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 material costs of slate aren't that cheap unless you are buying the box store stuff that has about a 40%-50% cull rate. And the installation costs for slate are a LOT higher than almost any other natural stone, which is in turn higher than any porcelain. Because even gauged slate will vary a lot, slate is a lot of work to get set correctly without a lot of lippage. It's best set in an old fashioned mud bed rather than with conventional thin set, and there simply aren't a lot of people out there that have the skills to do that anymore. Plus, it takes up more thickness for the floor, and you have to account for that from the beginning of the design if you want flush transitions. If this is to be a completely covered 3 or 4 season room, then I'd recommend some type of porcelain, even a faux slate if you like the look, together with underfloor electric heating cables, or hydrionic if you're doing a boiler. Electric won't soley heat the room in winter, but if you are using a woodstove, it will help keep your feet warm. If you do the PEX for the water, it will provide a toasty warm and comfortable environment for the winter months if you also use good quality windows. If you're not up for putting in high dollar windows, then forget heating the space int he winter and have a 3 season rather than 4 season room. You should make sure that your slab is insulated properly from the surrounding soil regardless of if you choose in floor heating or not if you want to use this in the colder months.

. You're essentially looking at making a thermal mass that simply swamps out the level of "losses" to the outside world. Thermally 100% correct I'd say . . if it's truly big enough, and can exchange it's heat with the surroundings efficiently enough. No matter HOW efficient the place could be; there will be losses . . . and at a time of year when you want them the least . . winter . . when they are also least available to replace. I'd say s'can the flat roof . . . put enough pitch on it to shed rain . . and . . perhaps more importantly; snow . . like metal roof. The weight can get incredible. Insulate the space between inside roof and the "attic" . . . will help cool in the summer, and avoid icicles in the winter. You are barking up the right tree with regards to surface area vs volume; but I believe that bees have it right: Believe that a hexagon, or septagon, or whatever they have; actually gives the most volume per lineal outside material. May not lend itself to livable space terribly well . . although bees seem to do fine with it . . Running tubing throughout the concrete mass I think would be a good idea . . . just don't pour all at once lest ye collapse forms as the weight / pressures can get quite high as the mass gets larger. Pressurize the tubing during the pour !! lest ye collapse it. As far as pumps / controls etc for circulating fluid; why not use passive thermo-syphon ? ? Only ONE moving part . . . a check valve. No motors / pumps / controls / sensors etc. Heat during the winter; and oodles of heated water during the summer months. Follow the KISS principle: Keep It Simple Stupid . . less crap to go wrong . . . easy to protect against freezing etc . . . Circulate well water through the mass in the summer . . get free cooling ( and likely some condensation ) while pre-heating your domestic hot water. Perhaps some cavities / "tunnels" through the mass . . which could have air blown through them to help exchange along better by virtue of more surface area ? ? ? Make the mass be part of the "architectural" design . . not just put there to serve the main purpose. Incorporate masonry stove etc into it . . as PART of the living space . . . shelving . . cubbyholes . . a small sitting area . . "couch" . . all as part of it ? ? While thinking of cheap AND efficient . . ever look into straw bale construction ? ? ? I've read some about it . . and it is certainly cheap . . and if PROPERLY done ( to exclude water infiltration ) will last a VERY long time. Low tech, cheap, works well. How's 'bout earth-bermed or "underground" construction . . . a few feet down and the temperature doesn't vary nearly so much . . . a much more constant "outside" temperature to your structure ? ? ? Don't forget that building very tight . . . . also means lack of fresh air . . . you'd have to have ERV or such to get that . . . and there are some losses with it. An interesting idea . . . curious what others may say . . and what you end up doing with it . . . . Bob

The stone restorers cleaned it as well as possible and told us the remaining rust stains have sunk into the stone and can't be removed. I've looked the problem up online and what I've found seems to confirm that. Also, one of the two upper slabs has two huge holes in it, one about 7" in diameter (I'm guessing it was for a normal vent hood or possibly an exhaust pipe for the wood stoves they used 100 years ago) and the other, higher up, 12" in diameter (it was for a huge commercial vent hood). The upper right slab has the least staining and no holes, so I'd like to use it as an island top if possible. The upper left slab, the one with the holes, has about a 3.5 foot x 2.5 foot part of it that's good looking and could be sliced into several windowsills. Hence my interest in getting these slabs off intact, if possible. As for the electrical, what's behind these slabs is solid brick covered in plaster. It's like a chimney but not -- the actual chimney starts on the floor above (there's a fireplace in that room, a second-floor bedroom, sitting on top of a solid brick tower that goes down to the foundation). So on top of not being able to run electrical, it's not a surface I personally would want to try and attach anything heavy to, such as a vent hood or upper cabinets.