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Proposed Changes to DCA 6 – Prescriptive Residential Deck Construction Guide Page 1 Copyright © 2009 American Forest & Paper Association, Inc. Prescriptive Residential Wood Deck Construction Guide Based on the 2009 International Residential Code 7HEREInternational Residential Code (IRC) ;BRACKETEDIRC= RECOMMENDEDIRC IRC RECOMMENDEDIRC PROVISIONSIRC OR%VERY BEENIRC CONSTRUCTION Page 2 2 PRESCRIPTIVE RESIDENTIAL WOOD DECK CONSTRUCTION GUIDE American Wood Council #/.4%.43 -).)-5- $%#+).' */)34 "%!- $%#+ */)34 4/ "%!- */)34 0/34 2)- &//4).'3 ,%$'%2 02/()")4%$ ,%$'%2 &2%% 34!.$).' $%#+ '5!2$ '5!2$ 34!)2 34!)2 34!)2 34!)2 &2!-).' -).)-5- WOOD OR LUMBER WWW ALSC ORG DURABLE #EDARS PROCESS !MERICAN SUCH ;2 GROUNDAPPROVED SUITABLE ASTM F 1667 INCLUDE NAILS ANSI/ASME B18.6.1 MEETANSI/ASME B18.2.1 LAG %DGE ON FASTENERS NEEDS ;2 = ▪ PRESERVATIVE ZINC COATED BRONZE GALVANIZEDASTM A 153, Standard Specification for Zinc Coating (Hot-Dip) on Iron and Steel Hardware, FOR FOR ▪ BE COATED WITHASTM B 695 ▪ ANCHORS STAINLESS FABRICATIONASTM A 653, Standard Specification for Steel Sheet, Zinc-Coated (Galvanized) or Zinc-Iron Alloy-Coated (Galvannealed) by the Hot-Dip Process COATING AFTERASTM A123, Specification for Zinc (Hot-Dip Galvanized) Coatings on Iron and Steel Products. ▪ LOCATED SHALL ▪ SHALL JURISDICTION HOT EXPERIENCE SNOW NOT &LASHING2 = OF APPROVED!LUMINUM NOT WITH #OPPER INSPECTION OTHER HEREIN Page 3 PRESCRIPTIVE RESIDENTIAL WOOD DECK CONSTRUCTION GUIDE 3 American Forest & Paper Association 4ABLE FORA 3PECIES !#1 " !#1 # !#1 $ #! " #U. 7 3OUTHERN $OUGLAS .2 (EM &IR 0ONDEROSA 2ED 3PRUCE 0INE &IR .2 .2 .2 .2 2EDWOOD .2 .2 .2 .2 .2 A !SSOCIATIONBook of Standards $%#+).' !LL LUMBER ACCORDANCE #OMMITTEEPolicy for Evaluation of Recommended Spans for Span Rated Decking Products (November 5, 2004) !TTACH NAILS APPROXIMATELY CONNECTION BE ANGLE DECKING SUPPORTS $ECKING SUBSTITUTED AUTHORITY */)34 4HE BEARING AT LENGTH SPAN 4ABLE* 3PECIES 3IZE *OIST 7ITHOUT 7ITH* 3OUTHERN X g g g g g g X g g g g g X g g g g g $OUGLAS ,ARCH 30& X g g g g g g X g g g g g g X g g g g 2EDWOOD 7ESTERN 0ONDEROSA 2ED X g g g g g g X g g g g g g X g g g g g g 3EE GRADE Page 4 4 PRESCRIPTIVE RESIDENTIAL WOOD DECK CONSTRUCTION GUIDE American Wood Council &IGURE &IGURE &IGURE Page 5 PRESCRIPTIVE RESIDENTIAL WOOD DECK CONSTRUCTION GUIDE 5 American Forest & Paper Association BEAM SIZE & ASSEMBLY REQUIREMENTS Deck beam spans shall be in accordance with Table 3 and can extend past the post centerline up to LB/4 as shown in Figure 3. Joists may bear on the beam and extend past the beam centerline up to LJ/4 as shown in Figures 1A and 2, or the joists may attach to the side of the beam with joist hangers as shown in Figure 1B. Joists shall not frame in from opposite sides of the same beam. See JOIST-TO-BEAM CONNECTION details, Figure 6. Where multiple 2x members are used, the deck’s beam is assembled by attaching the members identified in Table 3 in accordance with Figure 4. [Table R602.3(1)] Table 3. Deck Beam Spans (LB)1 for Joists Framing from One Side Only Joist Spans (LJ) Less Than or Equal to: Species Size4 6' 8' 10' 12' 14' 16' 18' Southern Pine 2-2x6 7' - 1" 6' - 2" 5' - 6" 5' - 0" 4' - 8" 4' - 4" 4' - 1" 2-2x8 9' - 2" 7' - 11" 7' - 1" 6' - 6" 6' - 0" 5' - 7" 5' - 3" 2-2x10 11' - 10" 10' - 3" 9' - 2" 8' - 5" 7' - 9" 7' - 3" 6' - 10" 2-2x12 13' - 11" 12' - 0" 10' - 9" 9' - 10" 9' - 1" 8' - 6" 8' - 0" 3-2x6 8' - 7" 7' - 8" 6' - 11" 6' - 3" 5' - 10" 5' - 5" 5' - 2" 3-2x8 11' - 4" 9' - 11" 8' - 11" 8' - 1" 7' - 6" 7' - 0" 6' - 7" 3-2x10 14' - 5" 12' - 10" 11' - 6" 10' - 6" 9' - 9" 9' - 1" 8' - 7" 3-2x12 17' - 5" 15' - 1" 13' - 6" 12' - 4" 11' - 5" 10' - 8" 10' - 1" Douglas Fir- Larch2, Hem-Fir2, SPF2, Redwood, Western Cedars, Ponderosa Pine3, Red Pine3 3x6 or 2-2x6 5' - 5" 4' - 8" 4' - 2" 3' - 10" 3' - 6" 3' - 1" 2' - 9" 3x8 or 2-2x8 6' - 10" 5' - 11" 5' - 4" 4' - 10" 4' - 6" 4' - 1" 3' - 8" 3x10 or 2-2x10 8' - 4" 7' - 3" 6' - 6" 5' - 11" 5' - 6" 5' - 1" 4' - 8" 3x12 or 2-2x12 9' - 8" 8' - 5" 7' - 6" 6' - 10" 6' - 4" 5' - 11" 5' - 7" 4x6 6' - 5" 5' - 6" 4' - 11" 4' - 6" 4' - 2" 3' - 11" 3' - 8" 4x8 8' - 5" 7' - 3" 6' - 6" 5' - 11" 5' - 6" 5' - 2" 4' - 10" 4x10 9' - 11" 8' - 7" 7' - 8" 7' - 0" 6' - 6" 6' - 1" 5' - 8" 4x12 11' - 5" 9' - 11" 8' - 10" 8' - 1" 7' - 6" 7' - 0" 6' - 7" 3-2x6 7' - 4" 6' - 8" 6' - 0" 5' - 6" 5' - 1" 4' - 9" 4' - 6" 3-2x8 9' - 8" 8' - 6" 7' - 7" 6' - 11" 6' - 5" 6' - 0" 5' - 8" 3-2x10 12' - 0" 10' - 5" 9' - 4" 8' - 6" 7' - 10" 7' - 4" 6' - 11" 3-2x12 13' - 11" 12' - 1" 10' - 9" 9' - 10" 9' - 1" 8' - 6" 8' - 1" 1. Assumes 40 psf live load, 10 psf dead load, L/360 simple span beam deflection limit, L/180 cantilever deflection limit, No. 2 grade, and wet service conditions. 2. Incising assumed for refractory species including Douglas fir-larch, hem-fir, and spruce-pine-fir. 3. Design values based on northern species with no incising assumed. 4. Beam depth must be equal to or greater than joist depth if joist hangers are used (see Figure 6, Option 3). Figure 3: Beam Span Types Page 6 6 PRESCRIPTIVE RESIDENTIAL WOOD DECK CONSTRUCTION GUIDE American Wood Council &IGURE $%#+ ! LOCATION TYPE &IGURE Figure 5. Typical Deck Framing Plan Page 7 PRESCRIPTIVE RESIDENTIAL WOOD DECK CONSTRUCTION GUIDE 7 American Forest & Paper Association JOIST-TO-BEAM CONNECTION Each joist shall be attached to the beam as shown in Figure 6. Joists may bear on and overhang past the beam a maximum of LJ/4. Use Option 1 or Option 2 to attach the joist to the beam. Option 1 shall only be used if the deck is attached to the house with a ledger (see LEDGER ATTACHMENT REQUIREMENTS) or as shown in Figure 23. Mechanical fasteners or hurricane clips used as shown in Option 2 must have a minimum capacity of 100 lbs in both uplift and lateral load directions. Joists may also attach to the side of the beam with joist hangers per Option 3. Joists shall not frame in from opposite sides of the same beam. See JOIST HANGERS for more information. Hangers, clips, and mechanical fasteners shall be galvanized or stainless steel (see MINIMUM REQUIREMENTS). Figure 6: Joist-to-Beam Detail JOIST HANGERS Joist hangers, as shown in Figure 7, shall each have a minimum download capacity in accordance with Table 3A. The joist hanger shall be selected from an approved manufacturer’s product data based on the dimensions of the joist or header it is carrying. Joist hangers shall be galvanized or stainless steel (see MINIMUM REQUIREMENTS). Use joist hangers with inside flanges when clearances to the edge of the beam or ledger board dictate. Do not use clip angles or brackets to support joists. Table 3A: Joist Hanger Download Capacity Joist Size Minimum Capacity, lbs X X X Figure 7: Typical Joist Hangers POST REQUIREMENTS All deck post sizes shall be 6x6 (nominal) or larger, and the maximum height shall be 14'-0" measured to the underside of the beam. Posts shall be centered on footings. Cut ends of posts shall be field treated with an approved preservative (such as copper naphthenate) [R402.1.2]. The beam shall be attached to the post by notching the 6x6 as shown in Figure 8 or by providing an approved post cap to connect the beam and post as shown in Figure 10. All 3-ply beams shall be connected to the post by a post cap. All thru-bolts shall have washers under the bolt head and nut. Attachment of the beam to the side of the post without notching is prohibited (see Figure 9). Page 8 8 PRESCRIPTIVE RESIDENTIAL WOOD DECK CONSTRUCTION GUIDE American Wood Council &IGURE 2EQUIREMENTS &IGURE #ONDITION 2)- !TTACH SHOWN SHOWN REQUIREMENTS &IGURE 0OST &IGURE Page 9 PRESCRIPTIVE RESIDENTIAL WOOD DECK CONSTRUCTION GUIDE 9 American Forest & Paper Association &//4).'3 3EE THICKNESS !LLSHALL PLACED SURFACE #ONTACT THE VERIFIED PLACEMENT DETERMINES CAPACITY THE DETERMINED #,/3%2 (/53% %,%6!4)/. (/53% $O ENCLOSED BEFORE 0RE MANUFACTURED -).)-5- 4ABLE "EAM 3PAN ," *OIST 3PAN ,* 2OUND &OOTING $IAMETER 3QUARE &OOTING $I &OOTING 4HICKNESS g g g g g g g g g g g g g g g g g g g g g g g g g g g g #OORDINATE REQUIREMENTS &IGURE Page 10 10 PRESCRIPTIVE RESIDENTIAL WOOD DECK CONSTRUCTION GUIDE American Wood Council ,%$'%2 ;2 = '%.%2!, EQUAL OR WALL 7HEN JOIST NEW EXISTING A 3EE 3)$).' EXTERIOR INSTALLATION RESISTANT CONNECTION -).)-5- CONTINUOUS BE INTRUSION AND -!.5&!#452%$ *OISTv ! INCLUDE SUCH COMPOSITE LUMBER SUPPORT (OWEVER BAND DECK SUBMISSION -!.5&!#452%$ CONNECTED PREFABRICATED SPECIFIC ARE ENDS TRUSSES INTENDED RESIDENTIAL USES TRUSS SUBMISSION Attachment of Residential Decks to Wood Truss Floor Systems REQUIREMENTSWWW SBCINDUSTRY COM &IGURE &IGURE &LOOR THE Page 11 PRESCRIPTIVE RESIDENTIAL WOOD DECK CONSTRUCTION GUIDE 11 American Forest & Paper Association &IGURE &IGURE &IGURE Page 12 12 PRESCRIPTIVE RESIDENTIAL WOOD DECK CONSTRUCTION GUIDE American Wood Council 02/()")4%$ !TTACHMENTS AND PROHIBITED &IGURE %XTERIOR DECK $%#+3 &IGURE ,%$'%2 /NLY !.#(/23 $ECK 4HE NOMINAL BOARD CONSTRUCTED 4ABLE 2%15)2%-%.43 4ABLE .OMINAL $ECK *OIST 2IM OR "AND g AND LESS g TO g g TO g g TO g g TO g g TO g g TO g #ONNECTION /N #ENTER 1 The tip of the lag screw shall fully extend beyond the inside face of the band joist. 2 The maximum gap between the face of the ledger board and face of the wall sheathing shall be ½". 3 Ledgers shall be flashed or caulked to prevent water from contacting the house band joist (see Figures 14, 15, and 16). 4 Lag screws and bolts shall be staggered per Figure 19. 5 Deck ledgers shall be minimum 2x8 pressure-preservative-treated No.2 grade lumber, or other approved materials as established by standard engineering practice. 6 When solid-sawn pressure-preservative-treated deck ledgers are attached to engineered wood products (minimum 1" thick wood structural panel band joist or structural composite lumber including laminated veneer lumber), the ledger attachment shall be designed in accordance with accepted engineering practice. Tabulated values based on 300 lbs and 350 lbs for 1" and 1-1/8" EWP rim board, respectively. 7 A minimum 1"x9½" Douglas fir-larch laminated veneer lumber rim board shall be permitted in lieu of the 2" nominal band joist. 8 Wood structural panel sheathing, gypsum board sheathing, or foam sheathing not exceeding one inch thickness shall be permitted. The maximum distance between the face of the ledger board and the face of the band joist shall be one inch. 9 Fastener spacing also applies to southern pine, Douglas fir-larch, and hem-fir band joists. Page 13 PRESCRIPTIVE RESIDENTIAL WOOD DECK CONSTRUCTION GUIDE 13 American Forest & Paper Association Placement of lag screws or bolts in deck ledgers The lag screws or bolts shall be placed as shown in Figure 19. The lag screws or bolts shall be staggered from the top to the bottom along the horizontal run of the deck ledger (see Figure 19). Proper installation of lag screws or bolts shall be verified by the authority having jurisdiction. Figure 19: Ledger Board Fastener Spacing and Clearances Thru-Bolts Thru-bolts shall have a diameter of ½". Pilot holes for thru-bolts shall be 17/32" to 9/16" in diameter. Thru-bolts require washers at the bolt head and nut. Expansion and Adhesive Anchors Use approved expansion or adhesive anchors when attaching a ledger board to a concrete or solid masonry wall as shown in Figure 15 or a hollow masonry wall with a grouted cell as shown in Figure 16. Expansion and adhesive anchor bolts shall have a diameter of ½". Minimum spacing and embedment length shall be per the manufacturer’s recommendations. All anchors must have washers. Lag Screws Lag screws shall have a diameter of ½" (see MINIMUM REQUIREMENTS). Lag screws may be used only when the field conditions conform to those shown in Figure 14. See Figure 20 for lag screw length and shank requirements. All lag screws shall be installed with washers. Figure 20: Lag Screw Requirements Lag screw installation requirements: Each lag screw shall have pilot holes drilled as follows: 1) Drill a ½" diameter hole in the ledger board, 2) Drill a 5/16" diameter hole into the band board of the existing house. DO NOT DRILL A ½" DIAMETER HOLE INTO THE BAND BOARD. The threaded portion of the lag screw shall be inserted into the pilot hole by turning. DO NOT DRIVE LAG SCREWS WITH A HAMMER. Use soap or a wood- compatible lubricant as required to facilitate tightening. Each lag screw shall be thoroughly tightened (snug but not over-tightened to avoid wood damage). Page 14 14 PRESCRIPTIVE RESIDENTIAL WOOD DECK CONSTRUCTION GUIDE American Wood Council &2%% 34!.$).' $ECKS WALL &IGURE PROVIDED !33/#)!4%$ 0,!#%$ %8)34).' #,/3%2 7!,, BASEMENTS RECOMMENDED BASEMENT &IGURE $%#+ $ECKS WITH &IGURE Page 15 PRESCRIPTIVE RESIDENTIAL WOOD DECK CONSTRUCTION GUIDE 15 American Forest & Paper Association $IAGONAL PARALLEL SHOWN BRACING AT BRACING OR DOES BLOCKING THE DIAGONAL BRACING ADJACENT SHOWN &REE STANDING THE SHOWN MUST PANEL FASTENING EXPANSION CONCRETE 6%.%%23 &)%,$ &ASTENERS FOR REQUIRED FLASHING 2%15)2%-%.43 $ECK 7HERE &IGURES ANCHORED VERTICAL;2 = LATERAL IN DEVICES PER DESIGN 3EECommentary INFORMATION &IGURE (OUSE &IGURE FOR '5!2$ !LL HAVE CONSTRUCTION JURISDICTION &IGURE Page 16 16 PRESCRIPTIVE RESIDENTIAL WOOD DECK CONSTRUCTION GUIDE American Wood Council '5!2$ $ECK WITH 'UARD JOISTS 'UARD JOISTS WITH THESE ANCHORS INSTALLED INSTRUCTIONS &IGURE &IGURE Page 17 PRESCRIPTIVE RESIDENTIAL WOOD DECK CONSTRUCTION GUIDE 17 American Forest & Paper Association 34!)2 3TAIRS REQUIREMENTS 4ABLE !LL SHALL X SHORTEN AND BOLTS CENTERED FOOTING &IGURE !N THE)F VERTICALg INTERMEDIATE!LL STAIR FREE STANDING 3TAIRS &IGURE;2 = MINIMUM CAN OF LANDING SERVED OF THAN;2 = &IGURE &IGURE &IGURE 4ABLE 3TRINGERS 3PECIES #UT 3TRINGER 3OLID 3TRINGER 3OUTHERN X X $OUGLAS (EM &IR X X 2EDWOOD 0ONDEROSA X X LARCH ASSUMED Page 18 18 PRESCRIPTIVE RESIDENTIAL WOOD DECK CONSTRUCTION GUIDE American Wood Council &IGURE &IGURE 34!)2 !LL AT4HE HANDRAIL PLANE INCHES ;2 = (ANDRAILS COMPOSED MATERIAL EQUIVALENTSHALL HAVE THAN WITH ù SIDES SMOOTH RUN RISER RETURN MAY ;2 = &IGURE &IGURE Page 19 PRESCRIPTIVE RESIDENTIAL WOOD DECK CONSTRUCTION GUIDE 19 American Forest & Paper Association 34!)2 7HERE THE BEAR ANDSHALL UNDISTURBED WHICHEVER ON 3TRINGERS OR GUARDS 2%15)2%-%.43 BOTTOM POST 34!)2 3TAIRWAYS LANDING 4HE (OWEVER ACCEPTABLE &IGURE &IGURE &2!-).' !LL FRAMED A WIDER REDUCE POST &//4).'3 THAN(EADERS LOCATED g JOIST 4RIPLE HEADER JOISTg ARE EXTEND* &IGURES SIDE " SHALL CAPACITY USED THROUGH INCH JOIST FREESTANDING 4ABLE #APACITY *OIST -INIMUM X X X Page 20 20 PRESCRIPTIVE RESIDENTIAL WOOD DECK CONSTRUCTION GUIDE American Wood Council Figure 35: Detail for Framing Around a Chimney or Bay Window Traditional and Engineered Wood Products It is intended that this document be used in conjunction with competent design, accurate fabrication, and adequate supervision of construction. While every effort has been made to insure the accuracy of the information presented, the American Forest & Paper Association and its members do not assume responsibility for errors or omissions in the document, nor for designs, plans, or construction prepared from it. Those using this document assume all liability arising from its use. Copyright © 2007, 2009, 2010 American Forest & Paper Association, Inc. 01-10 Page 21 Copyright © 2009 American Forest & Paper Association, Inc. Commentary to Prescriptive Residential Wood Deck Construction Guide DCA 6 Foreword This Commentary to DCA 6 – Prescriptive Residential Wood Deck Construction Guide has been requested by builders, building officials, and others, to provide background information and example calculations for various sections and tables of DCA 6. The DCA 6 Commentary follows the same organization as DCA 6. Discussion of a particular provision in DCA 6 is found in the DCA 6 Commentary by locating the same section or subsection found in DCA 6. Not every section of DCA 6 has a corresponding commentary section. The DCA 6 Commentary provides background information intended to give the reader an understanding of the data and/or experience upon which the provision is based. One or more examples of the calculation procedures used to produce several of the tables are given to illustrate the scope of conditions covered by the table. The provisions of DCA 6 come primarily from the International Code Council’s International Residential Code (IRC). In developing the DCA 6 Commentary, data available from laboratory tests and experience with structures in-service was analyzed and evaluated for the purpose of providing a consistent explanation. It is intended that this document be used in conjunction with competent design, accurate fabrication, and adequate supervision of construction. Therefore, AF&PA does not assume any responsibility for errors or omissions in the DCA 6 Commentary, nor for designs or plans prepared from it. Inquiries, comments, and suggestions from readers of this document are invited. American Forest & Paper Association Background In August 2006, the American Forest & Paper Association’s American Wood Council (AWC) Technical Committee formed an ad-hoc task group to address prescriptive provisions for residential wood deck construction. Representatives of the wood products industry, home builders, connector manufacturers, building officials, and truss industry were represented on the task group. The Technical Committee urged the Task Group not to “reinvent the wheel,” but to review existing information to determine if there was something on which to build. One resource reviewed was a document developed by the Fairfax County, Virginia Department of Public Works and Environmental Services titled “Typical Deck Details.” With Fairfax County’s permission, this became the basis for DCA 6. Since Fairfax County’s Typical Deck Details was developed for a specific geographic location, DCA 6 was expanded to apply on a national basis (e.g. addition of western lumber species). The first version of DCA 6 was posted to the AWC website in October 2007. Page 22 C2 Prescriptive Residential Wood Deck Construction Guide – Commentary American Wood Council "ASIS !SDCA 6 PROVISIONS #ODEInternational Residential Code (IRC) DCA 6 2006 IRC DCA 6 CHANGES CHANGES IRC DCA 6 BASED2009 IRC !LTERNATIVE ! NOT ANDIRC!N ALTERNATIVE SHALL THE INTENT MATERIAL INTENDED CODE v7HILEDESIGN FOR BUILT MATERIALS PROCESS 3ERVICES 2EPORT TYPICALLY FINAL MATERIALS -).)-5- DECKS THAT CONSIDEREDDCA 6 .ON RESIDENTIAL DESIGN PRESERVATIVE CONTACT !SSOCIATION IS PRESERVATION BY CONSENSUS BASED PRESERVATIVE EVALUATION %VALUATION %VALUATION WOOD HELICAL ASTM F 547 hRING SHANKv LUMBER RINGASTM F1667 PROVIDEDDA4: Post Frame Ring Shank Nails !& 0! ACCORDANCE2005 National Design Specification® (NDS®) for Wood Construction EQUATIONS NDS DISTANCE BOLTS ACCELERATE FASTENERS !ZOLE CONNECTORS RIGOROUSLY MANUFACTURERS CORROSION COATED CORROSION GALVANIZED FROM HTTP WWW AWC ORG (ELP/UTREACH FAQ #ORROSION HTML ANDDCA 6 DCA 6 HAVE DISTRIBUTED PSF BEEN DRIFTINGDCA 6 CONSERVATIVELY DISTRIBUTED Page 23 Prescriptive Residential Wood Deck Construction Guide – Commentary C3 American Forest & Paper Association 4HEIRC PROVISIONSIRC AS h2 WHERE EQUAL REGIONS DESIGNED 3EVERAL 4HISIRC IN MPH h2 4HE OF 3EISMIC DETERMINED %XCEPTION $ETACHED LOCATED FROM IRC hx7HERE WALL !LUMINUM CONTACT PRESERVATIVES COPPER !#:! CORRODE IRC OR OFFICIAL !LTERNATIVE -ATERIALS $%#+).' 4HE Policy for Evaluation of Recommended Spans for Span Rated Decking Products PROVIDES DECKING DIFFERENT DIFFERENT SPECIFIC ASSIGNED 4HIS OR OF REQUIRES ANALYTICAL THESE !,3# PROCEDURE 4HE FOLLOWING ONLY #ONTENT USING ELASTICITY ,OAD FOLLOWING SPAN A ALLOWABLEASTM D2555D245 !NNEX EXCEEDS ON NORMAL B FIBERASTM D2555 ANDD245 STRESS MIDPOINT ASSUMES 3EE!LTERNATIVE -ATERIALS !,3# Page 24 C4 Prescriptive Residential Wood Deck Construction Guide – Commentary American Wood Council */)34 *OIST 4HE BEARING AT LENGTH MAXIMUM BEAMS JOIST ANALYZED CALCULATORWWW AWC ORG WITHOUT DCA 6 &OR UNIFORMLY SHOWN .O 3PAN CANTILEVERS PSF .O POINT X SAME *OIST CENTERLINE* OR HANGERS BE !LLOWING WITHOUT TO )NCISING $OUGLAS SPANS .ORTHERN PINE SPECIES SINCE WOODHEARTWOOD RESISTANT PERMITTED ON ARE SPANS 4ABLE -AXIMUM 3EE "%!- $ECK EXTEND" &IGURE JOISTS ASSUMED SPAN APPROPRIATE CONDITION 7ITH SIZE TABULATED CALCULATE WHERE OPPOSITE ARE BEAM SPANS 2EFRACTORY COMBINED DESIGN THAN APPLIED SPECIES DIFFERENCES CONTROL LOAD Page 25 Prescriptive Residential Wood Deck Construction Guide – Commentary C5 American Forest & Paper Association $%#+ ! STRUCTURAL INCLUDE STRINGERS BOARD TYPICAL &IGURE */)34 4/ "%!- *OIST TO BEAM FORCES GRAVITY WHILE LOADS THAT END -ANUFACTURERS MIS INSTALLATIONS AS */)34 4HE WORST O C SPAN WITH THEREFORE 4ABLE Page 26 C6 Prescriptive Residential Wood Deck Construction Guide – Commentary American Wood Council 0/34 IRC SECTION WOOD DCA 6 &URTHER g NOTCHING OR SO DESIGNEDNational Design Specification® (NDS®) for Wood Construction 0ROHIBITING POST WOOD FROM FASTENERS &OR REMAINING SUFFICIENT THE AVAILABLE AND 0ROVISIONS!LTERNATIVE ALLOW IF ORDER CAP ENOUGH NOTCH FOR INCH MAY ONTO MANUFACTURED MANUFACTURER CONNECTING POST !SSUMING AND MAXIMUM RESULT &//4).'3*" 4HIS SOUTHERN SITUATION OTHER SAME CALCULATED THIS USED REQUIRED POST &//4).'3 &OOTING SOIL OFIRC 4ABLES ARE 0OST │ ⎠ ⎞ │ ⎝ ⎛ + │ ⎠ ⎞ │ ⎝ ⎛ + = , , , , 2 " " * * WHERE *" 3QUARE R B = 2OUND π R D = &OOTING - ≥ D T &IGURE 4 2 0 " 4 2 0 " 4 2 0 " Page 27 Prescriptive Residential Wood Deck Construction Guide – Commentary C7 American Forest & Paper Association 4ABLE THICKNESSES #OORDINATING ANCHORmeans LENGTH ,%$'%2 !CCORDINGIRC THE THE LOWERED MAXIMUM OF SHEAR A 4HE &IGURENDS RESPECTIVELY NDS FASTENER BOLTS 0ERNDS ON BOARD l FOOTNOTENDS BETWEEN POTENTIAL TENSION OF 4ABLE "EAM 3PAN ," *OIST 3PAN ,* 2OUND &OOTING $IAMETER 3QUARE &OOTING $I &OOTING 4HICKNESS g g g g g g g g g g g g g g g g g g g g g g g g g g g g #OORDINATE REQUIREMENTS Page 28 C8 Prescriptive Residential Wood Deck Construction Guide – Commentary American Wood Council 4HE OF IS CONNECTIONS THE ADJUSTED 3OLVINGE DE RD VB !SSUMING HORIZONTALV SHEARV #-I ALLOWABLE 6IRGINIA #ARRADINE THAT THE THE INTERIOR MINIMUMER ONE HALF BOLTS VALUESE X DE DE X E DE X E DE 4HE LEDGER WORK 0OSSIBLE IRC .OTE FOR REQUIREDE BOLT LAG STACKED SHOWN TOER AND "ASED X #ONTINUOUS PREVENT ALTERNATIVE WITH BECAUSE DECK #ONNECTION BLOCKS NOT BLOCK FOR UNKNOWN POINT TEST RECOMMENDED 4ABLE FOR *OIST g LESS g TO g g g g TO g STACKED &IGURE 2EQUIREMENTS ,EDGER Page 29 Prescriptive Residential Wood Deck Construction Guide – Commentary C9 American Forest & Paper Association DECK STABILITY The requirement for diagonal bracing when a deck is greater than 2 feet above grade is applicable to both free- standing decks and decks supported by a ledger. If the deck is attached to the house as shown in Figures 14, 15, 16, or 23, an alternative to knee braces for deck stability (Figure 22) is installation of decking at a 45 degree angle to the deck joists. Decks are stiffer laterally with diagonally oriented lumber decking versus decking installed perpendicular to joists. With respect to hold down tension devices, IRC R502.2.2 requires anchorage to the primary structure for both vertical and lateral loads as applicable. Further, the IRC includes hold down tension devices as a prescriptive means to achieve compliance with the lateral load connection requirements without requiring engineering. Figure 23A was taken directly from the FEMA Home Builder's Guide to Seismic Resistant Construction (FEMA 232) which refers to it as an “above-code recommendation.” In lieu of the prescriptive hold down tension device specified, an alternate engineered connection detail is permitted or the deck can be designed to be free-standing. While Item 7 of DCA 6 Minimum Requirements states that the document does not address wind or seismic design issues, some interpret R502.2.2 to be applicable in all cases since lateral loads can be developed by other sources including people moving or dancing on a deck. Another interpretation is that the term “as applicable” in R502.2.2 means the provision is only required for code prescribed loads. The only code prescribed lateral loads are wind and seismic. Where deck joists are perpendicular to the house floor joists, blocking between house joists and boundary nailing of the house floor diaphragm to the blocking is required. GUARD REQUIREMENTS Figure 24 requires that openings not allow the passage of a 4" diameter sphere. However, it does not address openings underneath a fixed deck bench used in place of guards. All openings, including those underneath benches used in place of guards, shall not allow the passage of a 4" diameter sphere. Additionally, if fixed seating is adjacent to guards, the guard height should be measured from the seat rather than the deck surface. This will help minimize exposure to falls over the top of the guard due to individuals standing on deck seats. IRC Table R301.5 requires guard in-fill components (all those except the handrail), balusters, and panel fillers to be designed to withstand a horizontally applied normal load of 50 pounds on an area equal to 1 square foot. This load need not be assumed to act concurrently with any other live load requirement. Baluster connection requirements shown in Figure 24 have been designed to resist that load. GUARD POST ATTACHMENTS Both the IRC and International Building Code (IBC) specify that guardrails and handrails be capable of resisting a minimum concentrated live load of 200 lbs applied in any direction. Commonly used residential guardrail post connections were laboratory tested at the required load level for a code-conforming assembly per the IBC (Loferski et al., 2006). A commercially available connector, typically used in shear wall construction, was tested in a post-to-deck residential guardrail assembly. The connection passed a load test based on code provisions for a “tested assembly.” Connection details in Figures 25 and 26 reflect these test results. A minimum requirement of 1,800 lbs for the hold down connector ensures adequate capacity (Loferski et al., 2005) for a 36" maximum rail height. A higher rail height requires design of a higher capacity connector. Manufacturers’ tabulated values for hold down connectors typically include a load duration (CD) increase of 60% since connectors for shear walls are used to resist wind and seismic loads. The 200 lbs concentrated load requirement for guard rails is assumed to be a 10 minute load duration (e.g. it would not see a maximum 200 lbs outward load for more than 10 minutes cumulatively in its lifetime). Therefore, CD=1.6 is used for hold downs in this application. This section requires deck guard posts to be at least 4x4 nominal with a reference bending design value not less than 1,100 psi to ensure sufficient bending stress in the post. Assuming the lever arm is 39.5" (36" + 1.5" deck board + 2" edge distance), the bending moment is 39.5" x 200 lbs = 7,900 in-lbs. Bending stress, f b , is calculated as follows: M/S(4x4) = 7,900 in-lbs / 7.146 in3 = 1,106 psi. No. 2 grades of all Table 2 species meet this requirement with the following assumptions. The adjusted bending design value, F'b, is based on a wet service factor, CM = 0.85, and incising factor, Ci = 0.80 (Douglas fir-larch, hem-fir, spruce-pine-fir). A load duration factor, CD = 1.6, is assumed for consistency with the hold down device used to connect the guard to the joist. Figures 25 and 26 show minimum and maximum spacing requirements for bolts in deck joists and deck rim boards. The 5" maximum spacing is per footnote 2 of NDS Table 11.5.1D. This requirement is based on potential shrinkage of the joist or rim board which could create tension perpendicular to grain stresses if the outer edges of the deck joist or rim are constrained by bolts. Page 30 C10 Prescriptive Residential Wood Deck Construction Guide – Commentary American Wood Council STAIR REQUIREMENTS Figure 29 shows 5/4 boards spanning 18" or less. As noted under DECKING REQUIREMENTS commentary, specific products classified by size as decking are usually assigned a recommended span of 16" or 24". Additionally, IRC Table R301.5 footnote (c) requires a 300 lb concentrated load check on stair treads. Analysis revealed that 2x6 No. 2 southern pine works for a 34.5" span (36" – ¾" bearing at each end) when the 300 lbs is distributed across 2 inches (e.g. 150 pli). This is based on L/288 deflection criteria (ICC ES Acceptance Criteria 174 requires 1/8" deflection limit: 36"/0.125" = 288). Other species will not calculate for that span using 2x6. Solid stringers were analyzed as simple span beams using the horizontal span not the actual stringer length. Cut stringers were analyzed with 5.1" depth which is based on 7.75:10 rise to run ratio. A size factor, CF, of 1.0 is used since 2x12 is the size basis. STAIR FOOTING REQUIREMENTS Stair stringers should be supported by bearing at the end where the stairway meets grade. The detail shown assumes a 40 psf live load and 10 psf dead load over a tributary area of 18" and one-half of the maximum span permitted for solid stringers (16'-6" for southern pine and 13'-3" for other species). This calculates to 625 lbs and 500 lbs, respectively. For southern pine, seven #8 wood screws would be required. Northern species would require eight #8 wood screws (16d box or common nails would be comparable). While bolts are sometimes used for this detail, proximity to the end of the stringer could lead to splitting of the stringer – especially cut stringers. The 2x4 bearing block alleviates this situation. However, in addition to the bearing block, bolts would also be required to provide lateral support if a guard post is used. FRAMING AT CHIMNEY OR BAY WINDOW IRC R502.10 on framing of openings states: “Openings in floor framing shall be framed with a header and trimmer joists. When the header joist span does not exceed 4', the header joist may be a single member the same size as the floor joist. Single trimmer joists may be used to carry a single header joist that is located within 3' of the trimmer joist bearing. When the header joist span exceeds 4', the trimmer joists and the header joist shall be doubled and of sufficient cross section to support the floor joists framing into the header. Approved hangers shall be used for the header joist to trimmer joist connections when the header joist span exceeds 6'...” Trimmer Joist Size and Span Limited by Concentrated Load from the Header Where the header frames into the trimmer joist, a concentrated load is created. This condition was evaluated assuming one ply of a double trimmer joist carries the uniform load and one ply carries the point load from a 6' header. The analysis revealed that the distance from the end of the trimmer joist to the point where the header frames into it – designated as dimension “a” – must be limited. The maximum distance was calculated based on joist spans given in Table 2. A maximum distance of a = 3' was chosen to cover common framing conditions. Triple trimmer joists are required on each side of the header if joist spacing is 12" or 16" o.c., or if the trimmer joist span exceeds 8'-6"; otherwise a double trimmer joist is permitted. If “a” is less than that shown in Table C7a, a double trimmer joist is also permitted. Bending and shear were checked to determine the reduction in a double trimmer joist span when carrying a 6' header. For a simple span beam, with a concentrated load offset from the center, maximum moment is calculated as Pab/LJ and maximum shear is calculated as Pb/LJ, where P is the concentrated load based on the tributary area carried by the header, b = LJ – a, and LJ is the trimmer joist span. Moment controlled for this analysis in determining amax. While shear was evaluated, the NDS permits the shear load to be reduced within a distance “d” (equal to the joist depth) from the end of the joist. With that reduction, shear did not control any of the spans evaluated. Page 31 Prescriptive Residential Wood Deck Construction Guide – Commentary C11 American Forest & Paper Association 4ABLE *OISTg A 3PECIES 3IZE AMAX 3OUTHERN X X X $OUGLAS &IR X X X 2EDWOOD #EDARS 2ED X X X )NCISING FIR LARCH $ESIGN ASSUMED 4HE ON SPACING COMBINATION* THE NEXT HANGER TRIMMER PERMITTED 4RIMMER THE "OLTS THE INTOBAND MOUNTED ATTACH LARGE WOULD THE ,%$'%2 THE PROVISIONSE THE BASEDNDS "ASED TO IN NUMBER SPAN UP* THE 4ABLE4RIMMER #APACITY 4RIMMER -INIMUM g g g g g g %XAMPLES DEEP TRIMMER SPAN THROUGH TRIMMER g 3EVERAL g * g ** g WHICH 0LACE THE 4ABLE* ON 0OINT ,EDGER 3IZE A A A 3OUTHERN X g g g X g g X g g g $OUGLAS ,ARCH 3PRUCE 0INE &IR X g g g X g g g X g g g 0ONDEROSA 2ED 2EDWOOD 7ESTERN X g g g X g g g X g g g !SSUMES AND )NCISING LARCH $ESIGN ASSUMED 3HADING FOR Page 32 C12 Prescriptive Residential Wood Deck Construction Guide – Commentary American Wood Council !SSUME g DEEP TRIMMER THE)F ATTACH THE g 3EVERAL g 0LACE THE 4ABLE g AT DEEP TRIMMER MAX (OWEVER IF THETHE JOIST g SOLUTIONS g THE References !MERICANPolicy for Evaluation of Recommended Spans for Span Rated Decking Products (November 5, 2004). 'ERMANTOWN -$ !MERICANDA4: Post Frame Ring Shank Nails !MERICANNational Design Specification (NDS) for Wood Construction, ANSI/AF&PA NDS-2005 !MERICAN AWPA Book of Standards. "IRMINGHAM !34- ASTM F547- 06 Standard Terminology of Nails for Use with Wood and Wood-Base Materials #ONSHOHOCKEN !34- ASTM D2555- 06 Standard Practice for Establishing Clear Wood Strength Values #ONSHOHOCKEN !34- ASTM D245 – 06 Standard Practice for Establishing Structural Grades and Related Allowable Properties for Visually Graded Lumber #ONSHOHOCKEN #ARRADINE AND #ONNECTIONWood Design Focus 6OL 3UMMER )NTERNATIONAL Acceptance Criteria for Deck Board Span Ratings and Guardrail Systems (Guards and Handrails) - AC174 7ASHINGTON -ARCH )NTERNATIONALInternational Building Code, 2009 Edition. 7ASHINGTON 9 )NTERNATIONALInternational Residential Code, 2009 Edition. 7ASHINGTON 9 ,OFERSKI 7OESTE 2ESIDENTIALWood Design Focus &OREST ,OFERSKI 0OSTJournal of Light Construction Page 33 Prescriptive Residential Wood Deck Construction Guide – Commentary C13 American Forest & Paper Association !00%.$)8 3!&%49IRC 2 REQUIRED ADJACENT OF AREA SHOULD INJURY DESCENDING GLASS THIS %XCEPTIONS SIDE S SURFACE HORIZONTAL AND GUARDRAIL PANELS 2 MORE 7HEN THE FLOOR PANEL LOAD GLASS THIS MUST &IGURE #OPYRIGHT
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