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A2 Prescriptive Residential Wood Deck Construction Guide -Appendix <br /> Appendix B to <br /> • 11 <br /> Prescriptive Residential <br /> Wood Deck :Construction uid Deslg,n <br /> DCA 6 - 2012 IRC Version <br /> TRIBUTARY AREA CALCULATIONS Figure B1. Examples of Tributary Areas. <br /> This Appendix B to.DCA 6—Prescriptive Residential <br /> Wood Deck Construction Guide has been requested by — - <br /> builders,building officials,and others, to provide an <br /> alternative to the assumptions of Table 4 Post Height for <br /> 6x6 and Footings Sizes for all Posts.DCA 6 is written to <br /> be as simple and easy to use as possible;however,this <br /> means that conservative assumptions often have to be <br /> made.This is especially true for Table 4,which assumes <br /> full cantilevers on both the joist and the beam. If full <br /> cantilevers are not present,the load will be less than pli <br /> i ® s <br /> assumed in Table 4,and the footing size will often 0 s ,w4.44:4,44,0*�� i : ' <br /> decrease and allowable post height will often.increase. af,4,00,*4444.'44.144W ; <br /> 314, <br /> This Appendix is an aid to calculating the loads on posts71 ' 0 $ <br /> and footings based on the actual deck.configuration. 14440*3-1•144/4'� � * 1 t <br /> Tributary Area i �: _7-4' 414%40.1,04,445440:,,40.;. <br /> Since uniform loading is prescriptively set for DCA 6, <br /> `; + <br /> only the area the post or footing is supporting needs to t.. � _ �f � <br /> be determined.This is called the tributary area and.is �peMtog <br /> �,. . <br /> shown in Figure B1..Tributary area of a center or corner <br /> post can be found from Figure B1 or by using the <br /> following formulas: r tAwm ; <br /> Kwieerlittlatootot <br /> 1 <br /> ACenterPost=(2JL+JO)(BL) Eq. B-1 Joist Length,Jr, <br /> The joist length is defined differently for this appendix <br /> A�a,rrerPosr=(..JL+Jo)(1BL+BO) Eq.B-2 than the main provisions of DCA 6.The joist length is <br /> 2 not the design span of the joist,but is from the ledger <br /> face to either the center point of the beam,if there is an <br /> where: overhang,or to the outside face of the rimboard if there <br /> A is tributary area(ft) is not an overhang. See Figure B2. <br /> JL is length of joist(.ft) <br /> Jo is length of joist overhang(ft) Joist Overhang Length,Jo <br /> B,..is the length of the beam span(ft) The length of the joist overhang is measure from the <br /> Bo is the length of the beam.overhang(ft) outside edge of the deck to the centerline of the beam. <br /> See Figure B2. If no overhang exists,zero is entered into <br /> equation B-1 or B-2 for Jo. <br /> American Wood Council <br />