I build in what may be a similar climate.

(Please note that gardening zones are not climate or hygrothermal zones. See International Energy Conservation Code (IECC) energy zone map below.)

I only use high-density spray foam on the rims.

But the way you describe your retrofit, the combination of Roxul with sealing may be more appropriate if you see a need for accessing any of the pipes that would be buried in the foam. (I can't imagine why you would need to access the wiring.) Unlike fiberglass, on which mould grows when wet, Roxul will not wick water and does not have to be replaced after heavy wetting. However, unless great effort is put into cutting the insulation to fit, there will be gaps that reduce the R value.

Whatever method you use, you might want to meet IECC minimums.

Beside referring to the table above, you can use the map on this link to find IECC county-by-county insulation requirements.

If this is an unfinished basement, termite shelter tubes will be visible on the foundation walls inside; and, for the same reason, be sure the foundation is exposed on the exterior.

There's no particular moisture problem. Sources of ignition will have to be shut off during application. Don't forget the water heater.

This post was edited by worthy on Wed, Oct 22, 14 at 0:02

Where do you get information that Roxul will wick water? There is a video (from Roxul) on youtube that shows it does not

Thanks! I made the edit. (That's what I meant to say in contrast to fiberglass.) Technically, fiberglass does not wick water either. But after it's heavily wetted, it lumps, supports mould growth and has to be replaced.

To illustrate Roxul's non-absorptive qualities, a seminar I attended by Dr. John Straube of Building Science Corp. sponsored by Roxul featured a cubic foot of the product in a bucket of water for the day. It remained dry and unaffected.

Thanks - that was my understanding as well!

OP-did you make your decision. I'm in Zone 4 also and addresing rim joists. I hope you don't mind a few questions:

What is the effect of ambient November temperature on applications of closed cell rim joist foam?

Is there a need to insulate rim joists temperorarily with "other" (if crawlspace concrete walls are not insulated, nor flooring) to buy time until ambient temperatures are more foam condusive?

What are advantages of closed cell vs open on rim joists? Or, is open cell (approved 2009) good enough?

Thanks all.

I can't answer your technical questions, but we did end up going with the contractor that proposed air sealing with 2" closed cell spray foaming, form fitting Ruxol into rim joist perimeter, and then spray foaming the seal. We felt that this was a better fit for our particular job (retrofit, a lot of pipes and wires). We also felt more comfortable with the contractor's proposal in general, which involved a great deal of additional work beyond the rim joists.

The work is getting done in about a month. We're keeping our fingers crossed that we made the correct choice, but in all honestly will probably not know for a long time--if ever.

Thanks everyone for your opinions and guidance.