Mind the Gap: Decking Tips
This is the fourth post in a series entitled “Mind the Gap,” and we’re still not telling you exactly what size gap you should use between your decking boards. We’re guessing that’s a little frustrating. Well, we’re getting to that, this time around. Really. But before we do, let’s do a little review. While you can slow the moisture exchange, you cannot stop it. The most significant types of wood movement occur across the width of a board (tangential) and across its thickness (radial). While you can’t prevent wood movement, you can plan for it. Wood typically holds the most moisture during summer months, making boards swell to their largest during that time. When boards are most swollen, gaps are smallest; no matter what size gap you have when you install a deck, those gaps will shift throughout the year in most environments.
In the scenario described in the last post with a 1x6 Ipe decking board, here’s what we’d recommend. If we were performing the installation during summer months, in an area where the humidity is high that time of year, we’d install it with a minimal gap — less than 1/8 inch, just enough to let rainwater drain off the deck’s surface. (Trust us: you don’t want standing water on your deck — or all the movement issues that come with that!) During winter, you’d have that ¼-inch gap most people see as ideal.
If we were installing the deck during the winter, we’d go with a ¼-inch gap — unless our job site was in a particularly humid climate. In that case, we’d add 1/16 or 1/32 to the gap. Of course, one extra factor might convince us to do things differently: a customer request. If a customer really wants a ¼-inch gap in July, we’d want to inform them of what that would mean for the rest of the year, but we would do our best to honor their request.
If you aren’t installing the deck in an area with high humidity, good for you! (And we must admit, we are a tad bit jealous.) While warmer air has the potential for holding more moisture than cooler air, wood movement is directly related to humidity levels, not temperature. So if you’re in, let’s say, Denver, Colorado, even a 70-degree shift in temperature can mean very little shift in humidity and wood movement. So a ¼-inch gap during the winter would pretty much mean a ¼-inch gap during the summer.
If you want to be able to punch in your wood species and location and figure out what kind of movement you can expect, there is an app for that! The Woodshop Widget offers some reliable shortcuts to figuring out all kinds of wood-related things. You can also find wood movement percentages on each species page on our main website (mcilvain.com).