Specifying weather-resistant siding

by Chad Diercks and Dale Knox
Severe weather can devastate communities and cause costly property damage, prompting designers and specifiers for commercial, multi-family, institutional, and industrial buildings to seek durable siding materials. Fiber cement has become a popular choice to satisfy requirements for both code compliance and improved property protection.

Storms, wildfires and other acts of nature are difficult to predict, but statistics show damage caused by these occurrences are increasingly expensive. Property damage in the United States caused by tornadoes, hail, floods, coastal storms, hurricanes, and blizzards totaled more than $26.5 trillion in 2012, according to a report from the National Weather Service.¹

Further, consumer insurance website Insure.com notes six of the top 10 costliest wildfires in U.S. history have struck in the last decade.² Four of the five most expensive hurricanes have also occurred since 2005. Hurricane Katrina is at the top with an estimated cost of $108 billion. Last year’s Hurricane Sandy, which struck the U.S. eastern seaboard in October, cost an estimated $65 billion.³

Considerations when specifying siding range from aesthetics and cost, to code compliance and safety. Two important issues for building owners are lowered maintenance and less risk—especially related to moisture.

For years, product specifiers relied on vinyl and wood siding as traditional go-to products for various projects. However, vinyl siding can be seriously damaged during storms with strong winds, hail, and flying debris. According to the National Storm Damage Center (NSDC) the most common types of storm damage to vinyl siding are cracking, chipping, and breaking.⁴

With the development of more durable materials, there has been growth in the use of fiber cement siding because it stands up better in both every day and extreme weather. Although the initial investment of fiber cement siding can be slightly higher than other siding options, the improved protection and lower maintenance provide a payback over the long term.

The specification process for institutional and industrial buildings can be more complex than other commercial buildings. For institutional buildings associated with a state or federal government agency, specified products are usually required to be manufactured in the United States, due to the Buy American Act. Industrial buildings involving chemicals have extra considerations related to fire and explosion prevention.

In assisting project managers with quality control by helping to navigate the complex demands large projects put forth on project teams, MasterFormat is helpful at providing the information needed to navigate such variables. It helps organize critical fire-related elements of the project so teams and owners are better aligned on the agreed-upon needs and wants required.

Many building plans start with evaluation of codes for fire ratings and weather hazards, which may significantly vary by region. Many state and municipal codes are based on the International Building Code (IBC) and then tailored to fit regional needs, which can make requirements stricter in some areas. IBC Section 1405.16, “Fiber-cement Siding,” specifically covers the usage and installation of the material. (See “Section 1405.16.”)

Disasters are often the impetus for regional code changes. In the 1990s, hurricanes in Florida drove regional change to the state’s building code, such as the inclusion of American Society of Civil Engineering/Structural Engineering Institute (ASCE/SEI) 7, Minimum Design Loads For Buildings and Other Structures, code adoption, and required missile impact-resistant glass and wall systems. A decade later, wildfires in California led to changes in the state building code. For example, eave, deck, and exterior wall protection, as well as elevated window fire endurance were updated. Some of these regional code changes have flowed over into the national model codes.

Due to recent storms, flooding has become a growing area of consideration, and one that will likely have more stringent codes in the future. For instance, the 2012 IBC requires exterior walls extending below the design flood elevation be constructed of flood-damage-resistant materials.

According to Section 1403.6, “Flood Resistance:”

For buildings in flood hazard areas as established in Section 1612.3, exterior walls extending below the elevation required by Section 1612 shall be constructed with flood-damage-resistant materials.

Additionally, 2012 IBC, Section 202 defines several key terms related to flood loads. They include:

• Design flood: flood associated with the greater of the following two areas: area with a flood plain subject to a one percent or greater chance of flooding in any year, or area designated as a flood hazard area on a community’s flood hazard map (or otherwise legally designated);
• Design flood elevation: elevation of the ‘design flood,’ including wave height, relative to the datum specified on the community’s legally designated flood hazard map. In areas designated as Zone AO, the design flood elevation shall be the elevation of the highest existing grade of the building’s perimeter plus the depth number (in feet) specified on the flood hazard map. In areas designated as Zone AO where a depth number is not specified on the map, the depth number shall be taken as being equal to 2 ft (i.e. 610 mm);
• Flood hazard area: the greater of the area within a flood plain subject to a one percent or greater chance of flooding in any year, or area designated as a flood hazard area on a community’s flood hazard map; and
• Flood damage-resistant material: any construction material capable of withstanding direct and prolonged contact with floodwaters without sustaining any damage that requires more than cosmetic repair.

However, the 2012 IBC does not list a specific standard defining flood damage-resistant materials. In lieu of a code-defined standard, one path to compliance may be to use U.S. Federal Emergency Management Agency (FEMA) Technical Bulletin 2, “Flood Damage-resistant Materials Requirements.”⁵

Fire protection
In some areas prone to wildfires, fire regulations are especially stringent. Over the last decade, wildfires have had an influence in design and construction specifications. For example, in 2006, the Wildland-Urban Interface Code was added to the California Building Code because many of the state’s buildings with combustible siding installed were damaged in wildfires.⁶ This code requires use of non-combustible or ignition-resistant materials (including siding) to be employed on buildings in high fire severity areas.

Fiber cement is roughly 90 percent sand and cement—materials that do not readily ignite. Fiber cement siding is also required to have a flame spread index of ‘0’ and a smoke developed index of ‘5’ or less when tested to ASTM E84, Standard Test Method for Surface Burning Characteristics of Building Materials. Fiber cement siding also meets the non-combustibility requirements as set forth in ASTM E136, Standard Test Method for Behavior of Materials in a Vertical Tube Furnace at 750 C (1382 F).

Some types of commercial buildings—such as hospitals—require non-combustible construction. As a non-combustible material, fiber cement siding performs well, but wood and vinyl may not be approved for certain projects. With enough heat, vinyl can soften and melt, causing the siding to sag; when it burns, it can release toxic fumes.

It is essential for a specifier to be aware of which siding choices comply with specific fire protection regulations.

For example, in addition to ASTM E84, fiber cement siding should comply with:

• 2012 International Wildland-Urban Interface Code, where Class 1, Ignition-resistant Construction is required—Section 504.5, Exterior Walls, permits approved non-combustible materials (e.g. fiber cement) on exterior walls;
• ASTM E136;⁷
• California Building Code, Chapter 7a, “Materials and Construction Methods for Exterior Wildfire Exposure, for use in Wildland Urban Interface Areas (i.e. high fire hazard severity zones);” and
• California’s Office of the State Fire Marshal’s (SFM) Building Materials Listing Program (BML), Section 8140, Exterior Wall Siding and Sheathing for Wildland Urban Interface (WUI), and 8160, Under Eave for Wildland Urban Interface.⁸

Compliance with these sections indicates that the siding is permitted to be used in Wildland-Urban Interface Fire areas.

Wind load and impact resistance
Not surprisingly, areas designated as high-velocity hurricane zones have stringent state codes. One of the strictest governing bodies is in Miami-Dade County in Florida. After Hurricane Andrew struck the state in 1992, the county’s Building Code Compliance Office was created to ensure buildings are double-checked for high-impact wind requirements.

A high wind load can create negative air pressure, which pulls siding away from a building. If installation instructions are followed per the manufacturer’s requirements, siding with the right impact-resistance and fasteners with proper hold capacity will prevent siding from being blown off buildings.

Impact by hail or storm debris can cause expensive damage to a building, prompting storm-susceptible areas to improve their building codes. Florida has a stringent code requirement for a building’s wall system to protect against debris generated by the high winds of a hurricane. Codes in some East Coast jurisdictions will likely change as a result of Hurricane Sandy. New York City’s mayor, Michael Bloomberg, has publicly stated he wants the city’s building code amended to address the issues presented by the ‘super-storm.’

In Freeport, New York, Hurricane Sandy brought winds in excess of 128.75 kph (80 mph) and flooding up to 2.1 m (7 ft) high. Many buildings along the water were destroyed, but the Long Island Harbor Master’s Quarters remained relatively unharmed.⁹ Designed with hurricanes in mind in 2007, the facility was cladded with fiber cement siding, which along with other exterior materials, protected it from wind and damage caused by impact and flooding. While many other nearby buildings needed rebuilding or extensive repair, the Harbor Master’s Quarters required no major external repair.

Flooding and moisture
According to FEMA, only Class 4 and Class 5 materials are acceptable for areas below the base flood elevation (BFE) in buildings located in special flood hazard areas.¹⁰ FEMA defines Class 5 flood-resistant materials as:

highly resistant to floodwater damage, including damage caused by moving water. These materials can survive wetting and drying and may be successfully cleaned after a flood to render them free of most harmful pollutants.

Once again, specifiers need to keep in mind specific code compliance when specifying siding that will resist the effects of flooding. For example, siding listed as a Class 5 flood-resistant material by FEMA is not affected after being submerged in a 72-hour flood. Once the water is drained and the material is dried, it may be reused. Conversely, wood siding is destroyed in water submersion, though vinyl may withstand some water exposure.

In most cases, siding is not going to fully protect a building in the event of a flood because the wall behind the siding may get wet and not properly dry. Currently, there is little guidance on flood resistance in IBC, but as costal populations continue to grow, it will likely become more stringent.

To reduce moisture during rain events for multi-family structures, a rainscreen application or air gap behind fiber cement panels provides a water management strategy to prevent water from getting trapped under the siding.

Oregon Residential Specialty Code, Section R703.1, (“General,”) requires a 3.1-mm (1/8-in.) gap behind the cladding to work as a rainscreen or ventilated façade. The high moisture in that state causes water penetration and decay, so the gap can help drain moisture out of the wall system to avoid mold and rot, making the building healthier.¹¹ This applies to multi-family dwellings and detached congregate living facilities, as well as single-family homes.

Appearance
In particular, commercial and multi-family buildings have two general types of aesthetic looks: traditional (horizontal lap siding or shingles) and modern (large-format rectangular panels). For the former, fiber cement siding enables the authenticity of real wood grain, but without the associated maintenance. Traditional looks would encompass lap siding, vertical siding in a board and batten application, or shingle siding with traditional trim applications. Often, material types and colors are mixed within a single commercial or multi-family building to further advance architectural interest.

While traditional styles dominate, the modern panelized look has become more popular—particularly for office and retail buildings, transportation facilities, and apartment or condominium buildings in urban areas. The sleek appearance often features smooth panels, sharp expressed joints with deep shadow lines, and exposed fasteners. Trims and fasteners can have a painted or metal finish.

Maintenance
Daily wear can take its toll on siding. Regular maintenance is necessary to preserve siding’s performance and appearance. Fiber cement siding tends to have better longevity than wood or plastic-based products because it resists cracking, warping, rot, and pest damage—even after exposure to harsh temperature and moisture.

Additionally, to meet the specific needs of a region, some fiber cement siding is engineered for the particular climate in which it will be used. This includes basing the production on individual climatic variables such as temperature range, ultraviolet light, and humidity. Using this data, products designed for use in various regions of the United States are formulated to protect against individual conditions.

Conclusion
Among the standard choices of vinyl, wood, and fiber cement, the final product is robust enough to stand up to extreme environmental conditions for buildings. Wood or vinyl siding is traditionally found in Type V construction, where exterior walls are made of combustible or non-combustible materials. If vinyl or wood siding is specified in Types I, II, III, and IV construction (i.e. non-combustible exterior walls), there must be compliance with limitations within the building code (e.g. 2012 IBC, Section 1406.2,Combustible exterior wall coverings). Fiber cement siding is permitted on exterior walls of Type I, II, III, IV, and V construction; this includes construction where exterior walls are required to be of non-combustible materials.

With growing concern to choose building products that preserve property investments for many years to come, product specifiers can feel confident about fiber cement siding to meet customer needs and regulatory requirements for a safe and durable structure.

Notes
¹ For more, visit the weather statics report from the National Weather Service at www.nws.noaa.gov/om/hazstats/sum12.pdf. (back to top)
² Read the June 2013 article “The 10 costliest wildfires,” by Barbara Marquand at www.insure.com/home-insurance/costliest-wildfires.html. (back to top)
³ Read Chris Dolce’s June 2013 article “Top 10 Costliest Hurricanes,” at www.weather.com/news/weather-hurricanes/ten-most-costly-hurricanes-20130524?pageno=1. (back to top)
⁴ Read the full article about vinyl siding damage at www.stormdamagecenter.org/siding-damage.html. (back to top)
⁵ For more, see www.fema.gov/media-library-data/20130726-1502-20490-4764/fema_tb_2_rev1.pdf. (back to top)
⁶ Learn more about California’s Wildland-Urban Interface Code at www.fire.ca.gov/fire_prevention/fire_prevention_wildland_codes.php. (back to top)
⁷ Reference ESR-1844, ESR-2290, and NER-405 published by International Code Council-Evaluation Service (ICC-ES). (back to top)
⁸ Review listings at osfm.fire.ca.gov/strucfireengineer/strucfireengineer_bml.php. (back to top)
⁹ For more information about how the Long Island Harbor Master’s Quarters held up after Hurricane Sandy at go to www.youtube.com/watch?v=VfdmuOkl6Aw&list=UUUpRl607QVjsTMX6NRsQEfw. (back to top)
¹⁰ See material class descriptions on page 6 of the FEMA technical bulletin, “Flood Damage-Resistant Materials Requirements,” at www.fema.gov/media-library-data/20130726-1502-20490-4764/fema_tb_2_rev1.pdf. (back to top)
¹¹ For more, see chapter seven of the 2011 Oregon Residential Specialty Code. Visit at ecodes.biz/ecodes_support/free_resources/Oregon/11_Residential/PDFs/Chapter%207_Wall%20Covering.pdf. (back to top)

Chad Diercks oversees product compliance and sustainability at James Hardie Building Products, which includes product testing and engineering, codes and standards development, warranty claims, and product technical support for North America. He has worked with the company for 14 years. Diercks is an officer on ASTM technical committee C17 on fiber-reinforced cement products, and sits on numerous other ASTM and ANSI technical committees related to the building industry. He can be reached at chad.diercks@jameshardie.com.

Dale Knox is a product manager at James Hardie Building Products, where he oversees the development and implementation of new products and specifications for the multi-family and commercial market segments. He is a civil engineer by training, with background in research and development, and his past roles at James Hardie include technical manager and research engineer. Knox has had the responsibility for product performance, installation practices, and building science. He can be reached at dale.knox@jhresearchusa.com.