CHOOSING MATERIALS

• If you choose pressure-treated lumber, you'll have a choice between 5/4 x 6 decking or 2" material (typically 2 x 4 through 2 x 8). The size and species of the decking you choose will determine the spacing between your joists. Recommended spacing for common decking boards is as follows:
  

• Determining Joist Size
  2x6s through 2x10s are the most common sizes used for joists. The beams that carry them are typically 4x6 through 4x10. Pressure treated lumber is generally less expensive than redwood or cedar, and can be used for the substructure even when the decking and railing will be other species.
  
  In most cases, you'll want to determine the spacing between beams first, then use joist size appropriate to that spacing. If the deck will be no more than 6' off the ground, a common recommendation is to space the support beams no more than 12' apart. As a rule, you'll only need one beam along the outer edge of the deck (a ledger bolted to the house supports the other end of the deck).

Beam Spacing	Joist Size (joists 16" o.c.)
Up to 8'	2x6 (Southern pine, Douglas fir, Western red cedar, S-P-F or Hem-Fir) 2x8 (redwood, Northern white cedar)
8' to 10'	2x8 (all species listed above)
10' to 12'	2x8 (Southern pine, Douglas fir, Western red cedar, S-P-F or Hem-fir) 2x10 (redwood, Northern white cedar)

Beam Spacing	Joist Size (joists 24" o.c.)
Up to 8'	2x6 (Southern pine, Douglas fir) 2x8 (Western red cedar, S-P-F, Hem-Fir, redwood or Northern white cedar)
8' to 10'	2x8 (all species listed above)
10' to 12'	2x8 (Southern pine, Douglas fir) 2x10 (Western red cedar, S-P-F or Hem-Fir, redwood or Northern white cedar)

• Determining Beam Size
  Since support posts are often run through the decking to serve as railing posts, the specifications below are given for posts that will be spaced no more than 6' apart with beams more then 12' apart. With these spacing specifications, 4x4 posts are adequate for any deck less than 6' off the ground.

Beam Spacing (round down to nearest foot)	Miniumum Beam Size (doubled 2" material may be used in place of 4" thickness)
Up to 6'	4x6 (Southern pine or Douglas fir) 4x8 (Western red cedar, S-P-F, Hem-Fir, redwood or Northern white cedar)
Up to 7'	4x8 (all species listed above)
Up to 9'	4x8 (Southern pine, Douglas fir, Western red cedar, S-P-F or Hem-Fir) 4x10 (redwood or Northern white cedar)
Up to 11'	4 x 8 (Southern pine or Douglas fir) 4x10 (Western red cedar, S-P-F, Hem-Fir, redwood or Northern white cedar)
Up to 12'	4x10 (all species listed above)

FIG. 1

PREPARATION AND LAYOUT

• Preparation
  First, prepare the ground under the deck by removing the sod. Slope the ground away from the house a minimum of 1" every 15' to provide drainage. Once the deck is finished, the ground should be covered with 6-mil black polyethylene to keep weeds from growing.
  
  Measure and mark the position of the ledger along the wall. The height of the ledger should be 1" below the bottom of the door plus the thickness of the decking, plus the depth of the joists. It makes no difference which way you set the joists, as long as your layout is consistent.
  
  Mount a 2x6 ledger to the wall with 1/2" lag screws. The ledger must be level, and the lag screws should be long enough to penetrate the studs at least 3". Use two lag screws at each end, and one at each wall stud in between. Install a "Z" shaped flashing above the ledger to shed water, or space the ledger away from the wall with washers (Fig. 1).
  
  
• Layout
  To establish the outside perimeter of the deck, measure out from each end of the ledger about 18" beyond the outside edge of the deck. Set up the batterboards, then run taut strings from each end of the ledger to the batterboards to establish the sides of the deck.
  
  Run a third string between the batterboards to establish the outside edge of the deck. Square the layout by measuring the opposite diagonals, then adjusting the ledger-to-batterboard strings until both measurements are equal.

FIG. 2

FIG. 3

FIG. 4

BUILDING THE SUBSTRUCTURE

• Footing and Piers
  Use a plumb bob from the string to establish the location of the footings. The holes for the footings must be deeper than the maximum frost penetration in your area, and deep enough to rest on undisturbed soil. It's a good idea to dig 6" deeper and fill the bottom of the hole with gravel, to allow drainage (Fig. 2).
  
  
• Mix concrete and pour the footings. As you finish each pour, set a precast pier on the footing so it extends about 6" above the ground level. Use a thin cement mix to bond the piers to the footings.
  
  
• Posts
  After the concrete has set, stand the posts on the piers. Use temporary braces and a level to plumb the posts. Once the posts are set, run a mason's line from the top of the ledger to each post and use a line level to mark it for cutting. The height of the post should be equal to the height of the ledger minus the depth of the beam that will be set on it.
  
  
• Beams
  Fasten post-to-beam connectors on top of the posts with nails and 1/2" x 5-1/2" hex bolts, then set the beams into the connector. Plumb and square the assembly, then secure the beams as you did the posts.
  
  
• Joists
  Mark the joist locations on both the beams and ledger, either 16" or 24" o.c., as per your design. Set the joists in place with the crowns up. If the deck is wide enough that you need two sets of joists, splice the connections by overlapping each pair of joists at least 1' and nailing them together with 8d galvanized nails (Fig. 3). Install blocking between the joists wherever required (Fig. 4). Blocking requirements are determined by your local building codes. Finally, nail the rim joist across the ends of the joists.