The deck can be considered a floor structure. It has joists to support the flooring material (decking), and posts and beams to hold the unit up off the ground, slightly elevated or higher.
Your deck design can be square, rectangular, multilevel or somewhat free-form. Plan and design the deck before buying any tools and materials. By doing so, you will eliminate many mistakes and save time and money throughout the project.
This is about building basics only. It does not address deck design in any detail. You probably can find deck design ideas in books at the library or at lumber yards.
You may need a building permit to construct a deck. Check with the building department authority in your neighborhood. The usual procedure is to submit a drawing of the proposed deck structure to the building inspector in the building department. Any changes to meet local codes and requirements will be indicated. If the plans are fine, you will be issued a building permit, usually for a fee. The permit may be time-limited, probably not to exceed 3, 6, 9 or 12 months.
The building inspector may visit your deck site during construction to check the foundation and structure. Keep in mind that the codes are to protect you. Another good idea is to let your neighbor know that you are building a deck. You may need the neighbors cooperation, especially if site access is needed by trucks.
Materials and Procedures
Most decks have certain building elements:
Concrete footings underground pads the piers sit on.
Concrete piers precast or poured foundation for posts.
Ledger two-by board attached to the house; supports ends of joists.
Posts vertical members that support beams.
Beams horizontal members that support joists.
Joists framing lumber that decking is attached to.
Rim (skirt) joists perimeter joists nailed across the ends of other joists.
Decking floor surface of deck.
As options, decks may also have railings, benches and stairs.
Wood used on decks should be rot-resistant. Pressure-treated lumber is a good choice for posts, beams and joists, while redwood, cedar or cypress are good choices for decking.
Footings and piers support the weight of the deck and are usually concrete (precast or poured in place).
Posts are typically 4x4s, but decks built very high off the ground (more than 8 feet) or which support unusually heavy loads may require 4x6 or 6x6 posts. When in doubt, check with an engineer or your building inspector. For sizing your beams, refer to the beam and span tables.
Installing the Ledger
When a deck is attached to the side of a house, one end of the deck joists is supported by a level pressure-treated, ledger board bolted to the house frame or foundation.
The ledger is usually the same size and material as the deck joists, and is attached to the house so that the top of the finished decking is 1 inch to 2 inches below the interior floor level. This helps to keep rain, snow and debris out of the house. Flashing protects the ledger and keeps water away from the side of the house.
Attaching the ledger early in the deck building process establishes the elevation of the deck, as well as its length and relationship to the house.
Laying out your deck on site is nothing more than outlining the size and shape of your deck on the ground using batter boards and string. Layout allows you to align and square the deck with the house and establish the locations of all foundation piers.
1) At each corner, stake out pairs of batter boards at right angles to each other, roughly 2 feet outside the actual dimensions of the deck. Batter boards are short 1x4s attached to 1x2 stakes. It is helpful for all batter boards to be at about the same elevation so that intersecting strings almost touch.
2) Attach string representing the outside of the deck and secure to nails on the top of the batter boards.
3) Check the corners (where the strings intersect) for square, and make sure the outer string is parallel with the ledger board (house). Take you time with the layout. It will be used to determine all other deck dimensions as you proceed. Measure often and keep moving the strings until you get it right. On sloped sites, remember to keep your tape measure level.
4) Establish the pier (post locations. Most posts are set back from the leading edge (and sometimes the side) of the deck by 12 to 24 inches. Measure the setback from the outside sting and pull another string representing the center of a row of piers. Attach the string to the batter boards. Add intermediate batter boards and strings for decks requiring more than one row or piers (posts).
5) Along the inner string, measure out the center-to-center spacing for each pier. Mark this on the string.
6) Drop a plumb bob from each mark to locate pier centers on the ground. Identify each center with a small stake.
7) Make sure no pier locations conflict with underground utilities. If so move, the pier(s) or have the utility moved.
8) The size of footings and number of piers (posts) is determined by soil conditions, the size of the deck, its expected load and the allowable span of beams and joists. Generally, for most deck, piers are placed on 5-foot to 8-foot center. If there will be heavy loads on the deck, have the inspector or engineer okay your plans.
Concrete Footings and Piers
The building codes in your community will often be very specific about the size and depth of footings and piers. However, here are several rules of thumb:
If possible, footings should be placed on undisturbed soil or rock. Compact any loose soil by tamping firmly with the end of a post or board.
Footings must extend below the frost line in your area (as much as 48 inches in the coldest parts of the country). Low-level decks can be supported by concrete blocks or precast pads/piers placed on compacted soil. However, this kind of foundation is prone to settling.
Footings usually are precast or poured concrete in square or circular shapes. Footings poured in good soil and supporting normal deck loads are typically 12 to 16 inches wide and 6 to 8 inches thick.
Piers sit on the footings, and may be precast or poured in place. In warmer climates (where the frost line is shallow), precast piers with attached metal post bases may be appropriate.
Piers are sized according to deck loads and the size of the posts they support. Typically, an 8-inch diameter form is sufficient for a 4x4 post.
Its a good idea to extend piers 2 inches to 6 inches above ground (grade level to protect posts ends.
Pouring Footings and Piers
Here are the procedures to follow for pouring footings and piers in place.
9) Temporarily remove layout strings.
10) Dig holes the diameter of your footing, and deep enough to exceed your local frost line. An auger of clamshell type posthole digger can be used to dig the holes; however, if you have a lot of holes to dig, consider contracting the job.
11) Remove any loose soil in the hole, and compact the bottom using a 2x4.
12) Cut, position and suspend pier forms 6 inches to 8 inches (footing thickness) above bottom of hole. The top of the form should extend a few inches above ground level. The form is held in place by nailing the top of the form to staked 2x4s spanning the hole. Forms may be made on site out of two-by material, but the easiest from material to use is tubular fiberboard (commonly known by the brand name Sonotube). It comes in 12-foot lengths and different diameters. An 8-inch diameter tube is commonly used for 4x4 posts.
13) Replace layout strings and use a plumb bob to check position of forms. Adjust if necessary.
14) Fill forms with concrete. The concrete will escape from the bottom of the form to create the footing, and it will fill the pier tube.
15) Insert reinforcing rod (rebar) into the tubes. Depending on local codes you may need one or more lengths. Make sure the rebar is embedded well below the surface of the concrete.
16) After concrete has set up a bit, smooth the top and insert a metal post anchor. Make sure the anchor is centered and level.
Setting Posts and Beams
Pressure-treated posts and beams are the aboveground foundation for the joists and decking. If they are installed straight, plumb and level the framing and decking should go smoothly. The following guidelines are for beams that are supported on top of posts
1) Temporarily place long, uncut posts on top of piers. Plumb and brace them.
2) Transfer the elevation of the (top of the) ledger board to the two outside posts. You can do this using a water level, line level, builders level or straight board with a 4-foot level on top.
3) From the marks on the posts, measure down the width of the ledger plus the width of the beam. That is the height the posts need to be (assuming ledger and joists are the same width, and that the joists are hung off the ledger with joist hangers).
4) Connect the lower lines on the two posts with a tight string. Mark the intermediate posts.
5) Number each post. Remove, cut, plumb and reinstall posts in their correct locations. Brace posts with scrap lumber.
6) Repeat process for any intermediate rows of posts.
7) Position and toenail beams over tops of posts. Make sure to place beams with the crowns up (the weight of the deck will tend to straighten them). Butt joints should be centered over posts and the outer ends of the beams should run long (uncut).
8) Reattach outside batter board strings (defining outside dimensions of deck). Plumb up from strings to ends of beams and mark.
9) Cut beams to length. Permanently attach posts to beams with galvanized metal connectors. Codes often require diagonal post-to-beam bracing if your deck stands high off the ground.
When a deck is attached to a house, the ledger supports one end of the joists; the other end is supported by a row (or rows) of beams. Joists must be big enough to accommodate your designed spacing and span. The most common sizes are 2x6, 2x8 and 2x10.
1) Lay out joist locations on ledger and beams. Measure and mark the correct spacing (usually 16-inch or 24-inch centers). The last two joists will often be spaced close to each other.
2) Attach joist hangers to the ledger, using galvanized hanger nails.
3) Install joists, making sure crowns are up. Insert one end tightly into joist hangers and position the other end on the beam layout. Leave joist ends long for now.
4) Toenail joists to beams with 16d galvanized nails (or use metal connectors). Nail joists to hangers with galvanized hanger nails.
5) Snap a chalk line to mark all joists for length. Cut with a circular saw.
6) Nail rim joist across ends of joists. Some codes require the use of blocking, crossbracing or bridging.
Once the framing is in position, the decking goes down. Decking boards are usually 2x4s or 2x6s (or a mix of both) and are most commonly nailed off perpendicular to the joists or diagonally.
1) Start decking at the house, leaving a ½-inch gap between the siding and the board. Make sure your first row of boards is straight, all other rows will key off of it. It is common for the ends of the deck boards to overhand the deck framing by 1 inch. Cut the ends of the first row to their exact length, but leave the ends of all other rows long.
2) Attach boards with either galvanized screws or 12d galvanized decking nails (they have a special screw shank for extra holding power). Center butt joints over joists. It may be necessary to drill pilot holes at the ends of boards to prevent splitting.
3) Separate deck boards to allow for expansion and contraction; if heavy and wet, separate boards no more than 1/16 inch as some shrinkage will occur; if light and dry, separate boards no more than 1/8 inch. Use a chisel or flat bar to pry crooked boards into line.
4) If you find rows of deck boards becoming skewed (not exactly parallel), dont try to correct the entire problem in one row. Adjust gradually over two or three courses. To be accurate, always check dimensions measuring from the first board.
5) When you are about 6 feet from finishing, check your layout. You want your last board to overhang the rim joists about 1 inch.