Contents · PDF fileContents: 1. UL Design No. W408 2-Hour Exterior Wall Assembly Updated...

Contents:

1. UL Design No. W408 2-Hour Exterior Wall Assembly Updated April, 2013

2. Engineering Evaluation for UL Design No. W408 1-Hour

Exterior Rating with Fiberglass Insulation and Brick Veneer Updated May, 2015

3. Engineering Extension for UL Design No. W408 2-Hour Fire

Rating from Exterior Side with 7/8”, 3-Coat Stucco Updated July, 2015

4. Engineering Extension for UL Design No. W408 2-Hour Fire

Rating from Exterior Side by addition of Exterior Gypsum Updated April, 2015

Design/System/Construction/Assembly Usage Disclaimer

! Authorities Having Jurisdiction should be consulted in all cases as to the particular requirements covering the installation and use of UL Listed or Classified products, equipment, system, devices, and materials.

! Authorities Having Jurisdiction should be consulted before construction. ! Fire resistance assemblies and products are developed by the design submitter and have been investigated by UL for compliance with

applicable requirements. The published information cannot always address every construction nuance encountered in the field. ! When field issues arise, it is recommended the first contact for assistance be the technical service staff provided by the product

manufacturer noted for the design. Users of fire resistance assemblies are advised to consult the general Guide Information for each product category and each group of assemblies. The Guide Information includes specifics concerning alternate materials and alternate methods of construction.

! Only products which bear UL's Mark are considered as Classified, Listed, or Recognized.

Fire-resistance Ratings - ANSI/UL 263

See General Information for Fire-resistance Ratings - ANSI/UL 263

Design No. W408

April 01, 2013

Bearing Wall Rating — 2 Hr when EXPOSED TO FIRE ON INTERIOR FACE ONLY

Bearing Wall Rating — 1 Hr when EXPOSED TO FIRE ON EXTERIOR FACE ONLY, see Item 4 and 6

For Wood Studs, Finish Rating — 50 min when EXPOSED TO FIRE ON INTERIOR FACE.

For Wood Studs, Finish Rating — 17 min when EXPOSED TO FIRE ON EXTERIOR FACE.

Load Restricted for Canadian Applications — See Guide BXUV7

Design No. W408 BXUV.W408

Fire-resistance Ratings - ANSI/UL 263 Page Bottom

Page 1 of 3BXUV.W408 - Fire-resistance Ratings - ANSI/UL 263

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1. Wood Studs — Nom 2 by 4 in., spaced 16 in. OC with double 2 by 4 top and single 2 by 4 in, bottom plates, with 2 by 4 in. lateral bracing at 96 in. OC max. Studs effectively fire stopped. As an option, nom 2 by 6 in., spaced 24 in. OC with double 2 by 6 top and single 2 by 6 bottom plates, with 2 by 6 in. lateral bracing at 96 in. OC max may be used in lieu of 2 by 4 studs and plates. Studs effectively fire stopped.

2. Gypsum Board* — 5/8 in. thick, 4 ft. wide, two layers applied vertically. Base layer nailed to wood studs and bearing plates 6 in. OC. with 6d cup-head drywall nails, 1-7/8 in. long. The face layer, with joints staggered from base layer, nailed to the studs and bearing plates over the base layer, 8 in. OC. with 8d cup-head drywall nails, 2-3/8 in. long. Type W screws of the same length, head diameter, as the nails and at the spacing described for nails may be used instead of nails.

UNITED STATES GYPSUM CO — Type SCX

3. Joints and Nailheads — Gypsum board joints covered with tape and joint compound. Nail or screw heads covered with joint compound.

4. Batts and Blankets* — Faced or unfaced mineral fiber insulation, 3-1/2 in. thick, nom 3.0 pcf, friction fit in the wall cavity between stud, plates, and cross bracing.

See Batts and Blankets* (BZJZ) category for names of Classified manufacturers.

4A. Batts and Blankets* — As an option to Item 4, when the Fire Resistance Rating is for a fire on the Interior Face only and the Fire Resistance Rating for the Exterior face is not required. Faced or unfaced glass fiber insulation, 3-1/2 in. thick, nom 0.65 pcf, friction fit in the wall cavity between stud, plates, and cross bracing.

See Batts and Blankets* (BZJZ) category for names of Classified manufacturers.

5. Building Units* — Building units nailed to the wood framing with 1-7/8 in. long, 6d nails, spaced 6 in. OC. on the perimeter and 12 in. OC. in the field. Vertical joints centered on studs. Horizontal joints backed with nom. 2 by 4 wood blocking.

BARRIER TECHNOLOGY CORP — Type Blazeguard 2-Side

LOUISIANA-PACIFIC CORP — Type LP FlameBlock 2-Side

6. Exterior Sidings — One of the Exterior Siding as specified in Item 6A to Item 6D are required for 1 hr Fire Resistance



Rating for fire from the Exterior Face, optional for 2 hr Fire Resistance Rating for fire from Interior Face.

6A. Exterior Wood Siding — Min 11/32 in. thick, 4 ft wide wood plywood siding panels or 7/16 in. thick, 4 feet wide OSB siding panel. Installed with long dimension of sheet (strength axis) or face grain parallel with studs. Vertical joints centered on studs. Horizontal joints over nom. 2 by 4 in. wood blocking. Attached to studs through the Building Units, Item 5, on the exterior side of wall with 8d nails, 2-1/2 in. long spaced 6 in. OC at perimeter of panels and 12 in. OC in the field.

6B. Exterior OSB Lap Siding — Min 7/16 in. thick, OSB lap siding fastened to studs through the Building Units, Item 5, with nails or screws, at the locations specified by the manufacturer.

6C. Cementitious Stucco — Portland cement or synthetic stucco systems with self-furring metal lath. Thickness from 3/8 in. to 3/4 in. depending on system, fastened to studs through the Building Units, Item 5, with nails or screws, at the locations specified by the manufacturer.

6D. Fiber Cement Siding — Fiber Cement Lap or Vertical Siding. Minimum 5/16 in. thick, fastened to studs through the Building Units, Item 5, with nails or screws, at the locations specified by the manufacturer.

6E. Brick — Brick veneer, meeting the requirements of local code agencies. Brick veneer attached to the studs with corrugated metal wall ties attached to each stud with 8d cement coated nails, every sixth course of bricks.

7. Exterior Facings — Exterior Facing specified as Item 7A and 7B is not permitted for 1 hr Fire Resistance Rating for fire from the Exterior Face, optional for 2 hr Fire Resistance Rating for fire from Interior Face.

7A. Vinyl Siding — (Optional) - UL Classified exterior plastic siding (molded plastic), fastened to the building units or wood panel sheathing with nails or screws, at the locations specified by the manufacturer.

7B. Exterior Facings — (Optional - Not Shown) - Any exterior facing approved by the Authority Having Jurisdiction installed in accordance with the manufacturer's installation instructions.

*Bearing the UL Classification Mark

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Last Updated on 2013-04-01

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PRIEST & ASSOCIATES CONSULTING, LLC

4607 Verdi Road Solutions for the TX Office 1-877-505-7743 Pleasanton, TX 78064 Building Materials Industry Western Regional Office 360-957-0311 www.priestassociates.com

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ENGINEERING EVALUATION

Engineering Extension for the LP

UL Design W408 Exterior Wall Assembly

One Hour Exterior Rating with Brick Veneer

Project No. 10288-05

Prepared for:

Louisiana-Pacific Corporation 414 Union Street

Suite 2000 Nashville, TN

May 4, 2015

Priest & Associates Consulting Solutions for the Building Materials Industry Page 2

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Abstract

An evaluation has been performed of a modification to LP’s UL W408 exterior wall design. This evaluation is provided for the purpose of demonstrating that when nominal 4 in. brick is employed as exterior cladding, the exterior side of a W408 assembly can provide a 1 hour fire resistance rating for the wall system when glass fiber batt is used as wall cavity insulation. Priest & Associates Consulting (PAC) has successfully determined that this amended design is capable of complying with a 1 hour fire resistance classification for the exterior side of the wall construction when tested in accordance with ASTM E119 “Standard Test Methods for Fire Tests of Building Construction and Materials”.

The conclusions reached by this evaluation are true and correct, within the bounds of sound engineering practice. All reasoning for our decisions is contained within this document. Submitted by,

Howard Stacy Senior Scientist 360-957-0311 Reviewed and Approved,

Deg Priest President


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INTRODUCTION Louisiana-Pacific Corporation (LP) has a UL Design Listing, W408, which incorporates LP FlameBlock 2-sided sheathing. This listing provides for a 2 hour fire rating from the interior, and a 1 hour rating when tested from the exterior with the condition that mineral wool batt is used as wall cavity insulation. The exterior surface of the framing is clad with one layer of 2-Sided LP FlameBlock and is allowed various combustible and noncombustible claddings. The purpose of this analysis is to provide the justification for extending the design to allow for an exterior rating of 1 hour when glass fiber wall insulation is used in conjunction with nominal 4 in. brick exterior cladding. REFERENCED DOCUMENTS

1. Underwriters Laboratories Fire Resistance Directory, UL Design Nos. W408 & U356. 2. 2012 International Building Code. 3. Brick Industry Association, “Fire Resistance of Brick Masonry”, Technical Notes on Brick

Construction, No. 16, March 2008.

EVALUATION This evaluation is based on a comparative analysis of the elements of the UL W408 and U356 design listings (Ref. 1), and is supported by a review of the prescriptive allowances for brick masonry construction set forth in Chapter 7 of the International Building Code (Ref. 2) and by the Brick Industry Association (Ref. 3). This evaluation specifically addresses the additional fire resistance time imparted to the exterior of the wall system by the use of nominal 4 in. brick cladding. The fire resistance of brick masonry veneer is used as the justification for the amendment to the W408 allowances. Comparison to a Comparable Listed Assembly The allowance for a 1 hour rating from the exterior side of W408 with brick veneer is directly supported by an analysis of comparable components used in the UL U356 design. This design allows for a 1 hour rating from the interior side only, with the exception that both sides of the assembly are rated for 1 hour when nominal 4 in. brick cladding is used as exterior cladding. The U356 design is summarized as follows:

Figure 1. U356 Assembly

1. Interior wall membrane (UL Item #2, see Figure 1) - 1 layer of ⅝ in. type X gypsum wallboard

(USG Type SCX). 2. Nominal 2x4 wood studs (UL Item # 1) - spaced 16 in. on center, effectively fire stopped, or

2x6 wood studs spaced 24 inches OC. 3. Wall cavity insulation (UL Item #4) – mineral fiber or glass fiber insulation, 3½ in. thick,

minimum R-13 thermal insulation rating. 4. Exterior sheathing (UL Item #5) – minimum 7/16 in. thick.


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5. Exterior Sidings (UL Item #6) a. Vinyl Siding b. Particle Board Siding – hardboard exterior sidings including panel or lap siding c. Wood Structural Panel or Lap Siding d. Cementitious Stucco – minimum 3/8 in. thickness e. Fiber Cement Siding – lap or panel siding f. Brick Veneer – any type of nom. 4 in. wide brick veneer. When brick veneer is

used, the rating is applicable with exposure on either face. Notable in this design is the allowance for the 1 hour fire rating from both sides when nominal 4 in. brick veneer is used. This also allows for either glass fiber or mineral fiber wall cavity insulation. The W408 design differs from U356 in that 2-sided FlameBlock is used in place of unrated wood structural sheathing. The use of fire resistant FlameBlock sheathing in W408 provides for a more robust system than U356. Since the use of brick veneer and glass fiber insulation in U356 is allowed a 1 hour rating from the exterior, it simply follows that W408, with brick and glass fiber insulation, can be given the same allowance. Contribution of Brick Veneer to Fire Resistance The contribution of brick veneer to the fire resistance of a wall assembly can be determined by calculating the equivalent thickness of the brick. This approach is used by the IBC and other model building codes to determine fire resistance ratings of walls without the need for testing to ASTM E119. The fire resistance rating of brick is determined by its equivalent solid thickness (Ref. 3). For a typical solid brick unit conforming to ASTM C216, the equivalent thickness is obtained by subtracting the volume of core spaces, approximately 25%, from the total gross volume of the brick unit. The resulting thickness is then compared to the requirements given within the building code. For solid brick with nominal 25% core void area, the requirement for equivalent thickness as shown in Table 721.1(2) of the 2012 IBC is 2.7 inches for a 1 hour fire rating. This equates to an actual thickness of 3½ inches for the brick veneer. This supports the provision given in U356 for a 1 hour rating from both sides when nominal 4 in. brick is employed as the exterior cladding, and provides additional justification for the amendment to W408.

TABLE 721.1(2) RATED FIRE-RESISTANCE PERIODS FOR VARIOUS WALLS AND PARTITIONS

MATERIAL ITEM NUMBER CONSTRUCTION

MINIMUM FINISHED THICKNESS FACE-TO-FACE (inches) 4

hours 3

hours 2

hours 1 hour

1. Brick of clay or shale

1-1.1 Solid brick of clay or shale. 6 4.9 3.8 2.7 1-1.2 Hollow brick, not filled. 5.0 4.3 3.4 2.3

1-1.3 Hollow brick unit wall, grout or filled with perlite vermiculite or expanded

shale aggregate. 6.6 5.5 4.4 3.0

1-2.1

4" nominal thick units at least 75 percent solid backed with a hat-

shaped metal furring channel 3/4 " thick formed from 0.021" sheet

metal attached to the brick wall on 24" centers with approved

fasteners, and 1 /2" Type X gypsum wallboard attached to the metal furring strips with 1"-long Type S

screws spaced 8" on center.

— — 5d —


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Amended W408 Design Based on the discussion above, the amended UL W408 exterior wall design with brick veneer cladding includes the following components when a 1 hour exposure from the exterior is considered (beginning from the interior):

1. Interior wall membrane - 2 layers of ⅝ in. type X gypsum wallboard (USG Type SCX) 2. Nominal 2x4 wood studs - spaced 16 in. on center, effectively fire stopped, or 2x6 wood studs

spaced a maximum of 24 in. OC. 3. Wall cavity insulation – mineral fiber or glass fiber insulation, full cavity thickness. 4. Exterior sheathing - 1 layer 2-sided LP FlameBlock. 5. Any type of nominal 4 in. thick brick veneer.

CONCLUSION Priest & Associates Consulting (PAC) has successfully determined that the amended W408 design incorporating brick veneer and glass fiber wall cavity insulation is capable of complying with a 1 hour fire resistance classification from the exterior side when tested in accordance with ASTM E119 “Standard Test Methods for Fire Tests of Building Construction and Materials.”


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Appendix A

Ref. See ASTM D6513‐08Ultimate Average Stud Load Calculation ‐ account for charred depth in area and buckling calculations

Lumber 2x6 Douglas Fir Select Structural Gradesize b (in.) d (in.) Effective depth, de % remaining Cross Section

1.5 5.5 3.3 60

stresses Fc (psi) 1700 FC* (psi) ‐ ult 1 hr 3343.05E ave (psi) 1900000 Emin (psi) 690000

Section Properties A (sq in.) 4.95

NDS 2012 Equation 3.7‐1 Cp 0.345021FCE 1274.939le/d 35c 0.8

Fc' (psi) ‐ ult 1153.422

Pr (lb/stud) ‐ ult 5709.439


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Project No. 10288-09 Revision 1

Prepared for:



July 28, 2015


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Abstract

An evaluation has been performed of a modification to LP’s UL W408 exterior wall design. This evaluation is provided for the purpose of demonstrating that the substitution of ⅞ in. cement plaster for one layer of ⅝ in. type X exterior gypsum sheathing on the exterior side of a W408 assembly will allow a 2 hour fire resistance rating for the wall system when tested from both sides. Priest & Associates Consulting (PAC) has successfully determined that this amended design is capable of complying with a 2 hour fire resistance classification for both sides of the wall construction when tested in accordance with ASTM E119 “Standard Test Methods for Fire Tests of Building Construction and Materials”.


Howard Stacy Senior Scientist 360-957-0311 Date: July 28, 2015 Reviewed and Approved,

Deg Priest President Date: July 28, 2015


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INTRODUCTION Louisiana-Pacific Corporation (LP) has a 2 hour UL Design Listing, W408, which incorporates LP FlameBlock 2-sided sheathing. This listing currently provides for a 2 hour fire rating from the interior, and a 1 hour rating when tested from the exterior. The exterior surface of the framing is clad with one layer of 2-Sided LP FlameBlock and is allowed various claddings. The purpose of this analysis is to provide the justification for extending the exterior rating to 2 hours when a ⅞ in. cement stucco system is included as the face layer of protection. The extension of data allowing for a 2 hour exterior rating when one layer of ⅝ in. type X exterior gypsum sheathing is added as a face layer has been previously addressed under PAC EEV 10288-03. This evaluation includes the rationale establishing the equivalence of ⅞ in. cement stucco to ⅝ in. type X gypsum sheathing in this type of wall design. REFERENCED DOCUMENTS

1. Underwriters Laboratories Fire Resistance Directory, UL Design No. W408. 2. Underwriters Laboratories Test Report No. 11NK10558 “Fire Endurance Performance of Load

Bearing Wall Assemblies”, September 15, 2011. 3. Priest & Associates Consulting (PAC) Engineering Evaluation 10288-03 “Engineering

Extension for the LP UL Design W408 Exterior Wall Assembly”, April 3, 2015. 4. 2015 IBC Table 721.1(2), Item 15-1.3. 5. Gypsum Association Fire Resistance Design Manual, GA-600, GA File No. WP 8420.

DESCRIPTION The proposed modification to the W408 wall assembly consists of the addition of a ⅞ in. cement stucco system as described in GA File No. WP8420 and Item 15.1.3 of IBC Table 721.1(2) over the base layer of 15/32 inch 2-Sided LP FlameBlock on the exterior side of the wall assembly. Mineral fiber insulation shall be installed at full thickness in the stud cavities. This modification is designed to increase the fire resistance rating from the exterior side to 2 hours. The published UL W408 exterior wall design currently includes the following components and allowances for exterior facings when a 1 hour fire rating from the exterior is considered (beginning from the interior):

1. Interior wall membrane (UL Item #2, see Figure 1) - 2 layers of ⅝ in. type X gypsum wallboard (USG Type SCX).

2. Nominal 2 by 4 in. wood studs (UL Item # 1) - spaced 16 inches on center, effectively fire stopped, or 2x6 wood studs spaced 24 inches OC. Lateral bracing at 96 in. OC.

3. Wall cavity insulation (UL Item #4) – mineral fiber insulation, 3½ in. thick, nominal 3 pcf density (for exposure from the exterior side).

4. Exterior sheathing (UL Item #5) - 1 layer 2-sided LP FlameBlock. 5. Exterior Sidings (UL Item #6)

a. Exterior Wood Siding – minimum 11/32 in plywood siding panels, or 7/16 in. OSB siding panels.

b. Exterior OSB Lap Siding – minimum 7/16 in. c. Cementitious Stucco – minimum 3/8 in. thickness. d. Fiber Cement Siding – lap or panel siding, minimum 5/16 e. Brick

Figure 1. Horizontal Section of W408 construction.


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EVALUATION This evaluation is based on an analysis of the elements of the W408 design listing (Ref. 1), a review of the UL fire resistance test report leading to the development of the listing (Ref. 2), a comparison of the W408 design to UL design listings (U305 and U301) allowing for similar fire resistance classifications, and an examination of the fire performance characteristics of 2-sided FlameBlock in the W408 design. This evaluation specifically addresses the expected fire resistance time imparted to the wall system by the addition of a ⅞ in. cement stucco system to the exterior of the assembly when mineral fiber insulation is installed in the stud cavities. Contribution of Mineral Fiber Cavity Insulation to Fire Resistance The UL testing of the combination of the 2-Sided FlameBlock and mineral fiber stud cavity insulation resulted in a 1 hour unrestricted loadbearing fire rating on the exterior side (Ref. 2). In this test, the 3½ in. thick, nominal 3 pcf mineral fiber batt insulation enhanced the level of fire resistance and played a significant role in the attainment of the 1 hour rating. This is due to the fact that, unlike glass fiber insulation, which will reach its melting point in the later stages of the test and slump from its original position, mineral wool batts remain in place during the entire fire exposure and continue to provide thermal protection to the sides of the studs as well as to the unexposed side of the wall. The fire resistance contribution of mineral wool insulation in a wood stud wall assembly has been previously detailed in PAC EEV 10288-03 (Ref. 3). Comparison of 2-sided FlameBlock/Mineral Wool Insulation to ⅝ in. Type X Gypsum Wallboard A 1 hour fire rating is given for the fire exposed exterior side of the W408 assembly when mineral fiber cavity insulation and 2-sided FlameBlock are used. This wall system provides the same degree of fire resistance as a “conventional” uninsulated 1 hour wood stud construction faced with ⅝ in. type X gypsum wallboard (GWB) (reference UL Design No. U305). These two constructions can be considered interchangeable in terms of fire resistance, since the UL listing for W408 does not restrict the allowable load for the assembly. The addition of a layer of fire rated ⅝ inch type X GWB to the U305-type construction results in the 2 hour rated U301 assembly. As the “exterior” W408 configuration is shown to provide the same level of fire resistance performance as a U305 wall, it follows that the addition of a layer of ⅝ type X gypsum sheathing to this assembly would result in a 2 hour rating such as that for the U301 design. As described in PAC EEV 10288-03, the argument was made that modifying the W408 configuration by the addition of one layer of ⅝ in. type X exterior gypsum sheathing to the exterior 2-sided FlameBlock layer would be expected to achieve a 2 hour exterior rating when tested to ASTM E119. Comparison of ⅞ in. Cement Stucco to ⅝ in. Type X Gypsum Wallboard The equivalence of a 1 hour exterior wood stud wall assembly protected on the exterior with a ⅞ in. cement stucco system to a 1 hour rated U305-type wood stud wall assembly protected on both sides with ⅝ inch type X GWB is shown in the prescriptive wall design described in Table 721.1(2) Item 15-1.3 in the 2015 (and earlier versions) IBC. This equivalence is used as the justification for the substitution of the ⅞ in. cement stucco system for a layer of ⅝ inch type X GWB in the 2 hour exterior W408 design described herein (and in Ref. 3). Amended W408 Design The amended UL W408 exterior wall design includes the following components and allowances for exterior facings when exposure from the exterior is considered (beginning from the interior):

1. Interior wall membrane - 2 layers of ⅝ in. type X gypsum wallboard (USG Type SCX). 2. Nominal 2 by 4 wood studs - spaced 16 inches on center, or 2 by 6 wood studs spaced a

maximum of 24 in. OC. Studs effectively fire stopped. 2 by 4 or 2 by 6 in. lateral bracing at 96 in. OC. Fire Retardant Treated (FRTW) studs are allowed to be substituted for untreated studs.


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3. Wall cavity insulation (UL W408 Item #4) – mineral fiber insulation, 3½ in. thick, nominal 3 pcf density for 2 by 4 studs, 5½ in. thick for 2 by 6 studs.

4. Exterior sheathing - 1 layer 2-sided Category 15/32 in. LP FlameBlock, applied as described in W408.

5. Exterior gypsum sheathing – minimum ⅝ in. type X. 6. As an option to Items 5 and 7c, ⅞ in. cement stucco may be installed on the exterior surface

of the 2-sided FlameBlock, in accordance with Item 15-1.3 of IBC Table 721.1(2). 7. Exterior Sidings

a. Exterior Wood Siding – minimum 11/32 in plywood siding panels, or 7/16 in. OSB siding panels

b. Exterior OSB Lap Siding – minimum 7/16 in. c. Cementitious Stucco – minimum 3/8 in. thickness d. Fiber Cement Siding – lap or panel siding, minimum 5/16 in. e. Brick f. Steel Wall Panels

CONCLUSION Priest & Associates Consulting (PAC) has successfully determined that the amendment of the W408 design by the addition of ⅞ in. cement stucco system installed in accordance with code allowances to the exterior side of the listed wall assembly together with mineral fiber wall cavity insulation is capable of complying with a 2 hour fire resistance classification from both directions when tested in accordance with ASTM E119 “Standard Test Methods for Fire Tests of Building Construction and Materials.”



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Project No. 10288-03

Prepared for:



April 3, 2015


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Abstract

An evaluation has been performed of a modification to LP’s UL W408 exterior wall design. This evaluation is provided for the purpose of demonstrating that the addition of one layer of ⅝ in. type X exterior gypsum sheathing on the exterior side of a W408 assembly will allow a 2 hour fire resistance rating for the wall system. Priest & Associates Consulting (PAC) has successfully determined that this amended design is capable of complying with a 2 hour fire resistance classification for both sides of the wall construction when tested in accordance with ASTM E119 “Standard Test Methods for Fire Tests of Building Construction and Materials”.


Howard Stacy Senior Scientist 360-957-0311 Date: April 3, 2015 Reviewed and Approved,

Deg Priest President Date: April 3, 2015


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INTRODUCTION Louisiana-Pacific Corporation (LP) has a 2 hour UL Design Listing, W408, which incorporates LP FlameBlock Plus 2-sided sheathing. This listing provides for a 2 hour fire rating from the interior, and a 1 hour rating when tested from the exterior. The exterior surface of the framing is clad with one layer of 2-Sided LP FlameBlock and is allowed various claddings. The purpose of this analysis is to provide the justification for extending the exterior rating to 2 hours when one layer of ⅝ in. type X exterior gypsum sheathing is added as a face layer. REFERENCED DOCUMENTS

1. Underwriters Laboratories Fire Resistance Directory, UL Design No. W408. 2. Underwriters Laboratories Test Report No. 11NK10558 “Fire Endurance Performance of

Load Bearing Wall Assemblies”, September 15, 2011. 3. Western Fire Center, Inc. (WFCi) Report No. 15016, “Fire Performance of Research-Scale

Wall Assemblies”, LP Building Products, March 5, 2015. 4. Takeda, H. and Kahsay, F., “The Effects of Insulation on the Fire Resistance of Wood-stud

Walls”. 5. American Wood Council, “National Design Specification for Wood Construction”. 6. ASTM D6513, “Standard Practice for Calculating the Superimposed Load on Wood-frame

Walls for Standard Fire-Resistance Tests”.

DESCRIPTION The proposed modification to the W408 wall assembly consists of the addition of one layer of ⅝ inch exterior gypsum sheathing over the base layer of 15/32 inch 2-Sided LP FlameBlock on the exterior side of the wall assembly. Mineral fiber insulation will be installed at full thickness in the stud cavities. This modification is designed to increase the fire resistance rating from the exterior side to 2 hours. The published UL W408 exterior wall design currently includes the following components and allowances for exterior facings when exposure from the exterior is considered (beginning from the interior):

1. Interior wall membrane (UL Item #2, see Figure 1) - 2 layers of ⅝ in. type X gypsum wallboard (USG Type SCX).

2. Nominal 2x4 wood studs (UL Item # 1) - spaced 16 inches on center, effectively fire stopped, or 2x6 wood studs spaced 24 inches OC.

3. Wall cavity insulation (UL Item #4) – mineral fiber insulation, 3½ in. thick, nominal 3 pcf density (for exposure from the exterior side).

4. Exterior sheathing (UL Item #5) - 1 layer 2-sided LP FlameBlock. 5. Exterior Sidings (UL Item #6)

a. Exterior Wood Siding – minimum 11/32 in plywood siding panels, or 7/16 in. OSB siding panels.

b. Exterior OSB Lap Siding – minimum 7/16 in. c. Cementitious Stucco – minimum 3/8 in. thickness. d. Fiber Cement Siding – lap or panel siding, minimum 5/16 in. e. Brick

Figure 1. Horizontal Section of W408 construction.


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EVALUATION This evaluation is based on an analysis of the elements of the W408 design listing (Ref. 1), a review of the UL fire resistance test report leading to the development of the listing (Ref. 2), the comparison of the W408 design to UL design listings (U305 and U301) allowing for similar fire resistance classifications, and an examination of the fire performance characteristics of 2-sided FlameBlock sheathing based on research-scale testing (Ref. 3). This evaluation specifically addresses the additional fire resistance time imparted to the wall system by the addition of a layer of ⅝ in. type X exterior gypsum sheathing to the exterior of the assembly when mineral fiber insulation is installed in the stud cavities. Contribution of Mineral Fiber Cavity Insulation to Fire Resistance The UL testing of the combination of the 2-Sided FlameBlock and mineral fiber stud cavity insulation resulted in a 1 hour unrestricted loadbearing fire rating on the exterior side (Ref. 2). In this test, the 3½ in. thick, nominal 3 pcf mineral fiber batt insulation enhanced the level of fire resistance and played a significant role in the attainment of the 1 hour rating. This is due to the fact that, unlike glass fiber insulation, which will reach its melting point in the later stages of the test and slump from its original position, mineral wool batts remain in place during the entire fire exposure and continue to provide thermal protection to the sides of the studs as well as to the unexposed side of the wall. The graphic presented in Figure 1 (from Ref. 4) demonstrates the shielding of the sides of the studs that mineral fiber insulation provides throughout the course of an E119 fire test. This provides for the improvement in the overall fire resistance of the wall. This shielding is due to the minimal shrinking of mineral fiber insulation at elevated temperatures. Although this illustration shows the use of ½ in. type X gypsum wallboard (GWB) as fire-side membrane protection, comparable stud charring behavior is expected with the FlameBlock wood structural panel. This is particularly true for the location shown with the “open” joint.

Figure 1. Effect of mineral fiber Insulation on fire resistance of wood studs. The shielding of the stud allows for the use of the generally accepted linear charring rate for solid wood, 1.5 inches per hour. Comparison to Comparable Listed Assemblies Since a 1 hour fire rating is published for the fire exposure exterior side of the W408 assembly when mineral fiber insulation is used, and this wall construction exhibits the same degree of fire resistance as a “conventional” uninsulated 1 hour wood stud construction faced with ⅝ inch type X gypsum wallboard (GWB) on both sides (reference UL Design No. U305). These two constructions can be considered interchangeable in terms of fire resistance, since the UL listing for W408 does not restrict the allowable load for the assembly. The addition of a layer of fire rated ⅝ inch type X GWB to the U305-type


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construction results in the 2 hour rated U301 assembly. As the “exterior” W408 configuration is shown to provide the same level of fire resistance performance as a U305 wall, it follows that the addition of a layer of ⅝ type X gypsum sheathing to this assembly would result in a 2 hour rating such as that for the U301 design. It is our contention, therefore, that modifying the W408 exterior configuration by the addition of one layer of ⅝ in. type X exterior gypsum sheathing to this wall construction containing mineral fiber insulation can achieve in a 2 hour rating when tested to ASTM E119. The exterior gypsum sheathing shall be installed in accordance with the base layer GWB attachment requirements as described in Item 2 of the listing. Fasteners shall be increased in length to accommodate for the FlameBlock base layer thickness, and the face layer joints shall be staggered from the 2-Sided FlameBlock layer. Extension of Data Supported by Research-scale Testing In support of the allowance for a 2 hour rating from the exterior, a 2 hour research-scale E119 test (assembly dimensions 5 ft wide x 4 ft high) was performed on a wall assembly constructed with 2x6 D. fir (Select Structural Grade) and is shown in Figure 2. This test was reported in WFCi Report No. 15016 (Ref. 3).

Figure 3. Horizontal Section of Research-scale test construction.

It should be noted that the use of steel siding is considered a worst case due to its high heat transfer and the fact that it will rapidly heat up and equilibrate with the E119 furnace temperature. This test was designed to evaluate the charring behavior of the wood framing during a 2 hour fire resistance exposure, and is used for an estimation of residual axial strength of the remaining wood stud member. A depiction of the cross section of the remaining studs after the fire exposure is provided in Figure 4. Using the procedures detailed in Chapter 16 of the National Design Specification (NDS) for Wood Construction, the residual axial strength of the wood stud section reduced for fire exposure can be estimated from the average ultimate strength properties taken from reference design values. From the referenced research-scale testing, the residual section area of the 2x6 members in the wall system exposed for 2 hours to E119 fire exposure conditions was approximately 5 in2, or 60% of the original section of the 2x6. From ASTM D6513, the allowable load for a 2x6 stud braced by sheathing (D. fir, Select Structural grade) in a 10 ft high wall is determined to be 5208 lb/stud. Calculating for the reduced section area of 60%, the ultimate strength of the residual section becomes 5709 lb/stud (Appendix A).


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Figure 4. Cross section of remaining studs (drawing taken from WFCi report).

Since the “ultimate strength” is the maximum axial load that the stud can support before failing, the load carrying capacity of the residual member is greater than the load applied in the E119 full scale test, indicating that the load-carrying capacity of the wall structure would not have been exceeded at the 2 hour fire rating period. In other words, the 2x6 framed wall structure, protected with one layer of 2-Sided FlameBlock and one layer of ⅝ in. type X gypsum wallboard would be expected to maintain a 2 hour fire resistance classification. Amended W408 Design The amended UL W408 exterior wall design includes the following components and allowances for exterior facings when exposure from the exterior is considered (beginning from the interior):

1. Interior wall membrane - 2 layers of ⅝ in. type X gypsum wallboard (USG Type SCX) 2. Nominal 2x4 wood studs - spaced 16 inches on center, effectively fire stopped, or 2x6 wood

studs spaced a maximum of 24 inches OC 3. Wall cavity insulation (UL Item #4) – mineral fiber insulation, 3½ in. thick, nominal 3 pcf

density for 2x4, 5½ in. thick for 2x6 (for exposure from the exterior side) 4. Exterior sheathing - 1 layer 2-sided LP FlameBlock 5. Exterior gypsum sheathing – minimum ⅝ in. type X 6. Exterior Sidings

a. Exterior Wood Siding – minimum 11/32 in plywood siding panels, or 7/16 in. OSB siding panels

b. Exterior OSB Lap Siding – minimum 7/16 in. c. Cementitious Stucco – minimum 3/8 in. thickness d. Fiber Cement Siding – lap or panel siding, minimum 5/16 in. e. Brick f. Steel Wall Panels


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CONCLUSION Priest & Associates Consulting (PAC) has successfully determined that the amendment of the W408 design by applying one layer of ⅝ in. type X exterior gypsum sheathing to the exterior side of the listed wall assembly, in conjunction with mineral fiber wall cavity insulation is capable of complying with a 2 hour fire resistance classification from both directions when tested in accordance with ASTM E119 “Standard Test Methods for Fire Tests of Building Construction and Materials.”


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Appendix A

Ref. See ASTM D6513-08Ultimate Average Stud Load Calculation - account for charred depth in area and buckling calculations

Lumber 2x6 Douglas Fir Select Structural Gradesize b (in.) d (in.) Effective depth, de % remaining Cross Section

1.5 5.5 3.3 60

stresses Fc (psi) 1700 FC* (psi) - ult 1 hr 3343.05E ave (psi) 1900000 Emin (psi) 690000

Section Properties A (sq in.) 4.95

NDS 2012 Equation 3.7-1 Cp 0.345021FCE 1274.939le/d 35c 0.8

Fc' (psi) - ult 1153.422

Pr (lb/stud) - ult 5709.439

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