IIBEC Interface October 2022 Continuous insulation provides a means to comply with modern energy conservation codes and can provide various other building code–required functions for building enclosures. Continuous insulation is defined as follows in the International Energy Conservation Code (IECC)1 and ASHRAE Standard 90.1:2 Continuous insulation (c.i.): insulation that is uncompressed and continuous across all structural members without thermal bridges other than fasteners and service openings. It is installed on the interior or exterior or is integral to any opaque surface of the building enclosure. This definition allows some limited thermal discontinuity to occur for fasteners attaching components such as the c.i. material, cladding, fenestration, and even structural ledgers placed on the surface of a c.i. to avoid major thermal discontinuities (such as thermal bridging). Even so, the amount or size of these fasteners should be specified to minimize their cumulative effect as relatively small and repetitive point thermal bridges.3 But these fasteners must also be able to adequately transfer the weight of cladding, furring, fenestration, or structural loads from ledgers that are surface mounted and attached over a layer of c.i. These two competing design objectives should be optimized and the content of this article provides guidance for that purpose. BACKGROUND The use of only fasteners to attach cladding and other exterior architectural or structural building components through a layer of c.i. is not without its challenges. First, the c.i. material must have sufficient compressive resistance or rigidity to resist fastener draw-down forces during installation and shear-transfer reaction forces that may cause compression during service. For example, if an exterior insulation material is not sufficiently rigid (that is, it has low resistance to compressive deformation), it will tend to compress due to these connection forces. In such cases, the code definition for continuous insulation will not be satisfied because the thermal performance of the insulation layer is altered (that is, not continuous in thickness or R-value). A common example of this compression condition occurs when metal roofing and siding panels are installed over blanket insulation that is placed over purlins and girts in metal building construction. Consequently, other means of attachment or support of cladding and exterior building components through a layer of compressible exterior insulation may become necessary to avoid compression, such as the use of steel shear tabs, metal Z-furring projecting through the exterior insulation layer, or specialty thermal break support devices. Because these attachment methods use elements that are not fasteners as required by the definition of continuous insulation (and can be substantial thermal bridges), the exterior insulation and cladding support method would not comply with the energy code’s definition of and prescriptive R-values for c.i., even though it solves the compression problem. These practical difficulties do not mean that such applications do not have thermal value. They simply mean that the previously mentioned application conditions do not permit the exterior insulation to be considered as c.i. as defined and intended by energy codes and standards. They also mean that energy code compliance and thermal performance for such assemblies must be demonstrated by use of an assembly U-factor analysis (including the impact of thermal transmission through the cladding support devices penetrating the exterior insulation layer or compression that occurs at through-fastened exterior components). For example, Appendix A of ASHRAE 90.12 provides tabulated U-factors for masonry walls where masonry veneer ties are penetrating a layer of exterior c.i., such as foam plastic insulating sheathing c.i. (FPIS c.i.). As addressed later in this article, it also is possible to place a conventional metal brick tie onto the surface of FPIS c.i. where only the tie fastener penetrates the FPIS c.i., such that compliance with the c.i. definition is maintained without having to determine a U-factor for energy code compliance. There are also a number of proprietary brick ties designed for this application with an “offset” connection to the structure to allow for a thickness of FPIS c.i. As a means to avoid the above practical and energy-code-compliance difficulties or inefficiencies, this article focuses on designing fastener connections through c.i. of rigid foam Cladding and Building Enclosure Component Connections through Foam Plastic Continuous Insulation: Design and Prescriptive Code Compliance By Jay Crandell, PE This paper was originally presented at the 2021 IIBEC International Convention and Trade Show. October 2022 IIBEC Interface • 17 plastics, particularly FPIS. These products include expanded polystyrene (EPS), extruded polystyrene (XPS), and polyisocyanurate (PIR). Important to the topic of this article, FPIS is available in a wide range of compressive strengths (for example, 10 psi to 100 psi or more) and is capable of supporting significant structural loads of various types. For example, FPIS can be specified to support building foundation loads with design compressive loads of up to 3000 psf or more, even including a safety factor of 3 to 5 applied to the material’s nominal compressive strength to control deformation and creep. The conservatism of the safety factor generally depends on load duration (for example, sustained dead versus transient live or snow loads) and duty cycle (for example, lift truck loads versus column loads on a structural concrete slab with underlying FPIS insulation for a refrigerated warehouse). Consequently, with proper design and specification, FPIS materials are capable of providing a rigid exterior c.i. layer through which cladding and building component attachments can be made to the underlying structure using only fasteners. Thus, compression deformation becomes negligible and fasteners can be used for exterior building component attachments so that the FPIS complies with the code definition for continuous insulation and can satisfy the required R-values for c.i. Code-compliant FPIS products are manufactured in accordance with ASTM C5784 and ASTM C1289.5 These standards provide a foundation for complying with various building code and energy code provisions governing the use of FPIS in residential and commercial building construction.1,2,6,7 In particular, these ASTM standards provide a basis for specifying types of FPIS materials on the basis of compressive resistance properties. FPIS materials are water resistant and have relatively high R-values per inch ranging from about R-4 per inch to more than R-6 per inch. For this reason, FPIS products are often used as c.i. for building foundations, walls, floors, and roofs as a means to comply with modern energy conservation codes and standards. Because of the relatively high R-value per inch, they also minimize the thickness of c.i. required to meet energy code requirements and this also helps with designing and specifying cladding and building component attachments through FPIS (as will become evident later in this article). In addition, FPIS products can provide several building enclosure functions beyond just c.i. when they are properly integrated with a building enclosure assembly, including water-resistive barrier, air barrier, and water-vapor control. These various applications and functions of FPIS, including other code-compliance considerations such as fire safety and wind resistance, have been addressed in greater detail in two prior IIBEC conference papers and presentations.8,9 For additional information on these matters, including technical guidance, design resources, research, and code-compliance listings, refer to https://www.continuousinsulation.org. Two common wall assembly applications with c.i. are shown in Fig. 1. One is considered a “hybrid” wall with a combination of exterior FPIS c.i. and cavity insulation. The other uses exterior c.i. only and is known as the “perfect wall” because it maximizes the protection of the structure from thermal and moisture cycling by substantially decoupling it from the exterior environment. As mentioned, FPIS can serve multiple “control layer” functions when used in either of these assembly approaches. In both of these approaches, cladding, furring, and other structural or architectural building components are ideally placed on the surface of the rigid foam sheathing insulation and attached through it with an appropriate fastener schedule to minimize thermal-bridging effects and maintain compliance with the energy code’s definition of continuous insulation. For support of gravity loads, such as those caused by the weight of cladding or structural live and dead loads on a roof or deck ledger, the fasteners through the FPIS layer to the primary structural system must provide sufficient shear capacity and stiffness. As a bonus, the use of stainless steel fasteners can add durability to exterior component connections through FPIS while also reducing heat transfer through the fasteners (stainless steel has about one-third the thermal conductivity of a regular carbon steel fastener). CLADDING AND BUILDING COMPONENT CONNECTIONS THROUGH FPIS Regardless of the number of functions that FPIS c.i. may be used to provide for a given building enclosure assembly, one thing is certain: exterior wall coverings and even structural building components must be fastened or supported through it to the underlying structure. The remainder of this article focuses on how to properly attach such components through FPIS to the underlying structure while minimizing thermal bridging and maintaining conformity with the energy code’s definition of continuous insulation. The following two approaches to code compliance are addressed: 1. Prescriptive requirements for cladding and furring connections through FPIS to wood, cold-formed steel framing, or wood structural panels (WSPs). 2. Engineering design procedures for various types of building component connections through FPIS to the structural frame or substrate. The technical basis of the prescriptive solutions and design procedures that follow is described in Applied Building Technology Group research report no. 1503-02, “Attachment of Exterior Wall Coverings Through Foam Plastic Insulating Sheathing (FPIS) to Wood or Steel Wall Framing.”10 That report and the data and references described therein serve as Figure 1. Example wall assemblies with continuous insulation. Source: Reproduced by permission from Applied Building Technology Group (ABTG), “Model Moisture Control Guidelines for Light-Frame Walls: A Building Code Supplement for Builders, Designers, and Building Officials,” 2017, http://www.appliedbuildingtech.com/rr/1701-01; and J. H. Crandell, “Assessment of Hygrothermal Performance and Design Guidance for Modern Light-Frame Wall Assemblies,” in Advances in Hygrothermal Performance of Building Envelopes: Materials, Systems and Simulations, ed. P. Mukhopadhyaya and D. Fisler. West Conshohocken, PA: ASTM International, 2017, 362—394, http://dx.doi.org/10.1520/STP159920160097. Note: AB = air barrier; FPIS = foam plastic insulating sheathing; VR = vapor retarder; WRB = water-resistive barrier. 18 • IIBEC Interface October 2022 the basis for prescriptive cladding attachment provisions found in the International Building Code6 (IBC) and the International Residential Code7 (IRC). Refer to 2021 IBC Sections 2603.12 and 2603.13 and 2021 IRC Sections R703.15 and R703.16. These prescriptive cladding and furring attachment requirements have been included in the IBC and IRC since the 2012 editions. In addition, Table R703.3.3 of the 2021 IRC provides for attachment of lightweight cladding through up to 2-in.-thick FPIS to minimum 7/16-in.-thick WSP sheathing; thus, it does not require fastening to studs for this limited condition. Alternatively, such connections directly to WSP installed over a layer of FPIS c.i. also are permissible, but placing WSP over FPIS c.i. must consider the impact to shear wall bracing capacity of the WSP (as done for some proprietary sheathing panels with FPIS c.i. laminated to the interior side rather than the exterior side of a structural panel). Prescriptive Cladding and Furring Attachment through FPIS Several important general requirements for use of the codified prescriptive cladding and furring attachments through FPIS are addressed in this article: 1. All of the codified prescriptive provisions are engineered to work with and require use of minimum 15 psi compressive resistance FPIS as specified in accordance with ASTM C578 or ASTM C1289. They address FPIS thicknesses up to 4 in., depending on the fastening schedule and cladding weight. 2. The provisions address support of cladding weight by a fastener transferring shear through a layer of FPIS to the structure. Therefore, these provisions are intended to supplement fastening requirements for each type of cladding found in the code or the specific cladding manufacturer’s installation instructions (unless those instructions specifically address installation over FPIS). The more stringent fastening schedule should apply. 3. To maintain wind or seismic out-of-plane load resistance—that is, fastener design withdrawal strength—the fastener must have sufficient length to penetrate through the FPIS layer and maintain the required minimum embedment in wood framing or engagement of fastener threads in cold-formed steel framing. 4. Fasteners must be installed in a manner to adequately draw all intervening material layers together without over- or underdriving resulting in problems such as warping of materials or gaps between material layers. However, more recent research has shown that a drainage plane gap up to 3/8 in. thick, provided by an intervening drainage mat rather than furring placed behind lath for stucco (one-coat and three-coat varieties inclusive), can be tolerated with use of the prescribed attachments and design procedure discussed later in this article.11 This is important to be able to address new stucco drainage requirements in the 2021 editions of the IRC and IBC for moist climates (much of the United States). Back ventilation or improved drainage behind other types of cladding is also a recommended practice, particularly for moist climates. 5. The fastener schedules and permissible FPIS thicknesses will vary according to the cladding weight supported (including all materials outbound of the FPIS layer). The cladding weight categories are as follows. • 3 psf: vinyl siding, wood lap siding, most fiber cement siding • 11 psf: three-coat stucco • 18 psf: medium-weight adhered masonry veneer • 25 psf: heavy adhered masonry veneer These examples are not inclusive of all cladding types or weights. Refer to cladding manufacturer data for actual unit weight Figure 2. Illustration of cladding and furring attachments through FPIS to CFS framing. Note: CFS = cold-formed steel; FPIS = foam plastic insulating sheathing. and, for absorptive claddings, a “wet” weight should be used. 6. Fasteners, framing materials, and FPIS materials must comply with the specifications and minimum properties referenced in the tables and table notes. For masonry or concrete structural substrates, the IRC and IBC require an engineered design or use of fastener manufacturer data because commonly used concrete/masonry fasteners are proprietary. While the code provisions use commodity (standardized) fasteners for wood and steel framing, proprietary fasteners may also be used, but must be analyzed in accordance with the engineering procedure addressed below. Where the scope limitations of the design procedures are not satisfied, design lateral (shear) values for a given fastener or connection scenario should be determined in accordance with a suitable test methodology consistent with that used to develop the design procedure and IRC and IBC code provisions derived from that procedure; refer to ABTG research report no. 1503- 0210 for a description of the test methodology and performance criteria, which were based on applying ASTM D1761 connection shear tests October 2022 IIBEC Interface • 19 including also long-term shear tests to evaluate creep stability under constant load. Prescriptive Cladding and Furring Attachment through FPIS to Cold-Formed Steel Framing Figure 2 illustrates cladding direct attachment over FPIS (no furring) and also furring attachment over FPIS. The requirements for direct cladding attachment and furring attachments over FPIS are shown in Tables 1 and 2, respectively. It is important to note that the figures included in this article focus only on detailing connections. The wall assembly details will require additional components or materials for code compliance, depending on design conditions. Prescriptive Cladding and Furring Attachment through FPIS to Wood Framing Figure 3 illustrates cladding direct attachment over FPIS (no furring) and also furring attachment over FPIS. The requirements for direct cladding attachment and furring attachments over FPIS are shown in Tables 3 and 4, respectively. Table 1. Siding minimum fastening requirements to cold-formed steel framing for direct cladding attachment over FPIS to support cladding system weight Note: Tabulated values are based on minimum 33 ksi steel for 33 mil and 43 mil steel and 50 ksi steel for 54 mil steel or thicker. Screws shall comply with the requirements of ASTM C1513. FPIS shall have a minimum compressive strength of 15 psi in accordance with ASTM C578 or ASTM C1289. DR = design required; FPIS = foam plastic insulating sheathing; o.c. = on center. 1 in. = 25.4 mm; 1 psf = 0.0479 kPa; 1 psi = 6.895 kPa; 1 ksi = 6.895 MPa. Figure 3. Illustration of cladding and furring attachments through FPIS to wood framing. Note: FPIS = foam plastic insulating sheathing. 20 • IIBEC Interface October 2022 Lightweight Cladding Prescriptive Connection through FPIS to WSP Sheathing In accordance with Section R703.3.3 of the IRC, direct connection of lightweight claddings (maximum 3 lb/ft2 unit weight) through FPIS (maximum 2 in. thick) to WSPs (minimum 7/16-in. thickness) can be done in accordance with Fig. 4 and Table 5. The cladding fastener must be of sufficient length to penetrate a minimum of ¼ in. beyond the back side of the WSP sheathing. Also, fastener minimum size and maximum spacing must comply with the cladding manufacturer’s installation instructions, especially where the instructions require a more stringent fastening Table 2. Furring minimum fastening requirements to cold-formed steel framing for application over FPIS to support cladding system weight Note: Table values are based on the following: • Wood furring of Spruce-Pine-Fir or any softwood species with a specific gravity of 0.42 or greater per NDS. • Minimum 33 mil steel hat channel furring of 33 ksi steel. Steel hat channel shall have a minimum 7/8 in. depth, 11/4 in. web width, and ½ in.-wide flanges with web or flanges bearing on FPIS surface. • Cold-formed steel framing of indicated nominal steel thickness and minimum 33 ksi steel for 33 mil and 43 mil steel and 50 ksi steel for 54 mil steel or thicker. Screws shall comply with the requirements of ASTM C1513. Furring shall be spaced a maximum of 24 in. o.c. in a vertical or horizontal orientation. • In a vertical orientation, furring shall be located over wall studs and attached with the required fastener spacing. • In a horizontal orientation, furring shall fastened at each stud with a number of fasteners equivalent to that required by the fastener spacing. If the required fastener spacing is 12 in. o.c. and the studs are 24 in. o.c., then two fasteners would be required at each stud (24/12 = 2). In no case shall fasteners be spaced more than 24 in. apart. FPIS shall have a minimum compressive strength of 15 psi, in accordance with ASTM C578 or ASTM C1289. DR = design required; FPIS = foam plastic insulating sheathing; NDS = American Wood Council (2018); o.c. = on center. 1 in. = 25.4 mm; 1 psf = 0.0479 kPa; 1 psi = 6.895 kPa; 1 ksi = 6.895 MPa. Figure 4. Illustration of lightweight cladding attachment through maximum 2-in.-thick FPIS to minimum 7/16-in.- thick wood structural panel sheathing. Note: FPIS = foam plastic insulating sheathing. October 2022 IIBEC Interface • 21 schedule. Where applicable, this is one of the simplest means of connecting cladding through foam sheathing where a steel- or wood-frame wall is sheathed with WSPs. Supplemental Prescriptive Furring Requirements for Wind Load Resistance For furring materials and their attachment to a structure, prescriptive wind pressure resistance requirements are typically not available in the locally applicable building code and design values for typical 1×4 wood members used as furring are not available because they are only appearance graded. This concern affects wall assemblies using furring, with or without the presence of FPIS under the furring. Therefore, Tables 6 and 7 are provided to supplement the prescriptive or designed furring connection requirements through FPIS as addressed in the previous tables for support of cladding weight. The more stringent fastening schedule for cladding weight support or wind load should apply. The tabulated allowable wind pressure resistance values in Tables 6 and 7 must be equal to or greater than the components and cladding allowable stress design (ASD) negative (suction) pressure wind load required by the locally applicable building code. Because these tables are only representative of an appropriate furring design for wind pressure resistance, the applicability for a specific use should be verified for suitability prior to use. The tabulated design values are based on analysis to determine which of the following limits the design: furring bending, fastener withdrawal, or fastener head pull-through. Allowance for Brick Tie Attachments through FPIS Continuous Insulation Section R703.8.4 of the IRC permits typical brick ties, such as corrugated straps, to be attached with only the fastener penetrating the FPIS c.i. layer where it is of sufficient length to maintain the embedment into framing or minimum 7/16-in.-thick WSP sheathing for withdrawal resistance. This applies to only the scope of the IRC where wall components and cladding ASD wind loads are 30 psf or less (refer to IRC Section R703.3.2, “Wind Limitations”). This connection strategy works only because anchored masonry veneers are separately supported and do not rely on the brick tie for support of the veneer weight. Therefore, resisting out-of-plane loads is of primary concern. For this reason, use of corrosion-resistant screws for Table 3. Siding minimum fastening requirements to wood framing for direct cladding attachment over FPIS to support cladding system weight Note: Table values are based on wood framing of Spruce-Pine-Fir or any wood species with a specific gravity of 0.42 or greater in accordance with NDS.13 Required fastener minimum penetration shall be permitted to include thickness of wood structural panel sheathing materials. Nail fasteners shall comply with ASTM F1667, except nail length shall be permitted to exceed ASTM F1667 standard lengths. Fasteners of equivalent or greater diameter and bending strength shall be permitted. FPIS shall have a minimum compressive strength of 15 psi in accordance with ASTM C578 or ASTM C1289. DR = design required; FPIS = foam plastic insulating sheathing; o.c. = on center. 1 in. = 25.4 mm; 1 psf = 0.0479 kPa; 1 psi = 6.895 kPa. 22 • IIBEC Interface October 2022 Table 4. Furring minimum fastening requirements to wood framing for application over FPIS to support cladding system weight Note: Table values are based on wood framing and furring of Spruce-Pine-Fir or any wood species with a specific gravity of 0.42 or greater in accordance with NDS.13 Nail fasteners shall comply with ASTM F1667, except nail length shall be permitted to exceed ASTM F1667 standard lengths. Wood screws and lag screws shall comply with NDS Appendix L and ANSI/ASME B18.6.1. Other approved fasteners of equivalent or greater diameter and bending strength shall be permitted. Required fastener minimum penetration shall be permitted to include thickness of wood structural panel sheathing materials. A minimum 2× wood furring shall be used where the required siding fastener penetration into wood material exceeds ¾″ and is not more than 11/2″, unless approved deformed shank siding nails or siding screws are used to provide equivalent withdrawal strength, allowing the siding connection to be made to a 1× wood furring. Furring shall be spaced a maximum of 24″ o.c. in a vertical or horizontal orientation. • In a vertical orientation, furring shall be located over wall studs and attached with the required fastener spacing. • In a horizontal orientation, furring shall be fastened at each stud with a number of fasteners equivalent to that required by the fastener spacing. If the required nail spacing is 12″ o.c. and the studs are 24″ o.c., then two (2) nails would be required at each stud (24/12 = 2). In no case shall fasteners be spaced more than 24″ (0.6 m) apart. FPIS shall have a minimum compressive strength of 15 psi, in accordance with ASTM C578 or ASTM C1289. DR = design required; FPIS = foam plastic insulating sheathing; o.c. = on center. 1 in. = 25.4 mm; 1 psf = 0.0479 kPa; 1 psi = 6.895 kPa. Table 5. Lightweight cladding minimum fastening requirements for attachment through maximum 2-in.-thick FPIS to minimum 7/16-in.-thick wood structural panel Note: Horizontal spacing of fasteners along siding is based on a siding width (distance between horizontal rows of fasteners) of 12 in. For other siding widths, multiply required horizontal spacing by 12/w, where w is the siding width in inches. Use of this table is limited to the wind load scope limits for cladding attachments in accordance with Section R703.3.2 of the International Residential Code (that is, maximum 30 psf negative design wind pressure). FPIS = foam plastic insulating sheathing; o.c. = on center. 1 in. = 25.4 mm; 1 psf = 0.0479 kPa. October 2022 IIBEC Interface • 23 tie attachment may be preferable, especially when attaching to minimum 7/16-in.-thick wood sheathing underneath. When fastened through FPIS, use of stainless steel fasteners will not only maximize durability but also reduce the thermal conductivity impact of the tie fastener as mentioned previously. Engineered Design of Cladding and Building Component Connections through FPIS Where applicable, the calculation procedures in this section should be used by a registered design professional to determine the lateral (shear) and withdrawal design values for fastener connections through FPIS to the underlying structure or substrate. The lateral design value calculation procedures provided below are applicable to FPIS having a maximum 4-in. thickness and a minimum 15 psi compressive strength in accordance with ASTM C578 or ASTM C1289. They also apply only to attachment of cladding, linear components or members such as furring or ledger, and panel products installed over FPIS. In addition, the general requirements for the prescriptive provisions listed previously also apply to use of these engineering procedures. Design of Connections through FPIS to Cold-Formed Steel Framing The installation and design of screw-type connections shall comply with AISI S100,12 Section J4, with the additional requirements indicated in (a) and (b) as follow for connections including a layer of FPIS sandwiched between the connected parts. Where screw fasteners are installed through FPIS, the fastener length shall be sufficient to provide a minimum of three threads of penetration through the cold-formed steel member receiving the fastener tip. a. Tension allowable design values. Nominal tension design values for screw connections shall be determined in accordance with AISI S100, Section J4.4, and divided by a safety factor of not less than 3.0 to derive an allowable design tension value. b. Shear allowable design values. Nominal shear strength design values for screws shall be determined in accordance with AISI S100, Section J4.3.1, and divided by a safety factor of not less than 3.0 to derive an allowable shear design value. Where the connection includes a layer of FPIS sandwiched between the connected parts, the following additional requirements and limitations shall apply: i. For connections using #8 or #10 screws, AISI S100, Eq. J4.3.1-1 [Pns = 4.2 (t2 3d)1/2Fu2] shall be multiplied by one of the following gap effect reduction factors Gr as applicable: • For #10 screw in 54 mil (0.054 in. [1.370 mm]) and 50 ksi (345 MPa) steel: Gr = 0.17—0.0048r • For #10 screw in 43 mil (0.043 in. [1.09 mm]) and 33 ksi (228 MPa) steel: Gr = 0.19—0.0066r • For #8 or #10 screw in 33 mil (0.033 in. [0.838 mm]) and 33 ksi (228 MPa) steel: Gr = 0.16—0.0064r where Gr = gap effect reduction factor for use with AISI S100, Eq. J4.3.1-1 r = dsep/d dsep = separation between connected steel parts caused by thickness of FPIS, in. (mm) d = nominal screw diameter = 0.164 in. (4.17 mm) for #8 screws = 0.190 in. (4.83 mm) for #10 screws ii. The value of r shall not exceed 21. iii. For 0 < r < 2, calculated Gr in accordance with item i does not need to be less than 1-r/2. iv. A larger steel thickness and screw size than indicated in item i for the respective Gr equations shall be permitted, provided the Table 6. Furring minimum fastening requirements for application over FPIS to resist allowable stress wind pressure (wood frame structure). Note: FPIS = foam plastic insulating sheathing; o.c. = on center. 1 in. = 25.4 mm; 1 psf = 0.0479 kPa. 24 • IIBEC Interface October 2022 Pns value calculated in accordance with AISI S100, Eq. 4.3.1-1, uses the screw size and steel thickness as indicated in item i for the respective Gr equations. v. The material against the screw head shall be minimum 33 mil and 33 ksi steel, minimum 3/8-in.-thick wood or wood-based material with a specific gravity of not less than 0.42, or equivalent. The gap reduction factors provide control of long-term deflection (creep) and limit shortterm deflection to 0.015 in. based on evaluation of test data to develop and confirm the design methodology.10 With application of the gap reduction factors to control joint deflection, the resulting safety factors are typically much greater than the minimum safety factor of 3 required by the AISI S100 standard for connections without FPIS or a gap in the joint. The minimum 15 psi compressive resistance and maximum 4-in. thickness for FPIS are associated with the test data upon which the gap reduction factor equations are based.10 Higher compressive resistance FPIS may provide improved performance, but the design provisions are based on this typical minimum value. Design of Connections through FPIS to Wood Framing The installation and design of connections using dowel-type fasteners (that is, nails and screws) shall comply with the American Wood Council’s National Design Specification for Wood Construction13 (NDS), including the additional requirements indicated in (a) and (b) as follow for connections including a layer of FPIS sandwiched between the connected parts. a. Allowable withdrawal design values. Withdrawal design values for dowel-type fasteners shall be determined in accordance with NDS, Section 12.2. Where dowel-type fasteners are installed through FPIS, the specified fastener length shall be sufficient to provide the design penetration into wood framing. b. Reference lateral design values. Reference lateral (shear) design values for dowel-type fasteners shall be determined in accordance with NDS, Section 12.3, with the following modifications and limitations where the connection includes a layer of FPIS sandwiched between the connected parts: i. The reduction term Rd, in accordance with NDS, Table 12.3.1B, shall not be less than 3.0. ii. The yield limit equations in accordance with Table 1-1 of AWC Technical Report 12, “General Dowel Equations for Calculating Lateral Connection Values,”14 which include a gap parameter g equal to the thickness of FPIS sandwiched between connected parts, shall be used in lieu of the yield limit equations in NDS, Table 12.3.1A. iii. The minimum fastener penetration in the main member (member receiving the fastener tip), including the thickness of WSPs attached to the main member, shall comply with NDS and shall not be less than 1 in. for screws or 1¼ in. for nails. iv. The minimum specific gravity of wood materials being connected shall be 0.42. The use of a minimum Rd value of 3.0 controls long-term creep and limits initial deflection to not more than 0.015 in. for dowel-type fasteners of ¼-in. diameter or less, FPIS of minimum 15 psi compressive resistance and maximum 4-in. thickness, wood materials of 0.42 specific gravity or greater, and the fastener penetration in the main member as indicated previously.10 With application of the Rd value of 3.0 under these conditions of use, the resulting safety margins relative to ultimate lateral capacity are typically greater than 5. Design Procedure Applications The previously detailed engineering procedures provide for calculation of fastening solutions beyond the limited prescriptive solutions and fastener schedules for cladding and furring connections presented earlier. For example, they can be used to evaluate the following: • Cladding and furring connections that use alternative fastener schedules and even pro- Table 7. Furring minimum fastening requirements for application over FPIS to resist allowable stress wind pressure (cold-formed steel frame structure). Note: FPIS = foam plastic insulating sheathing. 1 in. = 25.4 mm; 1 psf = 0.0479 kPa. Higher compressive resistance FPIS may provide improved performance, but the design provisions are based on this typical minimum value. October 2022 IIBEC Interface • 25 prietary types of fasteners, such as self-tapping wood lag screws, which may have better yield strength and stiffness than commodity fasteners, resulting in improved performance (that is, able to accommodate heavier loads or thicker FPIS) • Load-bearing structural building component connections through FPIS, such as deck or roof ledgers, for code-compliant structural capacity and joint stiffness (Fig. 5) • Various architectural building components attached to a structure through FPIS, such as window and door awning frames or shading device support systems • Structural sheathing connections through a layer of FPIS (where FPIS is used as “undersheathing”— that is, structural sheathing placed over top of FPIS—not the more typical case of “oversheathing”—that is, FPIS placed over top of structural sheathing) • Window and door frame anchorages through FPIS or through plastic or wood shims in a rough opening gap to enable calculation of shear capacity to support fenestration weight (or transverse wind loads) as a means to achieve or demonstrate compliance with fenestration industry standards for anchorage design, such as AAMA 2501.115 This design need, however, may only arise for anchorage and support conditions not prescriptively addressed in the fenestration manufacturer’s installation instructions or where equivalent substitute anchors are considered as permitted by the code. CONCLUSION This article has reviewed code-compliant prescriptive solutions and design procedures for attachment of cladding, furring, and various architectural and structural building components through FPIS c.i. The primary goals of these prescriptive requirements, design procedures, and details are to provide a means to maintain structural integrity while also promoting thermal continuity and efficient construction of a building enclosure when FPIS is specified as c.i. Some of the key takeaways from this article include the following: • The connection provisions addressed herein offer many options to provide structurally efficient, energy-efficient, practical, and durable means of constructing and designing codecompliant and high-performance building enclosures that use FPIS c.i. • The prescriptive connection options and design approaches presented are necessary to meet the intent of model energy codes and standards (for example, IECC and ASHRAE 90.1), particularly their shared definition for continuous insulation, thereby allowing compliance to be achieved by simply meeting required prescriptive insulation R-values for c.i. • The presented connection provisions also meet the intent and requirements of model building codes (for example, IRC and IBC) for proper attachment of cladding and furring on walls with FPIS c.i. • The same provisions can also be used to design structural connections through a layer of FPIS c.i., such as roof and deck ledgers. • Finally, the use of connection provisions addressed in this article helps support compliance with improved water vapor control provisions in modern building codes, whereby FPIS c.i. can provide a uniform, stable, and dry environment within building enclosure assemblies. REFERENCES 1. International Code Council (ICC), International Energy Conservation Code. Country Club Hills, IL: ICC, 2021. 2. American Society of Heating, Refrigerating and Air- Conditioning Engineers (ASHRAE), Energy Standard for Buildings Except Low-Rise Residential Buildings, ANSI/ ASHRAE/IES Standard 90.1. Atlanta, GA: ASHRAE, 2019. 3. Applied Building Technology Group (ABTG), “Repetitive Metal Penetrations in Building Thermal Envelope Assemblies,” ABTG Research Report No. 1510-03, 2016, http://www.appliedbuildingtech.com/rr/1510-03. 4. ASTM Subcommittee C16.22, Standard Specification for Rigid, Cellular Polystyrene Thermal Insulation, ASTM C578-18 (West Conshohocken, PA: ASTM International, 2018). 5. ASTM Subcommittee C16.22, Standard Specification for Faced Rigid Cellular Polyisocyanurate Thermal Insulation Board, ASTM C1289-17. West Conshohocken, PA: ASTM International, 2017. 6. ICC, International Building Code. Country Club Hills, IL: ICC, 2021. 7. ICC, International Residential Code. Country Club Hills, IL: ICC, 2021. 8. J. H. Crandell, “Continuous Insulation: Research, Applications, and Resources for Walls, Roofs, and Foundations” (paper presented at RCI International Convention and Trade Show, Orlando, FL, March 14–19, 2019), https://iibec.org/wp-content/uploads/2019-ctscrandell. pdf. 9. J. H. Crandell, “Applying Recent Building and Energy Code Advancements for Durable and Energy-Efficient Building Enclosures” (paper presented at IIBEC 2020 Virtual International Convention and Trade Show, June Figure 5. Porch roof ledger and soffit ledger connection detail through 4-in.-thick FPIS.* Source: Building Science Corp., National Institute of Standards and Technology (NIST) project no. NI ST NZERF, CAD (computer-aided design) DWG file A-PLOT-DETL-NZERTF, 2009, https://www. nist.gov/system/files/nzertf-architectural-plans3-june2011.pdf. * Using the previous design procedure for connections to wood framing through FPIS, two 3/8-in. lag screws (or similar-capacity proprietary self-drilling wood screws) were used for the roof ledger connections to each stud at 24 in. on center. Soffit ledger connections are less substantive (smaller or fewer fasteners) due to lower connection forces and this distinction minimizes thermal bridging and cost. Note: FPIS = foam plastic insulating sheathing. 1″ = 1 in. = 25.4 mm; 1′ = 1 ft = 0.305 m. 26 • IIBEC Interface October 2022 13, 2020), https://iibec.org/iibec-events/applying-building- energy-code-durable/. 10. Applied Building Technology Group (ABTG), “Attachment of Exterior Wall Coverings Through Foam Plastic Insulating Sheathing (FPIS) to Wood or Steel Wall Framing,” ABTG Research Report No. 1503-02, March 2015, http://www.appliedbuildingtech.com/ rr/1503-02. 11. P. Gunderson and K. Kaufmann, “Attachment of Heavy Claddings over Foam with and without Drainage Gaps” (prepared for USDA Forest Products Laboratory by Home Innovation Research Labs, Upper Marlboro, MD, March 2020), https://www.homeinnovation.com/~/ media/Files/Reports/Attachment-of-Heavy-Claddings- Over-Foam-With-and-Without-Drainage-Gaps.pdf. 12. American Iron and Steel Institute (AISI), North American Specification for the Design of Cold-Formed Steel Structural Members, AISI S100-16 (Washington, DC: AISI, 2016). 13. American Wood Council (AWC), National Design Specification for Wood Construction. Leesburg, VA: AWC, 2018. 14. AWC, “General Dowel Equations for Calculating Lateral Connection Values,” Technical Report 12. Leesburg, VA: AWC, 2015. 15. American Architectural Manufacturers Association, Voluntary Guideline for Engineering Analysis of Anchorage Systems for Fenestration Products Included in NAFS, AAMA 2501-20. Schaumburg, IL: Fenestration and Glazing Industry Alliance, 2020. Please address reader comments to chamaker@ iibec.org, including “Letter to Editor” in the subject line, or IIBEC, IIBEC Interface Journal, 434 Fayetteville St., Suite 2400, Raleigh, NC 27601. Jay Crandell has over 30 years of experience in construction, engineering, and innovative building technology research for private- and public-sector clients. He has conducted benchmark studies of major natural disasters as well as research to address significant structural, energy, and building science challenges. His work has helped to propel many innovative technologies into the International Code Council’s codes and consensus standards. He has published on various engineering, construction, and building science topics. 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