When you’re planning a deck project, one of the common terms you might encounter is 5/4 decking (pronounced 5 quarter). But how thick is 5/4 decking, and what does that fraction mean? Let’s break it down by understanding how lumber sizing works and why this particular term came about.
The Thickness of 5/4 Decking
In simple terms, 5/4 decking refers to decking boards that are 1.25 inches thick (or 1 ¼”). However, that’s the nominal size. Once the boards are milled and planed to their final dimensions, the actual thickness is typically around 1 inch.
This size is common for deck boards because it’s a good balance between strength and affordability. It’s slightly thinner than a standard 2x board (which is typically 1.5 inches thick after milling) but still thick enough to provide durability and stability for most decking applications.
How Lumber Sizing Works
Lumber is often referred to by its nominal size, which is not the same as its actual size. The nominal size is the size of the lumber before it is milled and planed smooth. After milling, the lumber ends up slightly smaller. For example:
- A 2×4 board is actually 1.5 inches thick and 3.5 inches wide.
- A 1×6 board is actually 0.75 inches thick and 5.5 inches wide.
In the case of 5/4 decking, the nominal size of 1 ¼ inches gets reduced to roughly 1 inch thick after it is planed. The width of 5/4 decking is typically 5.5 inches, the same as standard 1x or 2x decking boards.
Why Is It Called 5/4 Decking?
The term 5/4 originates from the lumber industry’s older way of referring to the thickness of wood in quarters of an inch. Each “quarter” represents ¼ inch, so 5/4 literally translates to five quarters of an inch, or 1.25 inches.
This method of measurement is a holdover from when lumber was typically rough-cut and unplaned, and it gives a more accurate indication of the wood’s size before it was processed.
Why Use 5/4 Decking?
Now that we know what 5/4 decking means in terms of thickness, you might wonder why this specific size is used so often. There are a few reasons:
- Affordability: 5/4 boards are generally less expensive than thicker 2x boards, making them a budget-friendly option for homeowners.
- Weight: They are lighter than 2x boards, which makes them easier to handle and install.
- Strength: Even though they’re thinner than 2x boards, 5/4 decking still offers plenty of strength for typical residential decks. When installed with the appropriate joist spacing (usually 16 inches on center), they provide excellent durability.
Conclusion
5/4 decking, despite its nominal size of 1 ¼ inches, typically finishes to about 1 inch thick after milling. This size has become popular for decks due to its balance of strength, weight, and affordability. The term “5/4” reflects the lumber industry’s historical way of measuring thickness in quarters of an inch, a system that has stood the test of time.
When planning your deck, understanding how lumber sizing works ensures you get the right materials for your project. If you’re considering 5/4 boards, they’re a solid choice for both performance and value, giving you a beautiful and long-lasting deck.