I am constructing stairs off of a deck 84" in height. The customer wants the stair to start at 5' width and expand to 8' at bottom ( 7" riser, 12" treads, probably 7/8 steps).
The treads will be constructed out of 5/4 trex accent decking ( 1'' thick, 5 1/2" width ). Two planks together, 11.5" tread.
I am looking for a plan to construct the framing for this stair. I plan on using 2 x 12 for the stringers, but am unsure how to disperse the load as the stairs get wider to eventually reaching 8' at the last tread before you step onto a concrete pad. I believe I should have no more than 12" between stringers to prevent sagging using the trex as treads.
sounds like you are a pro, more or less, looking for help for your job. This is a DIY forum. There are some pro forums out there where you should look for assistance, or hire a carpenter that knows what he is doing.
sounds like you also need to speak to the manufacturer of Trex to get their engineering specs so you can design your stairs so as to be able to adequately carry the load without excessive deflection.