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Prescriptive Residential Wood Deck Construction Guide-Commentary C5 BEAM SIZE &ASSEMBLY REQUIREMENTS though design values for these naturally durable species Deck beam spans are in accordance with Table 3 and can are lower than design values for these refractory species, extend past the post up to L13/4 as shown in Figure 3. the incising factors applied to strength and stiffness Beams are sized based on tributary load from joists values of refractory species offset the differences. within the span limits shown in Table 2.Joists are Therefore, span differences are minimal. Additionally, assumed to span from one side only.Allowing joists to Ponderosa Pine and Red Pine were sized using Northern span from opposite sides of the beam without Species design values except that the incising factor was appropriate consideration could potentially lead to a not applied,since Ponderosa Pine and Red Pine are not condition where beam capacity is exceeded. incised when treated.Therefore,design values for the Northern Species combination(includes Ponderosa Pine With appropriate assumptions,Table 3 could be used to and Red Pine)are used to calculate spans for all of these size beams with joists spanning from both sides. Since species. tabulated values for beams assume 112 of the joist span to calculate tributary area, using 2 times the joist span for Glued-laminated timber beams are required to be treated cases where joists span symmetrically(equal joist spans) with oil-based preservatives in accordance with AWPA from opposite sides is acceptable. For example, assume UL When these preservatives are used,the glued- there are 8'-0"joists spanning from opposite sides of the laminated timber industry recommends that the NDS wet same beam. The column in Table 3 labeled for 16'-0" service factor(CM) not be used in this specific outdoor joist spans can be used to size a beam in this case. A application; therefore, all glued-laminated timber beams similar procedure is required for footing sizes. have been designed using design values based on dry service conditions. Douglas Fir-Larch,Hem-Fir and Spruce-Pine-Fir (refractory species)are combined with Redwood and Western Cedars(naturally durable species). Even DECK FRAMING PLAN For resistance of lateral loads,the deck is assumed to act A framing plan shows the layout of the primary as a diaphragm in an open-front structure. The decking, structural system. Examples of structural elements when nailed to the joists and rim joist,acts as sheathing include:joists, beams, ledger board,posts,footings, in this diaphragm. stringers,treads,and the type,size,and spacing of ledger board fasteners. Figure C5 shows an example of a Larger aspect ratios may be permitted where calculations typical deck framing plan. show that larger diaphragm deflections can be tolerated. • s-D t5.__ 1/01-a_ American Wood Council