Inspecting the Resiliency of Buildings and Structures in Flood Hazard Areas

Flooding is one of the most common and costly natural disasters to which our country is exposed. In the past five
years, every state in the United States has flooded and 21 states have experienced frequent flooding events,
according to Beverly Cigler in her book U.S. Floods: The Necessity of Mitigation. Altogether, from 1980 through 2019,
the United States has sustained 258 weather and climate disasters, for which overall damages and costs reached or
exceeded $1 billion, with the total cost of these 258 events exceeding $1.75 trillion.

More recently, Hurricane Harvey damaged or destroyed more than 200,000 homes and businesses, with massive flooding
from rainfall that reached 30 to 50 inches across the storm’s path. And Superstorm Sandy (considered a significant
flooding event) caused more than 305,000 homes, decks and porches to be significantly damaged or destroyed.

Unfortunately, homeowners insurance typically does not cover flood loss costs. While a National Flood Insurance
Program (NFIP) policy covers up to a certain amount, there is less than a 50 percent “take-up” rate for these
policies. For example, 80 percent of the homeowners with flooding caused by Superstorm Sandy did not have an NFIP
policy.

Those who live in flood hazard areas are left with the following options:

• Relocate out of the flood hazard area
• Elevate the building above current design flood elevation requirements in anticipation of future events
• Build to the required guidelines to prevent flotation, collapse or permanent lateral displacement from flooding

According to a National Climate Assessment study, more than $1 trillion of property and structures in the United
States are at risk of inundation from climate-caused sea level rise of 2 feet above current levels, which could
happen as early as 2050. For more information, visit the National Climate Assesment website: nca2014.globalchange.gov

To improve the resiliency of buildings and structures in flood hazard areas, it’s important to identify where the
current design flood elevation (DFE) is on the structure because construction standards are different for the parts
of the building, deck or porch at or below the design flood elevation. The DFE is always the base flood elevation
(BFE) plus freeboard (a factor of safety).

Also, there are different criteria for the type of flood hazard area (A Zone, Coastal A Zone or V Zone) in which the
building or structure is located.

To locate the flood category for a property, go to www.floodsmart.gov, click the FEMA Flood Map Service Center and
enter the address. Local flood insurance rate maps can provide the BFE, and the freeboard is usually 1 or 2 feet for
homes, but it may be higher depending on the adopted freeboard for the jurisdiction.

Whether the building or structure is following the guidelines of the NFIP Section 60.3(a)(3), the International
Residential Code® Section R322.1.2, or ASCE 24-Flood Resistant Design and Construction Section 1.5.1 (ASCE 24 applies
to all buildings and structures using the International Building Code®, and all buildings and structures in
floodways), the following principles apply:

If a proposed building site is in a flood-prone or flood hazard area, all new construction and substantial
improvements shall be:

• Designed (or modified) and adequately anchored to prevent flotation, collapse or lateral movement of the
  structure resulting from hydrodynamic and hydrostatic loads, including the effects of buoyancy
• Constructed with materials resistant to flood damage
• Constructed by methods and practices that minimize flood damage

This home lifted off of the foundation, knocked into the house next door, and floated down the street about
600 yards and sits in the bay at the end of the road.

Buildings and Homes

Providing a continuous load path is essential to resisting the hydrostatic, hydrodynamic, wave and impact forces from
water and objects carried by the water. In addition, flooding often comes with high winds associated with strong
thunderstorms and hurricanes, making all the links in the load path important. For flood-resistant construction,
focus on links 6, 7 and 8 (see illustration below).

Inspectors can review numerous parts of the building when it comes to elevated or raised foundations, including
whether or not HVAC units are elevated above the design flood elevations, whether floor framing is connected to the
support beam and whether there’s a connection from the support beam to the pile, pier or foundation.

Due to failures that occurred during Superstorm Sandy, where the connection was too close to the edge of the wood,
there are new details recommending that the strap connect above the centerline axis of the joist and below the
centerline axis of the beam. See details and pictures to the right.

Diagram courtesy of the Coastal Construction Manual — FEMA 55, Designing the Building, Figure 12-15.
Link #1 — Roof Sheathing to Roof Framing Link #2 — Roof Framing to Exterior Walls Link #3 — Top
Plate to Wall Studs Link #4 — Wall Sheathing to Window Header Link #5 — Window Header to Exterior Wall
Link #6 — Wall to Floor Framing Link #7 — Floor Framing to Support Beam Link #8 — Floor Support
Beam to Foundation (Pile)

A beam in a home that was rebuilt after being destroyed by a flood. The joists are resting on the beam and
the beam is sitting on the pier. Nothing is tying the framing to the foundation. Unfortunately, this home will be
subject to floating away in the next flood.

Note the wood failure or tearing perpendicular to grain because the connector fasteners were too close to
the edge of the wood.

FEMA detail showing a longer twist strap. Courtesy of FEMA — Improving Connections in Elevated Coastal
Residential Buildings (RA 1 February 2013, p.3).

In buildings and homes with solid foundations (not permitted in V Zones or Coastal A Zones when the design is
governed by ASCE 24), inspectors may want to look for the following:

When a building has a solid foundation in an A Zone, check to see that water is able to flow through the building and
meets the minimum requirement for openings. If they are non-engineered openings, the net open area shall be at least
1 square inch for each square foot of enclosed area, not less than 3 inches in any direction and account for louvers,
screens, faceplates or other covers so as not to impede the floodwaters.

In addition, if the building has a crawl space or if you are able to get underneath the first floor joists, look to
see that everything below the top of the first floor joists is connected to the wood member or foundation below.

Starting with the sill plate and the foundation, check to see if the sill plate is connected to the foundation and if
the rim joists, floor joists or both are connected to the sill plate or foundation. The photos below show failures of
the framing to the foundation.

Similar to elevated buildings, all the links in the load path must be strong enough to resist the flood waters. See
diagram below.

Uplift connectors shall bypass each other to prevent cross-grain tension of the band joist. Sill plate
anchors not shown.

Link #1 – Ledger to Main Structure Link #2 – Deck Frame to Main Structure (Lateral) Link #3 – Deck Boards Link #4 – Gaurdrail System to Framing Link #5 – Joist to Beam Link #6 – Beam to Post Link #7 – Post to Footing or Foundation Link #8 – Footing or Foundation

Decks and Porches

Buildings (that is, structures that include two or more outside rigid walls and a roof) and their contents may be
covered under a NFIP policy. However, property and belongings outside the building envelope are generally not
covered. Therefore, when a deck or porch is destroyed by a flood, the building owner or homeowner would have to pay
for the repair or rebuild.

As with homes and buildings, it is essential that decks and porches have a continuous load path to resist the
hydrostatic, hydrodynamic, wave and impact forces from water and objects carried by the water.

For flood-resistant construction of decks and porches, focus on links 2, 5, 6, 7 and 8 (see diagram below).

In addition to supporting the download of the deck and occupants, the footing must resist the lateral load of
occupant movement and flood waters, and must be deep enough to resist scour associated with floods. In V Zones, the
referenced standard (ASCE24) states that supports shall extend 10 feet below mean water level to account for the
potential of significant scour. However, because an inspector can’t inspect for footing or support embedment, the
first key point to look for is the post-to-footing or foundation.

Inadequate porch or deck post connections are common failures during a flood event. Once the posts are “washed away,”
there is nothing to prevent the porch or deck from collapsing.

The posts washed away from flooding on the porch and on this deck, causing the roof to collapse. There are
numerous options for connecting the posts to the concrete or wood framing after the porch or deck is built.

Joist hangers are good for supporting the download or uplift from the joists, but are not sufficient to
resist any lateral load from occupant movement or flood waters. As you can see from the photos on this page, these
decks were not able to resist the flood waters and deck platforms were pulled away from the main structure.

Some sort of lateral-load hardware is needed to carry the lateral load from occupant movement or flood
waters to the main structure.

Stairs

Codes state that stairways and ramps shall be designed and constructed to break away without causing damage to the
building or the structure, or shall be designed and constructed to resist flood loads and minimize transfer of flood
loads.

Inspectors may want to check whether the stairs are connected to the structure, deck or porch to determine if they
could cause damage if they separate during a flood event. In addition, for stairs to meet all the other requirements
and all the flood-resistant construction guidelines, the most economical way is for them to be independent of the
building or structure. See photos and labels below.

One of the most common violations for stairs is the riser opening. The flood requirements are for the riser to be
open or partially open to allow the flood waters to pass through the stairs. In addition to being open, they must not
allow the passage of a 4-inch sphere. Typically, they are either completely open (see photos below) or completely
closed (see photos below).

Stairs that are completely open and do not meet the 4-inch sphere requirement.

Stairs that are completely closed and do not meet the requirement to allow the flood waters to pass through
them.

The straps connecting the beams to the joists failed during a flood event due to inadequate corrosion
protection of the metal.

Corrosion Considerations

FEMA TB-2, which is referenced by the codes for flood-resistant materials, states that “performance of buildings that
are exposed to flooding is, in part, a function of the fasteners and connectors used to put the components together.
If corrosion occurs, buildings are less likely to withstand flood loads and other loads.” So, if you can identify red
rust on the connectors, fasteners or anchors, it should be reported.

Based on ASCE 24, exposed material below the design flood elevations shall be stainless steel or hot-dip galvanized
after fabrication.

Typically, connectors that are used in flood hazard areas meet the treated-wood requirement of ASTM A653,
G185 (Simpson Strong-Tie trade name for this galvanization is ZMAX®). ZMAX® connectors are hot-dip galvanized prior
to fabrication and, therefore, don’t meet the requirements of ASCE 24. Consequently, these products will corrode
prematurely and will not be effective when the flood occurs.

Conclusion

Inspecting homes, buildings, decks and porches to the requirements of flood-resistant construction will provide your
client with the peace of mind that, after a flood, they’ll be able to go back to their home or building with minimal
repairs needed.

Later in 2020, Simpson Strong-Tie will debut two new online courses requirements for buildings, homes, decks and
porches in flood hazard areas. Visit www.strongtie.com for more information.

There is much to know about the resiliency of buildings and structures in flood hazard areas. Inspectors may want to
do their own research to gather more information on this complex subject.