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C4 Prescriptive Residential Wood Deck Construction Guide -Commentary Table C2 which indicates where deflection controls Joist spans can cantilever past the beam up to Lo or L/4 overhang length. as shown in Figure lA and Figure 2,or the joists may attach to only one side of the beam with joist hangers as Joist spans are based on lumber size and joist spacing. shown in Figure I (however,joists shall not be The span of a joist is measured from the face of bearing attached to opposite sides of the same beam).Allowing at one end of the joist to the face of bearing at the other joists to span from opposite sides of the beam without end of the joist and does not include the length of the appropriate consideration could potentially lead to a overhangs.This method of measuring the"clear"span is condition where beam capacity is exceeded. for ease of construction and is commonly used by builders; however, it differs from standard engineering Incising factors are used for refractory species including practice,where span is defined as the distance between Douglas Fir-Larch,Hem-Fir,and Spruce-Pine-Fir. Hem- centers of required bearing, as in the 2012 NDS. To align Fir spans control for these three species combinations. the two differing definitions, 3-was subtracted from Ponderosa Pine and Red Pine were sized using Northern each allowable span in Table 2 to account for the Species design values except that the incising factor was difference between tabulating clear span and engineered not applied since Ponderosa Pine and Red Pine are not span. incised when treated. Since incising is not necessary for naturally durable wood(heartwood of the following Joist spans are limited to a maximum of 18'-0" to ensure species: decay-resistant Redwood and Cedars -corner appropriate design of beams and footings. If longer joist sapwood is permitted if 90 percent or more of the width spans are designed,joist hangers, beams,posts,and of each side on which it occurs is heartwood),Redwood footings will have to be analyzed to ensure appropriate and Western Cedar are also not incised. Since Ponderosa load path. See the span calculator at www.awc.org for Pine,Red Pine, Redwood,and Western Cedar have simple span conditions without overhangs, however comparable design values,Northern Species design spans shall not exceed 18'-0"when used in conjunction values are used to calculate the controlling spans for with DCA 6. these four species combinations. Table C2. Conditions Where Deflection Controls Overhang Length*. Joist Spacing (o.c.) 12" 16" 24" Allowable Overhang3 Species Size (Lo) 2x66 1s " 1", 1i,- 3" Southern Pine 2x8 1 18 • a 2x10 • 1 � �; 2' - 13 2x12 4' - 6" 4' - 2" 3' - 4" 2x66 0' - 11" 1' - 0" 1' - 2" Douglas Fir- 2x8 1' - 8" 1' - 13" 2' - 2" Larch, Hem-Fir, 2x10 2' - 10" 3' - " 2' - 9" Spruce-Pine-Fir 2x12 4' - " 3' - 11" 3' - 3" Redwood, 2x66 0' - " 0' - 10" 0' - 11" Western Cedars, 2x8 1' - " 1' - 7" 1 - 0" Ponderosa 2x10 2' 5" 2' - 7" 2' - 8" Pines, Red Pines 2x1 2 3' - K., 3' - 9" 3' - 1 " Shading indicates overhang is deflection controlled.See Table 2 for footnotes. American Wood Council