Does material length matter for this method of miter joint? I'd like to join a 4' piece to a 16' piece, both will get direct sunlight, winter temps can go as low as -15°F . I'm in a semiarid climate, low to med humidity. I'm using Trex Transcend Lineage. TIA!
Deckorators Voyage Series Decking actually has very little expansion/contraction due to its mineral-base composition. Bit of a pain to work with, but should be pretty stable. I've also seen AZEK glue-only miter joints last just fine with expansion and contraction, and that stuff DOES expand/contract a fair bit, so I wouldn't worry about it.