The Ideal Deck Board Thicknessdepends on the hardness and bending strength of the material. Pressure treated (PT) pine and cypress, composite and redwood are readily available in 5/4 x 6” boards because this is the thickness needed for building strong decks with joists that are 16” apart – on center (O.C), an industry standard. Cedar is available in 5/4 x 6 and also 2 x 6 boards. Cedar is quite a bit softer than the others mentioned. So some folks want a thicker board. None of these boards are purchased in 1 x 6 dimensions as deck boards because they simply would not be firm enough to build a deck the doesn’t flex.
Brazilian Deck Boards, on the other hand, are most often sold in 1 x 6 dimensions. Brazilian deck boards are six to ten times harder than cedar and three to four times harder the PT and composite material. So, it is understandable that Brazilian ipe decking boards are much firmer than any other commonly available deck material even when they are 75% as thick as most other deck boards. Folks first comparing the attributes of Brazilian ipe decking boards to other materials available often price 5/4 x 6 lumber but this is not a good performance comparison. 1 x 6 Brazilian ipe decking boards are firmer, last longer and build a stronger deck than every other commonly used deck material. A lumber importer that is commonly asked about this comparison made this video, which clearly depicts the strength comparison between Brazilian ipe decking 5/4 and 4/4 thick boards. His conclusion from this study is that the difference in deflection between a 1 x 6 deck board and a 5/4 x 6 board is only 1 mm or 1/24th”. This is a 300 pound man standing on only ONE board. Because of the size of his footprint, this man would normally be standing on at least two boards. This minor deflection emphasizes the fact that 1 x 6 dimensions for Brazilian ipe decking boards is ample.
Joist Spans can be adjusted to add more strength and reduce flex on a deck. Adding a few extra joists to make the joist spans 12” rather than 16” adds quite a bit of strength and firmness to a deck – MUCH more than using 5/4 x 6 boards. Adding more joists also costs a lot less money than paying for thicker Brazilian ipe decking boards. Adding joists to make smaller joist spans does NOT make all decks firmer. Composite decking material manufactured with plastic and no wood fillers sags between the joists over time no matter how close the joist spans are. The sag is reduced but they still sag. Reducing joist spans for PT and cedar decks will improve the firmness of the deck but will not increase the life of the decking, which is the weaker attribute.
More comparisons at CompositeDecking.ME