Widht of TREX gap?

Would you call out the spacing between these TREX boards? The underneath the boards are very wet. Would you call the size of these joist hangers on the 2 X 12’s?





  • Trex decking must be gapped, both end-to-end and width-to-width. Gapping is necessary to facilitate drainage and for the slight thermal expansion and contraction of Trex. Another reason for gapping is to account for the shrinkage of the pressure-treated joists. Following the proper gapping will ensure that your deck looks great year after year.
  • Width-to-width: above 40° F = 1/4" gap, below 40° F = 3/8" gap.
  • End-to-end: above 40° F = 1/8" gap, below 40° F = 3/16" gap.
  • Abutting solid objects (walls, posts, etc.): above 40° F = 1/4" gap, below 40° F = 1/2" gap.

Trex expands quite a bit due to sunlight and temperatures, maybe when you inspected it was warm and expanded.
This material will not rot, so moisture is not an issue here I believe.

Benefits of Composite Deck Materials

<LI itxtvisited=“1”>Does not deteriorate or rot as quickly as real wood <LI itxtvisited=“1”>Resists fading and heat damage <LI itxtvisited=“1”>Easy to install <LI itxtvisited=“1”>Requires less maintenance than a real wood deck; no sanding, staining, sealing or refinishing is required <LI itxtvisited=“1”>Surface designed to prevent slipping when wet

  • Does not splinter or sliver like real wood decking material

As far as the hangers, Simpsons Strong Tie makes 2"x10" hangers for both 2x10 and 2x12 combinations. I would not note that as a defect.

Hope this helps a bit.

Marcel :):smiley:

It did. Thanks!!

Addittional information that might help Buck;

**Trex Decking Installation Tips **

Trex being versatile, enables it to be easily used for intricate shapes, angles and patterns requiring no special tools.

Cutting Trex is best done with a carbide blade 18-24 teeth. If you use a miter box use a 10-12 inch saw with less than 30 teeth. A router is handy and will create nice edges on the Trex .

Trex can be hammer down or preferably use a screw gun, which makes your trex more secure by using screws.

Use a screw with fewer threads per inch, and must be an exterior type. Hidden fasteners can be also used.

Gapping: Gap both end to end and width to width in Trex. This of course, allows for slight expansion and contraction, plus drainage. From side to side or width to width, your gap should be ¼ inch. Temperatures below 40 degrees require 3/8 inch gap.
End to End gap must be at 3/16 inch below 60 degrees. Above 60 degrees 1/8 inch gap.

Joists: The joists for the deck’s foundation are best at 12" on center even though you can use 16 inch on center. By staying 12" on center it will prevent any flex in the decking board between the joists on hot days. Nailing bocks between the joists is also a good idea. It will greatly aide or stabilize the frame form movement.


Marcel :):smiley:

I have a question about gapping. I live in Eastern Tennessee and the winter can get down into the 20’s and summer max heat index of around 105 so what should I gap the trex at?