Even though composite deck materials are becoming more popular by the day, it’s still really tough to beat the look, feel, and finish of a nice cedar deck.
That said, cedar deck boards aren’t just expensive to work with – they can also be prone to shrinking based on ambient humidity levels. The boards, finish and the fasteners you use make a huge difference in mitigating this issue.
Here’s how to make sure that your cedar deck boards stay (roughly) the same size going forward.
Will Cedar Deck Boards Shrink?
Though it might come as a little bit of a shock to you that Cedar boards are prone to shrinking, it’s important to remember that all wood construction materials – hardwoods, softwoods, and even pressure-treated materials – are prone to the same thing.
All Wood Shrinks
The only wooden materials that are less likely to move and shift (and shrink) are engineered materials. And that’s really only because they have been – no surprise here – engineered to be a stable and reliable solution matter what.
Wood is a natural material. It’s filled with all kinds of fibers, is quite porous, and reacts a lot to its environment. Especially when it comes to moisture content and humidity.
What Causes Cedar Boards To Shrink?
In a particularly wet or humid environment you should expect cedar to swell up and expand, sometimes quite a bit. In particularly dry environments with next to no humidity, though, it’s not unreasonable for your cedar wood materials to shrink right up.
Up until relatively recently people felt that temperature had a big role to play in whether or not cedar wood materials were going to shrink or expand as well.
New research shows that temperature has almost no real effect whatsoever, and definitely nowhere near the same kind of impact that humidity has.
It’s all about how much moisture the cedar wood material can suck into itself (or how much it expels) that determines what happens to its overall dimensions.
How Much Will Cedar Shrink?
Just how much is cedar going to move on you?
While the total amount of shrinkage you experience with cedar materials will be heavily influenced by the conditions we mentioned a moment ago (just how much humidity you’re dealing with), on average you can expect shrinkage of about 1/8 of an inch and about the same as far as expansion goes.
Now, that’s just a general rule of thumb kind of figure.
Sometimes cedar is only going to move 1/16 of an inch or so even in really humid environments. Other times you might be looking at ¼ of an inch or even ½ an inch of shrinkage, especially if things are bone dry.
A lot of that has to do with the kind of fasteners that you used to cement that wooden construction materials in place, the grain structure and cellular makeup of the wood itself, and a whole host of other factors (many of which you’ll have little control over at all).
It’s hugely important to account for cedar to shift and move every time you work with it, though.
The last thing you want to do is get everything perfectly dialed in, cut and installed on a really humid – or really humidity free – kind of day, only to have the humidity shift and change over the next few weeks and your deck to end up looking like it’s wrinkled.
Does Cedar Expand?
As highlighted a moment ago, cedar does have the potential to expand – usually just as much (if not a little less) than its ability to shrink.
Granted, it takes quite a bit of extra humidity for cedar to really swell up and go crazy. We are talking about relative humidity levels that get up near 70% or higher – and sometimes considerably higher than that.
The dryer the cedar material (the longer that it has been dried out), the less likely you are to be dealing with a full on sponge.
That might sound a little counterintuitive. After all, wouldn’t a bone dry chunk of cedar want to suck up as much moisture as it could?
Well, if that chunk of cedar was dried out for an extended amount of time (we are talking about months, if not years) the cells that would have soaked up all that extra humidity may no longer be capable of working as hard as they would have been while still somewhat “green”.
This is why air dried cedar that has been slowly dried over a number of years is so expensive compared to kiln dried cedar that still has a little bit of “rebound” left in it.
Cedar Deck Spacing Tips
At the end of the day, the best thing you can do when working with cedar material on your deck is to simply account for a 1/8 shift in one direction or another to keep things nice and consistent.
This usually means spacing your deck boards apart by 1/8 of an inch, recognizing that if things shift and change (one way or the other) you’re still going to have at least a little bit of space between your boards no matter what.
On top of that, it’s a good idea to “lock down” cedar boards to the existing framing with construction adhesive and durable fasteners.
Remember that any of the moisture that the deck framing sucks up into itself is inevitably going to try and be pulled into the cedar as well. By putting a chemical barrier down between the two (high quality construction it easier) you not only locked down the material and prevent squeaking or creaking but you also inhibit that moisture transfer, too.
Closing Thoughts
Yes, you should expect your cedar deck boards to shrink at least a little bit when the environment gets a little on the dryer side of things. The fall and winter are where you’re going to see the most shrinkage as the air is the driest.
You should even expect a little bit of expansion, too, in the spring and summer – particularly when the humidity starts to climb.
Account for that when building out your cedar deck, though, and you won’t have too much headache to deal with.
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