Stairs, decks and fences
Deck board calculator: boards, screws and hidden clips
A deck surface is rows of boards across the joists. Count the rows, the boards per row and the joist crossings, and you have the boards and the fasteners to buy.
How many deck boards do I need?
Divide the deck's width across the boards by the board width plus the gap, and round up: that is the number of rows. Multiply the rows by the deck length divided by the board length, add waste, usually 10 percent, and round up.
Example. A deck 16 ft long, along the boards, and 12 ft wide. Boards 5 1/2 in wide with a 1/8 in gap: 144 ÷ 5.625 = 25.6, so 26 rows. With 16 ft boards that is 26 boards, or 29 with 10 percent waste. With 12 ft boards it is 26 × 16 ÷ 12 = 34.7, or 39 with waste.
Where do the joints go?
When the boards are shorter than the deck, every butt joint has to land on a joist, and the joints should be staggered from row to row. That is why shorter boards need more waste.
How many deck screws do I need?
Each board gets two screws where it crosses a joist. The joists run across the boards: a 16 ft deck with joists at 16 in on center has 192 ÷ 16 + 1 = 13 joists.
Example. 26 rows × 13 joists = 338 crossings, so 676 screws. Boxes are sold by count or by weight, so check the box.
Hidden clips instead of screws
A hidden fastening system uses about one clip per crossing, so 338 clips here. Some systems hold two boards with one clip; follow the maker's guide, and its gap.
What gap should deck boards have?
It depends on the material and how wet the wood is when you lay it. Composite and PVC boards come with a gap from the maker; wet treated lumber is often laid tight because it shrinks. Read the instructions for your boards.
Decking in Clad
Clad's decking tool takes the deck size, the board width, the gap, the board length, the joist spacing and the waste, and gives the rows, the boards to buy, the screws at two per crossing and the number of hidden clips. With a price per board it adds the cost to the job's shopping list, and the deck stairs for the same deck can go in the same job.