Deck Framing
We recommend building decks with 2x10 lumber for joists and 2x10 or 2x12 for the ledger. 2x10 or 2x12 sized lumber or LVL is best for most residential decks.
Beams
Many standard deck sizes that measure between 10' and 15' out from the house can use a triple 2x10 flush beam. A flush beam has joist hangers on it that secure the joists to it. Decks that are 16' out from the house will usually need to have a drop beam that the joists rest on, and should be set back 12"-24" set back from the front of the deck
If you wish to have posts spaced more than 10 feet apart, an LVL may be your best option for a beam. If less than 10 feet is acceptable, it will be easier and less expensive to use 2x10 or 2x12 for a beam.
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Material
Typically, two or three layers of treated southern yellow pine 2x10, 2x12, or similarly sized LVLs are used, because they are strong enough to allow posts to be spaced 8-12 feet apart, depending on joist lengths. LVLs can span even further, if that's desired.
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Quantity
On a rectangular deck less than 20 feet wide, you'll order a board for each layer of the beam you need. If your beam is longer than 20, you can use multiple beam sections, but ALWAYS seamed over a post. If you're using a drop beam, you'll need 2 additional beam pieces for your front rim (to attach joist ends to) in addition to the drop beam boards.
Joists
Joists are the pieces of 2x10 framing that usually run straight away from the house, and directly support the deck boards. Most low-maintenance decking requires that the joists be spaced no more than 16" apart from each other.
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Material
We recommend treated 2x10 southern yellow pine joists for stiffness, which can span about 15 feet between supporting points like joist hangers or dropped beams. 2x8s can be used, but we recommend only using then when spanning 10 feet or less. If you'd like to use a flush beam and have a deck that's 16' out from the house, you can upsize to 2x12s. If your city allows it, you may be able to use 2x10s spaced 12" on center for clear spans longer than 15 feet.
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Quantity
Figuring out the number of joists spaces can usually be done by dividing the deck width (in inches) by 16, and and rounding up to the nearest number.
Once you know how many joist spaces there are, you can subtract 1 to get the number of field joists. If you want to have double joists on the ends for a more stable railing, add 4 to the joist number. If you only need a single joist on either rim, just add 2.
Decking
Deck boards are typically installed perpendicular to the deck joists. The length of the boards (12', 16', or 20') and optional border boards are chosen strategically to minimize how much decking is cut off and thrown away.
For example, a 16 foot wide deck should have 16 foot long boards and wouldn't need a border, and a 14 foot wide deck could use 12 foot long boards and have a double picture frame around the deck. Adding the double border on both side edges of the deck adds almost a foot of decking to either end, making the covered area wide enough to frame a deck that's just under 14' wide.
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Length
Since random-seaming composite decks is not recommended, you may need different board lengths, depending on your deck width and border choice. Since deck boards usually come in 12', 16', and 20' lengths, you should add the width of any borders, then round up the deck width to the nearest decking length, for each section. If your deck is over 20 feet wide, it may be wise to "split" the deck with a single mullion board for a clean seam, and treat each half like its own deck. For example, splitting a 24 foot wide deck into two 12 foot halves means you can use 12 foot boards.
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Quantity
Since most deck boards are 5-1/2" wide, and the gaps between boards is about 1/8", the intervals of each board will be (at most) 5-5/8". Take the dimension of the area you are covering (in inches), measuring in the same direction as the joists, and divide it by 5.625" and round up. This will get you the number of boards needed for that area.
If you have 192" from the house to the front of the deck, and divide that by 5.625, you get a number just over 34. Rounding up means that you'll have to trim one board to be less than full width, which you can cut and use against the house, with the cut edge against the wall. All your main boards will be full width, and the trimmed board's cut edge will be hidden next to the house and may tuck underneath the siding.
Railing
Most deck railing panels are available in 6' and 8' panels, and will be trimmed onsite to be equal lengths along each side. Horizontal cable railing may require different distances between posts, depending on the style, and the posts will have hole drilled depending on how the cable is running through the post.
Using a 13 foot straight run as an example, with panels available in 6' and 8' lengths, we'd first divide 13' by 8'. The result is 1.625, which means that two panels would cover the distance, but almost 3 feet of railing would be scrapped. If we try with 6' panels, just over 2 panels would be needed, which is less efficient since nearly 5 feet of railing material would be trimmed and thrown away. All things considered, 8 foot panels on this straight run would be most efficient.
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Transition Posts
To find the panel lengths needed, you will want to know what railing system you are using and the panel lengths that are available. Once you know that, add posts at every corner, top of stair (on the deck surface), bottom of stair (on the bottom step or landing), and next to the house wall. The remaining spaces will be your straight runs.
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Straight Runs
Take the length of the straight run (in inches), and divide it by the longest panel length (in inches), and round up the result to the nearest whole number. Subtract one from that number, and that will be the number of posts you'll need, spaced out evenly between the end posts. Once those posts are spaced evenly, you can count the spaces between them to get the number of panels. Dividing the length of the straight run by the number of spaces will get you the length for each panel. Round up to the nearest panel length available.
