As part of a cost reduction effort for a place we are building near Livingston Montana, our builder has suggested reducing the floor decking from 1 1/8″ to 3/4″ OSB.     The Architect’s structural engineer as signed off on this with the caveat that the floor will be somewhat bouncier.    The joists are 9 1/2″ TJI that span about 13′.  We are putting bamboo wood flooring in initially, with the idea that we will put in slate or tile at a later date.   

Are we likely to be OK with the thinner subfloor?  

I think I will probably be fine for the bamboo, but worry a bit about the tile/slate.  I will be asking the engineer to get us the deflection by the next meeting, but was thinking I would probably need to add another layer of subfloor when I do the slate in the future.

The next question is actually the one I am most concerned with. In order to achieve this, and not disrupt the finely tuned plans of the architect :-), the builder proposes to add 7/16″ OSB strips on top of the sill plate.  Although creative and “out of the box thinking,” I am worried that it is a little too much so.

I would assume he is still doing a standard PT sill bolted to the foundation wall, presumably with the bolts through the OSB and the studs toenailed through the OSB into the sill.

Any opinions on this latter approach?    Resistance to rot? Structural issues?

Thanks,
DonH