How to Calculate Material Decking on a Diagonal

Written by tom raley
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Building a deck can enhance the look as well as the feel of your home. These outdoor living spaces have evolved from a plain wooden platform to intricately designed multilevel decks. While you may not be designing a deck of this magnitude, simply installing the deck planking on a diagonal pattern can give the deck an entirely new feel and appearance. This new look will, however, raise your material cost.

Skill level:
Moderately Easy

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Things you need

  • Tape measure
  • Pad and pencil

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  1. 1

    Draw out your deck design, including all posts, stairs, railings and floor joists. In order to get a material list for everything except the deck planking, take a physical count from your drawing. This will give you the exact number needed. On most items, you will want to add 5 per cent to allow for damages or mistakes (waste). For items such as your concrete post supports, you can purchase the exact amount needed.

  2. 2

    Take a very careful measurement of your deck. For this example, we will say the planned deck will be 16 feet by 14 feet. Calculate the exact number of boards it will take to cover this area. If you intend to cover the deck with 2 inch by 6 inch boards, you will add the width of the board plus the width of any opening you plan to leave between the boards. You must note that a 2" by 6" is not actually 6 inches wide; it is actually 5 1/2 inches wide. If you plan to leave a half-inch gap between boards, this would mean three boards would cover 18 inches.

  3. 3

    Calculate the total wood needed to cover the deck. In our example, the deck is 16 feet by 14 feet. To calculate our total material need, we will assume we are to purchase 2 inch by 6 inch by 14 foot boards. We will need enough to cover 16 feet of deck. Multiple the width of the deck by 12 inches (168), then divide this by 18 (amount of space covered by three boards plus spacing) and you have 9.33. Since each of these 9.33 units contains three boards, you will multiple the 9.33 times 3 to get 27.99 14-foot boards to cover the deck. Round this up by 5 per cent for waste, and you need approximately 30 boards.

  4. 4

    Perform your final calculation to determine your material needs. Building a deck with a diagonal pattern will increase the amount of waste due to trimming. Most contractors estimate a diagonal deck pattern requires 15 per cent more wood than a standard pattern. Take your total need of 30 boards and increase it by 15 per cent (30 x 1.15) to determine your total material need. Your total is 34.5 boards, which you will always round up to the next highest number; in this case, 35. This is the approximate amount of decking you will need to cover a 16 foot by 14 foot deck in a diagonal pattern.

Tips and warnings

  • When deciding on the size gap to leave between the boards, remember you will have some wood shrinkage, which will increase the gap size over time.

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