Yet another consideration in the continuing saga. We are trying to decide between a full ICF basement and increasing the ground floor sqft on a slab ranch style home. It seems that it would be cheaper to increase the foot print.

How many SQ/FT are you considering?

We built on a walk-out basement, partially because of our sloping ground, and partially because we wanted one. By having a full basement, we could double our square footage in the future if needed, plus it gives us a lot of storage. As a result, we were able to build a much smaller house. We are in a mild climate (upstate SC), and our unconditioned basement has never gone below 60 in the winter, or above 78 in the summer. The outdoor temperatures have ranged from a low of 3 to a high of 107. Admittedly, these extremes are rare and brief.

Another consideration is comfort. We lived in a slab home in FL for 30 years, and I find a concrete slab to be very hard on the feet and back. The slight give of a suspended floor is noticeably more comfortable. Also, I like being able to easily access the under floor utilities for service and repair. We had a pipe fail in our FL home, and had to cut and jackhammer the slab to get at it.

We are trying to limit the ground floor to 1900 sqft if we build with a basement.

For any level of energy efficiency that a basement has, you can build above ground space to be as efficient. So I'd focus on cost/usefulness issues (include a frost protected shallow foundation and truss designs that include space for ducts). I expect that wearing flip-flops would add a lot more underfoot give than any wood joist floor, but actual data would be interesting.

slab on grade is instant thermal mass for passive solar and lowers construction costs. Today's code calls for sleeves if water and gas supply pipes penetrate concrete floors -- jackhammers not required for repair. Dr. Scholes has a cheaper palliative for sore feet than a full basement. Storage is an issue, as is mechanicals.

A multi-story building nearly always has a lower $/sf cost than a single story building. This is largely because all the square footage can be accommodated under a smaller and lower cost roof. Excavation and construction of basement square footage is a significant expense. If you live in location with a deep frost line, constructing a basement starts to have merit. However, living in a single level home without any stairs is a delightful luxury which becomes even more satisfying as you get older and desire to stay in your home. A single level ranch style home using slab-on-grade and full hip roof with large overhangs is also an ideal candidate for reduced cost ICF construction, hydronic radiant floor heating, passive solar heating and overall high energy performance in general. Yes, you do need consider what you place under the slab and make sure that it can be easily repaired/serviced without needing to jack hammer the slab.

You have to consider what is used in your area. I'm in upstate NY and you almost never see residential houses with on slabs. It would drastically effect your resale value here if your house was on a slab. The most energy efficient part of your house will be the basement, hands down, if you build it with icf.

For me and my builder, having the same above ground sq footage would be quite a bit more expensive than having 1/3 of the total square footage underground (2 floors above, 1 below). but I also did not build with ICF, we just did R15 foam on 5 sides (different kinds of course).

I also agree , here in Vermont, a house on a slab would be looked over when you go to resell.

I think you mean to say that finishing a basement is cheaper if you're going to have a basement anyway. Dunno how a slab on grade would not be less expensive than a basement. Even a finished basement would be hard pressed to equal percentage of living space in my house with mechanicals squeezed into a 4.5x4.5 chimney chase. (ie took up about 50 SF of floor space.)

i think the Original poster is talking about making the 1st floor bigger as an alternative to having a basement.

If you just added enough sq ft for mechanicals, i'm sure you would save money. But if you wanted to offset the whole basement sq footage it should be a lot more to build above ground.

can anyone give me a ballpark on FPSF foundation cost per square foot for my own knowledge?

The study cited here says FPSFs cost 15 percent to 17 percent less than standard frost wall and footings, or $800 to $6000 depending on how deep you have to go. http://www.probuilder.com/frost-protected-shallow-foundations To get an unfinished basement, add excavation, an extra couple feet of wall, first floor joists and decking, stairs and windows. I paid about $12/sf in 2010 for an ICF frost wall and a 4-inch floating slab over 4 inches of xps. (1k sf first floor plus attached 2-car garage.) Even with longer walls and more roof, I seriously doubt you spend less per SF of usable space below ground than above.

The part about usable is key. Given free rein, the trades will spread all over the basement because they don't want to work on top of each other. A builder I know added an interior wall four feet from an exterior wall on the short side of the house and told the trades, Here, this walkway is all yours. Utility suffers more if there's no egress window and the basement floor won't drain to the sewer.

Plus footing drains, sump pump, basement wall exterior waterproofing/drainage, etc. And even then, basements seem to have more flooding problems - not sure I'd ever put a wood floor in one. With a 7' attic and a garage, I don't need my basement for storage or work space.

No one needs a basement. Try to find one in the south west USA...

Has a decision been made?

Sailawayrb's post pretty much defines the best options for us and thank you Sailawayrb. Enough floor space for a mechanical room, mud room entrance with half bath, energy heel truss roof and radiant hydronic heat . Still working on overcoming the challenges of moving from the Midwest to the Northwest. Hopefully using Borst Engineering and Construction. We really like this house design and floor plan.
http://www.houseplans.com/plan/1920-square-feet-3-bedrooms-2-bathroom-farm-house-plans-0-garage-33237. Without the offsets in the baths and dining room and eliminating the patio glass door in the master bedroom .