applying decking diagonally can often reduce or eliminate the number of butt joists on decks that are over 20 wide. in some cases, you may decide that it easier to use a division board to create one continuous seam across the deck surface.
composite decking weight vs. wood; the way to calculate the spacing on deck joists is based on common sense and a knowledge of your materials. longer, thinner joists will need to be set closer together for optimal structural integrity, while shorter, wider joists can be set further apart.
each joist should be spaced no more than a maximum of 400mm apart. we recommend as a rule of thumb purchasing 1x joist per square metre of decking. composite joists from wpc decking can be utilised for most domestic decking and wall cladding projects and we highly recommend they are used in conjunction with a hard concrete base.
the closer the joists are to each other, the greater the distance they're able to span safely. two-by-twelve douglas fir joists spaced 12 inches apart on center, for example, can span 20 feet, 7 inches, but the same joists spaced 24 inches part can only span 14 feet, 7 inches.
if you have seen the deck joist span table, you already understand the relationship between joist span and joist spacing. the closer you space joists, the longer you can span joists up to a point. for determining beam spans distance a beam can span between supporting posts , consider the following concept.
though there's no legal standard for screw spacing, an even spacing looks best. don't put the screws three inches apart on one board and four inches apart on the next. pick a spacing and stick with it.
let's also assume that the framing material is 2 southern pine douglas fir spans would be similar, but you should verify them . most deck builders would typically support the free end of a deck this size on a beam made from two 2x12s supported on three posts set 7 feet 6 inches apart.