Corps of Engineers, December 1984.
9, "Foundation Analysis and Design," Second Edition, Joseph E, Bowles, McGraw-Hill Book
Co., New York.
Glossary
Base flood - The flood that has a I-percent probability of being equaled or exceeded in any
given year (also referred to as the IOO-year flood).
Base Flood Elevation (BFE) - The height of the base flood, usually in feet, in relation 10 the
,National Geodetic Vertical Datum of 1929 or other datum as specified,
Basement - Any area of a building having its floor sub grade (below ground level) on all sides,
Coastal High Hazard Area -, ,An area of special flood hazard extending from offshore to the
inland limit of a primary frontal dune along an open coast and any other area subject to high-
velocity wave action from storms or seismic sources, '
Federal Emergency Manage~ent Agency (FEMA) ~ The independent federal agency that, in
addition to carrying out other activities, overs~es the administration of the National Flood Insur-,,
ance Program.
Federal Insurance Administration (FIA) - The component of FEMA directly responsible for
administering the Naiional Flood Insurance Program., '
, . ~. .
Flood Insurance Rate Map (FIRM) - The insUrance and floodplain management map issued
by FEMA that identifies, on the basis of detailed or approximate analyses, areas of I DO-year
, flood hazard in a community, ' , " , ' '
Floodprone area:"'" Any'land area susceptible to being inundat~d by floodwater, from any
source.
,/ .
. .. .
Lowest floor ~ The lowest floor of the lowest enclosed area of a building, including a base-' ,
ment. Any NFIP-compliant unfinished or flood-resistant enclosure useable solely for parking of
vehicles, building access; or storage (in an area other than a basement) is not considered a','
building's lowest floor. '
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'Special Flood Hazard Area (SFHA) - Area delineated on a Flood Insurance Rate Map as
, being subject to inundation by the bas~ flood and designated as Zone A, AE, AI-A30, AR, AO,
AH, V, VE, orVI-V30, '
Substantial damage - Damage of any origin sustained by a structure whereby the cost of
restoring the structure to its before-damaged condition would equal or exceed 50 percent of the
market value of the structure before the damage occurred. , :"
Substantial improvement - Any reconstruction, reh~b;litation, addition, m othe~-
of a structure, the cost of which equals or exceeds 50 percent of the market value of the structure
before the "start of construction" of the improvement. This term includes structures that have
incurred "substantial damage," regardless of the actual repair work performed,
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DEVELOPMENT SERVICES ' ~
PLANNING DEPARTMENT
225 FIFTH STREET
SPRINGFIELD, OR 97477
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Gretchen Post
2033 Inland Way
Springfield, OR 97477
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DEVELOPMENT SERVICES ' " ~
PLANNING DEPARTMENT
225 FIFTH STREET
SPRINGFIELD, OR 97477
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Shawn O'Hara
Pacific Kay Contractors
48 Irving Road
Eugene, OR 97404
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