In the wonderful world of decking two standard thicknesses are sold: 4/4 and 5/4, which end up being close to ¾” and 1” respectively once they’re finished. These thicker boards provide stability, whether the climate is wet or dry, even amid extreme swings in temperature and moisture levels. Thicker boards help ensure that your deck remains flat and free from checking, even years down the road. Beyond those standard thicknesses, there is also a third option, which is between the ¾” and 1” thick sizes, known as “plus-sized decking.” Approximately 2 mm thicker than the ¾” thickness, it’s advertised as being more stable because of the added thickness. Is it worthwhile to purchase plus-sized decking? Is it just another inexplicable American lumber trend? Let’s take a look.
The Market for Plus-Sized Decking
The European standard decking thickness is actually the 21 mm stuff, what Americans consider “plus-sized decking.” The wetter climate in Europe demands this thicker product, and South American mills have responded by producing these thicker decking boards in species such as Ipe and Cumaru. Since they’re already cutting them for European markets, they offer them to U.S. suppliers as well. No problem, right? Well, not yet, but when you consider where they get the plus-sized decking, you may want to reconsider your verdict.
The Scenario with Plus-Sized Decking
To saw the 21 mm plus-sized decking, the mill has to start with the same rough stock they’d use to saw the 5/4 material also sold in the U.S. Instead of the additional thickness, though, close to ¼” is planed off the board. The importer ends up being charged the same as they would have been if the boards had been sawn to 5/4 thicknesses, while the mill gets to make more money on each shipment, since more finished volume fits into each shipping container. The importer (and end use customer) loses thickness that they’re paying for anyway, while the mill wins out — never mind the unnecessary waste.
The Purpose of Plus-Sized Decking
Now that we realize there’s needless waste and that the buyer is getting less than they’re paying for, let’s re-evaluate the reason that plus-sized decking has come into play. One of the species sawn to plus-sized decking is Ipe, which is already incredibly stable. Compared to Ipe in 4/4 (really ¾”) thickness, Ipe with an additional 2 mm is arguably not worth the cost. And if you’re going to spend the extra money anyway, why not go with 5/4 (actually 1”) thickness?
Cumaru might be a little different, because it’s not as stable as Ipe. Here at J. Gibson McIlvain, we don’t carry Cumaru that’s thinner than 5/4. Since Cumaru is much less expensive than Ipe, we think that whatever you might save by going with a thinner board would be a mistake. Once it warps and buckles, you can’t go back. So since the 21 mm “plus-sized decking” is actually thinner than 5/4 material, we do not carry or recommend Cumaru in that size.