Ipe is, by far, the most prestigious decking lumber species on the market — and we sell plenty of it around here. But for those looking for an alternative to Ipe, Jatoba is an oft-overlooked possibility. So as we began to do in Part 1, we’re going to continue comparing the two decking lumber species, starting with a continuation of an explanation regarding how they compare when it comes to stability.
Stability Comparison, Continued
If the ratio of tangential to radial movement were 1.0, that species could be described as isotropic, with equal movement in all directions. Ipe demonstrates nearly isotropic movement with 8% tangential movement and 7% radial movement for a ratio of 1.1. Jatoba’s 7.1% tangential movement compared to its radial movement of 3.8% gives it a ratio of 1.9.
When it comes to practical application of these numbers, though, what’s more significant is how much moisture content varies from one face of a given board to another. So if one face is getting a lot of sun while the opposing side is shaded as it faces the ground — which is pretty much going to be the case for most decks — there’s a strong likelihood that the board will cup within the same grain plain, regardless of the species and its stability ratio. This, of course, makes installation extremely important. As long as you have proper ventilation beneath the deck as well as proper spacing between boards, almost any decking species will perform quite well.
So while Ipe’s numbers make it appear to be more stable, in real life Jatoba’s slightly lower density means more empty space between each cell of the lumber; as a result, it actually lends toward greater elasticity, creating less of a likelihood of cupping when one side tries to shrink or expand while the other remains constant. Don’t get us wrong: Ipe is a stable species too; just don’t think its performance will result in greater stability than Jatoba.
When it comes to stiffness, another term used in the lumber industry is Modulus of Elasticity, which can be abbreviated as “MOE.” Measured in pounds per square inch, stiffness or MOE is going to tell us how much a decking board in a particular species will flex under foot traffic between joists. Not only can this measurement be helpful in comparing species, but it can also inform the kind of spacing used in the substructure.
The MOE of Ipe is 3120 and that of Jatoba is 2745. Obviously, that makes Ipe the stiffer species. (We’ve also looked at the possibility that some Ipe structures are actually supported in ways that are overkill, considering Ipe’s extreme stiffness.) If we were using those numbers to help determine the spacing of supports, we’d realize we could install an Ipe deck on 24-inch centers and still not get any bounce. For Jatoba, we’d need 16-inch centers instead. In reality, most decks are built with either 16-inch or 12-inch centers anyway, so you’ll be safe with Jatoba. While Ipe won’t give you any bounce, neither will Jatoba.
Continue reading with Part 3.