Helping out sis’ and wanted to double check w/ u guys to make sure she gets top notch work. Here is what I’ve got:

>Zone 6 heating climate
>Crawl space w/ 4″ layer of crushed stone over dirt(damn!)
>FHA unit in crawl space
>Bath fan vents to crawl space
>Crawl space floor is below grade

My plan of attack:

> Vent bathroom to outside (bath is in middle of home, I was thinking I would continue exhaust through basement to ext sill joist)
> Install 2″ foam between joists and around entire rim. Seal edges with foam.
> Rake stone to one side, lay poly(8 mil?) and tape to foam.
> Mastic FHA duct work
>Cover poly with all stone and lay other side with same detail.
> Talk about gutters and other ways to prevent infiltration from the outside.

My questions are, should I put in an basement exhaust fan as well? Do u think I need to cover the foam w/ a 15 min fire barrier? And…do you agree I should insulate the walls and not the floor?

I appreciate your expert opinions!!!!