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FEMA 550 Recommended Residential Construction for the Gulf Coast

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Many homes need to be elevated less than 8 feet ... up to 15 feet above grade. Deep ... House widths can readily be increased by bay widths (14 feet) ... – PowerPoint PPT presentation

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Title: FEMA 550 Recommended Residential Construction for the Gulf Coast


1
FEMA 550 -Recommended Residential Construction
for the Gulf Coast
  • Building on Strong and Safe Foundations

April 2006
2
FEMA 550 - Recommended Residential Construction
for the Gulf Coast
  • Background
  • Hurricane Katrina confirmed that homes need to be
    higher to avoid flood damages
  • Interim Advisory Base Flood Elevations (ABFEs)
    Issued Fall 2005 increase Base Flood Elevations
    up to 15 feet (/-)
  • New BFEs are scheduled to be completed in 2006

3
Homes need to be built higher...
4
FEMA 550 - Recommended Residential Construction
for the Gulf Coast
  • Many of the foundations historically used are not
    adequate for the higher flood elevations
  • New Approaches to elevate homes are needed

5
FEMA 550 - Recommended Residential Construction
for the Gulf Coast
  • Project Goals
  • Develop multi-hazard residential foundation
    concepts
  • Provide designs for specific homes that can used
    off the shelf
  • Provide designs that, when needed, can be
    modified by local engineers with a minimal amount
    of effort
  • Satisfy needs of 80 of homes being rebuilt in
    the Gulf Coast
  • Use conventional materials and methods where
    possible
  • Develop foundations that will support many of the
    Mississippi Renewal Forum Pattern Book home
    designs
  • Get input from local builders

6
FEMA 550 - Recommended Residential Construction
for the Gulf Coast
  • Flood Issues

7
FEMA 550 - Recommended Residential Construction
for the Gulf Coast
  • Flood Zones
  • V Zone
  • Breaking wave height Hb three feet or greater
  • Open foundations required
  • Coastal A Zone
  • Breaking wave height Hb 1.5 feet to 3 feet
  • Open foundations recommended
  • Non Coastal A Zone
  • Breaking wave height Hb lt 1.5 feet
  • Either open or enclosed foundations allowed

8
FEMA 550 - Recommended Residential Construction
for the Gulf Coast
9
FEMA 550 - Recommended Residential Construction
for the Gulf Coast
  • Elevation Required
  • Homes must be elevated to the BFE
  • BFEs are referenced to a vertical datum
    (NAVD/NGVD)
  • Local topography provides some elevation
  • Topography must be considered when determining
    how high H above exterior grade a home must be
    elevated
  • Many homes need to be elevated less than 8 feet
  • Relatively few homes will need to be elevated
    over 20 feet

10
FEMA 550 - Recommended Residential Construction
for the Gulf Coast
11
FEMA 550 - Recommended Residential Construction
for the Gulf Coast
Example Home located on site with an estimated
flood elevation of 18 ft. Site elevation is 14
ft NAVD. Home would need to be elevated 4 ft
(18 14) above grade.
12
FEMA 550 - Recommended Residential Construction
for the Gulf Coast
  • Elevation
  • Designs provided for a range of foundation
    heights
  • Enclosed foundations up to 8 feet
  • Open foundations up to 15 feet
  • Designs provided for one and two-story homes
  • Designs for V-Zone, Coastal A-Zone and
    Non-Coastal A Zone

13
FEMA 550 - Recommended Residential Construction
for the Gulf Coast
  • Flood Zones
  • A Zone (enclosed foundations) limited wave action
  • Coastal A Zone (recommended open foundations)
    limited wave action
  • V Zone (open foundations) wave action
  • Wave action taken into account for V Zone
    foundations
  • Also
  • Scour
  • Erosion

14
FEMA 550 - Recommended Residential Construction
for the Gulf Coast
  • Wind Issues

15
FEMA 550 - Recommended Residential Construction
for the Gulf Coast
  • Wind Speed1
  • Gulf Coast Communities
  • 120 to 150 miles per hour (3-second gust)
  • A small area SE of Pascagoula, MS and the SW tip
    of Plaquemines Parish, LA have design wind speeds
    in excess of 150 mph
  • 1ASCE 7-02/International Building Code

16
FEMA 550 - Recommended Residential Construction
for the Gulf Coast
17
FEMA 550 - Recommended Residential Construction
for the Gulf Coast
  • Analysis and Design Issues

18
FEMA 550 - Recommended Residential Construction
for the Gulf Coast
  • Analysis
  • Determine loads that the foundation must resist
  • Includes loads on the elevated home
  • Wind
  • Dead loads
  • Live loads
  • Loads imposed directly on the foundation
  • Dead loads
  • Wind loads
  • Flood loads

19
FEMA 550 - Recommended Residential Construction
for the Gulf Coast
  • Loads Determined for a Design Event
  • 50 year (MRI) for wind MRI Mean Recurrence
    Interval
  • 100 year (MRI) for flood
  • Seismic (in some areas)
  • Snow (in some areas)
  • Others
  • Building Codes
  • IRC
  • IBC
  • Consensus Standards Guidance Documents
  • ASCE 7-02 FEMA 55 Coastal Construction
  • ASCE 24-98 Manual

20
FEMA 550 - Recommended Residential Construction
for the Gulf Coast
  • Loads on Home

21
FEMA 550 - Recommended Residential Construction
for the Gulf Coast
  • Loads on Foundation

22
FEMA 550 - Recommended Residential Construction
for the Gulf Coast
  • Load Combinations
  • Address simultaneous loading
  • Wind, flood, gravity, etc.
  • Chapter 2 of ASCE 7
  • Basic load combinations (apply everywhere)
  • Dead load, live load, wind load, etc.
  • Adds flood loads
  • V and Coastal A (150)
  • Non-Coastal A (75)

23
FEMA 550 - Recommended Residential Construction
for the Gulf Coast
24
FEMA 550 - Recommended Residential Construction
for the Gulf Coast
  • Design
  • After loads are determined design foundation to
    resist those loads
  • Engineering Consensus Standards
  • American Concrete Institute - ACI (concrete)
  • American Institute of Steel Construction Inc -
    AISC (steel)
  • National Design Standard NDS (wood)
  • Others

25
FEMA 550 - Recommended Residential Construction
for the Gulf Coast
  • Designs
  • Case A - Driven Braced Timber Pile - Deep
  • Case B - Steel Pipe Pile with Grade Beam - Deep
  • Case C - Driven Timber Pile with Grade Beam -
    Deep
  • Case D - Grade Beam/Waffle Foundation - Shallow
  • Case E - Masonry Crawl Space Foundation - Shallow
  • Case F - Masonry Stem Wall Foundation - Shallow
  • Case G - Grade Beam/Mat Foundation - Shallow
  • Foundations reviewed by Gulf Coast Homebuilders
    Association

26
FEMA 550 - Recommended Residential Construction
for the Gulf Coast
  • Case A - Driven Braced Timber Pile
  • Good for V, Coastal A, or A Zones
  • Maximum height above ground level is 10 feet
  • Deep foundation

27
FEMA 550 - Recommended Residential Construction
for the Gulf Coast
  • Case B - Steel Pile with Grade Beam
  • Concrete column above ground level
  • Good for V, Coastal A, and A Zones
  • Suitable for elevations up to 15 feet above grade
  • Deep foundation

28
FEMA 550 - Recommended Residential Construction
for the Gulf Coast
  • Case C - Driven Braced Timber Pile with Pile Cap
  • Concrete column above ground level
  • Good for V, Coastal A, and A Zones
  • Suitable for elevations up to 15 feet above grade
  • Deep foundation

29
FEMA 550 - Recommended Residential Construction
for the Gulf Coast
  • Case D - Grade Beam/Waffle Foundation
  • Good for A Zones (and Coastal A where scour and
    erosion is limited)
  • Maximum height above ground level is 8 feet
  • Shallow foundation

30
FEMA 550 - Recommended Residential Construction
for the Gulf Coast
  • Case G - Grade Beam/Mat Foundation
  • Concrete column on concrete grade beam
  • Reinforced slab provides additional uplift
    resistance
  • Good for A zone
  • Maximum height above ground level is 8 feet
  • Shallow foundation

31
FEMA 550 - Recommended Residential Construction
for the Gulf Coast
  • Case E - Masonry Crawl Space Foundation
  • Good for A Zone only
  • Maximum height above ground level is 8 feet
  • Shallow foundation

32
FEMA 550 - Recommended Residential Construction
for the Gulf Coast
  • Case F - Masonry Stem Wall Foundation
  • Good for A Zone only
  • Maximum height above ground level is 4 feet
  • Shallow foundation

33
FEMA 550 - Recommended Residential Construction
for the Gulf Coast
? Acceptable NR Not Recommended ?
Not Permitted
34
FEMA 550 - Recommended Residential Construction
for the Gulf Coast
  • Design Approach for use
  • Design foundation in modules
  • Combine modules to create an actual building
    footprint
  • Modules are for one and two story homes

35
FEMA 550 - Recommended Residential Construction
for the Gulf Coast
  • Modules
  • Design foundation in modules
  • Design for minimum 24 by 28 house
  • Design for maximum 42 depth
  • Expand by 14 by 24 bay
  • House widths can readily be increased by bay
    widths (14 feet)
  • House depths can not readily be increased or
    decreased and will require custom designs

36
FEMA 550 - Recommended Residential Construction
for the Gulf Coast
37
FEMA 550 - Recommended Residential Construction
for the Gulf Coast
  • Typical foundation footprint
  • 24 by 14 bays
  • Maximum 42 depth (with additional row of piers)

38
FEMA 550 - Recommended Residential Construction
for the Gulf Coast
  • Gulf Coast Builders Review
  • Deep Open Foundations (Cases A, B C)
  • Piles are new approaches for residential
    construction in many Gulf Coast areas
  • Pile Driving Contractors are not abundant in all
    areas of the Gulf Coast
  • Minor adjustments to existing construction
    methods required - not considered a major hurdle
  • Wood piles not anticipated to be widely used but
    they wanted to have the option

39
FEMA 550 - Recommended Residential Construction
for the Gulf Coast
  • Shallow Open Foundations (Cases D G)
  • Similar to existing coastal building practice
  • Concrete columns are recommended where masonry
    has historically been used
  • Minor adjustments to existing construction
    methods required but not a major hurdle
  • Enclosed Foundations (Cases E F)
  • Known construction technique
  • Common practice for elevation in A zone

40
FEMA 550 - Recommended Residential Construction
for the Gulf Coast
  • Costs
  • Cost in manual will be based on March 2006 prices
  • General costs for the foundations have been
    evaluated by construction contractors along the
    coast.
  • Costs for Pile Driving have the greatest
    variability in much of the Gulf Coast
  • Costs variations expected as reconstruction
    commences
  • Labor prices rising due to demand
  • Material prices rising with increased demand
  • Economy of scale for homes reconstruction should
    be sought

41
FEMA 550 - Recommended Residential Construction
for the Gulf Coast
  • Model Home evaluated for cost estimates as 28
    foot by 42 foot home elevated 8 feet
  • Cost adjustments will be provided for taller and
    shorter foundations
  • Open Deep Foundations 20K
  • Open Shallow Foundations 10K
  • Closed Shallow Foundations 8K

42
FEMA 550 - Recommended Residential Construction
for the Gulf Coast
  • Foundations for Other Homes - If home doesnt
    match criteria used in the designs
  • Elevations greater than 15 feet
  • Slender homes (less than 24 feet deep)
  • Homes with flat roofs or roofs greater than 1212
    pitch
  • Very heavy (gravity) or very light homes (uplift)

43
FEMA 550 - Recommended Residential Construction
for the Gulf Coast
  • If home doesnt match criteria used in the
    designs
  • Consult with a licensed professional engineer to
    design the foundation
  • Analyze loads per IBC/IRC or ASCE 7
  • Use the Coastal Construction Manual, FEMA 55, for
    guidance on issues not covered in the Model Codes
    (IBC or NFPA 5000) and Standards (eg. ASCE-7,
    ASCE-24)
  • Recommend following guidance found in other FEMA
    publications to make homes more hazard resistant
    than criteria contained in Model Codes

44
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