Decking Boards

Board counts go wrong at the first step, because nominal width is not actual width.

A "5/4 × 6" deck board measures 5½ inches. So does a 2×6. Most composite boards are 5½ or 5.5 depending on brand. Divide a deck width by 6 and you are short by close to a tenth before you start.

The repeat, not the width

What actually decides the row count is actual width plus the gap — the repeat. And the gap is not optional in either direction.

Pressure-treated lumber is sold wet and shrinks, so it goes down tight at about ⅛ inch. Composite expands with heat and needs the manufacturer's gap, usually ¼. Cedar and ipe are sold dry and sit between.

Gap too tight on composite and it buckles in July. Gap too wide on wet treated lumber and by autumn you have gaps that swallow a phone.

Layout costs boards

Straight runs waste about 5%. Diagonal at 45° wastes 15%, because every board is cut at both ends and the offcuts fit nothing. Herringbone runs 20%.

Order the full allowance in one go — diagonal offcuts are not reusable elsewhere on the deck.

Two screws at every crossing

One screw per board-joist crossing lets the board cup and lift at the corner, and that is the single most common reason a deck looks tired after two summers.

Read the end grain

Lay boards bark-side up. A board cups away from its bark side, so bark-up sheds water off the crown instead of holding it in a trough.

Butt joints

Stagger them so no two adjacent rows meet over the same joist, and double the joist under every joint. A butt joint on a single joist gives each board about ¾ inch of bearing, which is not enough for either.