I know this question was just asked, I would just like some more info.

I have 400sf of 3/4 x 3 1/4 red oak, over 3/4 plywood above basement. This is new construction. The new home owner wants the wood to run parallel to joists. I told the builder that it just wasn't done this way, and he told me that he checked around and that it was ok to do. Ken, your previous post advised either laying additional 1/2 plywood or to cross block the joists.

My question is, exactly what are the risks of laying it parallel. I just want to be a little more educated when I again protest this to the builder. All (good) advice welcome! Thanks.

Have your know it all builder accept full responsibility, by having him sign a waiver of liability, releasing you from any fault when the sh..stuff hits the fan.

Don't let someone else tell you how to do your job, unless your their employee, unless you like being on the edge and skirting bankruptcy.

Here is some info from NOFMA, THE authority on hardwood flooring in the US.
On pg. 5 of the installation manual, it says to run the flooring at "right angles to the joists."
https://www.nofma.org/Portals/0/Publica ... Floors.pdf
On pg. 2 of this article by Mickey Moore, technical directer for NOFMA, he states that when running parrallel to the joists, either add 1/2" plywood OR 2x6 blocking every 24".
https://www.nofma.org/Portals/0/Publica ... 010_03.pdf
Go to these links and print out the specs and show them to your builder. If he refuses, do what floorguy says, get a signed release of liability.