Specific material requirements for deck construction vary according to the deck's design and local building codes. For example, building a freestanding 12-by-16 deck requires different materials than building a deck attached to an existing structure. Despite project-specific differences, conventional deck structures share several features, including foundations, framing, decking and railing. If you learn about common deck features and the coverage rates of typical deck construction materials, you can develop a materials list that suits your unique circumstances.
Nearly any type of foundation system is suitable for a 12-by-16 deck. Common choices include poured concrete footings, concrete tubular form footings and prefabricated concrete pier footings. If you're using poured footings or tubular forms, you must determine the required footing depth before calculating the concrete requirements. In cold climates, footings must extend beyond the frost line, which is often more than 4 feet deep. In warm climates, piers may rest directly on grade. Since you'll need a footing for each post, you must determine the allowable post spacing before calculating the foundation material requirements. The post spacing depends on the allowable span of the beams or girders that support your deck joists. Larger beams or girders can stretch for greater spans. Consult your local building authority for information regarding footing depth and beam span.
Posts, beams and joists are the basic framing materials for conventional wood decks. The dimensions of framing lumber vary according to the loads that the lumber will support and the requirements of local building codes. In general, 4-by-4 lumber is the minimum acceptable size for posts and 2-by-6 is the minimum acceptable size for girders and joists. Note that you may laminate several 2-by-6 beams to create a stronger girder with longer allowable spans. The spacing between joists, and therefore the required amount of joist lumber, varies according to the species of the decking lumber you use. Stronger decking species allow 24-inch joist spacing, weaker species usually require 16-inch spacing. Note that many codes require rot-resistant lumber species or preservative-treated wood for framing materials that sit near ground level.
The term "decking" refers to a deck's exposed floor surface or planks. Deck planking material requirements vary according to the size of the decking that you're using and the orientation of the planks. Planking installs perpendicular relative to joists. Therefore, you might need planks that run across the 12-foot dimension of the deck or planks that run across the 16-foot dimension of the deck. Both 12- and 16-foot boards are readily available, so it's possible to cover the deck's length with a single plank. Once you determine the length, you must select the width. Most builders use 2-by-4 or 2-by-6 decking. Keep in mind that decking width affects the spacing between floor joists.
Estimating Deck Planks
With the lumber size chosen, you can determine the total number of planks by dividing the width of a single plank by the distance that the planks must cover. For example, if you're laying the planks parallel to the 12-by-16 deck's 12-foot dimension, divide the width of a single plank by 16 feet. If you're laying them parallel to the 16-foot dimension, divide the width of a single plank by 12 feet. Remember to subtract the drainage space between planks from the result; a common spacing is 1/8 inch. Also, it's a good idea to add several planks to your final figure. Extra lumber allows you to fix mistakes without running back to the lumberyard.
Railing and Finish Materials
Railing and finish materials vary according to the deck design. Conventional decks use 4-by-4 posts, 2-by-4 rails and 2-by-2 balusters. Typical spacing between railing posts is 6 feet. While naturally hardy species -- such as redwood and cedar -- don't require finishing, pine and fir benefit from waterproofing, painting or staining. You can calculate the finish coverage according to product-specific coverage guidelines; the coverage area of a 12-by-16 foot deck is 192 square feet.
Fasteners, Brackets and Sundries
Your materials list also includes fasteners, such as corrosion-resistant nails or screws. Joining posts to footings, beams to posts, and joists to beams often requires construction connectors, such as post caps and joist hangers; calculate the amounts according to your deck frame's design. Common sundries include finishing supplies, such as paint trays and brushes.