Good design. in the case of decks. means that all the different parts—foundation. framework, and deck surface—work together in a structure that has the appearance you want and the sturdiness you need Arriving at this goal requires that you coordinate the structural elements (See sketch below) SO that the finished product suits your tastes and budget and meets local building requirements
After you settle on a location for the deck and the materials you expect to use in its construction, concentrate first on the topside features. Such as the surface, steps. railings, and other elements that stand out visually Ther design (or have a professional design) the supporting substructure and foundation
The following pages are your Introduction to the specifications and techniques necessary to design a wood deck As you work, you may wish to refer to the chapter “Building Your Deck for help in drawing parts of your deck in detail
The simplest and most economical decks to build are those with squared-off sides Curved decks are possible. though they usually require more complex support systems. Multilevel decks connected by steps, stairs. or ramps require more work than sTrule-leve’ decks.
Structural view of a deck
Tips for drawing plans
To draw deck plans you need graph paper with 8 squares to the inch, plus a ruler, a couple of medium pencils, and an eraser To determine dimensions and grade levels on the construction site, you also need a tape measure (a 50-foot tape Is most convenient). a carpenter’s level or line level, mason’s twine, and a Supply of 1 by 2 or 2 by 2 stakes, each about 18 inches long and pointed at one end Use your scale drawing as a reference
Plan & elevation views
A deck’s basic surface pattern and substructure should be drawn in plan views (seen from above looking straight down) Arrangement of the substructure, railings. and other vertical members should be drawn in elevation views (Seen Straight-on from one side) Attachments and other details should be drawn from the view that most Clearly shows their construction
Drawing to scale
The scale of a drawing is the number of inches or feet represented by each square on the graph paper Generally. the more squares used to represent 1 foot or I inch ot actual deck dimensions. the more precise and useful your plans will be
A scale in which 6 Squares equal 1 tOOt (6 1 ) works well for deck surfacing patterns and general arrangements of foists. beams and posts In the 6 1 scale. 1 square equals 2 inches. However, a scale larger than 6′.1 should be used for details of railings, benches, and other relatively small features. For these. the easiest scale to work with is 1 square equaling 1 inch. Tape several sheets of graph paper together if you need a larger drawing area than one sheet
Designing the deck surface
Because deck-surfacing materials such as tile and concrete are best laid with the aid of a professional, and because the installation of other materials may vary with each manufacturer, design suggestions given here deal only with wooden decking materials
Patterns for dimension lumber
As the drawing below indicates. you can lay decking lumber perpendicular or diagonal to the foists (or to beams. If icxsts are not used). or in several variations. as long as you provide support under each end of each piece Generally speaking, the more complex the deck pattern, the more complicated the substructure must be.
You will eliminate unnecessary waste and on-site cutting if you design your deck so that it can be surfaced with lumber in readily available standard lengths of 8. 12 16, 20 (redwood’s maximum length). or 24 feet. Decking lumber should be spaced slightly to allow for drainage, ventilation and expansion and contraction of the wood Commonest spacing is 3’10 inch. Narrower spacings between lumber tend to trap decaying leaves and other litter that can be troublesome to extract Wider spacing allows small items such as utensils to slip through the deck, high heels to catch between planks
Standard parallel patterns. The simplest. soundest. and most economical decking patterns are those made of 2 by 4 or 2 by 6 lumber laid parallel and spaced. running the full length or width of the deck Whether the decking runs across the length or width depends on the deck’s substructure, decking should be laid perpendicular to foists (or to beams. ii the design does not call for ioists) For example. when a deck attached to a house uses a ledger attached lo a wall as a suppon for joists. the joists run perpendicular to that wall. so the decking must be parallel or diagonal to the wall regardless of dimension. On the other hand, low-level decks without lasts usually have beams running the deck’s long axis, the decking then lies at right angles to the beams. across the deck’s width Varying lumber widths. The simplest variations of parallel deck patterns make use of Iwo or more different widthsof 2-inch dimenson lumber Many combinations are possible, several are illustrated below.
Eight Designs For Surface Design
Parallel Deck Patterns
“On-edge” patterns are created when 2 by 3s or 2 by 4s are laid on their sides (on edge), usually directly on beams On-edge decking is expensive and heavy but can span long distances between supports—an advantage if you want to eliminate the clutter of joists in a high-level deck. or if you want to keep a Simple substructure under a low-level deck.
Diagonal decking. If you intend to lay dimension lumber diagonally over the substgfcture, design the beams Or psts closer than normal, because a plank laid diagonally must span a greater distance than the same board laid perpendicular to its support Board ends can be trimmed to a complementary angle to make them flush with the house wail
Checkerboard patterns. TO create a checkerboard effect, divide the total deck area into equal squares and then surface the squares n alternating directions
The deck must be rectangular or square and the checkerboard modules at least 3 feet but not more than 4 feet square Multiples of four are simplest to work with However, if your deck dimensions are in odd feet or feet plus inches —for example, 11 feet 7 inches by 19 feet 3 inches—convert the dimensions to inches and divide into equal squares Keep in mind that support spacings also must correspond evenly to the squares dimensions. blocking between joists or beams will be necessary for support under every end of every piece of surface lumber
Sul:glowing To design either a tongue-andgroove or plywood Sublloor for a deck surfaced with rubberized coatings, ceramic or clay tiles, Or vinyl. sandwich a layer of overlapped building paper (15-pound asphalt felt) between two wood surfaces. as the illustration below indicates. And II you use boards, run the top boards either at right or 45° angles to the lower ones If using mortar or concrete. plan to add another layer of builder’s paper or polyethylene sheeting over the top layer of wood.
Tongue–&–grooye subfloors. Tongue-and-groove boards are laid like dimension lumber but without the spacing. Decks with these boards should be designed with a slight slope to allow adequate drainage and you should plan to seal the lumber with a waterproof coaling.
Plywood subfloors. Two considerations are important when designing with plywood as a deck subfloor. First, be certain that the plywood is thick enough to span
spaces between joists or beams without bowing. The usual choice is 3/4 -inch. though thicker plywood with T&G edges Can eliminate the need for joists. Second. make sure that all square edges are supported either by a beam, a joist, or blocking between beams or lasts Blocking may be omitted when plywood is milled with T&G edges
Designing the substructure
With your deck surface drawn in p;an view. you are ready to design the decks supporting framework. In the tables that follow are specifications for different arrangements of the substructure’s joists. beams, and posts
Deck loads & heights
Building codes in many areas require a substructure to be strong enough to support 40 pounds of “live’ load per square foot. plus 10 pounds of “dead” weight The tables and other design information are based on this “40 plus 10 p s loading at deck heights up to 12 feet Decks higher than 12 feet above grade (even at only one post), or decks that must bear heavy snow loads or large planters may require cross bracing and stronger posts – designs best left to a structural engineer or other professional.
Allowable spans & spacings
A span is the distance deck planks, lasts, or beams must bridge. spacing is the distance between pst and lost, beam and beam, or post and post (see illustration on next page) Both are critically important to proper substructure design. because they determine the ultimate strength or weakness of the support system A deck with joists SpaCed too far apart will simply sag beneath your weight and feel oddly elastic underfoot The maximum safe spans and spacings for lumber of different dimensions depend on the wood species and grade you plan to use in the deck’s construction
How to use the tables
Use the five tables that follow to find the proper sizes. spans. spacings. and heights for the substructure elements As you work through them, you II find that you can create a number of equally effective joist-beampost combinations. some more economical and attractive than others. Before you settle on one design, compare its cost and appearance against several other possibilities—and be sure the size lumber you want is available.
Also keep these points in mind
- These tables are developed from the Uniform Building Code (UBC) and other sources that may not meet all local code require. ments Use them for planning and design, but also check with your building department
- All beam and post dimensions are for sawed lumber. such as a 4 by 6 that measures 31/2 by 5• inches after surfacing You cannot build an equally strong beam by sandwiching two 2 by 6s. because they measure only 3 (2 times 11/2 inches) by 51/2 inches
- As you work out spans. spec-wigs, and post heights. remember that those given in the tables are maximum limits. You can always choose shorter spans, closer spacings. or larger joists. beams, and posts
Table 1: Strength groupings of common softwoods. Start your design with Table 1 to Lnd the strength grouping of the wood species you plan to use in construction These groupings include lumber
species graded No 1 or better and are based on each species’ bending strength, stiffness. and ability to withstand compression (You may find it more economical to use different spec es of lumber for different parts of the deck, for example. if you’ve decided on redwood for the surface, you may want to use Douglas f it for the substructure )
Table 2: Choosing decking spans. Next, using information from Table 1, workout the maximum spacing you can use between joists. or between beams if your design eliminates joists.
Spacing between joists and beams depends on the maximum allowable span for your choice of decking You have the option of designing a deck without lasts by using more beams (useful if you want a low, ground-hugging deck or an uncluttered substructure). though more beams mean more posts and piers. Compare costs before you decide
Table 3: Maximum joist spans& spacings. Next. use the information you ve gathered from Tables 1 and 210 determine the correct Size and length of pests for the spacings determined in Table 2
Table 4: Beam sizes & spans. The psi length from Table 3 or decking span from Table2 determines spacing between the beams. The choices you have in beam spacing may be limited by the lumber sizes available
Table 5: Minimum post sizes. To determine the post size from
Table 5. you need to know the strength group of wood for the posts (Table 1). the beam spacing (Table 4). and the post spacing. (The post spacing s identical to the beam span established in Table 4 ) Multiply the beam spacing (in feet) by the post spacing (in feet) to determine the load area that each post supports Then, from Table 5. select a post size that meets your height requirements
If you have a choice, choose a post with the same thickness as the beam—et will simplify construction.
Keep in mind that. despite the inherent strength in a deck s basic members. bracing is normally used to provide lateral stability and to help distribute loads evenly See page 79 for information on bracing for joists (bridging) and for posts.