TECHNICAL BULLETIN
TB-213
May 2013
Flood Damage-Resistant Material Considerations
Introduction
After hurricanes Ivan (2004) and Katrina (2005) the National Flood Insurance Program (NFIP) regulations modified its requirements
for design criteria for new construction and significant remodels. These criteria defined a Base Flood Elevation (BFE) in special flood
hazard areas (SFHAs). The BFE is based on the expected height of flood water during a flood that has a 1% chance of being equaled
or exceeded in any given year (commonly called the 100-year flood).
NFIP requires that the lowest floor of a building be at or above the BFE height. It also requires that all building materials, with a few
exceptions like some wiring, used below the BFE be “Flood Damage-Resistant Materials.”
Current definitions and requirements of flood-resistant materials and floor height requirements are found in FEMA’s Technical
Bulletin 2, “Flood Damage-Resistant Materials Requirements for Buildings Located in Special Flood Hazard Areas in accordance
with the National Flood Insurance Program.” (TB 2) Here. Additional information can be found in FEMA’s “Home Builder’s Guide to
Coastal Construction” which is a compilation of 37 fact sheets providing technical guidance for the construction of coastal
residential buildings. Here. The following presents a brief overview of BFE material requirements, design considerations, and
Weyerhaeuser’s position on using Trus Joist® engineered wood products (EWP) below BFE.
What is a “Flood Damage-Resistant Material”?
The NFIP defines a flood damage-resistant material as “any building material capable of withstanding direct and prolonged contact
(i.e., at least 72 hours) with floodwaters without sustaining significant damage (i.e., requires more than cosmetic repair).” The cost
of cosmetic repair should be less than the cost of replacing building materials. Although flood-resistant materials typically are
referred to for areas below the BFE, they may be appropriate in areas above the BFE in order to limit the amount of damage caused
by wind-driven rain. All building materials below the BFE must be flood damage-resistant, regardless of expected or historic flood
duration. (1)
FEMA furthers classifies building materials into 5 categories according to their ability to resist flood damage. Table 1, next page,
shows the classes and their descriptions. Note that only Class 4 and 5 materials are acceptable for use below BFE.
Page 1 of 7
This document supersedes all previous versions. If this is more than one year old, contact your dealer or Weyerhaeuser representative.
, Weyerhaeuser, Forte, Javelin, Microllam, Parallam, Silent Floor, TimberStrand, TJI, TJ, and Trus Joist are registered trademarks and Edge, Edge Gold and TJ-Pro
are trademarks of Weyerhaeuser NR. © 2013 Weyerhaeuser NR Company. All rights reserved.
1.888.453.8358 ● www.woodbywy.com
TECHNICAL BULLETIN
TB-213
May 2013
Page 2 of 7
This document supersedes all previous versions. If this is more than one year old, contact your dealer or Weyerhaeuser representative.
, Weyerhaeuser, Forte, Javelin, Microllam, Parallam, Silent Floor, TimberStrand, TJI, TJ, and Trus Joist are registered trademarks and Edge, Edge Gold and TJ-Pro
are trademarks of Weyerhaeuser NR. © 2013 Weyerhaeuser NR Company. All rights reserved.
1.888.453.8358 ● www.woodbywy.com
TECHNICAL BULLETIN
TB-213
May 2013
Acceptable Flood Damage-Resistant Materials
The following are examples of materials currently considered flood-resistant:





Preservative-treated or naturally durable (as defined in the IBC) lumber,
Concrete meeting certain requirements,
Reinforced and fully grouted masonry,
Structural steel coated to resist corrosion, and
Insulation consisting of plastics, synthetics, or closed-cell foam.
The following are examples of materials that are unacceptable below the BFE:






Normal, water-soluble adhesives specified for above-grade use or adhesives that are not resistant to alkali or acid in
water, including groundwater seepage and vapor.
Materials that contain paper-based materials, wood-based materials, or other organic materials that dissolve or
deteriorate, lose structural integrity, or are adversely affected by water.
Sheet-type floor coverings (e.g., linoleum, vinyl) or wall coverings (e.g., wallpaper) that restrict drying of the materials they
cover.
Materials that becomes dimensionally unstable when subject to wetting and drying.
Materials that absorb water excessively or maintain high moisture content after submergence.
Wiring, outlets, and electrical components not designed to be flood resistant.
TB 2 provides an extensive table that lists specific building materials and their approved uses and classification. Currently for wood,
only ratings for solid wood products are provided, shown in Table 2 (excerpt of TB 2 table). Together with the requirements listed
above, they can help specifiers determine the acceptability of engineered wood products for use below BFE.
Page 3 of 7
This document supersedes all previous versions. If this is more than one year old, contact your dealer or Weyerhaeuser representative.
, Weyerhaeuser, Forte, Javelin, Microllam, Parallam, Silent Floor, TimberStrand, TJI, TJ, and Trus Joist are registered trademarks and Edge, Edge Gold and TJ-Pro
are trademarks of Weyerhaeuser NR. © 2013 Weyerhaeuser NR Company. All rights reserved.
1.888.453.8358 ● www.woodbywy.com
TECHNICAL BULLETIN
TB-213
May 2013
Additionally, TB 2 allows for materials and products not listed to be evaluated for flood damage-resistance requirements using the
manufacturers’ literature (i.e., specifications, materials safety data sheets, test reports) or to be used if accepted by the local
official. Currently, Weyerhaeuser engineered wood products literature does not report on flood-resistant ratings or acceptability in
BFE applications.
Note that some combinations of acceptable structural and finish materials can negatively impact the classification. Although the
materials listed are considered flood-resistant materials, some sidings and wall coverings may need to be removed from framing
members following a flooding event in order to allow the system to properly dry. For instance, sheet-type floor coverings (linoleum,
rubber tile) or wall coverings (wallpaper) restrict drying of the materials they cover.
Many jurisdictions will provide a list of approved flood-resistant materials that can be used in their local coastal environments.
Check these lists and include all proposed construction and materials in approved plans.
Flood Resistant Material Standard
In an attempt to standardize the acceptability of materials for use in construction below BFE, an ASTM Standard Practice: Standard
Practice for Determining the Flood Damage Resistance Rating of Materials and Assemblies (referred to as the “the standard” in
this document) is currently in development as of 2013. This standard attempts to define the testing and results that will determine
whether building materials and assemblies are considered to be flood-damage resistant. While still in a draft format and subject to
change before becoming an enforceable standard, the proposed standard adds clarity to the definition of flood resistant material
that may be of use.
The standard describes the water immersion testing required for the purpose of evaluating flood effects on physical properties, as
well as elevated temperature and humidity testing for evaluating the specimen’s ability to be cleaned and restored to serviceability.
The standard does not address performance requirements for resisting other hazards associated with flooding (e.g. debris impact,
wave action, and contaminates in flood waters). The standard currently specifies tests for both material specimens and assemblies
to address the concerns of FEMA Technical Bulletin 2.
As of this writing, the standard defines “like new” requirements as a material that exhibits physical and mechanical properties
consistent with the requirements of the applicable material standard and manufacturer specifications for new products. Further,
the standard defines allowable retained dimensional change to be 2% or less of the control or a maximum of 0.2 inches.
When to Specify Flood Damage-Resistant Materials
Section 60.3(a)(ii) of the NFIP regulations requires that all new construction and substantial improvements in flood-prone areas be
constructed with materials below the Base Flood Elevation (BFE) that are resistant to flood damage. In general, a substantial
improvement is defined as the cost of the improvement being equal to or greater than 50% of the pre-flood value of the home.
Some jurisdictions have enacted more restrictive requirements.
Engineer/Architect Certification of Design
As part of the agreement for making flood insurance available in a community, the NFIP requires the community to adopt a
floodplain management ordinance that specifies minimum design and construction requirements. Those requirements include a
certification of the structural design and the proposed methods of construction (a similar documentation requirement appears in
the 2009 IRC, Section R322.3.6). It is recommended that the design professional use ASCE 24 and ASCE 7 as appropriate
engineering standards.
Page 4 of 7
This document supersedes all previous versions. If this is more than one year old, contact your dealer or Weyerhaeuser representative.
, Weyerhaeuser, Forte, Javelin, Microllam, Parallam, Silent Floor, TimberStrand, TJI, TJ, and Trus Joist are registered trademarks and Edge, Edge Gold and TJ-Pro
are trademarks of Weyerhaeuser NR. © 2013 Weyerhaeuser NR Company. All rights reserved.
1.888.453.8358 ● www.woodbywy.com
TECHNICAL BULLETIN
TB-213
May 2013
Specifically, NFIP regulations and local floodplain management ordinances require that:
1. A registered professional engineer or architect shall develop or review the structural design, specifications, and plans for
the construction.
2. A registered professional engineer or architect shall certify that the design and methods of construction to be used are in
accordance with accepted standards of practice in meeting these criteria. This may involve field inspections and the
sealing of certificates with a professional engineer’s seal.
There is no single certificate(s) used on a nationwide basis. Instead, local communities and/or states have developed their own
certification procedures and documents. Registered engineers and architects involved in coastal zone construction projects should
check with the authority having jurisdiction regarding the exact nature and timing of required certifications.
Meeting coastal construction and certification requirements is important not only for local code and jurisdiction acceptance, but will
have a direct impact on the insurability of and the flood insurance rates for the structure.
Structural Requirements
FEMA/NFIP structural requirements and recommendations, including referencing ASCE 24 free board requirements (adding free
board above BFE can significantly reduce insurance rates), as well as construction details can be found in the following FEMA
documents. Note that all applicable local building code requirements apply to structures in SFHAs, and if more stringent, supersede
NFIP requirements.






1.4: Lowest Floor Elevation. Here
1.6: Designing for Flood Levels above the BFE. Here
1.7: Coastal Building Materials. Here
9.1: Repairs, Remodeling, Additions, and Retrofitting – Flood. Here
TB 2, Flood Damage-Resistant Materials Requirements for Buildings. Here
Recommended Residential Construction for Coastal Areas. Here
Weyerhaeuser EWP Material
Since using appropriate materials directly impacts a structure’s insurability and can incur liability risks for the designer or specifier,
it is important that care is taken when considering using our EWP products in BFE applications. Given the current and pending
definitions of acceptable “flood damage-resistant” material, most Weyerhaeuser EWP building products will not meet the
requirements for use below BFE and are best used above the BFE.
With many EWP products, a limiting concern is swelling. For example, TimberStrand® LSL sill plates and studs may swell during a
flood event and can be expected to retain ½ of the swell when dried out. Additionally, exposure to flood water may potentially cause
a wavy surface appearance which may be a cosmetic concern. Table 3 indicates thickness swell in untreated EWP products for the
extreme case where moisture content is at or near the fiber saturation point throughout the full cross-section of the member. It is
not anticipated that moisture contents would reach this level in most flood conditions, but given the uncertain nature of flood
events, this high moisture content data is recommended for use in the decision making process . As the table demonstrates, none
of the untreated products shown would meet a possible requirement of 2% or less retained swell after wetting.
However, since the standard is not yet in force (projected completion 2015), it is up to the designer and the governing jurisdiction to
interpret the definition of “dimensionally unstable” and to determine allowable deformation for wood products. It is important to
address this point upfront so that expectations of performance and appearance in the post-flood structure are realistic.
Page 5 of 7
This document supersedes all previous versions. If this is more than one year old, contact your dealer or Weyerhaeuser representative.
, Weyerhaeuser, Forte, Javelin, Microllam, Parallam, Silent Floor, TimberStrand, TJI, TJ, and Trus Joist are registered trademarks and Edge, Edge Gold and TJ-Pro
are trademarks of Weyerhaeuser NR. © 2013 Weyerhaeuser NR Company. All rights reserved.
1.888.453.8358 ● www.woodbywy.com
TECHNICAL BULLETIN
TB-213
Table 3:
May 2013
SCL Dimensional Change at Different Moisture Exposures(1)
% Thickness (Width) Swell
Product
Wet(2)
(>30% MC)
LSL
LVL
PSL
18%
6-8%
10-15%
Recovery
from Wet
(3)
9%
3-4%
5-8%
% Depth Swell
Wet(2)
(>30% MC)
1%
4-6%
5-6%
Recovery
from Wet(3)
0.3%
1-1.5%
2-2.5%
% Length Swell
Wet(2)
(>30% MC)
Recovery
from Wet(3)
Depth
Negligible
Negligible
Negligible
1. From ‘as manufactured’ dimensions and moisture content.
2. ‘Wet’ assumes MC > 30% throughout the cross-section. Partially wetted product will exhibit lower percentage swell
than shown in this table.
3. ‘Recovery from wet’ assumes original manufactured moisture content.
Width
Structural material exposed to prolonged flooding may potentially experience degraded mechanical properties. Until the proposed
ASTM standard discussed previously is complete, there is no standardized method by which to determine the potential impacts of
flood exposure on mechanical properties. Currently, Weyerhaeuser has not evaluated our EWP products specifically for the effects
of flood exposure on mechanical properties.
Parallam® Plus PSL has been effectively flooded once already in the treating process, and, as a result, additional unrecoverable
swelling deformation is not a significant concern. Strength reductions due to the treatment process and anticipated in-service
moisture conditions have already been accounted for in the material’s allowable design properties. Therefore, we believe Parallam®
Plus PSL meets the NFIP criteria for construction below the BFE. However, the designer and the governing jurisdiction are ultimately
responsible for determining suitability for the specific end use application and conditions. For additional information, see
Weyerhaeuser’s Parallam® Plus PSL Specifier’s Guide, TJ-7102. Here.
StrandGuard® TimberStrand® LSL may be considered an acceptable material for below BFE construction based on the current
acceptability of Borate-treated solid-sawn lumber. A concern that may arise with this product is the potential leeching of the Zinc
Borate (ZB) treatment during a flood event. From a chemical efficacy standpoint, insufficient quantities of the treatment will leech
during a 72-hour flood event period, and the product should experience no additional decay as a result.
Note that ZB is not an effective moldicide, though since untreated lumber and exterior grade plywood are permitted in below BFE
construction, the potential for mold growth does not appear to be a limiting factor for acceptability. Potential changes in
mechanical properties, as well as swelling, are still points to consider when specifying StrandGuard® TimberStrand® LSL. Due to
the ambiguity in the current NFIP criteria, we are unable to make a definitive recommendation at this time regarding the use of
StrandGuard® TimberStrand® LSL as acceptable material for below BFE construction. Each designer and governing jurisdiction will
need to evaluate the suitability of StrandGuard® TimberStrand® LSL for their applications and region.
Page 6 of 7
This document supersedes all previous versions. If this is more than one year old, contact your dealer or Weyerhaeuser representative.
, Weyerhaeuser, Forte, Javelin, Microllam, Parallam, Silent Floor, TimberStrand, TJI, TJ, and Trus Joist are registered trademarks and Edge, Edge Gold and TJ-Pro
are trademarks of Weyerhaeuser NR. © 2013 Weyerhaeuser NR Company. All rights reserved.
1.888.453.8358 ● www.woodbywy.com
TECHNICAL BULLETIN
TB-213
May 2013
References





Flood Damage-Resistant Materials Requirements for Buildings located in Special Flood Hazard Areas in accordance with
the National Flood Insurance Program, Technical Bulletin 2, FEMA, August 2008.
Home Builder’s Guide to Coastal Construction, Sections 1.6, 1.7,9.1, FEMA, December 2010
Recommended Residential Construction for Coastal Areas, Building on Strong and Safe Foundations, FEMA 550, FEMA,
December 2009
(DRAFT) Standard Practice for Determining the Flood Damage Resistance Rating of Materials and Assemblies, ASTM, 22
March 2013
Engineered Wood Products Exposed to Floodwaters, Structural Magazine, April 2012, Adam Pittman, P.E., Weyerhaeuser
Company.
Page 7 of 7
This document supersedes all previous versions. If this is more than one year old, contact your dealer or Weyerhaeuser representative.
, Weyerhaeuser, Forte, Javelin, Microllam, Parallam, Silent Floor, TimberStrand, TJI, TJ, and Trus Joist are registered trademarks and Edge, Edge Gold and TJ-Pro
are trademarks of Weyerhaeuser NR. © 2013 Weyerhaeuser NR Company. All rights reserved.
1.888.453.8358 ● www.woodbywy.com