Trap I've see that type of framing bu in standard consrtucion material it creates problems with nail spacing. A standard sheet of plywood is as we know 4x8' and accepted construction framing is 2x4 spaced 16" on center. Or 2x6 spaced 24"on center.
The style wall you just showed eats lumber because most state will still only allow those spreads and now you have to use more wood than you need to. Remember that has to be an inspection on all the work he's doing so you can't just slide with it.
Oh If you could get me to a link on the R values of blown in insulation I need to do some reading on that.
JF:
Yes, of course you have to space 16 OC on both sides of the wall for both exterior sheathing and interior drywall.
This type of framing is cost effective in that it has a substantially lower operating cost for the structure. First cost is high (although it can be lower than some others) but the payback is fast through lower utility costs during all seasons. Besides, the original post had the structure size at between 64 and 80 square feet so utilizing this framing style for that small an area isn't such a big deal.
Cellulose insulation can be as much as R-4/inch. Compared to urethane foam at R-5/inch, that's pretty good especially when you take into account the significantly higher installation cost of urethane. Also take into account that urethane has substantially worse specs than cellulose in regard to flame spread and total smoke generated. Cellulose is treated with a fire retardant and has an installed 1 hour fire rating. Here is
your link.One other thing...ICFs are great, especially for below grade type work but proper installation is critical. A short wall typical of pier and beam construction is hard to screw up but basement walls (which is what would essentially be needed in a hillside application) are prone to voids in the concrete pour due to the greater height of the wall. Stirring or vibrating during the pour is good but no guarantee of a void free ICF wall (or any other formed concrete wall for that matter). Water proofing a below grade wall is also tricky and water will always find a way if a way exists. A French drain around the below grade portion will be helpful but no guarantee, either, of a leak free wall. And depending on the local water table a hillside application is every bit as likely to have water issues as a full basement.
I also wouldn't hesitate to pour the floor with 1.5 to 2 inches of foam board underneath. It's cheap and makes interior temperature control easier.
As to humidity...that's a function of two things. First is the relative humidity level of the air. Second is dew point. Electronic equipment (usually we are talking about computer rooms) has an ideal relative humidity range of 45% to 55%. Higher levels of relative humidity lead to corrosion related electronic failures. Lower levels lead to static electricity related electronic failures. The only way to know for sure if this is going to be a problem is to build it and then measure. The inverter can probably stand up to more extreme humidity conditions than computer room equipment.
Using a solar/hydro collector for this small space is probably the best way to go. If it was me, I would pour four or five inches of concrete on top of 2 inches of foam board (with 2 inches of edge insulation) and run 1/2 inch PEX tubing (closely spaced) through the slab. A mixing valve with an outside air reset controller will keep the heating water temperature at the appropriate setting. A tiny circulating pump controlled by a thermostat rounds out the system. Combined with an appropriately insulated building envelope this will probably give you the best temperature control in the heating season. Below grade during the cooling season will (depending on location) probably not require any mechanical cooling.