How to Lay Decking Boards | Straight Runs Need These Basics

Laying decking boards requires setting them perpendicular to the joists, leaving a consistent gap, and fastening each board at every joist it crosses.

The difference between a deck that looks professional and one that draws the eye for the wrong reasons usually comes down to the first few boards. Laying decking boards isn’t complicated, but it demands a straight reference line, proper spacing, and correct fastening. Here’s the order of work that gets it right the first time.

What Direction Should the Boards Run?

Install the boards perpendicular to the joists. That means each board runs across the framing members underneath, and every joist gets fastened to every board it crosses. Boards running parallel to the joists leave nothing solid to anchor into and will flex underfoot. If you’re working with a layout that requires a diagonal pattern, know that it creates more waste and needs more framing support.

Before you start, confirm the joists sit level and are spaced to your local building code. Fixing a low or crowned joist after the boards are down means pulling the whole deck apart.

How Do You Set the First Board Straight?

The first board sets the tone for every board after it, so spend the extra minutes getting it perfect. Measure the deck and order 10–15% extra material for waste and cuts. Mark each rim joist at a distance equal to one board width from the outside of the header joist, then snap a chalk line between those marks. Place the inside edge of your straightest board right on that line.

Depending on your layout, some builders prefer starting at the house wall, others at the front outer edge. Either works, as long as the reference line is true and the first board is the straightest one you have. Align the edge of that board parallel to the house.

How Far Apart and How Do You Fix the Boards?

Gap width depends on the material. For most wood and composite installations, 1/8 inch spacing works well; some composite manufacturers specify a 3 mm gap, and a UK guide recommends 5–8 mm for expansion. The goal is consistent spacing that allows water to drain and boards to expand without buckling. Use a spacer block cut to your chosen gap and check it every few boards, not just at the start.

For fastening, the standard approach for wood decking is two screws per joist, driven flush but not over-tightened. Place each screw 3/4 to 1 inch from the board edge, keep them at least 15 mm from board ends and 20 mm from outer edges, and drill pilot holes where the material tends to split. Use corrosion-resistant screws rated for exterior use; standard drywall screws will rust and fail.

Composite decking is a different job. Most systems require manufacturer-specific hidden clips rather than face screws. Locking clips attach to the joists, and the board grooves snap onto them. Make sure your clip profile matches your exact decking brand — NewTechWood, TimberTech, and Deckorators each use their own system.

Where Do End Joints Go?

Every board end must land on a joist, and joints should be staggered so they don’t line up across adjacent boards. A row of aligned end joints creates a weak line across the deck and looks like a mistake. Stagger them by at least one joist bay, or simply vary where each board ends.

Let the board ends run long past the deck edge, then trim them all at once with a circular saw and a straight guide for a clean, uniform overhang. A comfortable overhang is about 1 1/2 inches on each side. For bowed boards, pull them tight with clamps and toe-screw them where needed. Check your layout every couple of boards — a small error at board five becomes a visible wedge by board twenty.

Here’s the short version: straight reference line, boards across the joists, consistent gap, two screws per joist, staggered joints on solid framing. Get those four things right and the decking part of the build takes care of itself. When you’re ready to compare materials for the project, our roundup of the best boards for decking breaks down the top options side by side.