Question about post and beam floor structure

[bob57434]

Every plan I've seen for a post and beam floor system shows the floor joists attached to the sill beams with a mortise and tenon.  Couldn't you just rest the joist on top of the sill beam instead of making the two surfaces flush (with a mortise and tenon)? The joist would extend to the edge of the sill and the floor would be about 8" higher than the top of the sill.  It seems easier and stronger (you don't have to decrease the area of the joist but cutting a tenon).  You'd just have to make sure the post would come up between the joists and it would extend down beneath the floor about 8".

Is there a reason that I don't see this design anywhere?

Thanks.

[Don_P]

I try to do this whenever possible and have done it as a standard detail from several post and beam companies. Your thinking regarding not weakening a spanning girder is spot on. I block between the joists over the girder to hold everything in alignment.

[bob57434]

Mine is a simple 11'x14' one room cabin - no girder.  Eight 11' joists, 24" apart.  It seems better to adjust the spacing so the post doesn't rest on top of a joist (assuming that joist was as wide as the post)?

[Don_P]

Typically with post and beam and a conventional stick framed floor the posts do extend through the floor system to rest on the mudsill. a conventional floor system is built for unifoprm loading and a post and beam delivers point loads that can crush dimensional lumber.