Once you have determined the basic design of your deck, the next step is to choose your materials. The most common choices are pressure-treated (P/T) lumber (usually Southern pine), redwood, or cedar. As a rule, pressure-treated lumber is the best choice for the substructure; the species you use for the visible parts of the deck will depend on your budget and the look you want.
The span tables in this document will help you determine how much material you need, based on the species you choose. Although there is no such thing as an “average” deck, these instructions assume that your deck is attached to the house, is no more than 6″ off the ground, and has no special load requirements.
All design recommendations below are suggestions only, for estimating purposes. Always check local building codes before determining the final design. All design recommendations below are suggestions only, for estimating purposes. Always check local building codes before determining the final design.
Inside this document you will find information about:
Preparation and Layout
Building the Substructure
Decking and Railings
Decking-If you choose pressure-treated lumber, you’ll have a choice between 5/4 x 6 decking (1×5-1/2 actual size) or 2″ material (typically 2×4 through 2×8, all 1-1/2″ thick). 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:
5/4×6 PT Southern pine
2 inch thick redwood, western red cedar, S-P-F, Hem-fir, Northern white cedar
24″ maximum, 16″ preferred
2-inch Southern pine
Determining Joist Size-2x6s through 2x10s are the most common sizes used for joists. The beams that carry them are typically 4×6 through 4×10, often “built up” from doubled 2-inch lumber. 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 a 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).
Joist Size (joists 16″ o.c.)
Up to 8 feet
2×6 (Southern pine, Douglas fir, Western red cedar, S-P-F, or Hem-Fir)2×8 (redwood, Northern white cedar)
8 to 10 feet
2×8 (all species listed above)
10 to 12 feet
2×8 (Southern pine, Douglas fir, Western red cedar, S-P-F, or Hem-fir)2 x 10 (redwood, Northern white cedar)
Joist Size (joists 24″ o.c.)
Up to 8 feet
2×6 (Southern pine, or Douglas fir)2×8 (Western red cedar, S-P-F, Hem-Fir, redwood, or Northern white cedar)
8 to 10 feet
2×8 (all species listed above)
10 to 12 feet
2×8 (Southern pine, or Douglas fir)2×10 (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 that are no more than 12′ apart. With these spacing specifications, 4×4 posts are adequate for any deck less than 6′ off the ground.
Beam Spacing (round down to nearest foot)
Min. Beam Size (double 2″ material may be used in place of 4″ thickness)
Up to 6 feet
4×6 (Southern pine or Douglas fir)4×8 (Western red cedar, S-P-F, Hem-Fir, redwood, or Northern white cedar)
Up to 7 feet
4×8 (all species listed above)
Up to 9 feet
4×8 (Southern pine, Douglas fir, Western red cedar, S-P-F, or Hem-Fir)4×10 (redwood, Northern white cedar)
Up to 11 feet
4×8 (Southern pine or Douglas fir)4×10 (Western red cedar, S-P-F, Hem-Fir, redwood or Northern white cedar)
Up to 12 feet
4×10 (all species listed above)
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 if you plan to set the joists on the ledger and beams rather than using joist hangers. It makes no difference which way you set the joists, as long as your layout is consistent.
Mount a 2×6 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 (typically 16″ on center) in between. Install a “Z”-shaped flashing above the ledger to shed water, or space the ledger away from the wall with washers (see image).
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 batterboards (see image) as shown, 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. Take care to maintain the correct distance between the strings.
BUILDING THE SUBSTRUCTURE
Footing and Piers (see image) – 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.
Mix concrete and pour the footings. To find the number of 90# bags of ready-mixed concrete you’ll need for each 12×12 footing, measure the depth of the footing in inches and divide by 8. 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″x5-1/2″ hex bolts, then set the beams into the connector. Plumb and square the assembly, then secure the beams as you did the posts. If local building codes require it, install 2×6 diagonal cross braces and secure them with 1/2″x4-1/2″ lag screws (see image).
Joists (see first image below) – 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 (and if you set the joists over the beams rather than hanging them from joist hangers), splice the connections by overlapping each pair of joists at least 1′ and nailing them together with 8d galvanized nails (see second image below). Install blocking between the joists wherever required (see third image below). Blocking requirements are determined by your local building codes. Finally, nail the rim joist across the ends of the joists.
Stairs-Build any stairs you will need. Instructions for building outdoor stairs are covered in an accompanying brochure.
DECKING AND RAILINGS
Decking-Deck boards should be laid with the bark side up, and with both ends centered over a joist. Stagger the joints of side-by-side deck boards so they don’t line up. Notch the boards around posts or other obstructions, leaving 1/8″ space for drainage.
2″-thick deck boards should be spaced approximately 1/8″; most builders set a 16d nail between the boards as they fasten them. 5/4″‘x6″ pressure-treated decking may be placed with each board flush against the next; natural shrinkage will provide the proper spacing.
Fasten the deck boards at each joist (see image). Use two fasteners per support point for decking up to 6″ wide, or three fasteners for wider boards. Deck screws or clips are generally better than nails, but all fasteners must be hot-dipped galvanized, aluminum, or stainless steel (see image below). If you use nails, blunt the points by tapping them with your hammer, to avoid splitting the decking.
Let the decking run over the edge of the structure, then saw the ends off after all boards are laid.
Railings-Secure the railing posts at each corner of the deck, and on each side of the stairs. Then secure the field posts, spaced equally between the corners but no farther apart than allowed by local building codes (typically 6′). Nail the sub-railings and cap rail in place, then add the balusters.
TOOL AND MATERIAL CHECKLIST
Level and Line Level
2x2s and 1x4s for Batter Boards
Ready-mixed Concrete, Gravel
Lag Screws, Hex Bolts w/ Nuts and Washers
8d and 16d Galvanized Common/Box Nails
Lumber for Posts, Ledger, Beams and Joists
Brushes and Thinner
6 mil. Black Polyethylene
Check your state and local codes before starting any project. Follow all safety precautions. Information in this document has been furnished by the National Retail Hardware Association (NRHA) and associated contributors. Every effort has been made to ensure accuracy and safety. Neither NRHA, any contributor nor the retailer can be held responsible for damages or injuries resulting from the use of the information in this document.