Many decking customers have an idea of the size gap they’d like between their decking boards. The best response to such a request is a question: When do you want that size gap? No matter how eager you are to please your customer, you can’t promise them that the size of the gap won’t change. Why not? Because wood moves!
Decking boards expand and contract according the moisture levels in the air, making the size of the gaps between them constantly in flux. How you space the boards is going to be determined, in large part, by the time of year in which you install the deck; it will also take into consideration where your job site is located.
The majority of deck building takes place during the summer months when decks are most commonly used. As the thermometer registers 90 degrees and hotter temps, at least you know we’re at one extreme of wood movement, meaning that you don’t have to account for movement in more than one direction.
Typically, the summer months mean that decking will be swollen, due to high humidity — at least if your job site is located somewhere on the East coast, in the South, or across the Midwest. Those wood fibers, like a bundle of straws, suck up the air’s moisture, expanding the boards to their maximum.
How Gaps Can Grow
Wood movement may be predictable based on moisture content, but each species is unique, as well. For instance, a 1×6 Ipe decking board installed on a 96-degree day with 90% humidity will maintain a width of approximately 5.5 inches through the summer months. The boards have been installed with ¼-inch gaps between them.
However, as we move toward autumn, both the humidity levels and the temperature will begin to drop. Sometime in early October, we encounter a 65-degree day with 50% humidity, allowing the board to have shrunk by about 3/16 of an inch. Now that perfect ¼-inch gap is closer to a ½-inch gap, and your aunt just got her heel stuck between the boards at your annual fall party. The same deck, during winter, encounters 25-degree temperatures and humidity levels ranging from 25 to 30%. That ½-inch gap is more like a 5/8-inch gap, which is bordering on ridiculous.
How Gaps Can Disappear
Let’s reverse the above illustration: This time, let’s say that you install the same 1×6 Ipe decking boards in the winter, with the same ¼-inch gap between the boards. By the time the summer sun is hitting that deck, the boards will have expanded by more than a 1/4 inch.
In a best scenario, the boards will simply expand 1/8 inch on both sides, filling the gap. But in all probability, the movement will not be perfectly uniform, and your deck boards will experience some buckling. Because they have no place to go with their expansion, some of them will crack. The good news is that all that damage — and the expense and frustration that will come with it—can be avoided.
Continue reading with Part 2.
J. Gibson McIlvain Company
Since 1798, when Hugh McIlvain established a lumber business near Philadelphia, the McIlvain family has been immersed in the premium import and domestic lumber industry. With its headquarters located just outside of Baltimore, the J. Gibson McIlvain Company (www.mcilvain.com) is one of the largest U.S. importers of exotic woods.
As an active supporter of sustainable lumber practices, the J. Gibson McIlvain Company has provided fine lumber for notable projects throughout the world, including the White House, Capitol building, Supreme Court, and the Smithsonian museums.
Contact a representative at J. Gibson McIlvain today by calling (800) 638-9100.