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Decking Dimensions: What Size Deck Boards Do I Need?

Are you looking to DIY build a patio or a simple home deck but not sure what size to pick? You are not alone. 

Choosing a deck board’s size varies depending on several aspects as well as circumstances. If, for example, it needs to carry a number of people at once, then it is best to pick boards that are thick and larger in size. But if your patio is intended for occasional family gathering only, then a standard size will suffice.

Source: finehomebuilding.com

But the thing is, deck boards have a lot of extremely confusing sizes that only professional builders know. And for a DIY enthusiast like you, deciding which size to use would be difficult.

That said, this article covers everything you need to know about deck board sizes and how to choose the right one.

Factors to Consider in Choosing a Deck Board Size

There are two factors that you must consider first before deciding which size of decking board to use. These aspects will likely determine what size of decking plank is appropriate to use too.

Here’s how.

  1. The plank’s durability and sturdiness. Deck boards are made of different materials. And each material varies in terms of strength, performance and durability. Softwoods that are untreated like red cedar, for instance, are weaker. On the other hand, composite decking and hardwood planks are sturdy and are not susceptible to damages caused by moisture as well as insects.
  2. Joist spacing. Joist span or joist spacing refers to the length covered by the joist between two supporting structures. Essentially, a wide joist spacing requires a stronger deck board—or a thicker plank, in other words.

Common Deck Board Sizes

Deck boards come in several extremely confusing sizes. The size may differ depending on the type of wood or board as well. In fact, these construction materials are known to have two sizes (which I will expound on in the next section). 

On a good note, manufacturers produce decking boards in standard—or the ones customers commonly ask for—sizes. Wood decking, for example, is usually cut down to 5/4 x 4, 5/4 x 6, 2 x 6, and 2 x 4 sizes while a composite deck board typically comes in 20”, 16”, and 12” in lengths and varying widths.

The most typical size, on the other hand, is 16 ft. with 1-inch thickness—commonly referred to as the 5/4 decking.

Nominal Dimension vs. Actual Dimension

As mentioned, deck boards come in several, complicated sizes. And they have two correct and accurate sizes. One is called the “nominal dimension” and the other is the “actual dimension.”

But how do these two sizes differ? Here’s how.

  • Nominal Dimension. A deck plank’s nominal dimension refers to the cross-section dimension of the material before it has been surfaced or planed on all four sides. Thus, in essence, the value is larger compared to the “dressed” or actual dimension. 
  • Actual Dimension. The actual or dressed dimension, on the other hand, is the board’s measurement after the material is planed smooth. Hence, it is the final size or measurement. 

Moreover, below is a chart of common nominal dimensions of decking boards and their corresponding actual dimensions.

Nominal DimensionsActual Dimensions
5/4 x 61” x 5 ½”
2 x 41 ½” x 3 ½“
2 x 61 ½” x 5 ½”
2 x 81 ½” x 7 ½”

Deck Board Thickness and Its Importance

A decking board’s thickness varies depending on several factors. Things like the material’s strength, brand, and even style can affect the material. 

But on average, a deck board’s thickness ranges approximately between 1 to 1 ¼ inches, which is commonly found in a 5/4 size deck board. It is followed by 2 x 6 lumber with a thickness ranging between 1.2 inches and 1.5 inches.

Why Is It Important?

The material’s thickness plays a vital role as well. It, for example, usually determines the plank’s sturdiness and durability. A thicker deck board can support the weight of several people better than thin ones too, as well as avoid unnecessary sounds such as creaking.  

A decking board’s thickness also dictates the length it can cover between joists. Standard deck joists are between 12, 16, or 24 inches on-center. And in several building codes, the standard deck board thickness it uses is 5/4 x 6.

5 Deck Boards and their Nominal Dimensions

Composite Decking

Composite decking is a modern type of lumber typically used in building patios and house decks. Using a strong binding agent, it is made by combining wood fiber and plastic, contrary to traditional planks that are purely made of a specific type of wood.

Composite lumbers are recognized to be denser and stronger compared to other types of deck boards too. And because it’s a mixture of both wood fiber and plastic, the material is highly resistant to water and moisture. For that very reason, it is not prone to rotting, as well as mildew and mold buildup, unlike wood. 

Composite lumber can last up to 30 years, given that is properly maintained.

Nominal Dimensions: 5/4” x 6” x 12’

Cost: On average, an entry-level composite deck board costs around $28 per square foot, while a premium decking costs around $38 per square foot or more.  

Wood Deck

Unlike composite lumber, wood decking is purely made of wood and is untreated. It is available in a wide range of wood types, including fir, pine, and spruce. Aesthetically, they are pleasing to look at and are a great fit for traditional or country vibes. However, do take note that untreated wood decking easily fades and will eventually turn grey. It is also highly susceptible to rotting and is prone to insect infestation. 

Nominal Dimensions: 2” x 6” x12’

Cost: The average price of a wood deck ranges between $3 to $15 per square foot. 

Pressure Treated Plank

As its name suggests, a pressure-treated plank is a type of deck board that is chemically treated. These chemicals are applied to enhance the material’s durability, particularly its resistance to rot and insect damage. Still, despite the fact it is already chemically treated, it needs regular staining or sealing every two to five years. 

Nominal Dimensions: 5/4” x 6” x 8’, 12’, 16’, 20’Cost: The median cost of a basic pressure-treated planks ranges between $15 to $25 per square foot while high-end ones are around $25 to $35 per square foot.

Aluminum Deck Boards

Aluminum deck boards are a decking material that is made using extruded aluminum. It is either anodized or coated with powder finishes and is available in a wide array of colors, including silver and gray. The material is weatherproof and waterproof as well. It is also low maintenance and is highly resistant to warping, splinters, insect infestation, as well as mold and mildew buildup. 

Nominal Dimensions: 1” x 6” x 12’

Cost: The median price of aluminum decking ranges between $12 to $15 per square foot. 

PVC Boards

PVC board is a type of decking material that is purely made of polyvinyl chloride or plastic. It highly resembles wood and can last up to 50 years, given it is taken care of properly. It is expensive compared to other kinds of deck boards. Still, many homeowners and builders recommend it. It is not prone to insect infestation, rotting, and damage due to moisture.

Nominal Dimensions: 1” x 6” x 12’

Cost: The average price of PVC deck boards is around $5 to $13 per square foot.

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