extending posts

I am preparing to convert a dismantled barn into a residence. My problem is that the bottom of the girts in this barn are 6'4" and I need to raise that up a foot or so. I'm looking for opinions on the best way (specific joint) to extend the posts. It makes sense to retain the square mill joinery (very nice)and just lengthen the posts. I'm assuming the easiest thing to do would be to cut tenons which would resist torsion in more than one plane. I'm dealing with 8 x 8 red oak and the extensions would be the same

Dear Archerw,

Why bother extending the posts ?

Lots of buildings sit on brick sills and this approach can be used to adjust the building internal headroom clearance.

Does the building have all round timber sills ?

Ken Hume

I guess that would work. I was thinking of a basement and a the bricks would then be on a subfloor, right. I don't know the kosherness, codewise, of such a move. Don't I need a minimum of 7'? Thanks, Todd