Tag Archives: International Building Code

Success in the Balance: Form and function with balanced doors

Photo © Heather Collins Roe Photography

Photo © Heather Collins Roe Photography

by Mark Graves

Specifying doors is a complex task, given the various choices available to meet aesthetic and functional needs. When choosing a marquee entry, a specifier needs to consider several criteria.

First, the amount of traffic to the door must be anticipated. If the door’s location subjects it to constant use from foot traffic and exposure to the environment, the assembly needs to be a solid product resistant to deterioration and abuse. Second, the building’s wind and stack action pressure must be considered. The door needs to open easily and remain closed in all conditions. Third, the door must be able to be opened easily by all users, despite size and weight. Finally, if applicable, the door’s leaf projection to the exterior should be reviewed to prevent it from protruding onto the sidewalk area and possibly obstructing pedestrian traffic.

Available for more than 80 years, balanced doors can meet these challenges. Their design and solid construction means the fulcrum is inset at one-third the door’s width, which allows for large, heavy, and durable doors to be opened with relative ease. This design facilitates fluid opening and closing, even when strong external wind pressures and internal stack pressures exist, as the door works with—rather than against—these forces. This also ensures doors will remain closed and not flutter when confronted with uneven air pressure, ultimately reducing a facility’s energy costs.

Design options and possibilities
Balanced doors can complement any design, or act as the design centerpiece of the buildings they serve. Commonly offered in bronze, stainless steel, steel, aluminum, and wood, manufacturers can produce doors with virtually infinite combinations of materials, sizes, and designs. Sidelites and transoms can also be incorporated around the doors, but it is recommended architects and designers work with a curtain wall or storefront manufacturer to achieve a unified aesthetic between the door system and surrounding building area.

The main entrance of the Lakewood Cemetery’s Garden Mausoleum in Minneapolis showcases a pair of custom muntz-bronze balanced doors covered in decorative bronze grilles with a wide perimeter accent bronze trim. [CREDIT] Photo © Paul Crosby

The main entrance of the Lakewood Cemetery’s Garden Mausoleum in Minneapolis showcases a pair of custom muntz-bronze balanced doors covered in decorative bronze grilles with a wide perimeter accent bronze trim. Photo © Paul Crosby

A durable and design-flexible balanced door system can be composed of formed-up bronze or stainless steel. Sheet stock is bent and formed to desired specifications, and is flexible enough to accommodate details such as flush-type glazing, wider door stiles and rails, and various finish options.

Balanced doors made from formed stainless steel or bronze are constructed with a minimum stile and top rail of 69.8 mm (2 ¾ in.), and a minimum bottom rail height of 152 mm (6 in.), though 254 mm (10 in.) is recommended to comply with the current 2010 Americans with Disabilities Act (ADA). The formed-up glass stops can accommodate various glass thicknesses from 6.35 to 25-mm (¼ to 1-in.) insulated glass, and have the capacity to accommodate bullet-resistant or blast-mitigation glass by making the door slightly thicker.

The formed-up balanced door features a tie-channel assembly, which extends all the way up and around the vision opening. It is made up of individual channel shapes welded at the corners to form a sub-assembly slid between the door skins. It is then spot-welded (i.e. resistance) into place for superior door rigidity and longevity. The formed-up door also features top and bottom channels, which are placed between the interior and exterior skins. Both the door skin and subframe materials are 2.2-mm (0.09-in.) thick bronze or stainless steel, which is among the heaviest used in door construction.

Extruded aluminum balanced doors are a budget option similar in structural appearance to formed stainless steel or bronze balanced doors. Aluminum extrusions are used in place of the formed metal. Aluminum material is available in an almost limitless number of polyvinylidene fluoride (PVDF) or powder coating paint finishes, as well as traditional anodized finishes.

A balanced door pivots at two-thirds of the door, distributing the weight and creating a balance allowing the door to easily open. The bottom arm (shown above) is one of two connections between the door leaf and frame. One end of the bottom arm is connected to the door by a stainless steel pin which projects out of the door bottom pivot and engages into the arm. The other end of the bottom arm is welded to the full-height steel tube portion of the hinge pivot assembly.  [CREDIT] Photo © Heather Collins Roe Photography

A balanced door pivots at two-thirds of the door, distributing the weight and creating a balance allowing the door to easily open. The bottom arm (shown above) is one of two connections between the door leaf and frame. One end of the bottom arm is connected to the door by a stainless steel pin which projects out of the door bottom pivot and engages into the arm. The other end of the bottom arm is welded to the full-height steel tube portion of the hinge pivot assembly. Photo © Heather Collins Roe Photography

Stiles versus no stiles on a tempered glass door
For many years, architects have been designing entrances with less metal and more glass, which often leads to requests for tempered glass balanced doors. A tempered glass door may offer aesthetic benefits, but there are major issues that need to be considered when using them in a high-traffic exterior environment.

Balanced doors are available with tempered glass where the glass is the structure of the door, either with or without stiles. In either door type, full top and bottom rails are required to accommodate the balanced hardware, so patch block fittings are not an option.

Most balanced door manufacturers strongly recommend using stiles for added strength, door integrity, and energy efficiency. A narrow stile is in some cases unnoticeable, especially after the addition of push/pull or panic hardware.

Stiles provide edge protection and structural strength for a tempered glass door. When stiles are added, there is no exposed edge to the glass. This protects the vulnerable edge of the glass from possible damage and breakage, which could lead to personal injury and litigation. Glass deflection occurs as the glass gets taller. Glass is a flexible material; one way to mitigate this problem is to use vertical stiles on the glass edges.

On an aluminum tempered glass door, the narrow stiles are solid aluminum bar. On a stainless steel or bronze door, the stiles also use the solid aluminum bar and then are cladded to match the rest of the door using 2.2-mm (0.09-in.) cladding.

When architects specify tall doors over 2.7 m (9 ft), and are not using vertical stiles, 19-mm (¾-in.) glass is required. Adding narrow stiles, such as 25-mm (1-in.) aluminum stiles or 28.5-mm (1 1/8-in.) stainless steel or bronze stiles, allows the balanced door manufacturer to use 12.7-mm (½-in.) thick glass, in lieu of the 19-mm glass. This cuts down on the overall weight and cost of the door, as 19-mm glass is significantly more costly and heavier than 12.7-mm glass.

Stainless steel stile and rail-type balanced doors were used on New York by Gehry in New York City to provide a transparent aesthetic for the glass-enclosed lobby. [CREDIT] Photo © Barry Schwartz Photography

Stainless steel stile and rail-type balanced doors were used on New York by Gehry in New York City to provide a transparent aesthetic for the glass-enclosed lobby. Photo © Barry Schwartz Photography

There is no effective way to place weatherstripping on a door that does not have vertical stiles. Stiles allow the door to be properly weatherstripped, which is necessary due to more stringent energy codes including American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE) 90.1, Energy Standard for Buildings Except Low-rise Residential Buildings and the International Energy Conservation Code (IECC).

A 25-mm vertical stile allows polypropylene pile weatherstripping to be incorporated into the door. Without weatherstripping, there is poor energy efficiency. There are clear acrylic weatherstripping solutions that are taped on, but they tend to be ineffective and prone to discoloration and cracking. They also easily lose their adhesion and are often knocked off the door. With a stile, a tighter seal and a more energy-efficient solution can be created, in addition to eliminating wind noise that can occur when there are gaps around the door.

Frame options
A balanced door can be designed with a concealed hinge pivot shaft (within the vertical framing), making a full three-sided frame around the door, or more minimal framing can be used by having a header only with an exposed clad hinge pivot shaft. By exposing the hinge pivot shaft, it balances the metal used for the stile on the pull side as the eye is drawn to the vertical usage of metal.

The minimal frame approach is typically used in curtain wall applications and the shaft is often covered in the corresponding door material. The look is less bulky, but the balanced door still needs a header to contain the check and guide channel portion of the balanced hardware. Since there is no vertical framing and the shaft/cladding rotate, the header needs to be properly supported by the curtain wall material from above.

The custom balanced doors at the museum entrance of the Exploratorium in San Francisco feature stile and rail-type construction of painted extruded aluminum material. Photos © Heather Collins Roe Photography

The custom balanced doors at the museum entrance of the Exploratorium in San Francisco feature stile and rail-type construction of painted extruded aluminum material. Photos © Heather Collins Roe Photography

Engineering considerations
Engineering considerations to keep in mind to accommodate balanced doors include:

  • top and bottom arm swing interference;
  • hardware projection;
  • finish hardware; and
  • access to balanced door hardware.

A clear space needs to be provided for top and bottom arm swings and door travel to the interior. A balanced door projects to the interior—as the door opens, the heel edge swings inward and the arms rotate inward as well. This means there cannot be any interference with the ceiling for the balanced door to operate properly. For example, a soffit ceiling cannot be placed too close to the interior door opening adjacent to the doorframe’s back side. There needs to be enough room to allow the door to fully open.

The floor also needs to be kept free of interference for the balanced door path to the full open position. The floor cannot slope and, just as the ceiling above, the door needs room to allow the heel edge to swing in and the arms to rotate.

It is also important to ensure there are no columns or permanent obstruction blocking the heel edge. If the balanced doorframe is going to be partially recessed into an interior wall, it can be recessed about 38 mm (1 1/2 in.) and still provide enough space for the arms to rotate inward. A pocket in the surrounding wall material will be required if the frame is recessed more than 38 mm to allow the arms to fully rotate. If the frame is to be recessed into the exterior wall, the pull handle needs adequate clearance so it will not crash into the wall when the door is in the full open position.

Gotham West, a luxury rental apartment building in New York City, facilitates access with two single narrow stile bronze balanced door units with a satin finish. The narrow stile design features tempered glass construction, containing a top and bottom rail that secures the glass to the hinging mechanism. [CREDIT] Photo © Barry Schwartz Photography

Gotham West, a luxury rental apartment building in New York City, facilitates access with two single narrow stile bronze balanced door units with a satin finish. The narrow stile design features tempered glass construction, containing a top and bottom rail that secures the glass to the hinging mechanism. Photo © Barry Schwartz Photography

The hardware and grillwork projection off the door’s exterior face must also be considered. Most balanced door manufacturers advise against using a horizontal pull handle because it cannot go all the way across the door’s face without interfering with the door jamb, preventing the door from fully opening. The door handles provide visual cues, with a vertical pull indicating pull action and horizontal pull indicating a push action. Users with physical limitations, such as crutches, find it difficult to open a door with horizontal pulls. The maximum projection of hardware and grillwork off the exterior face of the door at hinge side is 12.7 mm (½ in.).

The same finish hardware items used on a conventional swing door can be used on a balanced door. This can provide design and usage continuity throughout a space. Balanced doors can accommodate:

  • push/pulls (except horizontal pulls);
  • deadlocks;
  • flushbolts; and
  • manual panic exit devices and electronic locking hardware (i.e. surface maglocks, concealed shearlocks, electronic latch retraction panic exit devices, and electric release strikes).

It should be noted there are specific guidelines addressing the use of panic devices on a balanced door set by the International Building Code (IBC) and the National Fire Protection Association (NFPA).1

IBC, Section 1008.1.10.2, “Balanced doors,” states:

If balanced doors are used and panic hardware is required, the panic hardware shall be the push-pad type and the pad shall not extend more than one-half the width of the door measured from the latch side.

NFPA 101 Life Safety Code, Section 7.2.1.13, “Balanced door assemblies,” states:

A pair of balanced doors offers a pleasing aesthetic to match the exterior of the decades-old Blessed Sacrament Cathedral in Greensburg, Pennsylvania. Both doors contain a total of six bronze panels—three on the front and three on the back—and weigh 317.5 kg (700 lbs), making the balanced design necessary to facilitate easy opening and closing. [CREDIT] Photo courtesy Ellison Bronze

A pair of balanced doors offers a pleasing aesthetic to match the exterior of the decades-old Blessed Sacrament Cathedral in Greensburg, Pennsylvania. Both doors contain a total of six bronze panels—three on the front and three on the back—and weigh 317.5 kg (700 lbs), making the balanced design necessary to facilitate easy opening and closing.
Photo courtesy Ellison Bronze

If panic hardware is installed on balanced door leaves, the panic hardware shall be of the push-pad type, and the pad shall not extend more than approximately one-half the width of the door leaf, measured from the latch stile.

This requirement helps reduce the force needed to open the door leaf. The panic hardware actuating bar should be close to the latch side of the door and away from the roller and hinge side. This arrangement is more effective when using push-pad panic hardware that readily instructs the user where to push instead of a crossbar-style panic device.

If using stiles, a design that can accommodate the hardware requirements should be specified. For example, a concealed vertical rod-type panic device can only be used on a stile and rail type door with a wider stile, not on a narrow stile tempered glass door.

Finally, it is important to keep the balanced door hardware accessible. If the balanced door hardware needs to undergo maintenance or repair, the guide channels and doorjambs cannot be concealed.

Conclusion
The long-term functional and aesthetic benefits a balanced door system provides make it a suitable choice for commercial, institutional, and monumental facilities. When making the decision to incorporate a balanced door into the building design, it is important to choose an experienced manufacturer skilled in the design and maintenance of balanced door systems. The manufacturer should have a strong reputation for lasting doors and serviceability.

All balanced door systems should be periodically maintained to ensure a long service life, and an annual inspection is recommended. It is important to select a manufacturer that offers a comprehensive warranty for the entire door system, including the door, frame, and balanced hardware.

Notes
1 For more information, visit www.iccsafe.org and www.nfpa.org. (back to top)

Mark Graves is the president of Ellison Bronze Inc. He has more than 30 years of experience in the general construction, architecture, and manufacturing industries. Graves has spent 25 years of his career manufacturing custom balanced doors with Ellison. He can be reached via e-mail at mgraves@ellisonbronze.com.

Design of Fire-resistive Exposed Wood Members

Photo courtesy Structurlam

Photo courtesy Structurlam

by Bradford Douglas, PE, and Jason Smart, PE

Designing for life safety is complex and multifaceted, and fire-related issues comprise a large portion of model codes. For nearly 15 years, a mechanics-based design method has been used in the United States to estimate the capacity of exposed wood members using basic wood engineering mechanics.

This mechanics-based design method first appeared in the 1999 version of Technical Report (TR) 10, Calculating the Fire Resistance of Exposed Wood Members (TR 10). This method was then incorporated into new design procedures of the 2001 National Design Specification (NDS) for Wood Construction. These procedures were later adopted into the model building codes through reference to the NDS for calculating fire resistance of wood members. The procedures have been used extensively for design of large, exposed wood members, but are now also beginning to be employed for estimating structural fire resistance of smaller exposed wood members.

Excerpt from Design for Code Acceptance (DCA) 2, Design of Fire-resistive Exposed Wood Members, Table 1 (one-hr). This shows tabulated one-hour design load ratios, Rs, for flexural members exposed on three sides. [CREDIT] Data courtesy American Wood Council

Excerpt from Design for Code Acceptance (DCA) 2, Design of Fire-resistive Exposed Wood Members, Table 1 (one-hr). This shows tabulated one-hour design load ratios, Rs, for flexural members exposed on three sides. Data courtesy American Wood Council

Wood buildings can be designed to meet rigorous standards for performance, which is why the International Building Code (IBC) allows the material’s use in a wide range of building types—including structures that are taller and have more area than some designers realize. Table 601 of the IBC shows the required fire resistance of building elements (i.e. structural frame, walls, floors, and roofs) for each construction type. Ratings are given in hours. The exception is Type IV, where the wood structural elements are assumed to have inherent fire resistance due to their required minimum dimensions—in other words, no fire resistance rating is necessary except for exterior walls.

Fire resistance is a measure of the length of time an assembly or structural element can sustain a given load when subjected to a standardized fire exposure condition. Fire resistance of wood members and assemblies may be established by any one of five means listed in IBC Section 703.3, “Alternative methods for determining fire resistance.” The most common methods are tested assemblies and calculated fire resistance.

Excerpt from DCA 2, Table 2 (two-hr), showing tabulated two-hour design load ratios, Rs, for compression members exposed on four sides.

Excerpt from DCA 2, Table 2 (two-hr), showing tabulated two-hour design load ratios, Rs, for compression members exposed on four sides.

Fire design of exposed wood members
The fire resistance of exposed wood members, including lumber, glued-laminated (glulam) timber, and structural composite lumber (SCL), may be calculated using provisions of NDS. This allowable stress design approach is referenced in IBC Section 722, “Calculated Fire Resistance.” The design procedure allows calculation of the capacity of exposed wood members using basic engineering mechanics.

Actual mechanical and physical properties of the wood are used, with member capacity directly calculated for a given period—up to two hours. Section properties are computed assuming an effective char rate (i.e. βeff) at a given time (i.e. t). Reductions of strength and stiffness of wood directly adjacent to the char layer are addressed by accelerating the char rate by 20 percent. Average member strength properties are approximated from existing accepted procedures used to calculate design properties. Finally, wood members are designed using accepted engineering procedures found in NDS for allowable stress design. (The design procedures presented in NDS Chapter 16 are not intended to be used for the design and retrofit of structures after a fire.)

For sawn lumber, glulam, and SCL, the nominal char rate (i.e. βn) is typically assumed to be 38 mm/hour (1.5 in./hour). For a given time in hours, the effective char rate is then:

β_(eff=) 1.8/t^0.187 in./hour

To calculate section properties of wood members, the effective char layer thickness (i.e. aeff), for structural calculations is computed as:

a_(eff=) 1.8t^0.813 in.

This photo showcases glued-laminated lumber (glulam). Photos courtesy Structurlam

This photo showcases glued-laminated lumber (glulam). Photos courtesy Structurlam

The 2012 and earlier versions of IBC have also contained an empirical calculation method for estimating the structural fire resistance of wood beams and columns exposed to a standard fire exposure for up to one hour. However, this empirical method has been removed from the 2015 IBC in favor of provisions contained within NDS Chapter 16 that are much broader in application and leave less room for design error.

Basis for NDS chapter 16 approach
AWC’s TR 10 contains full details of the NDS method as well as design examples.1 TR 10 was recently revised to incorporate a new section that supports the use of the design method with smaller dimension sizes associated with lumber joist floor assemblies. It also has revised design examples to match the 2012 NDS.

The revised design tables in Appendix A allow more accurate calculation of fire resistance of columns with any slenderness ratio. They also eliminate tabulation of special cases that can be misapplied, such as:

  • deleted beams exposed on four sides that are assumed to be fully braced throughout the fire rating;
  • columns only exposed on three sides, but assumed to be unbraced; and
  • tension members that do not resist flexure due to member dead load.

Finally, a new Appendix B that calculates the fire resistance of single-span lumber joists for any design stress ratio when joists are exposed on three sides and braced on the top edge was incorporated.

Simplified approach
AWC’s Design for Code Acceptance (DCA) 2, Design of Fire-resistive Exposed Wood Members has been revised to replace the empirical design equations currently in the 2012 IBC with simplified design information developed in accordance with the code-approved NDS fire design procedure for exposed wood members. The tables and examples have been rewritten for consistency with the approach outlined in the 2012 NDS and TR 10.

Supporting arches were used at the Boy Scouts of America Camp Fife project.

Supporting arches were used at the Boy Scouts of America Camp Fife project.

For beams and columns stressed in one principal direction, simplifications can be made to allow creation of load ratio tables. These tables can then be used to determine the structural design load ratio at which the member has sufficient capacity for a given fire resistance time. Tables in DCA 2 give load ratios corresponding to one-hour, 1.5-hour, and two-hour fire resistance ratings for specified member dimensions.

All tabulated load ratios apply to standard reference conditions where the load duration factor, wet service factor, and temperature factor equal 1.0 (CD=1.0; CM=1.0; Ct=1.0). For more complex calculations where stress interactions must be considered, or where standard reference conditions do not apply, designers should use the provisions outlined in TR 10, along with the appropriate NDS provisions.

Flexural members
Design load ratios (i.e. Rs) for fire design of flexural members for various beam sizes are tabulated in DCA 2 tables for one-hour, 1.5-hour, and two-hour fire resistance ratings. The Rs values given in these tables apply to three-sided exposure in which the beam’s top edge is protected from fire exposure (e.g. protected by the underside of a floor or roof). These tabulated values apply to flexural members loaded in bending about one axis only, and are continuously laterally supported along the compression edge. The dimension ‘d’ is the actual cross-sectional dimension measured in the direction normal to the axis about which bending occurs, and is not necessarily greater than ‘b’ (Figure 1).

To use the DCA 2 tables, the designer only needs to know the required fire resistance rating (FRR), the structural load ratio (Rs), and the beam dimensions. For example, when a beam is exposed on three sides and is protected by a floor deck bracing the compression edge, it is required to have a one-hour FRR. When the design professional wants to use a 152.4 x 330.2-mm (6 ¾ x 13 ½-in.) beam being loaded in bending about the strong axis, DCA 2 Table 1 (one-hour) shows a 152.4 x 330.2-mm beam would calculate to have a one-hour fire resistance rating if loaded to its full design load (Rs=1).

The entrance of the Rocky Mountain Elk Foundation building. [CREDIT] Photo courtesy Structurlam/OZ Architects

The entrance of the Rocky Mountain Elk Foundation building. Photos courtesy Structurlam/OZ Architects

OZ Architects used structural composite lumber (SCL) for the Rocky Mountain Elk Foundation building in Missoula, Montana.

OZ Architects used structural composite lumber (SCL) for the Rocky Mountain Elk Foundation building in Missoula, Montana.

Compression members
Design load ratios, Rs, for fire design of columns are calculated as the product of two ratios, Rs1 and Rs2. Values of Rs1 and Rs2 for various column sizes are tabulated in DCA 2 for one-hour, 1.5-hour, and two-hour fire resistance ratings. For cases in which the product of Rs1 and Rs2 is greater than 1.0, Rs should be taken as 1.0. These tables apply to cases in which all four sides are exposed to the fire; however, values calculated using these design load ratios may be conservatively applied when one or more sides of the column are protected. Both‘d’ and ‘b’ represent the dry dressed cross-sectional column dimensions. The dimension ‘d’ is the actual dimension measured in the direction perpendicular to the axis about which buckling is being considered, and is not necessarily greater than ‘b’ (Figure 2). The designer should consider buckling about both axes and use the lesser design value.

The tabulated Rs1 values are calculated based on a square column cross-section having dimensions ‘d’ by ‘d,’ and therefore must be multiplied by Rs2 for any column that is not square. Where ‘b’ is less than ‘d,’ Rs2 will be less than 1.0; and where ‘b’ is greater than ‘d,’ Rs2 will be greater than 1.0. The Rs1 values are derived using the more conservative value of the parameter ‘c’ from equation 3.7-1 of the NDS (for long columns, c=0.9 results in lower Rs1 values; for short columns, c=0.8 results in lower Rs1 values). This allows the design load ratios to be used with sawn lumber, structural glulam, or SCL. The Rs1 values are also based on the assumption that Emin’/Fc*= 350. As a result, the design load ratios (Rs) may conservatively be used for all species and grades where the ratio of Emin’ to Fc* is greater than or equal to 350.

CS_July_2014.inddTo use the tables, the designer only needs to know:

  • required fire resistance rating;
  • structural load ratio;
  • column dimensions;
  • unbraced length of the column; and
  • end support conditions.

For example, in a case where an exposed column is required to have a two-hour FRR, the designer may want to use a nominal 14×16 column with actual dry dimensions of 330 x 381 mm (13 ¼ x 15 in.). The column will have an unbraced length of 3.35 m (11 ft) in both directions, and can conservatively be assumed to have pinned end conditions on each end of the column (Ke=1.0).

Since the unbraced length is the same in both directions, buckling would tend to be about the 13¼-in. dimension. The effective length (i.e. Le) would be 3352 mm (132 in.) and the Le/d ratio would be 10. From DCA 2 Table 2 (two-hour), a square column that is 13¼ x 13¼ in. with Le/d=10 would have an Rs1=0.39. A 13¼ x 15-in. column buckling about the 13¼ in. dimension would have an Rs2=1.11. Therefore, the 13¼ x 15-in. column would calculate to have a two-hour fire resistance rating when loaded to 43 percent or less of its full design load (Rs = [Rs1][Rs2] = [0.39][1.11] = 0.43).

Timber decking
DCA 2 also provides tabulated design load ratios (Rs) for various decking types and thicknesses, corresponding to one-hour, 1.5-hour, and two-hour fire resistance ratings. The dimensions ‘b’ and ‘d’ given in these tables are the actual dry dressed dimensions of each individual member. The Rs values given in DCA 2 Table 3.1 are applicable to butt-joint timber decking fully exposed on one face and partially exposed on the sides, in accordance with NDS Section 16.2.5.

The Rsvalues given in DCA 2 Table 3.2 are applicable to double and single tongue-and-groove decking exposed only on one face. These calculation procedures do not address thermal separation.

Constr-Specfr-Douglas-Smart-Fire-140506_Page_3To use the tables, the designer only needs to know the required fire-resistance rating, the structural load ratio (Rs) and the decking type and dimensions. For example, a timber deck is required to have a 1.5-hour FRR, and the designer wants to use 4x tongue-and-groove decking. From DCA 2 Table 3.2, the nominal 4x tongue and groove decking (76.2 mm [3½ in.] actual thickness) would calculate to have a 1.5-hour fire resistance rating if loaded to 23 percent or less of its full design load (Rs=0.23).

Connections
Where a specified fire resistance rating is required, Section 16.3 of the NDS requires connectors and fasteners be protected from fire exposure. This protection can be achieved by any of the following:

  • wood members having dimensions sufficient to prevent the char front from reaching the connectors and fasteners for the duration of the required fire-resistance rating time—the char front can be calculated as: a=1.5t^0.813 in.;
  • fire-rated gypsum board having a finish rating greater than or equal to the required fire-resistance rating; and
  • any approved coating having a fire rating greater than or equal to the required fire resistance rating time.

Conclusion
Structural fire design provisions have been incorporated in Chapter 16 of NDS, which is referenced in Section 722.1 of the 2012 IBC as a method of calculating fire resistance of exposed wood members. A comprehensive discussion of this mechanics-based design procedure can be found in Technical Report No. 10, while DCA 2 provides a simplified design aid of this code-approved fire design procedure for several typical applications with exposed wood members. 2

Notes
1 For more information, TR 10, Calculating the Fire Resistance of Exposed Wood Members, is available at www.awc.org/pdf/TR10.pdf.
2 Additional information on building code requirements for wood can be found in the American Wood Council’s Code Conforming Wood Design documents, available at www.awc.org/codes/ccwdindex.php.

Brad Douglas, PE, joined the American Wood Council (AWC) in 1986, and serves as its vice president of engineering. Douglas directs a program aimed at developing state-of-the-art engineering data, technology, and standards on structural wood products, systems, and assemblies for use by design professionals and building officials to assure safe and efficient design and use of wood. He is a graduate of Virginia Tech. Douglas can be contacted at bdouglas@awc.org.

Jason Smart, PE, joined AWC in 2013 and is manager of engineering technology. Smart focuses on development and support for new and emerging technologies and related changes to design and model building code standards. He is a graduate of Virginia Tech with degrees in civil engineering, wood science and forest products, and timber engineering. He can be reached at jsmart@awc.org.

Specifying Weather-resistant Siding: Section 1405.16

Fiber cement siding complying with International Building Code (IBC) Section 1404.10, Fiber-cement Siding, shall be permitted on exterior walls of Types I, II, III, IV, and V construction for wind pressure resistance or wind speed exposures as indicated by the manufacturer’s listing and label and approved installation instructions. Where specified, the siding should be installed over sheathing or materials listed in Section 2304.6, and conform to the water-resistive barrier (WRB) requirements in Section 1403. Siding and accessories shall be installed in accordance with approved manufacturer’s instructions. Unless otherwise specified in the approved manufacturer’s instructions, nails used to fasten the siding to wood studs must be corrosion-resistant round head smooth shank and shall be long enough to penetrate the studs at least 25 mm (1 in.). The metal framing requires all-weather screws, which must penetrate the framing at least three full threads.

To read the full article, click here.

Specifying Weather-resistant Siding

All photos courtesy James Hardie Building Products

All photos courtesy James Hardie Building Products

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

Fiber cement siding enables buildings to stand up better in both everyday and extreme weather. This photo shows fiber cement siding used to renovate an existing pool complex in Moorhaven, New York.

Fiber cement siding enables buildings to stand up better in both everyday and extreme weather. This photo shows fiber cement siding used to renovate an existing pool complex in Moorhaven, New York.

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.

Fiber cement siding can be more durable than vinyl or wood for withstanding impacts from ice, hail, or storm debris. This image shows fiber cement siding on Lighthouse High School in the Bronx, New York.

Fiber cement siding can be more durable than vinyl or wood for withstanding impacts from ice, hail, or storm debris. This image shows fiber cement siding on Lighthouse High School in the Bronx, New York.

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

Fiber cement siding resists cracking, warping, rot, and pest damage. This image shows a panel system on a commercial building in Seattle.

Fiber cement siding resists cracking, warping, rot, and pest damage. This image shows a panel system on a commercial building in Seattle.

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.

This apartment complex in Grand Forks, North Dakota, employs fiber cement plank, panel, shingle, and trim.

This apartment complex in Grand Forks, North Dakota, employs fiber cement plank, panel, shingle, and trim.

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:

Orlando, Florida's multi-family SteelHouse building, designed by Poole & Poole Architecture, uses vertical fiber cement siding and soffit panels engineered for the climate.

Orlando, Florida’s multi-family SteelHouse building, designed by Poole & Poole Architecture, uses vertical fiber cement siding and soffit panels engineered for the climate.

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.

The Pacific Cannery Lofts employes fiber cement siding with attributes suitable for the Oakland, California climate. Photo © Kevin Wilcock/David Baker Architects

The Pacific Cannery Lofts employes fiber cement siding with attributes suitable for the Oakland, California climate. Photo © Kevin Wilcock/David Baker Architects

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.