span entries are listed for 2×6 through 2×12 joists and 12 in., 16 in., and 24 in. on-center spacing. the illustrations one for cantilever joists and one for flush rim-beam hung joists point out where joist span measurements are taken from the saddle of the ledger mounted joist hanger to the center
loads and deflection. for example, a two-by-twelve douglas fir beam supporting joists that span 8 feet must be supported by posts that are no further than 13 feet, 9 inches apart, while a southern yellow pine beam of the same dimensions, supporting the same joists, can have a post spacing of 17 feet, 6 inches.
maximum floor joist span for no. 1 and no. 2 grade of douglas fir are indicated below. max. dead load weight of structure and fixed loads 10 lbs/ft 2. live load is weight of furniture, wind, snow and more.. 1 psf lb f /ft 2 = 47.88 n/m 2; 1 ft = 0.3048 m
beam: 4x10 joists span up to: 8' beam span: 9' beam: 4x10 joists span up to: 10' beam span: 8' beam: 4x10 joists span up to: 12' beam span: 7' joists. the required width of a joist depends on its spanhow far it must travel between beams or between a beam and a ledger.
i put the built-up beam span table below but i would very rarely use a built-up beam in an exterior application where they are exposed to the moisture conditions like a deck. with the min. code for nailing they will still check, may warp and will shrink at the splices which allows moisture to get trapped with dirt promoting the compromise of the beams over time.
for example, in the joist span table below, the highlighted cell shows that 2' x 8' southern yellow pine joists, that have a grade of 2, and are spaced 24' apart can have a maximum span of 10 feet - 3 inches 10-3 if designing for a live load of 40 lbs/ft 2.
if you are designing a deck, one of the calculations that you need is the size of the lumber required to span the distances between the deck supports or deck supports and wall. the lumber span is from the inside of the support on one end to the inside of the support on the other end, as shown in figure 1.
a double 2x12 beam can span 12 feet; a 2 2x10 can span 10 feet and so on. dimensional lumber deck beam span chart the numbers in gray indicate the distance between the support posts.
when the deck joists are 8 ft. long, the beam can span 7-7. when building a deck with 7-ft. joists, you know the beam can span somewhere between 7-7 and 8-0, but you dont know exactly where. check with your local code official, or simply drop back to the shorter value in the table and assume the allowable span is 7-7.
12 span, 2x8s at 12 o.c., 2x10s at 16 o.c. or 2x12s at 24 o.c. use the beam size table and find the 8 post spacing column. with a 12 deck span, the beam may be either two 2x8s or two 2x10s, depending on wood used. case ii solution: use a to determine joist size and a b to determine beam
what is the greatest distance that 2x8 beams can be apart on a deck? i'm building a deck, and am using 2x8's for the beams, doubled up so that the posts are sandwiched between the two. what is the greatest distance that each set of beams can be from each other off center?
generally speaking, a 2x8 should be able to span 8 feet, so if you double them, then an 8 foot span between the posts should be ok. the joists should be 16' on center. if you use 2x8s for the joists, you can make you deck 10' wide by having the joists over hang the beams by 2'.
*joists may cantilever up to ¼ of the actual adjacent span. for example, a 2 x 12 joist placed 16 oc. spanning 16-6 between supports may cantilever up to an additional 4-1 ½ for a total maximum length of 20 -7 ½ southern pine deck beam maximum spans*.