1/2" High Density foam board is a R3(around $8-10 a sheet), the 4" is beaded styrofoam, not High density and is a 10.5(I found this for $8 a sheet).
Whoops, my mistake, the beaded is 3" thick, not 4 and is a R10.5
Eddie, my house in Tyler, very similar in size and layout but a 7.5/12 instead of a 10/12 had 30 weight tar paper, 1/2" double foil insulation board, then tin right over the foam board. We lived in it 3 years and it was along time ago, but I don't remember it being hard to cool (central air) or expensive. We heated with wood and the soapstone stove(44,000 btu and hr) in the great room would run you out and most of the time we cracked a couple of windows. I burned 3 cords of wood each winter to heat it. The two downstairs bedrooms were always cold, so on this house we will only have a master bedroom down and it will have a sliding barn door type wall 10-12' long that will stay open unless we have company. That is why I am thinking that a R12 will be sufficient...I could be wrong for sure. R30 or 60 will really run the cost of the roof up.
I have to be honest...money is an object and we are pushing our financial limits to the max. I will look around for a deal on some thicker panels, but keep in mind, if you have to turn a board on edge right on the decking you create a thermal bridge. Fir & SYP have a R value of about R1 per inch, so turning a 6" board on edge, then insulating between boards means you have a grid of R6 between the R20 insulation panels. A sandwich is a better way, all decking, all foam, then osb/ply/purlins then tin. No grid, no loss of R. To maintain the sandwich I just don't know how thick I can go before the foamboard will start to collapse under the purlins. Decking over real thick foambaord with osb instead of purlins will add about $1K to my existing design.
I scored a big old vintage('86) soapstone H1 off craigslist 2 years ago. This one takes 24" sticks and puts out 100,000 btu's an hr. It had been over fired with coal or had a flue fire as the 1/2" interior metal baffle had a grapefruit hole melted thru it. I rebuilt the whole stove and ran it in my shop last winter...awesome. Anyway, this big beast is going in the basement and I am going to
try and heat the entire house with it. I say try, because heating from a basement can be tricky, some work and others not so well. The air flow is the key and undisturbed cold air returning to the basement really makes or breaks it. Interior Layout, the location of the basement stairwell all come into air flow play. A second stove or fireplace will be above the basement stove and share the same 8" flue. So if I have to supplement heat I can fire the main floor wood burner. Just like in insulation there are two schools of thought about two wood burners on one flue. The newer generation of codes don't like it in some areas, but thousands of houses successfully do this all the time.
We will not have any A/C in the house, just ceiling fans and a power gable fan. We want to try I see if we can go without it....might be interesting
