add floor joist insulation ?

[dshop]

I am located in Raleigh, NC, temps. are 80's- 90's in the summer sometimes in the 20's in the winter. Humidity is a pain in the summer. The home was built in 2007 and has a nice standup crawlspace with no insulation under house. Is there a good advantage to having the underside of the house floor done with spray foam?
I have a 40x60 shop that is spray foam top to bottom that is very stable temp. wise.
Would adding the under floor spray foam help stabilize house temps. enough to justify the cost? I am thinking it would be a good thing to do.
any personal experience or advice would be appreciated.
thank you.

 

[The Cobbler]

are the crawlspace walls insulated?
If they are, I don't see a huge return on insulating the floor, if no, then it would be a good choice to add insulation, will make a huge difference

 

[TractorJeff]

What about the cold that comes up through the dirt?
Will ventilation become an issue?

 

[kaiser715]

Sealed, open, or conditioned crawlspace. If sealed, really no difference. Look up the "princeville nc field study" on crawls.

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