I have a few questions regarding installing a 7-1/2”x 5/8’ engineered flooring parallel to the floor joist. I am planning on installing the floor parallel to joist for aesthetic reasons, based on room layout and starting and running the floor with a true wall. My cousin, who is a professional of 15 years suggested running it parallel for those reasons as well. He has inspected my subfloor and is very pleased with the condition and firmness of my subfloor, and confident laying it parallel with joist with my current subfloor.

My subfloor is, 23/32 tongue and groove plywood cd exposure 1, nailed and glued to 2x10 joists on 16” centers. The flooring as I stated above is 7-1/2” x 5/8” engineered bamboo, plywood base with bamboo veneer. The manufacturer suggests for optimal installation a minimum of 1” subfloor is recommended.

I was reading the NWFA flooring installation for engineered floors and it says in Chapter 8, Part VI C. Choose a starting wall according to the most aesthetically or architecturally important elements in the room. Starting with the longest unbroken wall. —The way I read this is, being engineered I have freedom for a installation in running parallel.

I have been thinking of adding an additional 11/32” of plywood underlayment to meet the manufactures specs, and ease my mind to ensure a solid foundation, only want to do this once and don’t want to look back and wish I would have.. My cousin said I could be honestly feels I would be wasting my money given how solid my subfloor is, and because adding a layer would would raise the floor above some banister trim, and my current sliding patio door (so replacing).

Is my subfloor and engineered floor adequate for a solid install? Or should I add an additional layer of 11/32” plywood? Option ins and suggestions welcome, thank you.

Are you gluing, fastening or floating the flooring?
Whatever you decide, the sub-floor will support your flooring.

Nailing the flooring down, thanks.

I wouldn't add another layer of floor. Not worth the cost. You have 16" oc, you have a solid floor already. Maybe if you had 19, 2's for your joists it would be a different story.