Page 26 - Builder Brief October 2025

B U I L D I N G C O D E S
HOW BUILDING CODES
CAN – AND CAN’T –
HELP IN FLOODS
The devastating flash floods in Central Texas in July were
the latest in a string of tragic flooding incidents involving
rivers and streams. As with the mountain river floods in North
Carolina after Hurricane Helene, many people are wondering
how to prevent such disasters in the future.
Could enhanced building codes help save lives and
property in flood-prone areas? Perhaps. But it is important
to note there are already enhanced building codes required
in flood zones.
The International Residential Code (IRC) Section R306
and International Building Codes (IBC) Section 1612 spell
out construction requirements for structures built in flood
hazard areas. These provisions equal or exceed the minimum
construction standards established under the National Flood
Insurance Program (NFIP) required for communities to be
eligible for federal flood insurance for buildings constructed
in flood hazard areas.
The NFIP minimum construction standards and the I-Codes
require new construction and existing buildings that have been
substantially damaged by a flood or other event or substantially
improved in a remodeling project to be elevated above the
depth associated with a flood with a 1% chance of occurring
in a year (100-year flood). Construction in floodways — the
areas adjacent to a river or other flood source prone to the
deepest, fastest-moving floodwaters that cause the most
damage — is heavily restricted.
But the nature of flooding makes the uniform development
and application of standards, codes, and building requirements
very difficult. Floodplains come in many shapes and sizes,
including deep river valleys, broad floodplains adjacent to
lakes, and coastal areas subject to ocean waves and storm
surge.
For example, the Hill Country along the Guadeloupe River,
the Asheville region in North Carolina, and the Appalachian
areas of eastern Kentucky where severe floods recently
occurred are all characterized by mountain valleys and river
channels conducive to fast-moving waters and flash flooding.
This is in contrast to the areas of the Great Plains along the
Missouri and Mississippi rivers where floodplains are often
broad and floodwaters can be shallower and slower moving.
In the built environment, shallow urban flooding can occur
when storm drains get overloaded.
This variability is baked into flood zone management.
Flood Insurance Rate Maps (FIRMs) developed by FEMA
identify specific flood hazard areas around water based on
26 OCTOBER 2025 | GREATER SAN ANTONIO BUILDERS ASSOCIATION
the probability of flooding. These include the traditional 1%
annual chance (100-year) floodplains, known as special
flood hazard areas, floodways, and on some maps the 0.2%
annual chance (500-year) floodplain. These mapped flood
hazard areas are crucial in determining the risk basis for flood
insurance rates and the issuance of building permits.
Even predictive modeling can fail to account for anomalous
climate events. A meteorologist reported that 1.5 times more
moisture was transported to western North Carolina last year
than in any prior recorded event, and the North Carolina State
Climate Office said rainfall amounts were well past 1,000-year
flood levels.
Additional building codes will never be able to account
for these types of events. But buildings built to current
codes do withstand flooding far better than older structures.
Home owners also have the option to build their homes to
above-code standards, including for flood prevention, for
an additional cost.
An upcoming cost study from Home Innovation Research
Labs estimates the cost of 1 foot of elevation above grade
for a typical slab-on-grade home as ranging from $4,800 to
$12,200 depending on the method used and climate zone.
The incremental cost of an additional foot of elevation ranges
from $3,700 to $14,000. Those are significant costs for home
owners and renters, especially as America is facing a serious
housing affordability crisis.
In addition, Home Innovation Research Labs and NAHB
recently developed a series of guidelines published by HUD
for designing homes for natural hazards, one of which is
for water risks. Also, the National Green Building Standard
(NGBS) is currently set to be published in the next few months
with an updated standard. The standard includes topics such
as resiliency from water events.
A number of home building strategies and techniques
can be used to prevent flooding, although hazards persist.
Unfortunately, flooding is an intractable issue, but home
builders and remodelers are mitigating these risks and hazards
with new techniques and products based on science.