How to lay straight decking boards

decking boards, timber wedges, installing decking boards, spotted gum decking
Installing decking boards

The setting out of the decking boards will make or break any deck. We all have seen decks where the decking boards are not running in straight lines.

If you use the conventional method of using a spacer in between each decking board, eventually the decking boards look like they are starting to bend and curve. This is because most decking boards vary slightly in size. The more boards you install, the more the board’s variation in width becomes apparent.

So why do most building professionals and reality TV shows teach the spacer method? Simply because using a spacer is an easier method to teach and demonstrate.

There is another method that most builders and carpenters use. That is the set out what is known as your grid boards. Grid boards are every fifth decking board that is nailed down first, and then we fill in the spaces afterwards. This way we can space the boards in-between each grid board evenly. Using this method takes a little longer, however, it will result in a much neater result.

Keep reading for the step by step process on how to set out the grid boards. Alternatively, you can purchase the complete guide “Installing decking boards” for the complete process from set out to the installation of decking boards. On that note, let’s get started.

1- Measure the width of a few decking boards to work out how wide the average of the decking boards are, this is very important. Multiple the average width of the decking boards by 5 and then add 15mm. The 15mm allows for a 3mm gap between each decking board. The gap is required to allow the decking boards to expand in various weather conditions.

Average width of decking x 5 + 15mm (3mm gap between each board) = “Grid board spacing”

2- Start from the front of your deck and mark down the sides of your deck in multiples of the “Grid board spacing” measurement. This is so you can use a chalk line (a chalk line is a string line coated in chalk that when you flick it leaves a straight line of chalk) to mark all the joists that are in between and keep them straight. (Refer to “15 Most Common Deck Construction Mistakes” from for an example of decking that is not straight).

As you cannot mark the very front board as it will be overhanging the front of your fascia in mid-air (normally between 10mm to 20mm), and as you may have posts that the decking needs to be cut around. Make your first mark at, “2 x average width of decking + 6mm (6mm is the gap between two decking boards, this is so you can come back later to install these boards)”. Note: if you have rebates cut into your posts for the decking boards you will need to leave the front three boards off so you can get the decking boards that are cut around the posts without having to remove a row of decking boards later on.

3- Use a chalk line (a chalk line is a string line coated in chalk that when you flick it leaves a straight line of chalk) to mark a straight line on the top of your joists. As you go along flicking your chalk line, mark a big X on the opposite side of the line from the direction that you started marking from. The X is so you know which side of the line you are to nail your grid decking boards too.

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