Mind the Gap: Decking Tips
Why mind the gap? While all wood moves, decking lumber and other exterior applications subjected to ever-fluctuating moisture levels are particularly prone to movement. In Part 1 we learned about the three types of wood movement and how it affects the stability of any given lumber species. While we really can’t do anything to completely stop that movement, we can be smart about how we install decking lumber, allowing for the predictable movement that comes with environmental change. We can also take steps to make wide swings in moisture level at least less significant.
Remember how we compared a board to a bundle of hoses that can be filled with moisture? Well, as you know, not all parts of a hose can fill up with water or become empty of water all at once; the ends will always do so first. That issue is largely what leads to problematic wood movement in the form of bowing, cupping, twisting, and warping. In order to allow time for the middle portions of boards to catch up with the ends, one thing we can do is provide an adjustment time, allowing the board to come to an equilibrium with its new environment (even if by “new” we simply mean out in the sun instead of in the shade). At that point, warping won’t be nearly as likely, and though the moisture fluctuation will slow, it will never completely stop.
Other steps we can take in order to lessen wide swings in moisture levels is to keep lumber out of direct sunlight; instead, stack it in a place that allows for ventilation, and place small pieces between boards, to allow air to flow around each one in the pack. Then allow enough time for proper acclimatization; if you’re not sure how long will be enough, feel free to ask us; it depends on a combination of factors including when and where your lumber was harvested and milled and how drastic the change is between its former environment and your job site. Allowing enough time and providing an environment for even drying will go a long way toward helping avoid disaster.
Once your decking lumber has come into an equilibrium with where the boards will be installed, it’s key to carefully — you guessed it — mind the gap. Just like the moisture levels in those boards will shift as the hose-shaped fibers absorb and release water, the gaps will also shrink and grow throughout the year. So the first thing you need to realize about the gaps is that they will change; and you need to make sure your customer realizes that fact, too. If your customer says they want a ½-inch gap, your response should be something like this: “Okay, we can do that. But during what time of year would you like to have that size gap?”
Continue reading with Part 3.