The first consideration in deck building design is always how you plan to use it. If all you want is a place for sunbathing and small family gatherings, a small deck may suit your needs. However, if you plan to entertain large groups of people, you’ll need a deck the size of a large room.
Cost is always a consideration in deck building. One option is to build a deck in modules, adding on as you can afford to do so. You can save a lot of money if you build it yourself. It is almost always better to hire a professional contractor if you can afford it.
The least expensive deck is a single platform at ground level with simple safety railings. As you make the deck more complicated — adding more than one level or elevating the deck to a second-story entrance, for example — the cost will increase.
The type of material you use to build the deck is an important factor in its cost. The cheapest material used is pressure-treated pine. (Don’t be fooled into using cheap untreated pine for a low or ground-level deck –in less than five years you’ll have to replace the rotted deck.) Cedar, redwood and cypress are also used, but they cost more than pressure-treated pine.
Foundations are Key in Deck Building
A good deck begins with a good foundation. Posts must be anchored in the ground by burying them in concrete or attaching them to concrete piers. In some localities, pier blocks are accepted, but in many areas the posts or piers must extend several feet into the ground or at least 6 in. below the frost line.
Equally important is the fungal and insect resistance of the foundation. Decks that sit low to the ground and are surrounded by plants tend to be damp, and untreated posts, beams and joists are subject to rot. Even decks that are built on pier blocks are not safe from insects. Termites can travel through tiny cracks in the pier blocks and into the structure of the deck. Deck infestation can lead to an infestation in the home.
No matter what wood you choose for the decking, all posts, beams and joists should be made of pressure-treated wood. Ensure that it is rated for in-ground use and is stamped by an approved inspection agency or tagged with the manufacturer’s warranty. You can use cedar, redwood or stained pressure-treated pine for the decking and other above-ground parts.
Always submit your deck plan to your municipal planning or codes office for approval. Most cities require a building permit, and some deck-building codes are very strict.
The Deck Structure
Posts support the joists and beams throughout most of the deck area, but the ends of the joists near the house are typically attached to a ledger with joist hangers. Ledgers are attached to the foundation or rim joist of the house. If the deck is at the same level as the house siding the siding and ledger (if used) must be flashed, and clearance must be maintained between the siding the header joist and the decking for water drainage. See your local municipal engineer for approved methods.
When adding a deck to a home with a stone foundation where it’s not possible or desirable to attach a ledger to the house rim joist, you can place posts near the foundation to support the deck. Leave a 1-in.-wide space between the ends of the deck boards and the side of the house for water drainage.
Beams are attached to the sides of the posts with carriage bolts or lag screws. Joists may be placed on top of the beams or between them. If they’re placed on top, toenail the joists to the beams and fasten them to the ledger and timber joists with joist hangers or other framing fasteners. Use joist hangers to attach joists between the beams. When the joist length exceeds 8 ft., install blocking at 4-ft. intervals.
The distance between the beams (joist span) determines the load rating for decks. Spans vary for different species of wood and depend on the size and spacing of the joists, Most codes limit the maximum spacing of joists to 24 in, when they’re supporting 2x or radius-edge decking (see table, right). To keep radius-edge decking from feeling springy and when running deck boards at an angle, use 16-in. joist spacing. At one time, decks were required to support a 60-pound-per-square-foot live load and a 10-psf dead load. Today most municipalities have lowered the requirement to a 40-psf live load, which is the same as the requirement for private dwellings.
Deck Building Choices
The most commonly used lumber for decking is 2×4, 2×6 and 5/4×6 (radius-edge) boards. You can lay deck boards in patterns to create interest, or you can alternate 2×4 and 2×6 boards. On multilevel decks, making pattern changes at each level alerts people to the change of levels.
Be selective in choosing decking — the better it is, the longer it will last. Cracks and knots absorb water, and freeze-and-thaw cycles can quickly destroy a low-grade board.
When laying deck boards, proper orientation of the bark side is necessary to minimize cupping. If a board has a vertical grain, cupping is not a factor. But if it has a horizontal gain, you need to orient it so it will cup down rather than up. If the boards are dry, install them with the bark side up. When the boards get wet, the bark side of the board will expand more than the pith side, and the boards will cup toward the pith side. If the boards are wet, as many pressure-treated boards are, they should be installed with the bark side down. When these boards dry, they wi11 cup toward the bark side.
Moisture content also determines how much space you should have between the boards. If the boards are dry (with a moisture content of 19 percent or less), they should be installed with 1/8- to 1/4-in. spacing for water drainage. If the boards are wet, butt them together. They’ll shrink and form spaces as they dry.
Deck boards can be installed with nails or screws. As the boards shrink and swell with changes in moisture content, smooth-shank nails invariably pop out of the boards, so ring-shank nails are a better choice. However, screws are the best fasteners. They won’t pop, and they’re easier to remove if a board needs to be replaced. Use plated or stainless steel deck screws to prevent rust stains.
To avoid splitting the ends of the boards when driving fasteners, drill 1/8-in. clearance holes. When using dry pressure-treated pine, it’s a good idea to drill clearance holes at the intervening nail/screw locations as well.
Steps and Stairs
Deck stairs can be more expansive and have gentler rises and broader treads than indoor stairways. Codes usually require that stairs be at least 36 in. wide. You can buy precut stringers, which makes stair building easy. If you’re making your own stringers, use 2x10s or 2x12s.
The standard stairway has a 7-in. rise and an 11-in. tread. To lay out a standard stairway, determine the total rise from the ground to the top of the decking. Divide the total rise by 7 to determine the number of risers (round to the nearest whole number). Then divide the total rise by the number of risers to determine the exact unit rise. To figure the total run, multiply the trait run (11 in.) by the number of treads (one less than the number of risers).
To lay out the treads on the stringer, mark the rise on the tongue of your flaming square and mark the run on the blade. Beginning at the bottom of the stringer, position the square so the marks are flush with the edge of the stringer and mark the rise and run with a pencil.
Stairs with more than three risers require handrails at a height of 30 to 38 in. above the nosing (overhang) of the treads.
Deck Railings
Decks that are more than 30 in. above the ground at the edge of the deck require a 36-in.-tall guardrail. The guardrail can be incorporated into a bench or seat. Generally, codes require that ornamental closures be designed so that a 6-in.-dia. or larger object cannot pass through. The horizontal spacing between vertical members (balusters) should be 3-1/2 in. or less. Attach railings with screws rather than nails.
Finishing the Deck
Unpainted wood that is left outside will weather to a gray hue. This indicates degradation of the wood caused primarily by exposure to ultraviolet light. Decks should be protected with a stain or clear finish that contains a UV inhibitor and mildewcide. For the best protection, apply water-base finishes annually; reapply oil-base finishes every two years.
