I am designing my ICF home in the Seattle area.  I originally was putting in a full basement but after input from the boss of bosses, I'm cutting it down to partial.

My question is about the rest of the house that will have no basement under it.  Should I have a crawl space or pour the floor in contact with a suitable base on the ground? 

I think I could build thermal storage for heat under the direct contact floor and warm it with passive solar. 

If I use a crawl space I still have to put in some kind of sub floor on which to pour my concrete floor.

What do you pros suggest or is it really no matter if either is done correctly?

Thank you.  Duh! I knew I should have described the site. 

The site is five acres and pancake flat so my engineer can pick a good building site.  The partial basement will be fully inground.  The soil is sandy loam down to 3' and then hits 60' of solid hard pan.  The well report told me what's down there.

I'm thinking I will do the slab in the non-basement area.  Possibly I will excavate down to the hard pan build the foundation walls to slightly above the natural grade for good drainage and then backfill the slab area with layers of compacted crushed and rock dust to make a solar thermal storage.   (After I see how it worked for http://www.wdnichols.com/ from whom I got the idea.)

The Seattle area is not great for solar but a passive system that can store heat makes sense to me.  It's magnificantly sunny today after pouring rain yeaterday.