Decking installation is both a science and an art. Besides picking wood that is going to look attractive, you have to consider how well it’s going to hold up over time. One of the main factors to think about is wood shrinkage and expansion as it relates to deck board spacing (see Part 1). In this second article in our series on how to properly space decking boards, we’ll be looking at the impact of temperature as well as the differences in how wood moves depending on the manner in which the boards are cut.
Though fluctuations in temperature during the various seasons of the year can affect wood shrinkage and expansion, they don’t really have as big of an effect as humidity. Of course, in many areas of the country, humidity and heat tend to be related. Warm air can hold more moisture than cold air, so regions that tend to have high humidity see the humidity spike during the summer and drop during the winter. These dramatic changes in humidity really tend to make wood move.
Consider Time of Year
Because of the changes in temperature and relative humidity throughout the year, you’ll want to space your decking wood differently depending on the time of year. When you install a deck in a humid area, such as the Southeast, Midwest, or East Coast, during a summer heat wave, you’ll want to leave very little space between your boards. Why? Because that’s the time of year when the wood is already probably expanded close to its maximum size. You can expect to see the boards shrink considerably as the temperature cools and the humidity drops during the cooler months.
Consider the Cut of Your Decking Boards
Due to its organic nature, wood doesn’t move uniformly in all directions. The cut of boards you’re using can make a big difference when it comes to the rate at which your boards will shrink and expand. Flatsawn boards tend to see much more movement across the width of the board than do quartersawn boards.
Increase or Decrease the Amount of Space Between Boards Based on the Aforementioned Factors
If you know you’re installing a deck in a region of the country with large temperature and humidity level fluctuations, leave at least 1/4” of space between boards if you’re installing the deck during the winter. You may even want to add a 1/16” or 1/32” to be on the safe side if you’re in a very humid area. If you’re installing in such a location during a summer heat wave, leave just a sliver of space between boards for drainage as you know the boards are going to contract during the winter months. You should also remember to leave more space for flatsawn boards as opposed to quartersawn boards.
Once you take all of the factors we’ve examined in these two articles into consideration, you’ll be able to figure out how to space your boards in order to minimize the appearance of shrinkage and expansion. In the last installment of this three-part series, we’ll get into more of the specifics of how to space your wood as well as mention a few more helpful tips.