I am approaching my french doors on a diagonal install and would like advice on how to position the wood adjacent to the doors, how much gap to leave, and how to cover the gap.

I was thinking I need to put one or two rows running in the same direction as the doors and then tie the diaganonal field into the transitioin board(s). As can be seen in the picture, the existing shoe molding around the perimeter of the "fixed" doors only come out as far as the threshold under the door and will not cover any expansion gap.

Any advice would be appreciated.

http://flickcabin.com/public/view/16877

http://flickcabin.com/public/view/16878
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I would just but up against the molding that is in place providing its the same height, using a polyurethane adhesive to prevent squeeking. I would not worry about expansion if the door is providing a good seal.
Hope this helps

First, running two boards along the length of the threshold and butting the diagonal installation up to them, would be a horrible eyesore.
From looking at the pics, it appears that the threshold is higher than the surface of the new floor. So, I suggest using a 3/4 inch t-mould with one side cut off flush with the stem of the t-mould and butt this edge up to the threshold. The floor can then tuck under the other edge and allow for some expansion. Best visual appearance would be to run the t-mould under the casings at either end of the opening and mitre and return the ends into the wall. This will look as though it was a planned design feature, rather than something added to hide a problem.