[Greenbuilding] hardwood floor orientation

[Reuben Deumling]

The 115-year-old Douglas Fir flooring in my house is in poor shape. It sits
on joists 24" o.c. with no subflooring. In the heavily traveled areas all
the tongues and grooves are split. It squeaks a lot. I had it sanded and
refinished three years ago after pulling up layers of linoleum and carpet
which had been on it for many decades. They did a mediocre job. Now the
Glitsa finish is wearing off in the kitchen.
Since the flooring was original to the house and runs under all the walls I
can't well afford to take it out.
So I've decided to lay an oak floor on top of it. My question is
simple--which way do I lay the oak? Parallel with the existing boards, or
parallel with the joists they sit on? I've thought of diagonal, but think
that may not be such a grand idea. I'm disinclined to put down a layer
between the two so as not to exacerbate the height transitions at my hearth
and door sills, but I suppose I could be talked into something.

Thanks for your thoughts and advice.

Reuben Deumling