Well, maybe you can get away with dismissing and ignoring thermal mass effect in your neck of the woods. If we did that in southern Oregon, we would grossly over size HVAC equipment and install AC systems that are not needed. While I am sure this frequently occurs and clients are none the wiser, we prefer to design more accurately and aggressively to provide our clients with lower cost and higher performance design options.

There are reasons for thermal mass, the principal ones being, A, you live in dry hot climate where it is very effective, and B, your passive solar house could turn into an solar oven without it. The second is my reason, and my Frank Lloyd Wright homage performs pretty well, seasonal dehu problems notwithstanding. (Having the benefit of history, I knew that looking a FLW home and living in one are not comparable experiences.) In addition, there are reasons to build a concrete house and you'd want to understand mass effect before you start.

Absent a compelling reason, tossing out mass-adjusted R values isn't overly helpful. ORNL calculates them as an annualized figure to account for seasonal appearances and disappearances. But even that approach isn't entirely transparent if sailawayrb's R60ish falls into the average unweighted by the modest energy expenditures you'd expect in a southern Oregon summer. Ideally, you'll want the highest effective values in the season you need them most, which brings us back to hot and dry. Then there's the fact that walls are only one source of heat loss.

I'm with Dilettante. Make your case for ICF on design factors and quote R value at face value.

Just to be 100% clear and as I said before...it is entirely appropriate and proper to only quote the conventional R-value and NOT quote the potential thermal mass effective R-value benefit as was properly done for the Quadlock products. There is nothing worse than ICF companies making claims about ICF performance that can at best only be realized in certain areas that have a perfect diurnal climate about 70F. However, it is also entirely appropriate to properly account for and design for thermal mass effective R-value benefit in those areas where is can be used to great advantage. Accurate and aggressive design avoids over sizing HVAC systems which unfortunately is commonly done. Southern Oregon is one of those areas where thermal mass effective R-value benefit can be used to great advantage and this is why we developed our ICF performance calculator.

Oh, I should have also mentioned that passive solar is one of our passions too...in addition to hydronic radiant floor heating, water works projects and low energy building design. As you indicated, thermal mass is an important design aspect of passive solar and masonry heaters too. Just this month we were honored for our support to WaterWatch and by the international Masonry Heater Association:

WaterWatch Spring Newsletter

Masonry Heater Association Newsletter

I should say I admire sailawayrb's knowledge and her willingness to help people on this site. And she does have a design reason to offer up R60ish. She is a fan of radiant floors, as am I, and thus faces the inevitable question: Don't I need a heat pump anyway?

That said, the fact that she can say, "Well, no," is a rare answer east of the Rockies, under 5000 feet in elevation or some miles inland from the ocean. Her customers are pretty unique as well. If southern Oregon's mild climate, winter and summer, is not the most favorable in America for heat pumps, it has to be right up there. Custom versus off-the-shelf comes at a price. Getting back to OP, unless ICF is common in SW Florida, I'm guessing he can find better ways to combine concrete and foam.

Thanks toddm. I would fully agree that there are a multitude and perhaps even better ways to combine concrete and foam in Florida. My initial response to this post was for the OP to seek local guidance on some of their specific questions as I suspect that is where the best knowledge for their project resides. I am a big fan of ASHPs, especially mini splits and I often even recommend them in lieu of HR floor heating in our area. They can often be the best choice, especially if the building requires both heating and AC. I even recommended mini splits to the OP in my initial response. It’s just that in southern Oregon if you are doing new construction, you can totally avoid needing AC if you take advantage of thermal mass. One needs to accomplish an integrated design that fully considers passive solar design, thermal mass design and HVAC design for the given location to achieve great results.