structural modifications needed for Trex?

I am planning an addition that will include a large deck. It is L shaped with on leg being about 30'x10'6" and the other leg 33'x7'4". The contractor said to upgrade to trex over Pressure treated was $12,000. I said he was crazy because when I calculated things out using $38 for 5/4x6/x16 trex boards and $11 for the same dimension pressure treated deck boards the trex cost $2475 and pressure treated was $825 for a difference of only $1650. This is for decking only, the support will be pressure treated of course. He said that trex must be 12" OC compared to 16" OC for Pressure treated. I told him not according to trex web site. It states 16" OC as long as placed at 90 angles to the joists, as it would be. He said it is more labor intensive. Does not appear to be more labor to me. You use the same screws, gap boards like wood, seems exactly the same. Anyone with experience/knowledge with Trex?
Thanks

 

hammerash,

Let's make sure that I'm understanding you correctly.

You contractor has given a bid for the deck (560 sq. ft.) in PT, then said it would be an additional $12K to upgrade to Trex.

Is this just for the decking, or is he including the cost of upgrading the railing as well in the $12K?

If it's just for the decking, he's way out of line, UNLESS there is something about this deck that is driving the cost sky high that you haven't mentioned. The composite decks that I build from the ground up average about $21/SF for the deck itself. That works out to about $12K for the deck you are talking about, DONE in a composite, NOT the cost to upgrade from wood TO a comosite. You haven't mentioned stairs, but they average about $50/SF, so add that to the $12K i mentioned if there are any.

You also haven't mentioned railing -- how much is there? Composite railing will add about $100 per LINEAR FT. of railing. (That's not a typo -- I said one hundred dollars per linear foot!!)

You are correct -- Trex and almost all other 1" thick composites can be installed over joists spaced 16" O.C., provided they are perpendicular to the joists. To run the diagoanally, you ruduce the joist spacing to 12". That's the MAXIMUM. I set mine whatever works out evenly, as determined by the size of the deck, between 12" and 16". (If the deck is 33 X 7-1/2, with the joists being 7'-3' long, I'll be setting 26 joists at about 15-1/4" O.C. I'm cutting thirteen 2X6X16's to get 2 joists out of each one, and that gives me a piece left for a mid-span block as well.)