How to build a deck
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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 charts in this article 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 that there
are no special load requirements.
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:
- Choosing Materials
- Preparation and Layout
- Building the Substructure
- Decking and Railings
CHOOSING MATERIALS
Decking–If you choose pressure-treated lumber,
you'll have a choice between 5/4 x 6 decking (1x5-1/2 actual size) or
2" material (typically 2x4 through 2x8, 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:
|
Decking
|
Joist Spacing
|
| 5/4x6 P/T Southern pine |
16" maximum |
| 2 inch thick redwood, western red cedar, S-P-F, Hem-fir, Northern white cedar |
24" maximum, 16" preferred |
| 2-inch Southern pine |
24" maximum |
Determining Joist Size–2x6s through 2x10s are
the most common sizes used for joists. The beams that carry them are
typically 4x6 through 4x10, 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).
|
Beam Spacing
|
Joist Size (joists 16" o.c.)
|
| Up to 8 feet |
2x6 (Southern pine, Douglas fir, Western red cedar, S-P-F, or Hem-Fir)
2x8 (redwood, Northern white cedar) |
| 8 to 10 feet |
2x8 (all species listed above) |
| 10 to 12 feet |
2x8 (Southern pine, Douglas fir, Western red cedar, S-P-F, or Hem-fir)
2 x 10 (redwood, Northern white cedar) |
|
Beam Spacing
|
Joist Size (joists 24" o.c.)
|
| Up to 8 feet |
2x6 (Southern pine, or Douglas fir)
2x8 (Western red cedar, S-P-F, Hem-Fir, redwood, or Northern white cedar) |
| 8 to 10 feet |
2x8 (all species listed above) |
| 10 to 12 feet |
2x8 (Southern pine, or 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 that are no more than 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 feet |
4x6 (Southern pine or Douglas fir)
4x8 (Western red cedar, S-P-F, Hem-Fir, redwood, or Northern white cedar) |
| Up to 7 feet |
4x8 (all species listed above) |
| Up to 9 feet |
4x8 (Southern pine, Douglas fir, Western red cedar, S-P-F, or Hem-Fir)
4x10 (redwood, Northern white cedar) |
| Up to 11 feet |
4x8 (Southern pine or Douglas fir)
4x10 (Western red cedar, S-P-F, Hem-Fir, redwood or Northern white cedar) |
| Up to 12 feet |
4x10 (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 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
(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.
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
batter-boards as shown, then run taut strings from each end of the
ledger to the batter-boards to establish the sides of the deck.
Run a third string between the batter-boards to establish the
outside edge of the deck. Square the layout by measuring the opposite
diagonals, then adjusting the ledger-to-batter-board strings until both
measurements are equal. Take care to maintain the correct distance
between the strings.
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.
Mix concrete and pour the footings. To find the number of 90#
bags of ready-mixed concrete you'll need for each 12x12 footing, measure
the depth of the footing in inches and divide by 8. As you finish each
pour, set a pre-cast 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 2x6 diagonal cross braces and secure them with
1/2"x4-1/2" lag screws.
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 (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.
Install
blocking between the joists wherever required. 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. 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. 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
- Mason's Line
- Ready-mixed Concrete, Gravel
- Shovel
- Structural Connectors
- Adjustable Wrench
- Chalk Line
- 8d and 16d Galvanized Common/Box Nails
- Lumber for Posts, Ledger, Beams and Joists
- Railing Material
- Stain
- 6 mil. Black Polyethylene
- Plumb Bob
- 2x2s and 1x4s for Batter Boards
- Wheelbarrow
- Concrete Piers
- Lag Screws, Hex Bolts w/ Nuts and Washers
- Hammer
- Measuring Tape
- Screws
- Deck Boards
- Framing Square
- Brushes and Thinner
