You may not need to add more if you installed the first layer properly. Did you seal every edge of your foam between the joists with expanding canned foam and seal all the seams on the walls, as well as seal the transition from wall to ceiling?

You should also run your insulation down the entire wall(s) and seal that as well. I'm not sure going 1/2 way down will do much good.

Adding more insulation will only work if you have already done what I described above.

The key to using cut rigid foam is that it must be absolutely sealed from air exchange. The more gaps you have the quicker your space will equalized to the surrounding temperature and humidity.

This post was edited by rmtdoug on Fri, Jun 27, 14 at 16:29

Agreed.

Using canned foam in the rim joist area can be tricky since there's little room to keep the can inverted. Buy some vinyl tubing to extend your reach, and tape the tubing to a stick. (Trust me, it makes life easy.)

Homebound,

Thanks for tip on the canned foam. The tubing/stick idea made it much much easier to seal seams in ceiling.

Where I live the temperature of the ground at mid height of a basement wall is the temperature of well water which is about 50 to 60 degrees which is fine for white wine and a bit cool for red. But I don't know where you live.

I would concentrate on the ceiling. There is no reason to avoid air pockets but to reduce convection you could fill it with fiberglass batts. The exposed foam should be covered with 1/2" drywall. You might try the batts with the drywall and save the expense of foam board.