"I can offer three pieces of advice for laying decking boards," says deck construction and maintenance pro Chris Cohn. "The first is to waterproof the joists before laying decking, the second to use screws as your default fasteners and the third to pay attention to the lines made by the fasteners as well as those made by the boards." Cohn also offers a few tips for laying composite decking boards, which he handles differently than wood ones.
"There's a lot of room for small measurement errors when constructing beams and joists, and you can compensate for these errors when laying the decking,"
Chris Cohn -- Builder and decking expert
Planning avoids problems
The most difficult part of building a deck is constructing the foundation. If it was done correctly, you have straight joists to use as references, but you still shouldn't rely on them. "There's a lot of room for small measurement errors when constructing beams and joists, and you can compensate for these errors when laying the decking," says Cohn. "I always plan ahead so I don't come to a problematic situation at the end of the job, such as one in which the rim joist and the final decking board are running at different angles." He offers strategies to avoid this scenario.
Measure the distance from both ends of the rim joist that runs parallel to the decking boards and the building to which the deck attaches. All is good if the two measurements are within 6 mm (1/4 inch) of each other, but Cohn has seen differences of 5 cm (2 inches) and more. Strategies for compensation include:
• Dividing the difference into equal parts and arranging the gap between every third or more pair of boards -- depending on the difference and number of boards -- at a slight angle.
• Ripping some of the decking boards at a slight angle. Space these boards several rows apart.
- Cutting only the first board that goes next to the building at enough of an angle to compensate for the difference.
Joist preparation and layout
The most vulnerable parts of a deck are the intersections between the decking boards and the joists. Leaves and other debris tend to collect in the gaps, and when they get wet, the moisture creates ideal growth conditions for rot fungi. "Even pressure-treated wood is vulnerable," advises Cohn. "That's why I make a point of covering the joists with waterproof [roofing felt] before laying the decking." Cohn lays out all decking boards, then stacks them in order before fastening them. "That allows me to move boards around and minimise waste."
• Unroll enough roofing felt to cover the top edges of the joist from end to end and cut the felt into 15 cm (6 inch) strips with a knife. Staple a strip to the top of each joist.
• Lay out the decking so that all boards end on top of a joist. Each pair of butting boards should extend halfway over the joist.
• Stagger joints so that no two adjacent rows have joints on the same joist. A random joint pattern not only looks better, it's more stable.
• Let the ends of the boards hang over the edge of the deck. Cutting them all at the same time after the boards have been fastened saves time, and it makes a neater edge.
Fastening the boards
"Screws are better than nails; they hold more securely and can be removed more easily when repairs are necessary. If you have to use nails, make sure they're galvanized and at least 3 inches [7.5 cm] long." Cohn has a trick for avoiding splits when driving nails: "Place the nail on the board with the point facing up and give the point a whack with a hammer to dull it. I don't know why this works, but it does -- when you drive the nail, the wood won't split."
• Extend strings from one end of the deck to the other along the tops of the joists and use them as references to ensure that you drive the fasteners in straight lines. "Don't snap chalk lines," advises Cohn. "You'll never get the chalk out of the wood."
• Drive two fasteners into each intersection of a board and joist. Each one should be about 2.5 cm (an inch) from the edge of the decking board.
• Pre-drill holes for screws and nails on the ends of each board, where splits are most common.
Composite boards and hidden fasteners
"Don't use nails to fasten composite boards," cautions Cohn. "You can't sink the heads. Screws are better, but the best way is to use hidden fasteners. They attach to the joists and fit into grooves in the sides of the boards. If you didn't buy boards with grooves, you can cut your own grooves with a tablesaw." Most composite decking manufacturers supply hidden fasteners for their products, and you can also find generic ones.
For hidden fasteners to remain hidden, the front of the deck must have a fascia board that covers the edge of the first row of decking.
• Install the first row of fasteners inside the fascia board. Screw one fastener to each joist as close as you can get it to the fascia.
• Lay the first row, hooking the boards onto the fasteners, then install the fasteners on the back sides of the board. Use double-sided fasteners that can also hold the adjacent row of boards. Tighten the screws on these double-sided fasteners only halfway.
• Lay the second row of decking, then tighten the screws on the fasteners between the first and second rows, using a drill and screw bit.
• Continue laying the decking in this way until you reach the building. You may have to cut the last boards at an angle if the front of the deck and the building aren't parallel. Fasten the back edges of these boards with screws.
Spacing for drainage
Installing decking boards flush against one another is definitely not recommended, although some builders do it if they're laying new decking boards that are green and wet. They say that the boards shrink as they dry out and create a sufficient drainage gap all be themselves. That isn't how Cohn works. "I always make a spacing strip from 3/8-inch [1 cm] plywood. I put it between adjacent boards to ensure uniform spacing, and I make it large enough to easily pull out once the boards are installed. It's better than using a nail for spacing; it creates a nice, wide gap that won't collect dirt and allows water to drain easily."