Recommendations for framing for screening on top of Trex

by Scott Farnsworth
(Austin, Texas)

For the sake of my question I’ll describe my starting point as follows: Simple arbor on top of a Trex deck. The arbor is a cube. 8’ x 8’ x 8’. The ceiling is an 8’ x 8’ plane of corrugated fiberglass. The deck is Trex and is 16’ x 16’ (i.e. it sticks out 4’ in each direction beyond the four 6x6 posts that hold up the Arbor. In truth the deck arbor is bigger, taller, etc. but for the sake of this question this description works.

Our desire is to screen in the space, so screen in the four walls. Obviously one will need a door. The arbor is made of Rough Cedar. To match the framing for the screen system will 2x4 rough cedar. This means the footer will be a 2x4 piece of rough cedar running laid down on the Trex. The attachment is easy to imagine. What’s hard to imagine is what happens after it rains. The Trex/rough cedar joint would seem to wick and hold the rainwater and rot over time.

So the question is what to do? Do I smooth the bottom of the RC 2x4 face that’s touching the Trex and then caulk the joints? Do I use some Trex 2x4 as my footer?

Thanks in advance!

Scott