How to Lay Out Material for Decking

Lay out the decking material for a balanced, consistent installation.

Decking materials consist of parallel boards that run perpendicular to the joists. Laying out the decking material for installation includes measuring and calculating the widths of the first and last boards. After that, installation becomes a simple process of laying down the boards, keeping the gap between them consistent and screwing the boards to the joists. Some decks require an additional step to lay out and cut around railing posts.

Things You'll Need

• Tape measure
• Chalk line
• Framing square

Instructions

Decking Material Layout Calculations

1. Measure the deck frame parallel to the joists from one side of the deck to the other with the tape measure. This is the depth of the deck. Add the amount the deck boards will overhang the deck framing for the total deck depth. If they will overhang on both the front and the back, include an overhang amount for both. A typical overhang is 1 to 1 1/2 inches.

2. Lay 10 deck boards on the frame perpendicular to the joists with the edge of one board touching the next. Measure the combined width of the boards and divide by 10 for the average deck board width. Add 1/8 inch to the average width to include the spacing between boards for the total deck board width.

3. Divide the total depth of the deck by the total deck board width. Record the fractional amount for use in the next step. Round the result up to the next whole number. This is the number of boards required to cover the entire deck from front to back.

4. Multiply fractional amounts less than or equal to 0.5 by the board width. Add the result to the board width and divide by two. This gives the width of the first and last boards.

   Multiply fractional amounts greater than 0.5 by the board width. This is the width of the first board.

   Note that the board width is 1/8 inch less than the total board width.

Decking Installation Layout

1. Measure from the ledger board along the rim joist the width of the first board, but subtract the overhang amount, if any, from the measurement and mark the rim joist. Repeat this for the opposite side of the deck. The rim joists are the first and last joists on the outside of the deck.

2. Hold the chalk line on both marks and stretch it tight. Lift the line with one hand about 10 inches while keeping it taut and on the marks. Let go of the line so it snaps down onto the joists, leaving a chalked line across all the joists. This is the layout line for the first board. Align the board with this chalk line when you install it.

3. Allow the ends of the deck boards to overhang the rim joists during installation by 2 to 3 inches. Measure the overhang distance from the rim joist on each side and make a mark at the front and back of the deck on the deck boards. Snap a chalk line across the boards the using the two marks at the front and the back. This line is a cutting guide to cut all the board ends even. Do this on both sides of the deck.

4. Lay a deck board on the joists with the ends extending past the rim joists and the edge of the board against the railing posts. Place the framing square against the side of the post and across the deck board. Draw a line across the deck board on both sides of the post using the square as a guide.

5. Measure from the railing post to the previous deck board and subtract 1/8 inch. This is the cutout depth for the deck board just marked. Measure along the two lines on the deck board and mark the cutout depth on both lines. Hold the edge of the square on the two marks and draw a line. Mark an "X" on the cutout to avoid cutting out the wrong side of the board.

Tips & Warnings

• Finding the average width of the deck boards helps eliminate layout errors caused by inconsistent board widths.

• The calculations for the first and last board widths prevent having narrow boards less than 2 1/2 inches wide for the last board. Such narrow boards won't fasten properly to the framing, especially if they overhang the deck framing.

• Newly pressure treated lumber will shrink over time. If the boards are very fresh and you can see water escape when you pound a nail into one, decrease the board spacing by 1/16 inch or even eliminate it. If you don't reduce the gap, you'll end up with extra wide board spacing, which may be unsightly or even present a hazard for high heels.

References

• "Decks 1-2-3"; The Home Depot; 2001

Resources

• ManageMyLife.com: Build a Deck