Holly I don't know what I said that made you think my primary concern is budget. It is not. Our budget is more than enough for an ICF home with or without basement. However I don't know if building a basement is worth the extra expense or adds any value to our use of the home. We've toured several icf houses that are glorified mcmansion in the area 4000 sq ft monstrosities on basements. I've seen icf basements with traditional construction above and I didn't like them. I love the deep window sills, quietness, energy efficiency, safety ( and the list goes on and on) of an icf home. Traditional stick built is not something we would explore. We have discussed SIPs but ultimately i think we feel most comfortable with the experienced ICF builder. He has over 25 years experience with ICF. He now only builds ICF homes. We toured many of his homes all were well within our budget. But we haven't made the final decision yet. I mentioned the cost because it is a factor. ONE factor not the only or most important factor. I'm not sure if paying x dollars for a glorified storage unit makes any sense. That x would likely come at the cost of tree transplants, koi pond etc. All things we could do in the year or 2nd year after the build, but I would prefer doing now. I also was questioning how the choices impacted the livability and durability of the home. My point in this thread was to understand why people choose one over the other. I've found the answers pretty helpful. I'm not quite understanding the implication building on slab indicates disinterest in quality or interest only in cheapest building process. There is some debate that basements are not a "green" choice. Slab on grade is often used in passive solar homes for the thermal mass of the slab. We want high end finishes in a Eco friendly home. Here is where I'm throwing away money and will never have good resale. Then again we threw that out the window the moment we decided to build a more contemporary bi generational home :) Not every housing choice is about "smart money". Some decisions are a balance between wants, needs, livability and ultimately budget. Per others suggestions we had architect make some changes. It looks like our portion of the house would now be 1920 sq ft on slab with the new utility room and a few other changes to accommodate that room. The inlaw apt stayed at 788 sq ft. Right sized for us. But small by many people's standards. If the home is on basement it would be 1715 as we took out the utility room and didn't need to rework any rooms. Sorry if my original post gave the wrong impression that I was looking for the cheapest option.

the ROI is rarely there on spray foams in walls, if ever. Marketing BS has people thinking spray foam is the next step up from batts to ultimate energy savings. The truth is, unless you are going with closed cell (most do not) your wall r value increases 1 or 2 points, however you do get a boost in air sealing within the stud bays. However you still have a thermal bridge in either system, and spray foams can not address that, as well as air leaks at your top and bottom plates of your walls. I would be curious to see how you are getting r21 in your exterior walls. if they are using fiberglass batts, you arent hitting r21. For zone 6, it would be money in your pocket to increase that value (especially after thermal bridge and batt insulation short falls your whole wall r value is closer to r16) by adding exterior foam sheathing. The extra upfront cost of adding a couple inches of foam on the exterior will be cheaper then the spray foam upgrade, as well as decreases the thermal bridge shortfalls (reduced "cold drafting" on your walls) and provide a better air seal assuming seams are caulked/foamed/taped. Get your HVAC guys to do a load simulation and adding foam sheathing should reduce your tonnage for the equipment, thus reducing the upfront cost of it and offsetting some of the cost of the sheathing. After that, depending on your energy usage, rates, size of home, etc your payback on your sheathing will typically be less then 5 years. I would also recommend switching from batts (again, assume you are using them) and going with a blown product such as fiberglass or cellulose. It will do a better job of fully insulating the wall cavity. Finally not everything needs to be looked at as ROI. Some things will provide added comfort but not always come with a payback. Full foam below slab could be one of those items. I have had clients that do it and are happy they have, and I have clients that save the couple k and dont, and wish they have. One even took up their entire wood floor (floating) and added foam on the slab after the fact since it was so cold. These are people in your same climate zone 6. People never like to spend money on things they dont see, and insulation is typically the first area people do not always care about. Most builders do not understand air infiltration, thermal bridging, and how to do energy simulations and payback so most do not understand the advantages to increasing the shell insulation and tightness of the home. Most stick by code minimums (like in your case). Energy rates may be low at the moment. But do keep in mind...energy rates will always keep going up.

We built a small, 1400 sq ft one level, one bedroom home on a full, walk-out basement. Since it's open, and there's only one BR on the main level, it doesn't feel small at all. We considered going up as well, as I like the looks of a 1-1/2 or two story house. We went basement instead, for the following reasons: Our sloping ground was ideal for a walk-out basement. We built with ICF, so the basement was already well insulated. After living in FL for 30 years, we wanted a place of safety in bad weather. After living on a slab for 30 years, I prefer the slight give of a suspended floor. I can easily reach and service wiring, plumbing, and HVAC refrigeration lines from the basement. I was one old man, working alone, so the thought of climbing up on a two story roof gave me the willies. Due to careful work and multiple systems, our basement is snug and dry. With the ICF construction, our basement never falls below 60 F., or goes above 75 F. with no HVAC at all. I recently framed and drywalled interior walls to create a bedroom, bathroom, and large storage closet in the basement. I have room for another BR, and now wonder why I didn't rough it in at the same time. The only issue we've had with a one BR house is that there's no 'away' space except to go outdoors (or out to my barn). With the second bedroom in the basement, if I want to retreat to a quiet corner and read, we now have a space for that. Although we're almost always in the same room at the same time, don't underestimate the value of being able to get away, or to house an overnight guest (which we do fairly often).

Good catch! Which is it, Dr. Joe? 2009 "The best foams to use have a perm rating of greater than 1 perm for the thickness used. This means limiting extruded polystyrene insulation to less than 1-inch thickness for walls (more than 1 inch thick and they do not breathe sufficiently)...." BA-0309 2007 "The thickness of the XPS will depend upon the climate and whether additional insulation will be added in a frame wall. We recommend a minimum of 1 inch of XPS up to a maximum of approximately 2 inches." (emphasis added) I can only conclude he's become more conservative. As per BSC recommendations, I've used 1" XPS board directly on poured walls, followed by fg batts of R-10-R-13 between wood or light steel studs and vapour barriers when required by inspectors, though Building Science says they're not necessary. It's also a good idea to put strips of 1" XPS under the baseplates; this limits heat transfer and protects the plates in case of the inevitable leaks basements are subject to. Building expert Martin Holladay advises avoiding all moisture sensitive insulations below grade. You can substitute rockwool for fg. There's no point to an air gap. This practice was used in uninsulated basements. What it did was disguise the mould farm on the cold concrete wall behind the finished wall. Your usual "basement odour."