So here's my problem: I am laying solid 3/4 hw flooring and have to lay parallel to the joists in an addition to the house. The subfloor in the original house is fine but the subfloor in the addition built in 1987 over a garage is just 1/2 plywood over 2x8 joists spaced 16" on center. I can't lay an additional layer of plywood because of flooring height, so from what I've read it sounds like I need to block the joists under the addition. To do this I would need to pull down the drywall ceiling in the unheated garage. Would it be risky to lay the flooring and then block it out later this spring? I just wasn't prepared time-wise to take on this additional project and if I do I want to be able to re-insulate while I'm at it. It get's cold in MN this time of year!
Thanks!

In my experience when a 3/4 inch floor is installed over a half in plywood the flooring tends to arch with a change of moisture content as it expands from higher humidity. I think a combination moisture barrier glue would protect the floor from moisture below and increase strength of the floor. Blocking and insulation can be added later if necessary.