How Thick the Outdoor Deck Boards Should Be?

Thick Deck BoardsWhen it’s about time to find a deck builder, you dream of the summers you’ll spend outdoors. You check out cedar and ipe decks, compare costs, explore designs. The one thing you don’t do is think about the deck board thickness. Do you?

You are most likely puzzled at this point. Perhaps, a little disappointed since your dream of a beautiful cedar deck under your feet is interrupted for technicalities. Bear with us for a minute or two. Choosing the right outdoor decking board thickness is extremely important. It’s important for your safety and also, the longevity of your deck. You wouldn’t want to spend money on deck building and then, discover that you have omitted to consider one main element: the board thickness. Let us explain.

Common deck board thickness

The most commonly used thickness for deck construction is 1-1/4”. But you can also get boards 2” thick, while there are boards only ¾” thick. It depends on the material, how flexible it is, and its hardness rate. All is swell. Don’t you agree? You just go to your local deck contractor and let them tell you what you should get. Well, that’s the best thing you can do whether you want to replace the current boards but not the joists underneath, or opt for a brand-new deck installation.


Because the deck board thickness is not something abstract. It’s not something that you decide at random. And so, the experience of a deck company will make a very big difference.

Let us explain.

You choose the deck board thickness based on two things: the joist spacing and the strength of the wood.

What is the joist spacing?

Let’s explain what the joist of your ipe or cedar custom decks are first. They are the wooden frame under the deck floor. They are the base of the structure. They are usually attached to the house and have posts (depending on how high the structure will be) and become the support of the deck.

Now, the joists (the wooden boards that make up the infrastructure) have a space between them. This is measured by the mid-center of each joist to the next mid-center joist. This is the joist spacing – basically, from one joist to the other.

What’s the relation of joist spacing with the board strength?

joist spacingThe longer the space between the joists, the stronger the deck boards should be. Why? Because the bigger the space joisting, the larger the distance the deck boards are fastened. This make the boards susceptible. You will step and the board may bend – that’s why the flexibility of the wood also matters. That’s why the strength of the deck boards is important. If they are not strong, the deck boards will eventually give away.

The flexibility or bending strength of wood is measured with a key metric, known as MOR (Modulus of Rupture). It defines the material’s property (flexibility) when stressed (when you step on the board).

Naturally, not all deck materials have the same bend strength. Some, like pressure treated pines and red cedar are soft, weak. Hardwoods are strong.

And so, the deck material you choose affects the joist spacing. If, for example, there’s already a joist frame in your backyard and the joist spacing is pretty wide, you need strong deck boards. And vice versa. If you want to get a strong wood deck, you may have a large joist spacing. But if you prefer a soft wood, it’s important that the joist spacing is narrow.

And here’s where the deck board thickness also plays a role

If you opt for a soft wood, the thicker the board the better. Even if you choose a strong, hard wood, it’s best to get thick boards if the joist spacing is big. And it’s best to keep the joist spacing small if you prefer to get wide deck boards – as you can see, the width of the deck boards is also important.

To sum up, if the wood is strong, you can afford a wider joist spacing. To be sure the deck board is strong, you need to choose hardwood and/or thick boards. Think about it. When you step on the deck, the thicker the boards are and the narrower the joist spacing is, the more stable (and thus, long lasting) the structure is.