**Structural Design of your Deck**Now that you have the conceptual design for your deck, you need to develop the structural elements and material specifications for the project. This is a great exercise to help you get an understanding of the details of your deck regardless if you will be building the deck yourself or hiring a contractor for the job. The specifications that you decide on will be a part of the Construction Document you will either take to the building department for a permit, use to get bids on the project or use to build the deck yourself. Some special conditions that you will have to account for are steep slopes, unstable soil and specific building codes.

**Structural Design of your Deck**You will need to refer to your conceptual plan when estimating the materials that you need for your project. You will need to account for the materials used for the structure, for the finishing materials such as decking and stairs, and finally for the hardware and fasteners you will need.

**Create Dec Specs Form**Create a list and fill in the blanks on the Deck Specs form, which will give you the basis for completing your material list. Use the measurements from the conceptual plan created in the previous tutorial. The following steps will help you fill in the quantities for each item. When this list is complete, you will be able to set a budget for your deck project by getting an estimate from the lumberyard or putting the project out to bid.

**Estimate the Ledger**First, estimate the ledger. From your plans, estimate how many feet of wall will support the deck, and add 10% for waste. Note that you should always add a “waste factor,” of at least 10%.

**Estimate the Concrete**Estimate the amount of concrete you need. This project calls for concrete pads measuring eighteen inches by eighteen inches by twelve inches deep. That equals 2.25 cubic feet per pad, times the number of pads to figure the total cubic feet. Verify the standard in your area, as many areas, especially in colder climates, require deeper pads, and you will therefore need a lot more concrete. The goal is to have concrete pads that extend below the frost line, which could be as deep as forty-two inched. For each set of stairs add two cubic feet to support the bottom of the stairs; and don’t forget to add 10% for waste.

**Estimate the Concrete Piers**Estimate the concrete piers you need. Simply count the number of concrete pads; you will need a concrete pier for each pad, which are available from various home improvement centers.

**Estimate the Posts**Estimate posts you will need. You will need posts if your deck is over eighteen inches above the ground, as the piers will not rise above this level. Count the number of concrete pads and multiply that number by the average height of the deck above the ground.

**Estimate the Girders**Estimate the girders you will need. Girders are typically 4x6's and “run" the same direction as the deck boards. The plan calls for girders spaced six feet eight inches apart and supported by piers every six feet, but check the applicable span tables for your locality. Girders should be supported on three piers where possible—and therefore the minimum desirable length is twelve feet. Because the piers are six feet apart, the best girder lengths are multiples of six, and the longest manageable length will be eighteen feet.

**Estimate the Joists**Next estimate your joists. Joists are spaced sixteen inch on center and will run perpendicular to the girders and deck boards. To figure the number of joists, convert the length of the deck to inches, divide by sixteen, and round up. Add one to that to figure, which is the total number of joists, as you need one on each end. Multiply this number by the deck width (twenty feet) to estimate the total linear feet of 2x6 joists, and don’t forget your 10% waste factor.

**Estimate the Deck Boards**Now estimate the deck boards you will need. Our estimation uses 2 x 6 decking, and a 2 x 6 is usually 5 ½ inches instead of 6 as the name implies. So a linear foot of 2x6 will cover .46 square feet. Measure the complete area of your deck and divide it by 0.46. If you are using a wider or narrower deck material, divide the total area by the area of one linear foot of decking.

**Estimate the Stair Material**Now estimate the stair material you will need. This deck is thirty inches above the ground and has one set of stairs thirty-six inches wide. To figure the actual number of steps, measure the height of your deck from the ground, and divide by six inches, and account that the top step will be the deck itself. To figure out the stringer length, multiply the number of steps by sixteen inches for each stringer. Stairs up to thirty-six inches wide have two stringers, and stairs over thirty-six inches have three stringers. Steps typically have two 2x6's (the same as the deck), times the width of the stairs.

**Estimate the Ralings**Estimate the material you will need for the railings. There are three parts of the railing, the posts, the top and bottom rail and the balusters. You need to measure the open sides of the deck and add the stair rail. The stair rail length will be based on the stair stringer length from the previous step. Calculate one eight foot 4x4 (post) for each six feet of rail, two feet of 2x4 (top and bottom rail) for each one foot of rail and 2.2 1x2 (baluster) for each foot of rail.

**Estimate the Hardware**You also need hardware and fasteners to put together and finish your deck. You will need galvanized nails, metal connectors and bolts to connect your deck parts. Figure one pound of 16d galvanized nails for every ten square feet of deck. Each joist will require two joist hangars. Each post should have a post cap to connect it to the girder it supports; and count on one pound of galvanized nails for each ten metal connectors. Allow one bolt per foot of ledger, and be sure to measure the length necessary to "run" the bolt through the wall framing and install a nut and washer on the other side.