Structural Drying >> Metal Roof Leak From Hail Damage

Design and Construction in Coastal A Zones Hurricane Katrina Recovery Advisory FEMA December 2005 Purpose: To recommend design and construction practices in coastal areas where wave and flood conditions during the base flood will be less severe than in V Zones, Metal Roof Leak From Hail Damage but still cause significant damage to typical light-frame construction Key Issues

Recent post-storm investigations have shown that typical A Zone construction techniques (e.g., wood-frame, Metal Roof Leak From Hail Damage light gauge steel or masonry walls on shallow footings or slabs, etc.) are subject to damage when exposed to less than 3-foot breaking waves, which is the current threshold for V Zone conditions.

Coastal A zone buildings that employ typical residential Metal Roof Leak From Hail Damage and light commercial walls to elevate and support habitable space above the flood level will be susceptible to flood damage (see Figure 1). Laboratory tests and recent field investigations confirm that breaking wave heights as small as 1.5 feet will cause failure of these types of walls (see Figures 2 and 3).

Failure of wood-frame walls used to support a coastal building, which was subjected to shallow flooding, small waves, Metal Roof Leak From Hail Damage and floating debris (Hurricane Opal).Figure 2. Masonry walls destroyed by 3 feet of stillwater flooding and small waves (Hurricane Dennis).Figure 3. Failure of wood-frame wall, brick veneer, and windows as a result of 4 feet of stillwater flooding and small waves (Hurricane Katrina).

Other flood hazards associated with coastal waves (e.g., floating debris, high velocity flow, Metal Roof Leak From Hail Damage erosion and scour) also damage A Zone type construction in coastal areas (see Figures 4 and 5).Figure 4. Failure of A Zone type foundation in coastal area, not subject to V Zone conditions (Hurricane Fran). Damage to light frame walls due to floating debris and small waves. 

The damaged home was in the third row back from a bay shoreline (Hurricane Ivan).NFIP flood hazard mapping is generally divided into two categories, Metal Roof Leak From Hail Damage V Zone and A Zone. In coastal areas, the A Zone category could be subdivided into "Coastal A Zone” and "A Zone.” Base flood conditions in the Coastal A Zone will be similar to, but less severe than, those in the V Zone.

Base flood conditions in the A Zone will be similar to those in riverine or lake floodplains. The Coastal A Zone is not shown on the FIRM at present; Metal Roof Leak From Hail Damage therefore, communities, designers, and owners will have to determine whether a site lies within a Coastal A Zone.V Zone design and construction standards are recommended in Coastal A Zones subject to erosion, high velocity flow, and/or wave heights greater than 1.5 feet.

Illustration describing A Zones in Coastal Areas Coastal A: areas with potential for breaking waves and erosion during base flood A: areas with shallow flooding only, where potential for breaking waves and erosion is low[End illustration]Coastal A Zone, Defined[Begin text box]Coastal A Zone: area landward of a V Zone, Metal Roof Leak From Hail Damage or landward of an open coast without mapped V Zones. 

In a Coastal A Zone, the principal source of flooding will be astronomical tides, storm surges, seiches or tsunamis, Metal Roof Leak From Hail Damage not riverine flooding. During base flood conditions, the potential for breaking wave heights between 1.5 feet and 3.0 feet will exist (see Figure 6). Coastal A Zone design and construction practices described herein are not mandated by the NFIP, but are recommended for communities that wish to adopt higher floodplain management standards. 

Community Rating System (CRS) credits are available for doing so. Note that some Coastal A Zone practices may be required by the International Building Code, Metal Roof Leak From Hail Damage through its reference to ASCE 24-98.[End text box]Figure 6. Plan view showing Coastal A Zone landward of V Zone (source: ASCE 24-05).Coastal A Zone Construction Guidance 

Because of the presence of damaging waves, Metal Roof Leak From Hail Damage V Zone design, construction, and certification practices are recommended for Coastal A Zones. Coastal A Zone construction should include:Use of open foundations (pile or pier) designed to resist all base flood conditions (waves, high velocity flow, erosion and scour, floodborne debris). 

Where high velocity flow, scour, and erosion will not be experienced under base flood conditions, Metal Roof Leak From Hail Damage a traditional stem wall foundation may be acceptable – see Table 1. Elevation of the bottom of the lowest horizontal structural member supporting the lowest floor above the base flood wave crest elevation (see Figure 7).

Since waves Metal Roof Leak From Hail Damage and debris will be impacting on the floor joists and other foundation elements during the base flood, do not follow current NFIP minimum requirements that allow the lowest floor's walking surface to be set at the wave crest elevation in Zone A.Figure 7. Recommended post-Katrina building standards in Coastal A Zones.

Use of flood-resistant materials above the level of the walking surface of the lowest floor (in the event that future flooding exceeds the lowest floor Metal Roof Leak From Hail Damage level).Specification of connections between the foundation and the elevated building that are capable of withstanding simultaneous wind and flood forces. 

Post-Katrina investigations found many Metal Roof Leak From Hail Damage foundation-to-building connections to be deficient (see Figure 8). Figure 8. Post-Katrina investigations showed that many buildings were attached to foundation piers with light gauge metal straps. These straps failed in many instances. A stronger (preferably bolted) connection is recommended when attaching Coastal A Zone buildings to their foundations.

Use of space below the lowest horizontal structural member for parking, access, Metal Roof Leak From Hail Damage or storage only. Adding sufficient freeboard to allow parking beneath the building will not only reduce future flood damages, but will also lower flood insurance premiums.Use of screen, lattice, or breakaway walls if space below the elevated floor is enclosed. 

Note: until flood regulations are changed, breakaway walls in Coastal A Zones must be equipped with flood openings.Additional guidance for design and construction in Coastal A Zones can be found in FEMA 499, Metal Roof Leak From Hail Damage Home Builder's Guide to Coastal Construction. The publication is a series of 31 fact sheets that provide recommended design and construction practices for foundations, connections, building envelope, etc. 

Fact Sheet 2 summarizes recommended practices for Coastal A Zones, Metal Roof Leak From Hail Damage and references other fact sheets that provide more details.[Begin table]Table 1. Foundation Recommendations for Coastal A Zones (Users should read across from a foundation type to see under what soil and base flood conditions that foundation is acceptable. 

A foundation must be capable of resisting all base flood conditions likely to exist at the site, or it should not be used. For example, a properly constructed pier on a shallow footing will generally withstand 1.5- to 3.0-foot wave heights, but should not be used where soils are erodible, Metal Roof Leak From Hail Damage and where high velocity flow is possible, or where large floodborne debris may be present.)

Wave heights greater than 3.0 feet mapped as V Zone: fill, slab, crawlspace, Metal Roof Leak From Hail Damage wall foundations not permitted. Deep means sufficiently deep to withstand erosion and scour, including that induced by the presence of the foundation itself.

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